Doctoral Degrees (Crop Science)

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Aerial phenotyping tp identify superior sugarcane genotypes.
(2024) Hoffman, Natalie.; Joshi, Sheilesh Vinanay.; Singels, Abrahams.
Sugarcane is a globally important food and bioenergy crop which necessitates continual improvement through breeding to ensure its sustainable production under increasingly challenging environments. Compared to other major crops, yield gains in sugarcane have stagnated worldwide in recent years. This could be attributed to the resource-intensive and time-consuming nature of breeding a genetically complex crop with long growth cycles and large, diverse populations. The primary objective of sugarcane breeding is to develop superior genotypes with enhanced genetic gains, securing sustainable production for the future. Aerial phenotyping (AP) with high-throughput phenotyping sensor technologies and unmanned aerial vehicles (UAVs, commonly known as drones) could assist breeding by increasing selection efficiency and accuracy, uncovering genetic variation for yieldpromoting traits, and expediting large-scale trial screening. Key physiological traits governing canopy development and water use, namely green canopy cover (GCC) and stomatal conductance (gs), can be estimated from the aerially measured Normalized Difference Vegetation Index (NDVI) and canopy temperature (Tc), respectively. While promising, further research is required to evaluate the efficacy of AP in breeding. The study aimed to develop and test an AP procedure for identifying superior genotypes in sugarcane breeding. The specific objectives were to: (1) determine the impacts of ground (GCC and gs) and aerially measured traits (NDVI and Tc), on stalk dry mass yield (SDM) under well-watered (WW) and water deficit (WD) conditions; (2) develop an AP procedure for estimating gs, GCC and SDM from Tc and NDVI; (3) determine the genetic variation and broad-sense heritability of ground and aerially measured traits; (4) evaluate the feasibility and potential benefit of implementing AP to identify superior genotypes in breeding. These aims and objectives were addressed in three experimental phases. An unreplicated pilot trial with two genotypes grown under WW and WD conditions (~ 200 m2 in total) was used to establish preliminary relationships between ground and aerially measured traits under varying canopy and moisture conditions. Key findings were that FIPAR (fractional interception of photosynthetically active radiation - a surrogate measure of GCC) measured on the ground could be reliably estimated from NDVI, though the relationship required further investigation at partial canopy cover. Tc could be used to distinguish differences in measured gs between water treatments under moderate to severe stress conditions only. Overall, the experiment was used to formulate a preliminary AP protocol, with recommendations for further improvement in the subsequent phase. A replicated field trial with 54 genotypes, grown under WW and WD conditions (~ 3 ha in total) in plant and first ratoon crops, was used to assess trait correlations, genetic variation and broad-sense heritability of traits, and to refine the AP procedure. In line with previous research, the study confirmed FIPAR and gs as influential traits for determining SDM. FIPAR, measured at 2-3 months after crop start, could be used to identify high- and lowyielding genotypes, and could be predicted well from NDVI, at partial canopy for wellwatered crops. Breeding programs for irrigated environments could benefit from the early identification of superior genotypes if traits with high heritability, like FIPAR, can be accurately and rapidly phenotyped. Furthermore, results suggested that high gs benefits wellwatered crops, while relatively low gs could be advantageous in dry environments, though this requires further validation. Phenotyping of gs from Tc was mostly unreliable, and its practical application in breeding programs requires further evaluation on a larger, genetically diverse population with improved measurement procedures. It was concluded that NDVI and Tc, which both showed significant genotypic variation and moderate to high heritability, could be used to identify high- and low-yielding genotypes when measured early in the crop cycle in young, partially canopied, well-watered crops planted in multi-row plots. Novel results also showed potential for screening of drought tolerance using water treatment differences in Tc and SDM, which has not been reported previously for sugarcane. Overall, this research was used to establish an AP procedure for subsequent use in breeding trials. Lastly, the AP procedure was implemented in two rainfed early-stage breeding trials, with 1770 to 2130 genotypes, planted in replicated single-row plots over ~3.5 – 6 ha. This validation phase was used to test the utility of AP for enhancing selection accuracy and efficiency and contribute to yield improvement. The limited number of flights in the first trial prevented adequate capture of temporal and genotypic variations in aerially measured traits, which are necessary for accurate yield prediction. In the second trial, early estimates of NDVI and Tc, measured approximately 1.5 to 3 months after crop start in partially canopied, well-watered crops, showed significant genotypic variation, moderate to high heritability, and significant correlation with yield. Tc was also significantly correlated with yield when measured shortly after canopy closure but before row overlap due to crop growth. Despite these promising results, the AP procedure implemented in these early-stage breeding trials did not achieve the precision required for genotype selection. A comparison of direct (SDM-based) and indirect (based on aerially measured traits) selection approaches showed that the number of positive matches was mostly offset by a larger number of incorrectly identified genotypes using aerially measured traits. It was concluded that the effectiveness of AP in breeding is currently hindered by limitations in the precision of aerial measurements and challenges in breeding trial execution. The findings from this study highlight the potential and limitations of AP for physiological breeding. AP holds great promise for identifying genetic variation in yield-promoting traits, which could be leveraged in breeding for the identification of superior genotypes in irrigated environments, however further research is required to fully realize this potential. It is recommended to modify the design of early-stage trials by increasing plot length, number of rows, and row-spacing to facilitate accurate estimation of aerially measured traits using the developed AP procedure. Further efforts are also needed to overcome challenges inherent in breeding trial execution, such as lengthy planting periods introducing biases in early vigour, and variability in field soil composition, which directly and indirectly affect the quality of ground and aerially measured data. Should these recommendations be implemented, early screening of trials using AP could lead to shorter breeding cycles, the discovery of novel genetic variations, and improved selection efficiency, ultimately reducing the resourceintensive nature of traditional methods through early elimination of inferior genotypes from the program. In conclusion, this study demonstrates the potential of AP to enhance sugarcane breeding by facilitating the early detection of important yield-promoting traits, particularly in wellwatered crops. While AP shows promise to enhance sugarcane breeding, further work in refining its application is essential to fully realize its benefits. These research findings provide a strong foundation for future efforts to develop innovative breeding strategies and precision agriculture technologies.
Agro-morphological, nutritional and genetic diversity analyses of Bambara groundnut (vigna subterranea (L.) Verdc)
Hlanga, Nokuthula Cherry.; Modi, Albert Thembinkosi.
Bambara groundnut (Vigna subterranea (L.) Verdc) is a legume crop with potential to address food insecurity in sub-Sahara Africa. However, a lack of agronomic, genetic and nutritional information on the crop hinders its full potential utilization. Nineteen Bambara groundnut lines were evaluated in the field in 2017 and 2018 at two sites. The lines showed significant differences (P<0.05) for all the measured traits. Lines such as IITA686, Cream and Uniswa Red-R were found to have superior performance for multiple traits such as number of seeds per plant, seed mass per plant, plant height and mid-leaf width. The genetic variation among the Bambara groundnut lines was assessed using 20 polymorphic SSR markers The markers exhibited an average polymorphic information content (PIC) of 0.57 and the observed heterozygosity was 0.58, showing that the lines exhibited a considerable level of outcrossing. The lines were clustered into three groups based on the principal coordinate analysis. The highest genetic distance was 0.60 between Tiganecuru and S19. Lines such as IITA686, Cream and Uniswa Red-R that had good performance for multiple agronomic traits occurred within a genetic distance of 0.40 making them genetically divergent enough for generating crosses for Bambara groundnut improvement. The ash, fat, proteins, starch, calcium (Ca), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), phosphorous (P), sodium (Na), copper (Cu), and zinc (Zn), acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents were determined in the Bambara groundnut lines using combustion and chemical digestion procedures. The nutritional content varied significantly (p<0.05) among the lines with lines S19, Gresik, Pong-Br-UNK, Pong-Cr exhibiting high means for starch and protein content ranging from 11.05 to 11.94%. Genotypes Mix, Pong-Br-UNK, 42-1, Gresik, Uniswa Red-R, and Brown were clustered together based on their high starch, Na, Ca, fat, and Mn contents. The negative correlations among some of the nutritional content would be a challenge for simultaneous selection to breed nutritious Bambara groundnut lines. The lines with high content for multiple nutritional elements such as 211-57, Pong- Br-EN and Uniswa Red-G were recommended for production. It was imperative to determine interrelations among agronomic traits and nutritional content with seed mass for indirect selection. Among the agronomic traits, number of seeds (NS r=0.58, p<0.01), number of healthy seeds (NHS, r=0.51, p<0.05) and plant height (PH, r=0.45, p<0.05) exhibited the strongest associations with seed mass. These traits had NS, NHS and PH high direct effects on seed mass of 2.04, 1.72 and 0.60, respectively. These findings provide a means to facilitate indirect selection of genotypes with high seed mass productivity via proxy. Overall, the study found significant agro-morphological and genetic variation among the Bambara groundnut lines, which would be a prerequisite for Bambara groundnut improvement. The superior lines identified for multiple traits and genetic divergence were IITA686, Cream and Uniswa Red-R. Key words: Agro-morphology; Bambara groundnut; Genetic variation; Seed quality
Agronomic and physiological approaches to improving productivity of selected sweet potato (Ipomoea Batatas L.) cultivars in KwaZulu-Natal : a focus on drought tolerance.
(2014) Mgcibelo, Motsa Nozipho.; Modi, Albert Thembinkosi.
Sweet potato (Ipomoea batatas L) is a resilient food security crop with wide adaptation characteristics and hence can fit well under smallholder production. Its importance as a food security crop in relation to drought is still underestimated and fails to attract sufficient attention from agricultural researchers. The adaptive responses of different sweet potato cultivars to different agro-ecological areas may vary, and sweet potato is an important crop for small-holder farmers in KwaZulu-Natal (KZN) of South Africa, which has diverse agro-ecological areas. Adaptive responses of sweet potato cultivars in KZN’s ecological regions are not known. The possible varying adaptive responses may impact on the food and nutrition security role of sweet potato. This study evaluated the ecophysiology, growth, yield and nutritional composition of three locally bred sweet potato cultivars in response to a range of climates and soils from KZN, South Africa. With the help of smallholder farmers, field experiments were conducted at three sites located in three different agro-ecological areas (Deepdale, Umbumbulu and Richards Bay) of KZN. Agronomic, physiology and yield data were collected. Harvested roots were further analysed for selected nutrients (starch and β-carotene) and other metabolic responses to drought stress. A separate study on physiological and yield response of sweet potato to water stress was conducted under controlled environment. Metabolic analyses were conducted continuously during plant growth. Plant growth, physiological responses and yield were significantly (P ≤ 0.05) influenced by growth environment. Drought stress in Richards Bay resulted in poor plant growth, low yields and low nutritional content (starch and β-carotene content). High temperatures and evapotranspiration (ETo) were associated with drought stress. The other locations (Deepdale and Umbumbulu) where ETo was low showed increased plant growth, yields and nutritional content. The cultivars’ ecophysiology, growth and yield were not suitable for the Richards Bay agro-ecology/bioresource group. They were more suitable for Umbumbulu and Deepdale agro-ecology/bioresource groups. Under controlled conditions, the cultivars adapted to water stress through reduced canopy size. When fully-irrigated, they increased vegetative growth than storage root growth, thus resulted in low storage root yield. This suggested that the cultivars were drought tolerant and suitable for production in marginal areas. Leaf phytochemical content was high in sweet potato leaves compared to other common leafy vegetables. It was even higher in leaves of water stressed plants. This indicated that both leaves and storage roots can be utilised for improved food and nutrition security. Under marginal areas where storage root yield is compromised, the leaves can contribute to food and nutrition security. In areas where rainfall is not limited, communities can benefit from both storage roots and leaves.
Assessing variability in yield performance and nutritional quality of citron watermelon (citrullus lanatus var. citroides (L.H. Bailey) mansf. ex greb.) genotypes under drought conditions.
Mandizvo, Takudzwa.; Odindo, Alfred Oduor.; Mashilo, Jacob.
Research is needed to investigate the potential of Neglected Underutilized Crop Species (NUCS) such as citron watermelon, to increase crop diversity and mitigate the effects of prolonged drought because of climate change. Little is known about citron watermelon’s food quality attributes (seed popping yield, nutritional value, and lignin content). In addition, there is a need to understand the agro-morphological, physiological and biochemical characteristics associated with drought tolerance in citron watermelon. Therefore, the objectives of this study were: (1) to assess citron watermelon genotypes for food quality attributes (popping yield, chewability and nutritive value) of seeds based on visual appearance, (2) to screen citron watermelon accessions for drought tolerance using morphological and physiological traits, (3) to study the root system architecture of citron watermelon accessions and identify droughtadaptive root traits for cultivar improvement under water-stressed environments and (4) to reveal how citron watermelon responds to combined stress (water deficit and high temperature) with respect to growth, water status, reserve mobilization and metabolite partitioning at seedling stage. The first study determined whether citron watermelon seed’s nutrient composition and physical properties are related to the visual appearance of seed coat. Brown and red-coloured seeds have a higher popping yield than dark-coloured seeds with poor popping ability and are prone to burning during roasting. Seed coat thickness was closely related to hemicellulose contents and cellulose across all seed coat colours. High hemicellulose, cellulose and lignin contents were found in dark and red seeds associated with thick seed coats and increased chewing strength than white seeds. From a nutritional perspective, dark and red seeds were good sources of Cu, Zn, nitrogen and sulfur than brown seeds. Dark and brown seeds were good Mg sources, whereas dark and red seeds were vital sources of potassium. The second study determined variation in drought tolerance among South African citron watermelon landrace accessions for selection and use as genetic stock for drought-tolerance breeding in this crop and closely related cucurbit crops such as sweet watermelon. The forty citron watermelon accessions evaluated showed varying levels of drought tolerance based on morphological and physiological traits. These allowed five distinct groupings, namely: A (highly drought-tolerant), B (drought-tolerant), C (moderately drought tolerant), D (droughtsensitive) and E (highly drought-sensitive) based on various drought tolerance indices. The following accessions (WWM02, WWM-05, WWM-09, WWM-15, WWM-37(2), WWM-39, WWM-41 (A), WWM-46, WWM-47, WWM-57, WWM-64, WWM-66, WWM-68 and WWM-79) were categorized as highly-drought tolerant and accessions WWM-03, WWM-08, WWM-14, WWM-21, WWM-33, WWM-35(1), WWM-35(2), WWM-67 and WWM-76 as drought tolerant. These are useful genetic stocks for improving drought tolerance in this crop and related cucurbit crops, including sweet watermelon. The third study examined citron watermelon accessions’ root system architecture and identified drought-adaptive root traits for cultivar improvement under water-stressed environments. The study showed that plasticity and biomass allocation shift according to genotype, presumably to optimise the use of limited resources. The study found significant phenotypic variation in root architecture among citron watermelon accessions that may relate to differences in water uptake. The following traits of root system architecture (RSA) (total root length, root system width, convex hull area and total root volume) were associated with drought tolerance. Further, RSA traits such as root dry mass and root shoot mass ratio were highly correlated with root branch count, root system depth, total root length and leaf number. These traits are useful selection criteria for breeding and developing water-efficient citron watermelon accessions for cultivation in drought-prone environments. The fourth study identified multiple abiotic stress-induced modifications in different phytosterols (campesterol, sitosterol and stigmasterol) in the seedling axis (embryonic leaf and root) of genetically distinct citron watermelon accessions. Detailed evaluation of phytosterols was done and the effects of the changes observed in stressed plants were discussed.
Climate change and variability impacts on crop production in the low potential smallholder farming regions of Zimbabwe.
(2016) Jiri, Obert.; Mafongoya, Paramu L.; Chivenge, Pauline.
Climate change and variability is one of the most serious global problems affecting many sectors in the world. It is considered to be one of the most serious threats to sustainable development with adverse impact on environment, human health, food security, economic activities, natural resources and physical infrastructure. Southern Africa is one of the most vulnerable regions to climate change in the world, particularly because of widespread poverty, recurrent droughts, inequitable land distribution, over-dependence on rain-fed agriculture and low adaptive capacity. Yet rural farmers in southern Africa have managed to survive the vagaries of climate change over the years. The central argument in this study was that coping and adaptation strategies to climate change by local smallholder farming communities in Zimbabwe who traditionally relied on indigenous knowledge systems are at risk and less effective because the use of indigenous knowledge systems is becoming unreliable due to climate change and variability. The main objective of this study was to identify local smallholder farmers’ perceptions to climate change and variability and the influence of indigenous knowledge systems in deciding and adopting coping and adaptation strategies. This study used a combination of participatory and field data collection tools in Chiredzi District, one of the areas affected by climate change impacts in Zimbabwe. Household surveys, focus group discussions and key informant interviews were done in selected wards in the district. Field trials were done to identify climate smart cropping options to assist farmers in coping and adapting to climate change and variability. The results indicate that farmers use a variety of local indicators for weather forecasting and climate prediction, for adapting to climate change and variability. Integrating indigenous knowledge systems with climate scientists’ efforts can contribute to effective on-farm adaptation initiatives. One objective of this research was to identify IKS used by farmers to predict seasonal weather patterns, and the subsequent adaptation strategies. The information was collected using focus group discussions, household survey, and ethnographic interviews. Most farmers (72.2%) indicated that low rainfall is the major limitation to agricultural production. Without reliable local scientific weather forecasts the farmers use tree phenology, animal behaviour and atmospheric circulation as sources of local knowledge to predict the onset and quality of the season. These forecasts are then used for designing crop choices, planting dates and agronomic practices. Study results obtained show that the use of IKS in local farming communities is an effective way of building coping and adaptation strategies. The results revealed that IKS are being eroded and becoming less accurate in seasonal weather prediction. Therefore, future studies on IKS should use multiple methods that combine indigenous knowledge and scientific weather data in order to obtain more complete and accurate information for local area season quality prediction. Another study objective was to examine farmer perceptions on climate variability, current adaptive strategies and establish factors influencing smallholder farmers’ adaptation to climate change. The results showed that farmers perceived that there has been a decrease in annual rainfall and an increase in average temperatures. A linear trend analysis of rainfall and temperature data from 1980 to 2011 corroborated the farmers’ perceptions. Farmers’ adaptation options included adjusting planting dates and crop diversification. Off-farm income has reduced the dependence of the farmers on agriculture. A multinomial regression analysis showed that socio-economic factors such as gender, age, number of cattle owned, land size and average crop yields influenced farmer adaptation strategies. We conclude that although farmers are diverse in their socio-economic attributes, they exhibit homogeneous perceptions on changes in climate, which are consistent with observations of empirical climate data. These perceptions help to shape smallholder farmer coping and adaptation strategies. The variability of climate demands the use of a variety of agronomic strategies and crop choices in order to reduce vulnerability and increase resilience and adaptive capacity to climate change and variability. Traditional drought tolerant crops such as sorghum are often chosen when drought seasons are anticipated. However, there are certain crops, originating elsewhere, that could help the smallholder farmers increase diversity of crops that can be grown in changed climates. One such crop is tepary bean (Phaseolus acutifolias). Resource poor farmers, affected by drought effects of climate change, can adopt climate smart crops to achieve food, nutritional and heath security from combinations of cereals and legumes. This study revealed that these rural farmers are highly vulnerable and resilient, largely using indigenous knowledge systems to cope and adapt to climate change. Availability and access to scientific weather information to make cropping and other decisions at the local level remain key issues to usage of climatic data by rural farmers. One the other hand, indigenous knowledge is what they have been using but is also becoming unreliable due to climate change, increasing vulnerability and demanding more resilience. Integration of indigenous knowledge and scientific seasonal forecast seems to be a key possible thrust to reduce vulnerability, enhance resilience of rural farmers and increase their adaptive capacity. This study concludes that farmers can use indigenous knowledge systems to make adaptation decisions. However, there is need to integrate indigenous knowledge systems and scientific knowledge to reduce vulnerability and increase adaptive capacity of smallholder farmers. Climate smart crops provide a useful option for farmers affected by climate change and variability to improve food and nutritional security and livelihoods.
Conceptual conservation agriculture adoption in Zimbabwe.
(2018) Mugandani, Raymond.; Mafongoya, Paramu L.
The adoption of conservation agriculture is increasingly becoming important in southern Africa to sustainably increase food security, manage degraded lands and increasing resilience of agricultural systems to climate change. The practices is relevant to the smallholder farming systems of Zimbabwe where productivity is constrained by lack of access to agricultural inputs, decline in soil fertility and increasing rainfall variability. However despite years of research and extension, the adoption of the practice is very limited and piecemeal in Zimbabwe. Therefore, the main objective of the research was to get an in depth understanding of the barriers to adoption of conservation agriculture in Zimbabwe with specific reference to smallholder farmers. The study employed participatory approaches to collect data in Chivi, Murehwa and Mutoko districts. A pre - tested questionnaire was administered to three selected wards in each of the three district. The questionnaire was triangulated through focus group discussions, key informant interviews and personal observations in order to enhance the richness of our findings. Household survey data was analysed using Statistical Packages for Social Scientists and Statistical Analysis Software, while information obtained during key informant interviews and focus discussions was analysed through thematic analysis. Our results revealed that despite agriculture contributing to the livelihoods of the majority of the smallholder farmers, less than 10 % of the respondents had any formal agricultural training. On the other hand, the level of knowledge on conservation agriculture was high amongst the respondents. However, the non - adopters had an indifferent perception about the technology. The significant (P < 0.05) explanatory variables of the knowledge attribute were age, gender, education, visit to demonstration centres and years of practicing the technology, while the perception attribute was explained by age, gender, education, visit to demo sites, experience in conservation agriculture and agriculture. On the other hand, we found a weak but significant correlation between knowledge and perception (Rs = 0.36, P < 0.05), knowledge and adoption (Rs = 0.484, P < 0.05) but strong and significant correlation between perception and adoption (Rs = 0.808, P < 0.05). The later points to a very important point, that adoption of conservation agriculture can be improved by increasing positive perception of the farmers towards the technology. We also found out that the respondents adopted conservation agriculture through the knowledge (mean score of 2.13; standard error = 0.043)) and compliance (mean score of 2.02; standard error = 0.043) pathways. The explanatory variables of the knowledge pathway were education, experience in agriculture, agricultural training and visit to demonstration centers while the gender of the household was the significant variable in explaining the compliance pathway. The study also investigated access to equipment by smallholder farmers. The results indicate that the respondents had low access to conservation agriculture equipment (mean score of 1.72). The respondents indicated that availability, affordability accessibility and acceptability were the main non - socio - economic constraints to accessing conservation agriculture equipment. On access to agricultural markets, we found out that farmers had low level of access to markets (mean score of 1.814). Gender of household head (β = - 1.3196) and age of household head (β = - 0.63198) all had inverse but significant relationship with access to agricultural markets by the farmers. However, access to inputs (β = 2.3893), access to extension (β = 1.21) and belonging to agricultural groups (β = 0.887) all had positive and significant relationship with access to agricultural markets by the smallholder farmers. The study recommends closing negative perception gaps, understanding appropriate adoption pathways in the promotion of conservation agriculture and providing guidelines on “true” conservation agriculture, linking farmers to markets and improved access to conservation agriculture equipment as the main drivers of adoption of the technology among smallholder farmers in Zimbabwe.
Conservation agriculture and its impact on soil quality and maize yield: A South African perspective.
(2018) Sithole, Nkanyiso Justice.; Magwaza, Lembe Samukelo.
The countries in sub-Saharan Africa (SSA) are faced with the problem of soil degradation resulting from unsustainable soil management practices such as conventional tillage (CT) and the removal of soil biomass from crop land. Conventional tillage leads to deterioration of important soil physical properties, the decline in soil organic carbon (SOC) and increase the risk of soil erosion. The reduction of SOC further affects soil macrofauna which has important key roles in soil processes such as soil structural formation, decomposition of soil organic matter (SOM) and recycling of soil important nutrients. This combined with water scarcity, low inherent soil fertility, increasing population and the predicted negative impacts of climate change poses threat to the regions ability to self-supply enough food for current and future generations. In response to this conservation agriculture (CA) has been endorsed because of its powerful mechanism to adapt by increasing resilience to land degradation, drought and increasing water use efficiency. Soils under no-till CA have been recognised widely that they generally contain higher SOC, the key principal indicator of soil quality, than CT system. These responses, however, are site-specific and depends on soil type, cropping systems, climate, fertilizer application and other management practices. Moreover, most of the published literature on the effect of CA on soil quality parameters comes from cooler temperate regions. As a result, the effect of CA on soil quality parameters in sub-tropical semi-arid environments remains unknown or controversial. Therefore, the primary objective of the study was to assess the effect of no-till (NT), rotational tillage (RT), CT and nitrogen fertilizer application rates on selected physical, chemical and biological properties of the soil and, their influence on maize yield. The secondary objective of the study was to explore the use of visible to near infrared spectroscopy (VIS-NIRS) as a possible cheap alternative for SOC quantification. The study was conducted at Bergville in KwaZulu-Natal Province of South Africa. The trial was established in 2003/04 growing season. This area forms the most important part of rainfed maize production in KwaZulu-Natal Province. The trial was arranged as a split plot with randomized tillage strips forming the whole plot and rate of application forming the sub-plots which are randomized within the whole plots. The experiment included three tillage treatments: 1) no-till (NT) with permanent residue cover, 2) annual conventional tillage (CT) and 3) rotational tillage (RT) every after four years. Nitrogen was applied at three rates, namely; 0 kg/ha, 100 kg/ha and 200 kg/ha. Lime ammonium nitrate (LAN) was used as a source of nitrogen. Unsuitable soil management in agriculture is known to results in deterioration of soil health and the decline in biodiversity. The objective of the study in soil biological properties was to assess the effect of no-till CA on the abundance and order diversity of soil macrofauna in continuous maize monocropping system. Soil macrofauna was sampled at the end of the 2015/2016 growing season using 25 × 25 × 25 cm steel monoliths. The mean density of individual orders was significantly higher (p < 0.001) under NT (46%) and RT (38%) compared with CT (16%). However, the Shannon-Weaver index (H, E index) revealed that the diversity and evenness of orders were similar, H= 2.6 and E~ 1, for all treatments. Macrofauna patterns revealed that NT and RT contained a significantly (p < 0.001) higher population of orders Isoptera and Diplopoda. Order Isoptera was 51% and 17% higher in NT than CT and RT, respectively while in Diplopoda, NT was 39% and 2% higher than CT and RT, respectively. It was concluded that NT and RT mulch-based system favoured the development of macrofauna communities in the studied maize continuous monoculture cropping system but did not favour order diversity of macrofauna. This suggests the importance of crop rotation for the development of the more diverse macrofaunal population. Soil degradation associated with the loss of soil organic carbon (SOC) has been a major concern in sub-Saharan Africa because of the subsequent yield reduction. The objective of the study in soil physical properties was to investigate the effect of NT, RT, CT and N fertilizer applications rate on soil aggregate stability, infiltration, SOC and its size fractions at 0-10, 10-20 and 20-30 cm depth. Soil samples were taken at the end of 2015/16 growing season using soil auger. On average, total SOC did not vary (p > 0.05) across the tillage treatments, 27.1 t/ha (NT) vs 26.0 t/ha (RT) and 26.6 t/ha (CT), but varied with depth where it was stratified in the 0-10 cm depth in NT and RT. Particulate organic C, however, varied significantly (p < 0.05) across the treatments where it decreased with increase in tillage intensity but only in the 0-10 cm depth. Mean weight diameter (MWD) was high under NT and RT and this was correlated to higher infiltration observed in these treatments. The results of this study showed that reduced soil disturbance improves physical protection of SOC, soil structure and infiltration. Soil management practice may change soil chemical properties and thus fertility. The magnitude of change varies depending on soil type, cropping systems, climate, fertilizer application and management practices. The objective of this study on soil chemical characteristics was to assess the effects of tillage systems, residue retention and fertilizer application rates on the amount and distribution of soil major nutrients in the 0-10, 10-20 and 20-30 cm depth. The soil samples were taken at the end of 2015/2016 growing season using soil auger and transported to the University laboratory for chemical analysis. The concentration of total Nitrogen (N) followed the same trend as that observed in soil physical properties. SOC and N were found to be concentrated on the soil surface (0-10 cm depth). Phosphorus was significantly higher (p < 0.001) under NT (0.0213 t/ha) than in RT (0.0127 t/ha) and CT (0.00704 t/ha). A large amount of P was in the 0-10 cm depth in NT and it was distributed more uniformly under RT and CT. Potassium was also higher (p < 0.05) under NT (9.73 t/ha) than in CT (8.00 t/ha) and RT (9.52 t/ha). It was found to be uniformly distributed across the soil depths in all tillage treatments. The soils from NT and RT had lower pH values than CT at 0-10 cm depth while increased significantly in the lower depths. Cation exchange (CEC) capacity followed the same trend. The results indicated that NT treatment increased nutrient availability in the studied soil which was more linked to the distribution of SOC and variability of pH along the soil profile, thus this indicating the potential of implementing NT in the semi-arid environment. Resilient and sustainable soil management systems are needed to overcome soil degradation, arrest soil fertility decline and to offset the predicted negative impact of climate change. This study investigated the long-term (13 years) impact of soil quality parameters (soil physical, chemical and biological properties), N fertilizer application rate and rainfall on maize grain yield. On average (across the years) maize yields were higher in NT (12.3 t/ha) and RT (12.4 t/ha) under higher rate on N fertilizer application (200 kg/ha) than CT (11.8 t/ha). However, yields decreased in NT with the reduction of N fertilizer application rate in medium N rate (100 kg/ha) and low rate (0 t/ha). The yields decreased by 1.7 t/ha, 1.4 t/ha and 0.4 t/ha from high N application rate (200 t/ha) to medium N application rate (100 t/ha) in NT, RT and CT, respectively. Under low rainfall of < 400 mm/year and high N application rate (200 kg/ha), the yield was 9.13 t/ha, 7.96 t/ha and 7.00 t/ha in NT, RT and CT, respectively across the years. However, when the average rainfall was above 600 mm/year, yields averaged at 13.3 t/ha, 13.7 t/ha and 13.5 t/ha in NT, RT and CT under high N fertilizer application rate across the years. Principal component analysis (PCA) was performed to VI assess some biological, physical and chemical properties of the soil that contributed to maize yield. The results showed no parameter that seemed to be related to maize yield. This was attributed to the complex interaction of bio-physio-chemical parameters with the environment. The results of this study found that yields improve over time under CA and this was more pronounced during the drought period. Yields improvements under CA require the application of the higher rate of N fertilizer in correct amount. Therefore, it is recommended that CA is implemented in semi-arid subtropical areas to improve soil conditions, water conservation and to achieve optimum yields. Application of spectroscopy for assessment of soil nutrition in the field may be affected by the depth at which the radiation spreads to, the analysed nutrient, and management practices such as tillage systems. The visible to near infrared spectroscopy (VIS-NIRS) was explored as a technique to predict soil organic carbon (SOC) and soil organic nitrogen (SON) in soils differing in soil tillage management practices. Partial least square regression (PLSR) models were developed using the leave-one-out cross validation method. The models were then tested on independent samples (54) randomly selected from the total 324 samples. The best prediction model was observed for SOC with the coefficient of determination (R2) = 0.993, root mean square error of prediction (RMSEP) = 0.157% and residual predictive deviation (RPD) = 2.55 compared with R2= 0.661, RMSEP= 0.019%, RPD= 2.11 for SON. Considering the predictive statistics and accuracy created by the model in the prediction of SOC, VIS-NIRS can be recommended as a fast, accurate technique for SOC determination in the studied soil. This will significantly reduce the cost associated with SOC and SON analysis for researchers and farmers. UKUFINYEZWA KWENDABA YONKE JIKELELE Amazwe asezansi ne Afrikha abhekene nengwadla enkulu yokudicileka phansi nokuphelelwa umsoco komhlabathi. Lokuphelelwa umsoco komhlabathi kubangelwa izindlela zokutshala ezingalungile ezingahlali isikhathi eside njengokutshala lapho oqale ulime umhlabathi khona bese usebenzisa igeja ususe nokhula. Lokhukulima ngegeja bese ususa ukhula kubangela ukuthi umhlabathi unganothi ngoba usuke ususe amacembe namagatsha agayekile (noma ayimvuthuluka) abaluleke kakhulu ekwakheni inqalasizinda sokuthi umhlabathi ubumbane ubeyimbumba futhi ukwazi ukuthi unikeze izitshalo umsoco wokuthi zikhule kahle. Lezizimvuthuluka zezitshalo um
Cowpea seed quality in response to production site and water stress.
(2007) Odindo, Alfred Oduor.; Modi, Albert Thembinkosi.; Southway, Colin.
Cowpea (Vigna unguiculata. L) is an important African crop. However, it is also an underutilized grain legume. Consequently, there is not enough research data on cowpea seed physiology. Whereas there is evidence of cowpea being a drought tolerant crop, there is no evidence to associate plant drought tolerance with seed quality in response to water stress. This study sought to understand the effect of production site and water stress on cowpea seed quality development with respect to germination capacity and vigour. Patterns of raffinose family of oligosaccharides (RFO) during seed development to mature dry stage were used to physiologically relate seed performance to water stress. The effect of water stress and exogenous ABA on the accumulation of stress LEA proteins (dehydrins) in relation to seed quality development and germination was investigated. RFOs are known for their roles in desiccation sensitivity but no studies have shown their significance in cowpeas. Seeds of six cowpea cultivars were produced at two distinct growth sites characterised by irrigated and dry land conditions. The seeds were assessed during six developmental stages, for water content, dry matter accumulation, and performance. Harvested seeds were then planted in a pot experiment under controlled conditions to examine the effect of water stress on seed quality development and data collected during three developmental stages. Harvested seeds from the pot experiment were subsequently analyzed for changes in RFO accumulation during development using gas chromatography. The seeds were also used to investigate the effect of water stress and ABA on the accumulation of stress LEA proteins (dehydrins) in relation to seed quality development in cowpea. In addition, this study evaluated the use of image analysis as a method that can be used to objectively determine seed coat colour variation in cowpea. Statistical variation in individual seed’s solute leakage for cowpea cultivars differing in seed coat colour and produced under different environmental conditions was explored and correlations were done between seed conductivity test with other aspects of seed performance during germination. Furthermore the results of the conductivity test were compared with accelerated aging test, in relation to seed performance. The study provided evidence that cowpea seed lots produced under different environmental, and possibly management conditions may not differ with respect to seed quality as determined by germination capacity and vigour. However, significant differences between sites with respect to seed maturation patterns determined by water content and dry matter accumulation were observed. Adverse maternal environmental effects on the subsequent performance of seeds in a drought tolerant crop may not necessarily lead to poor performance. Cultivar differences in response to simulated drought conditions at the whole plant and tissue level can be considerable and highly variable; however, these differences may not have adverse effects on the germination and vigour of the seeds. Drought avoidance mechanisms at the whole plant level in cowpea are quite efficient in allowing the species to adapt to simulated drought conditions. These mechanisms may allow the cowpea cultivars to maintain metabolism and restore conditions for their continued growth under water stress; and produce few seeds of high germination capacity and vigour. Stachyose was found to be the predominant member of the raffinose family of oligosaccharides in cowpea. It is suggested that stachyose accumulation could be used as an indicator of stress tolerance in cowpea. However, the relationship between RFO concentration and the acquisition of desiccation remained as a matter of speculation in the present study and is still generally inconclusive. There was no evidence to suggest the acquisition of maximum desiccation tolerance is associated with maximum seed vigour. It is suggested in cowpea, which is drought tolerant, that maximum vigour does not necessarily imply the acquisition of maximum desiccation tolerance; rather there is a minimum level of desiccation tolerance that is required for the development of optimal seed vigour. The use of an in vivo approach in the study of LEA function in cowpea enabled the accurate comparison of two different groups of LEA proteins in developing cowpea seeds under conditions of water stress and in relation to germination and vigour. Both group 1 LEA and group 2 LEA (dehydrin) were shown to increase in concentration in response to water stress. In addition group 1 LEA protein was observed to be relatively abundant in cowpea seeds. A maternal influence on LEA protein gene expression under conditions of water stress, which may induce dehydrin accumulation vii during the earlier stages of seed development, was implied by the observation that dehydrin-like proteins were induced after two weeks of development in cowpea plants subjected to stress during the vegetative phase. In addition, the exogenous application of ABA delayed radicle protrusion; this was associated with a delay in the disappearance of LEA proteins and is suggestive of a relationship between LEA protein accumulation and the acquisition of desiccation tolerance. The study has demonstrated that image analysis can objectively discriminate seed coat colour variation in cowpea. Dark coloured seeds in general performed better than light coloured seeds; however seed coat colour was not always associated with better performance. A newly developed Aging Stress Differential Index (ASDI) has been used in this study to demonstrate a link between seed coat colour and sensitivity to water stress. The ASDI correlated well with the observations relating stress tolerance to stachyose accumulation. The skewed distribution patterns in individual electrical conductivity and the presence of extreme values may have implications with respect to the suitability of using standard statistical analyses which compare mean values to evaluate such data. In addition variation in individual electrical conductivity may also be influenced by cultivar differences and the chemical composition of the seed coat. Therefore associations between seed coat colour and electrical conductivity as a measure of performance should be treated with caution. The AA test does reflect changes in seed vigour, however ranked electrical conductivity values after AA did not consistently reflect differences in seed performance between cultivars and sites, and they did not correlate well with other aspects of performance.
Crop fertigation (nitrogen and phosphorus) with decentralised wastewater treatrment system effluents and effects on soil and groundwater.
(2018) Musazura, William.; Odindo, Alfred Oduor.; Buckley, Christopher Andrew.; Hughes, Jeffrey Charles.; Tesfamariam, Eyob Habte.
Urbanisation is contributing to increased informal settlements in peri-urban areas and municipalities are facing challenges in providing sanitation. The decentralised wastewater treatment system (DEWATS) is a low cost, water-borne, onsite sanitation technology that can potentially serve peri-urban areas. The DEWATS treats human excreta to produce effluent that contains mineral nutrients, especially nitrogen (N) and phosphorus (P). Discharging treated wastewater into water bodies may cause pollution. Considering water scarcity, poverty and hunger issues in most developing countries, reuse of treated wastewater in agriculture promotes sustainable development if done in an environmentally friendly manner. This study therefore aimed at understanding the effects on crops, soils and the environment of fertigating with DEWATS effluent. All the studies were conducted at Newlands-Mashu experimental site (30°57’E, 29°58'S), Durban, South Africa. A field experiment investigated the effects of DEWATS effluent on tissue cultured banana (Musa paradisiaca var Williams) and taro (Caucasia esculenta). The study was carried out in a randomised complete block design with two irrigation treatments (DEWATS effluent without fertiliser vs tap water + fertiliser). Two crops were grown in an intercrop over two cropping cycles using drip irrigation. Two sources of effluent from the DEWATS were used. Effluent after treatment through a horizontal flow constructed wetland (HFCW) was used during the first cropping cycle and anaerobic filter effluent (AF) was used in the second cropping cycle. Data was collected on soil leachates, soil chemical properties, water table level, crop growth, yield and nutrient uptake, with a focus on N and P. Fertigation with DEWATS significantly (p < 0.05) increased taro growth during the first cropping cycle. No significant differences (p > 0.05) were reported for crop yield, N and P uptake and leaching between treatments showing its potential to substitute for inorganic fertilisers. The AF effluent significantly (p > 0.05) increased soil inorganic N in the 0.3 m soil depth (rooting zone) after the second cropping cycle thereby acting as important N fertiliser source. Based on the findings no water table hazards due to low deep percolation and subsurface lateral flow was detected. However, subsurface drainage must be constructed in areas where water table rises to prevent groundwater pollution. A pot experiment was conducted to investigate fertigation of banana using DEWATS effluent on three different soil types. A factorial study was conducted in a complete randomised design. The treatments were three soil types (Inanda (Ia); Rhodic Hapludox / acidic clay soil, Sepane (Se); Aquic Haplustalf / clay loam soil and Cartref (Cf); Typic Haplaquept / sandy loam soil) * two irrigation sources (DEWATS effluent vs tap water + fertiliser) * four replicates. The Ia soil was collected from Worlds View, Pietermaritzburg (29°35′S, 30°19′E), the Cf soil from KwaDinabakubo, Hillcrest (29°44’S; 30°51’E) and the Se was from the field trial site at Newlands-Mashu. Soils for the tap water + fertiliser treatment were mixed with inorganic fertilisers based on recommended crop requirements before being packed in a 90 L pot. The study was carried out over 728 days and all soils were irrigated to field capacity. Data was collected on banana growth (total leaf area and plant height), yield, N and P uptake and leaching, and soil chemical properties. Use of DEWATS effluent significantly (p < 0.05) increased banana growth and yield in the Cf soil thereby showing ability of effluent to improve productivity in nutrient deprived soils. The NH4+-N and P concentrations significantly increased in all DEWATS effluent fertigated soils. Therefore, the effluent is a source of fertiliser that can potentially be used in place of conventional inorganic fertilisers. The N leached from the DEWATS treatment was significantly (p < 0.05) lower than from the tap water + fertiliser treatment hence its use is environmentally sustainable. In all soils fertigated with DEWATS effluent, N leaching was significantly high in Ia soil hence fertigation in such a soil needs proper scheduling. The soil water balance (SWB-Sci) model was used to simulate water, and N and P dynamics in DEWATS effluent fertigated soil. The model was calibrated and validated based on data collected in the field studies. The crop growth model was successfully validated as it met all the standard statistical criteria required (i.e. r2 > 0.8, MAE < 20 % and D > 0.8). High concentrations of inorganic N and P in topsoil fertigated with DEWATS effluent were simulated. Nitrate leaching was comparably higher in DEWATS effluent fertigated soils but without significant impact on ground water contamination in the respective soil. Therefore, the use of DEWATS effluent in clay soils is sustainable. The calculated land area required to fertigate banana and taro in an intercrop using effluent from each DEWATS was 117 m2·household-1 (23.3 m2·person-1). If banana is grown as a sole crop land requirement could have been Cf (290 m2 household-1; 58 m2 person-1), Ia (260 m2 household-1; 52 m2 person-1) and Se (200 m2household-1; 40 m2 person). Based on these findings it can be concluded that DEWATS effluent increases crop growth, yield, nutrient uptake and soil inorganic N and P within the rooting zone like more conventional practices. On-farm irrigation management practices such as scheduling with room for rainfall helps to prevent N and P leaching and rising water table. The SWB-Sci model is an irrigation scheduling and nutrient (N and P) management tool which may be used by decision makers and local governments in producing practical guidelines for sustainable wastewater use projects.
Crop suitability mapping for underutilized crops in South Africa.
(2022) Mugiyo, Hillary.; Mabhaudhi, Tafadzwanashe.; Chimonyo, Vimbayi Grace Petrova.; Kunz, Richard Peter.
Several neglected and underutilised species (NUS) provide solutions to climate change and create a Zero Hunger world, the Sustainable Development Goal 2. However, limited information describing their agronomy, water use, and evaluation of potential growing zones to improve sustainable production has previously been cited as the bottlenecks to their promotion in South Africa's (SA) marginal areas. Therefore, the thesis outlines a series of assessments aimed at fitting NUS in the dryland farming systems of SA. The study successfully mapped current and possible future suitable zones for NUS in South Africa. Initially, the study conducted a scoping review of land suitability methods. After that, South African bioclimatic zones with high rainfall variability and water scarcity were mapped. Using the analytic hierarchy process (AHP), the suitability for selected NUS sorghum (Sorghum bicolor), cowpea (Vigna unguiculata), amaranth and taro (Colocasia esculenta) was mapped. The future growing zones were used using the MaxEnt model. This was only done for KwaZulu Natal. Lastly, the study assessed management strategies such as optimum planting date, plant density, row spacing, and fertiliser inputs for sorghum. The review classified LSA methods reported in articles as traditional (26.6%) and modern (63.4%). Modern approaches, including multicriteria decision-making (MCDM) methods such as AHP (14.9%) and fuzzy methods (12.9%), crop simulation models (9.9%) and machine-learning-related methods (25.7%), are gaining popularity over traditional methods. The review provided the basis and justification for land suitability analysis (LSA) methods to map potential growing zones of NUS. The review concluded that there is no consensus on the most robust method for assessing NUS's current and future suitability. South Africa is a water-scarce country, and rainfall is undoubtedly the dominating factor determining crop production, especially in marginal areas where irrigation facilities are limited for smallholder farmers. Based on these challenges, there is a need to characterise bioclimatic zones in SA that can be qualified under water stress and with high rainfall variation. Mapping high-risk agricultural drought areas were achieved by using the Vegetation Drought Response Index (VegDRI), a hybrid drought index that integrates the Standardized Precipitation Index (SPI), Temperature Condition Index (TCI), and the Vegetation Condition Index (VCI). In NUS production, land use and land classification address questions such as “where”, “why”, and “when” a particular crop is grown within particular agroecology. The study mapped the current and future suitable zones for NUS. The current land suitability assessment was done using Analytic Hierarchy Process (AHP) using multidisciplinary factors, and the future was done through a machine learning model Maxent. The maps developed can contribute to evidence-based and site-specific recommendations for NUS and their mainstreaming. Several NUS are hypothesised to be suitable in dry regions, but the future suitability remains unknown. The future distribution of NUS was modelled based on three representative concentration pathways (RCPs 2.6, 4.5 and 8.5) for the years between 2030 and 2070 using the maximum entropy (MaxEnt) model. The analysis showed a 4.2-25% increase under S1-S3 for sorghum, cowpea, and amaranth growing areas from 2030 to 2070. Across all RCPs, taro is predicted to decrease by 0.3-18 % under S3 from 2050 to 2070 for all three RCPs. Finally, the crop model was used to integrate genotype, environment and management to develop one of the NUS-sorghum production guidelines in KwaZulu-Natal, South Africa. Best sorghum management practices were identified using the Sensitivity Analysis and generalised likelihood uncertainty estimation (GLUE) tools in DSSAT. The best sorghum management is identified by an optimisation procedure that selects the optimum sowing time and planting density-targeting 51,100, 68,200, 102,500, 205,000 and 300 000 plants ha-1 and fertiliser application rate (75 and 100 kg ha-1) with maximum long-term mean yield. The NUS are suitable for drought-prone areas, making them ideal for marginalised farming systems to enhance food and nutrition security.
Drought tolerance and water-use of selected South African landraces of Taro (Colocasia esculenta L. schott) and Bambara groundnut (Vigna subterranea L. Verdc)
(2012) Mabhaudhi, Tafadzwanashe.; Modi, Albert Thembinkosi.
Issues surrounding water scarcity will become topical in future as global fresh water resources become more limited thus threaten crop production. Predicted climate change and increasing population growth will place more pressure on agriculture to produce more food using less water. As such, efforts have now shifted to identifying previously neglected underutilised species (NUS) as possible crops that could be used to bridge the food gap in future. Taro (Colocasia esculenta L. Schott) and bambara groundnut (Vigna subterranea L. Verdc) currently occupy low levels of utilisation in South Africa. Both crops are cultivated using landraces with no improved varieties available. Information describing their agronomy and water–use is limited and remains a bottleneck to their promotion. The aim of this study was to determine the drought tolerance and water–use of selected landraces of taro and bambara groundnut from KwaZulu-Natal, South Africa. In order to meet the specific objectives for taro and bambara groundnut management, an approach involving conventional and modelling techniques was used. Three taro landraces [Dumbe Lomfula (DL), KwaNgwanase (KW) and Umbumbulu (UM)] were collected from the North Coast and midlands of KwaZulu-Natal, South Africa, in 2010. The UM landrace was classified as Eddoe type taro (C. esculenta var. antiquorum) characterised by a central corm and edible side cormels. The DL and KW landraces were classified as Dasheen (C. esculenta var. esculenta), characterised by a large edible main corm and smaller side cormels. A bambara groundnut landrace was collected from Jozini, KwaZulu- Natal, and characterised into three selections (‘Red’, ‘Light-brown’ and ‘Brown’) based on seed coat colour. Seed colour was hypothesised to have an effect on seed quality. Field and rainshelter experiments were conducted for both taro and bambara landraces at Roodeplaat in Pretoria and Ukulinga Research Farm in Pietermaritzburg, over two growing seasons (2010/11 and 2011/12). The objective of the field trials for taro and bambara groundnut was to determine mechanisms associated with drought tolerance in taro and bambara groundnut landraces. Experiments were laid out in a split-plot design where irrigation [fully irrigated (FI) and rainfed (RF)] was the main factor and landraces (3 landraces of either taro or bambara groundnut) were sub-factors. Treatments were arranged in a randomised complete block design (RCBD), replicated three times. Rainfed trials were established with irrigation to allow for maximum crop stand. Thereafter, irrigation was withdrawn. Whilst experimental designs and layouts for taro and bambara groundnut were similar, differences existed with regards to plot sizes and plant spacing. Trials were planted on a total land area of 500 m2 and 144 m2, for taro and bambara groundnut, respectively. Plant spacing was 1 m x 1 m for taro and 0.3 m x 0.3 m for bambara groundnut. Irrigation scheduling in the FI treatment was based on ETo and Kc and was applied using sprinkler irrigation system. Separate rainshelter experiments were conducted for taro and bambara groundnut landraces at Roodeplaat, to evaluate growth, yield and water-use of taro and bambara groundnut landraces under a range of water regimes. The experimental design was similar for both crops, a RCBD with two treatment factors: irrigation level [30, 60 and 100% crop water requirement (ETa)] and landrace (3 landraces), replicated three times. Irrigation water was applied using drip irrigation system based on ETo and Kc. Data collection in field and rainshelter trials included time to emergence, plant height, leaf number, leaf area index (LAI), stomatal conductance and chlorophyll content index (CCI). For taro field trials, vegetative growth index (VGI) was also determined. Yield and yield components (harvest index, biomass, corm number and mass) as well as water–use efficiency (WUE) were determined at harvest. Intercropping of taro and bambara groundnut was evaluated under dryland conditions using farmers’ fields at Umbumbulu, KwaZulu–Natal, South Africa. The experimental design was a RCBD replicated three times. Intercrop combinations included taro and bambara groundnut sole crops, a 1:1 (one row taro to one row bambara groundnut) and 1:2 intercrop combinations. The taro UM landrace and ‘Red’ bambara groundnut landrace selection were used in the intercropping study. Lastly, data collected from field and rainshelter experiments were used to develop crop parameters to calibrate and validate the FAO’s AquaCrop model for taro and bambara groundnut landraces. The UM landrace was used for taro while the ‘Red’ landrace selection was used for bambara groundnut. AquaCrop was calibrated using observed data from optimum (FI) experiments conducted during 2010/11. Model validation was done using observations from field and rainshelter experiments conducted during 2011/12 as well as independent data. Results showed that all taro landraces were slow to emerge (≈ 49 days after planting). Stomatal conductance declined under conditions of limited water availability (RF, 60% and 30% ETa). The UM landrace showed better stomatal regulation compared with KW and DL landraces under conditions of limited water availability. Plant growth (plant height, leaf number, LAI and CCI) of taro landraces was lower under conditions of limited water availability (RF, 60% and 30% ETa) relative to optimum conditions (FI and 100% ETa). The UM landrace showed moderate reductions in growth compared with the DL and KW landraces, suggesting greater adaptability to water limited conditions. The VGI showed a large reduction in growth under RF conditions and confirmed the UM landrace’s adaptability to limited water availability. Limited water availability (RF, 60% and 30% ETa) resulted in lower biomass, HI, and final yield in taro landraces relative to optimum conditions (FI and 100% ETa). For all trials, the DL landrace failed to produce any yield. WUE of taro landraces was consistent for the three irrigation levels (30, 60 and 100% ETa); however, on average, the UM landrace was shown to have a higher WUE than the KW landrace. Bambara groundnut landraces were slow to emerge (up to 35 days after planting). ‘Red’ and ‘Brown’ landrace selections emerged better than the ‘Light-brown’ landrace selection, confirming the effect of seed colour on early establishment performance. Plant growth (stomatal conductance, CCI, plant height, leaf number, LAI and biomass accumulation) was lower under conditions of limited water availability (RF, 60% and 30% ETa) relative to optimum conditions (FI and 100% ETa). The ‘Red’ landrace selection showed better adaptation to stress. Limited water availability resulted in early flowering and reduced flowering duration as well as early senescence and maturity of bambara groundnut landrace selections. The ‘Red’ landrace selection showed delayed leaf senescence under conditions of limited water availability. Yield reductions of up to 50% were observed under water limited conditions (RF, 60% and 30% ETa) relative to optimum conditions (FI and 100% ETa). Water use efficiency increased at 60% and 30% ETa, respectively, relative to 100% ETa, implying adaptability to limited water availability. The ‘Red’ landrace selection showed better yield stability and WUE compared with the ‘Brown’ and ‘Light-brown’ landrace selections suggesting that seed colour may be used as a selection criterion for drought tolerance in bambara groundnut landraces. The intercropping study showed that intercropping, as an alternative cropping system, had more potential than monocropping. Evaluation of growth parameters showed that taro plant height was generally unaffected by intercropping but lower leaf number was observed as compared with the sole crop. Bambara groundnut plants were taller and had more leaves under intercropping relative to the sole crop. Although not statistically significant, yield was generally lower in the intercrops compared with the sole crops. Evaluation of intercrop productivity using the land equivalent ratio (LER) showed that intercropping taro and bambara groundnut at a ratio of 1:1 was more productive (LER = 1.53) than intercropping at a ratio of 1:2 (LER = 1.23). The FAO’s AquaCrop model was then calibrated for the taro UM landrace and ‘Red’ bambara groundnut landrace selection. This was based on observations from previous experiments that suggested them to be drought tolerant and stable. Calibration results for taro and bambara groundnut landraces showed an excellent fit between predicted and observed parameters for canopy cover (CC), biomass and yield. Model validation for bambara groundnut showed good model performance under field (FI and RF) conditions. Model performance was satisfactory for rainshelters. Validation results for taro showed good model performance under all conditions (field and rainshelters), although the model over-estimated CC for the declining stage of canopy growth under RF conditions. Model verification using independent data for taro showed equally good model performance. In conclusion, the taro UM landrace and ‘Red’ bambara groundnut landrace selection were shown to be drought tolerant and adapted to low levels of water–use. The mechanisms responsible for drought tolerance in the taro UM landrace and ‘Red’ bambara groundnut landrace selection were described as drought avoidance and escape. The taro UM landrace and ‘Red’ bambara groundnut landraces avoided stress through stomatal regulation, energy dissipation (loss of chlorophyll) as well as reducing canopy size (plant height, leaf number and LAI), which translates to minimised transpirational water losses. This indicated landrace adaptability to low levels of water–use. The ‘Red’ bambara groundnut landrace selection showed phenological plasticity and escaped drought by flowering early, delaying leaf senescence, and maturing early under conditions of limited water availability. Performance of the ‘Red’ landrace selection lends credence to the use of seed coat colour as a possible selection criterion for drought tolerance in bambara groundnut, and possibly for other landraces with variegated seed. The taro UM landrace escaped drought by maturing early under conditions of limited water availability. The FAO’s AquaCrop model was successfully calibrated and validated for taro UM and ‘Red’ bambara groundnut landraces. The calibration and validation of AquaCrop for taro is the first such attempt and represents progress in the modelling of neglected underutilised crops. The calibration and validation of AquaCrop for taro requires further fine-tuning while that for bambara groundnut still needs to be tested for more diverse landraces.
Drought tolerance and water-use of selected South African landraces of Taro (Colocasia esculenta L. schott) and Bambara groundnut (Vigna subterranea L. Verdc)
(2012) Mabhaudhi, Tafadzwanashe.; Modi, Albert Thembinkosi.
Issues surrounding water scarcity will become topical in future as global fresh water resources become more limited thus threaten crop production. Predicted climate change and increasing population growth will place more pressure on agriculture to produce more food using less water. As such, efforts have now shifted to identifying previously neglected underutilised species (NUS) as possible crops that could be used to bridge the food gap in future. Taro (Colocasia esculenta L. Schott) and bambara groundnut (Vigna subterranea L. Verdc) currently occupy low levels of utilisation in South Africa. Both crops are cultivated using landraces with no improved varieties available. Information describing their agronomy and water–use is limited and remains a bottleneck to their promotion. The aim of this study was to determine the drought tolerance and water–use of selected landraces of taro and bambara groundnut from KwaZulu-Natal, South Africa. In order to meet the specific objectives for taro and bambara groundnut management, an approach involving conventional and modelling techniques was used. Three taro landraces [Dumbe Lomfula (DL), KwaNgwanase (KW) and Umbumbulu (UM)] were collected from the North Coast and midlands of KwaZulu-Natal, South Africa, in 2010. The UM landrace was classified as Eddoe type taro (C. esculenta var. antiquorum) characterised by a central corm and edible side cormels. The DL and KW landraces were classified as Dasheen (C. esculenta var. esculenta), characterised by a large edible main corm and smaller side cormels. A bambara groundnut landrace was collected from Jozini, KwaZulu- Natal, and characterised into three selections (‘Red’, ‘Light-brown’ and ‘Brown’) based on seed coat colour. Seed colour was hypothesised to have an effect on seed quality. Field and rainshelter experiments were conducted for both taro and bambara landraces at Roodeplaat in Pretoria and Ukulinga Research Farm in Pietermaritzburg, over two growing seasons (2010/11 and 2011/12). The objective of the field trials for taro and bambara groundnut was to determine mechanisms associated with drought tolerance in taro and bambara groundnut landraces. Experiments were laid out in a split-plot design where irrigation [fully irrigated (FI) and rainfed (RF)] was the main factor and landraces (3 landraces of either taro or bambara groundnut) were sub-factors. Treatments were arranged in a randomised complete block design (RCBD), replicated three times. Rainfed trials were established with irrigation to allow for maximum crop stand. Thereafter, irrigation was withdrawn. Whilst experimental designs and layouts for taro and bambara groundnut were similar, differences existed with regards to plot sizes and plant spacing. Trials were planted on a total land area of 500 m2 and 144 m2, for taro and bambara groundnut, respectively. Plant spacing was 1 m x 1 m for taro and 0.3 m x 0.3 m for bambara groundnut. Irrigation scheduling in the FI treatment was based on ETo and Kc and was applied using sprinkler irrigation system. Separate rainshelter experiments were conducted for taro and bambara groundnut landraces at Roodeplaat, to evaluate growth, yield and water-use of taro and bambara groundnut landraces under a range of water regimes. The experimental design was similar for both crops, a RCBD with two treatment factors: irrigation level [30, 60 and 100% crop water requirement (ETa)] and landrace (3 landraces), replicated three times. Irrigation water was applied using drip irrigation system based on ETo and Kc. Data collection in field and rainshelter trials included time to emergence, plant height, leaf number, leaf area index (LAI), stomatal conductance and chlorophyll content index (CCI). For taro field trials, vegetative growth index (VGI) was also determined. Yield and yield components (harvest index, biomass, corm number and mass) as well as water–use efficiency (WUE) were determined at harvest.Intercropping of taro and bambara groundnut was evaluated under dryland conditions using farmers’ fields at Umbumbulu, KwaZulu–Natal, South Africa. The experimental design was a RCBD replicated three times. Intercrop combinations included taro and bambara groundnut sole crops, a 1:1 (one row taro to one row bambara groundnut) and 1:2 intercrop combinations. The taro UM landrace and ‘Red’ bambara groundnut landrace selection were used in the intercropping study. Lastly, data collected from field and rainshelter experiments were used to develop crop parameters to calibrate and validate the FAO’s AquaCrop model for taro and bambara groundnut landraces. The UM landrace was used for taro while the ‘Red’ landrace selection was used for bambara groundnut. AquaCrop was calibrated using observed data from optimum (FI) experiments conducted during 2010/11. Model validation was done using observations from field and rainshelter experiments conducted during 2011/12 as well as independent data. Results showed that all taro landraces were slow to emerge (≈ 49 days after planting). Stomatal conductance declined under conditions of limited water availability (RF, 60% and 30% ETa). The UM landrace showed better stomatal regulation compared with KW and DL landraces under conditions of limited water availability. Plant growth (plant height, leaf number, LAI and CCI) of taro landraces was lower under conditions of limited water availability (RF, 60% and 30% ETa) relative to optimum conditions (FI and 100% ETa). The UM landrace showed moderate reductions in growth compared with the DL and KW landraces, suggesting greater adaptability to water limited conditions. The VGI showed a large reduction in growth under RF conditions and confirmed the UM landrace’s adaptability to limited water availability. Limited water availability (RF, 60% and 30% ETa) resulted in lower biomass, HI, and final yield in taro landraces relative to optimum conditions (FI and 100% ETa). For all trials, the DL landrace failed to produce any yield. WUE of taro landraces was consistent for the three irrigation levels (30, 60 and 100% ETa); however, on average, the UM landrace was shown to have a higher WUE than the KW landrace. Bambara groundnut landraces were slow to emerge (up to 35 days after planting). ‘Red’ and ‘Brown’ landrace selections emerged better than the ‘Light-brown’ landrace selection, confirming the effect of seed colour on early establishment performance. Plant growth (stomatal conductance, CCI, plant height, leaf number, LAI and biomass accumulation) was lower under conditions of limited water availability (RF, 60% and 30% ETa) relative to optimum conditions (FI and 100% ETa). The ‘Red’ landrace selection showed better adaptation to stress. Limited water availability resulted in early flowering and reduced flowering duration as well as early senescence and maturity of bambara groundnut landrace selections. The ‘Red’ landrace selection showed delayed leaf senescence under conditions of limited water availability. Yield reductions of up to 50% were observed under water limited conditions (RF, 60% and 30% ETa) relative to optimum conditions (FI and 100% ETa). Water use efficiency increased at 60% and 30% ETa, respectively, relative to 100% ETa, implying adaptabilityto limited water availability. The ‘Red’ landrace selection showed better yield stability and WUE compared with the ‘Brown’ and ‘Light-brown’ landrace selections suggesting that seed colour may be used as a selection criterion for drought tolerance in bambara groundnut landraces. The intercropping study showed that intercropping, as an alternative cropping system, had more potential than monocropping. Evaluation of growth parameters showed that taro plant height was generally unaffected by intercropping but lower leaf number was observed as compared with the sole crop. Bambara groundnut plants were taller and had more leaves under intercropping relative to the sole crop. Although not statistically significant, yield was generally lower in the intercrops compared with the sole crops. Evaluation of intercrop productivity using the land equivalent ratio (LER) showed that intercropping taro and bambara groundnut at a ratio of 1:1 was more productive (LER = 1.53) than intercropping at a ratio of 1:2 (LER = 1.23). The FAO’s AquaCrop model was then calibrated for the taro UM landrace and ‘Red’ bambara groundnut landrace selection. This was based on observations from previous experiments that suggested them to be drought tolerant and stable. Calibration results for taro and bambara groundnut landraces showed an excellent fit between predicted and observed parameters for canopy cover (CC), biomass and yield. Model validation for bambara groundnut showed good model performance under field (FI and RF) conditions. Model performance was satisfactory for rainshelters. Validation results for taro showed good model performance under all conditions (field and rainshelters), although the model over-estimated CC for the declining stage of canopy growth under RF conditions. Model verification using independent data for taro showed equally good model performance. In conclusion, the taro UM landrace and ‘Red’ bambara groundnut landrace selection were shown to be drought tolerant and adapted to low levels of water–use. The mechanisms responsible for drought tolerance in the taro UM landrace and ‘Red’ bambara groundnut landrace selection were described as drought avoidance and escape. The taro UM landrace and ‘Red’ bambara groundnut landraces avoided stress through stomatal regulation, energy dissipation (loss of chlorophyll) as well as reducing canopy size (plant height, leaf number and LAI), which translates to minimised transpirational water losses. This indicated landrace viii adaptability to low levels of water–use. The ‘Red’ bambara groundnut landrace selection showed phenological plasticity and escaped drought by flowering early, delaying leaf senescence, and maturing early under conditions of limited water availability. Performance of the ‘Red’ landrace selection lends credence to the use of seed coat colour as a possible selection criterion for drought tolerance in bambara groundnut, and possibly for other landraces with variegated seed. The taro UM landrace escaped drought by maturing early under conditions of limited water availability. The FAO’s AquaCrop model was successfully calibrated and validated for taro UM and ‘Red’ bambara groundnut landraces. The calibration and validation of AquaCrop for taro is the first such attempt and represents progress in the modelling of neglected underutilised crops. The calibration and validation of AquaCrop for taro requires further fine-tuning while that for bambara groundnut still needs to be tested for more diverse landraces.
The effect of maize-legume cropping system and nitrogen fertilization on yield, soil organic carbon and soil moisture.
(2015) Sebetha, Erick.; Modi, Albert Thembinkosi.; Owoeye, Lawrence.
Crop rotation and intercropping are regarded as better cropping in terms of yield improvement of both cereal and legume crops as compared to monocropping. A factorial experiment was carried out at three dryland localities of Northwest province (Potchefstroom, Rustenburg and Taung) from 2010/11 to 2012/13 planting seasons. The experiment consisted of three cropping systems, monocropping, intercropping and rotational cropping. Two rates of nitrogen fertilizer, zero and optimum levels based on soil analysis results prior to planting were applied on maize and cowpea plots. Soil moisture content was evaluated during three growth stages at different depths of the soil (0-15, 15-30, 30-60 and 60-90 cm) using gravimetric method. Parameters considered for the study included the followings: 100% tasseling/flowering, days to physiological maturity, plant height, number of leaves per plant, leaf area in maize, stem diameter in maize, ear length in maize, ear mass , kernel number per ear, hundred seed mass, grain yield in maize, LER, plant population at harvest and stover yield in maize, number of leaves and nodules per cowpea plant, pod length, seed per pod, pod mass at harvest, grain, field biomass yield at harvest, cowpea leaf, immature pod, seed protein content and maize seed protein, oil, starch and phosphorus content. The analysed soil chemical properties included soil organic carbon using Walkley Black method, soil Bray 1-P; N-NO3, N-NH4 and exchangeable K. Cropping system had significant effect (P < 0.05) on the growth and yield of maize. Cowpea-maize rotation and monocropping maize had tasseled earlier, reached days to physiological maturity earlier, had large leaf area, higher number of leaves per plant, ear mass, kernel number, seed mass, grain yield and stover yield. Maize-cowpea rotation and monocropping cowpea had significantly (P < 0.05) higher number of leaves per plant, seed per pod, pod mass, grain yield and field biomass yield than intercropped cowpea. Cropping system had significant effect (P < 0.05) on soil organic carbon; Bray 1-P and soil nitrate (N-NO3). The interaction effect of cropping system on cropping system x nitrogen x site on maize yield, cowpea growth, protein content and soil N-NO3 contributed towards significant of this study. The chapters of this thesis represent different studies presented as different articles. Chapter 1 is a general introduction to explain the study background and hypothesis. Chapter 2 is on the effect of maize-cowpea cropping system on soil moisture content. Chapter 3 is on crop rotation and intercropping cowpea with maize: maize growth and yield. Chapter 4 is on crop rotation and intercropping cowpea and maize: cowpea growth and yield. Chapter 5 is on the effect of crop rotation and intercropping on cowpea crude protein. Chapter 6 is on the maize seed quality in response to crop rotation, intercropping and nitrogen fertilization. Chapter 7 is on the effect of maize-cowpea cropping system on soil chemical composition. The last chapter 8 is a general discussion and conclusion.
Effects of biochar addition on soil nitrogen retention and vegetable uptake in intensive production systems, China.
(2017) Yu, Ying Liang.; Odindo, Alfred Oduor.; Pillay, Balakrishna.; Yang, Linzhang.
China has a limited area of cultivated land per capita and an increasing population. Maintaining a high crop yield is essential to meet the large food demand and to assure grain self-sufficiency. With the pace of economic development, the demand for vegetables keeps growing. In Southern China, many of the fields used to grow vegetables were previously under paddy production. Compared to the paddy production system, the vegetable production system is intensive with excessive use of nitrogen fertilizer. Excessive nitrogen fertilizer application has changed soil chemical properties and nutrient dynamics, and thus created a negative impact on sustainable agricultural development. A preliminary study was conducted in the absence of nitrogen fertilizer to determine the effect of field utilization conversion on soil nitrogen uptake by pakchoi. It was found that soil pH values and organic matter content decreased with intensive vegetable planting and nitrogen leaching loss was higher from vegetable soils compared to that from paddy soils. Although the soil mineral nitrogen content in vegetable soils was higher than that in paddy soils, nitrogen uptake by plants from vegetable soils was lower than that from paddy soils, and decreased quickly in the later growing seasons. The lower plant nitrogen uptake was attributed to the high nitrogen leaching loss and soil acidity caused by the excessive application of nitrogen fertilizer in vegetable production systems. Therefore, it is imperative to find suitable approaches to mitigate nitrogen leaching loss and soil acidity in vegetable production systems and promote nitrogen retention and vegetable nitrogen uptake for sustainable productivity. Biochar is a fine-grained and porous substance produced through pyrolysis processes, under oxygen-free conditions, from a wide range of biomass. In recent years, biochar has received more attention with regard to its capacity to increase crop yields by ameliorating the soil environment and regulating nutrient processes. According to previous studies, biochar is an option for mitigating soil acidity and nitrogen leaching problems in vegetable soils due to its alkalinity and adsorption properties. However, studies of biochar addition to vegetable production systems have not been well documented. The effect of biochar addition on leachate volume is still lacking. Whether the mineral nitrogen retained by biochar can be re-used by plants is still unknown. Few studies have investigated the effect of biochar addition on nitrogen processes and soil acidity under continuous growing conditions. Therefore, with the aim of determining the effect of biochar on soil nitrogen retention and vegetable nitrogen uptake, pakchoi was planted in a pot experiment during four continuous growing seasons with three biochar addition rates (0, 1% w/w and 5% w/w). In the 1st, 2nd and 3rd seasons, pakchoi was applied with 15N-labelled urea and in the 4th season no nitrogen fertilizer was provided. The results of this study were presented in four parts (soil nitrogen retention, soil acidity, vegetable nitrogen uptake and a distinction between two nitrogen sources in vegetable nitrogen uptake i.e. nitrogen left in the soil and nitrogen loss). The main conclusions are as follows: Biochar addition significantly increased the soil mineral nitrogen content by enhancing nitrogen retention in soils and soil nitrogen mineralization. Part of the mineral nitrogen retained by biochar was still bioavailable for plant uptake in the soil. Biochar significantly reduced nitrogen leaching loss by decreasing leachate volumes and nitrate concentrations in the leachate. Biochar addition significantly ameliorated or retarded soil acidity by promoting soil pH buffering capacity, reducing soil acidification rates and maintaining soil bases contents induced by biochar. The mitigation of soil acidity was not only as a result of biochar’s natural alkalinity but can also be attributed to the altered nitrogen processes (promotion of plant nitrate uptake, reduction of nitrification and nitrate leaching and maintaining soil bases contents) with the addition of biochar. Biochar’s mitigation of soil acidity was partly dependent on its effect on soil properties (such as bases contents) and processes (such as nitrification, nitrate leaching and plant nitrate uptake) rather than its natural alkalinity. Biochar maintained pakchoi yields and nitrogen uptake during four growing seasons. The fertilizer nitrogen recovery efficency was improved with an increase in the recovery of fertilizer nitrogen in the soil and the decrease in the recovery of fertilizer nitrogen in leachate. Fertilizer nitrogen was the major source for pakchoi nitrogen uptake, soil residual nitrogen and nitrogen leaching loss, while nitrogen from soil mineralization was the major nitrogen source for biochar retention. When nitrogen fertilizer was absent in the 4th season, the nitrogen fertilizer left in the soil from the 1st to 3rd seasons decreased sharply and fertilizer nitrogen retained by biochar was simultaneously released. The conclusion was that biochar addition could promote soil nitrogen retention and maintain high nitrogen uptake by vegetables in continuous growing seasons. However, the comprehensive effect of biochar on nitrogen loss still needs to be assessed before recommending extended utilization of biochar in vegetable production systems in China.
The efficacy of Moringa oleifera plant extracts against selected fungal and bacterial plant pathogens infecting selected vegetable crops in Zimbabwe.
(2018) Goss, Maria.; Mafongoya, Paramu L.; Gubba, Augustine.
Diseases and pests are among the major constraints to horticultural production worldwide, and this has been further exacerbated by mono-cropping production systems in response to increased food demands of an ever-expanding population. As a result, farmers have resorted to excessive chemical use in order to manage diseases and pests, and maintain high yields. However, excessive chemical use has been associated with negative environmental and health effects. Numerous studies have been carried out to determine antifungal and antibacterial properties in traditional medicinal plants aimed at developing bio-pesticides which can be utilized together with synthetic pesticides in integrated disease management strategies. One such alternative is the use of Moringa oleifera extracts. Currently, in-vitro studies carried out on Moringa antimicrobial action have mainly focused on controlling human enteric pathogens. It is against this background that this study was conducted during the 2014 – 2016 cropping seasons. The main objectives of the study were to: 1) determine farmers’ perceptions on vegetable disease incidence, prevalence and disease control methods in relation to seasonality and prevailing climactic conditions. 2) Evaluate effectiveness of Moringa leaf and seed plant extracts in suppressing growth and development of bacterial (Pectobacterium atrosepticum, Hall, Pectobacterium carotovorum subspp. brasilienses, Bur., Dickeya dadantii, Dick.) and fungal (Pythium ultimum, Trow., Rhizoctonia solani, Kuhn., Fusarium solani, Mart., Phytophthora infestans, Mont.) plant pathogens in-vitro. 3) Determine whether Moringa aqueous extract concentration influences the efficacy of its antimicrobial activity. 4) Determine whether Moringa bark aqueous extracts could exhibit antibacterial activity against four different pathovars of the Xanthomonas campestris, Pammel., pathogen. 5) Determine the antifungal and antibacterial efficacy of Moringa leaf, seed and bark aqueous extracts against selected fungal and bacterial pathogens infecting two crops Lettuce (Lactuca sativa, L.) and Cabbage (Brassica olearacea, L.) grown under greenhouse and open field conditions respectively. Initially, a survey was carried out to determine the perceptions of horticulture farmers on crop disease incidence and control methods in the sub-humid areas of Zimbabwe. Survey results revealed that farmers face more outbreaks of fungal diseases compared to bacterial diseases. In addition, farmers have noted an increase in disease incidence over the past 5 – 10 years. The survey further revealed that the majority of the respondents depend on chemicals to control diseases in their crops. Only a small percentage of the farmers use cultural or mechanical alternative disease control methods. However, none of the respondents utilize botanical or bio-pesticide disease control strategies to manage these diseases. There is need to raise awareness among farmers regarding the negative health and environmental effects of increased chemical use and the potential of using bio-pesticide strategies in plant disease management. Field and greenhouse trials were conducted over three growing seasons using the completely randomized block and split plot experimental designs set up as factorial trials. The laboratory results exhibited the efficacy of Moringa leaf, bark and seed aqueous extracts in significantly controlling the growth of fungal (Pythium ultimum, Rhizoctonia solani, Fusarium solani and Phytophthora infestans) and bacterial (Pectobacterium carotovorium subspp. brasiliensis, Pectobacterium atrosepticum and Xanthomonas campetris pv campestris) pathogens. There were significant interactions between Moringa aqueous extract source and concentration which influenced the antimicrobial action of the extracts (P = 0.001). The results from the greenhouse and field studies revealed that Moringa leaf, seed and bark aqueous extracts significantly controlled bottom rot (Rhizoctonia solani) and stem/root rot (Fusarium solani) diseases in lettuce and black rot disease (Xanthomonas campestris pv campestris) in cabbages (P < 0.05). Disease suppression was more effective at higher concentrations of the Moringa aqueous extracts, whilst the highest disease severity occurred at the lowest Moringa aqueous concentration levels. However, Moringa seed aqueous extract demonstrated higher antibacterial activity against black rot disease and antifungal activity against test pathogens (P < 0.05). Moringa seed and leaf aqueous extracts also significantly enhanced head weight and diameter in lettuce. Moringa aqueous extracts can therefore be considered as bio-pesticides in Integrated Crop Disease Management strategies, and these can be a viable, and environmentally friendly alternative to chemical use. Based on our findings, it is recommended that further in-vivo studies to improve extraction protocols, and determine ideal application methods be carried out to improve Moringa aqueous extract bio-pesticide efficacy. These should be carried out in selected crop pathogens of economic importance. Currently, there is very little literature regarding in-vivo crop, pathogen and bio-pesticide interaction studies with Moringa. Training workshops and demonstration plots to impart knowledge and skills to farmers on preparation and utilization is key to enhance uptake.
Emerging and new pests under climate change in Limpopo Province, South Africa.
(2018) Phophi, Mutondwa Masindi.; Mafongoya, Paramu L.
Vegetable production is constrained by pests such as weeds, insects and diseases. The damage caused by pests and diseases can be highly exacerbated by climatic changes and variability. Poor agricultural practices play a role in increasing greenhouse gas emissions which contribute to climate change. Climatic factors such as increased temperature, increased carbon dioxide levels and erratic rainfall are responsible for influencing pest distributions, pest migration and increased pest population. Distribution and migration of pests can also result from globalization, trade and movement of people. Poor biosecurity and phytosanitary measures are also involved in bringing new pests in countries. This study was conducted in Limpopo Province in four municipalities of Vhembe District (Mutale, Musina, Makhado and Thulamela). Quantitative and qualitative techniques were used in data collection. Data was collected through questionnaire surveys, focus groups discussions and key informants. Farmers were randomly selected from a list provided by extension officers in each municipality. Three focus groups were conducted in each municipality consisting of seven women, seven men and a combined group of seven men and women. Statistical Package for Social Sciences (SPSS) was used to compare mean differences between different variables. Means and significant differences between means were declared at P ≤ 0.05. The aim of this study was to evaluate the presence of new and emerging pests in Limpopo Province. The major objectives of the study were to evaluate farmer’s perception on climate change and new and emerging pests, to determine the control measures used by farmers to manage vegetable insect pests, to evaluate the role of institutions on insect pest management, and to determine new and emerging pests in the district. Results of the study indicated that long dry spells, late rainfall and warmer winters were major indicators of climate change in Limpopo Province. Famers in all municipalities perceived aphids as major problematic insect pests to vegetables and were not significantly different from each other (P > 0.05). The highest percentage of aphid prevalence was found in Mutale municipality (82.1%) and the lowest was found in Thulamela municipality (66.7%). Tuta absoluta (South American tomato pinworm) and Spodoptera frugiperda were reported as new insect pests in Vhembe District. Tuta absoluta was only reported in Musina municipality. Spodoptera frugiperda was significantly higher in Makhado irrigated system (72%) and was significantly different from Musina municipality (8.3%) and Thulamela dryland system (19%). Bagrada hilaris (bagrada bug) and Acanthoplus discoidalis (armoured bush cricket) were observed as emerging pests in the district. Thulamela dryland system (73%) was significantly different from Thulamela irrigated system (33%) and Musina municipality (41%) in terms of Bagrada hilaris prevalence. Musina municipality (50%) was significantly different from the rest of the municipalities with respect to Acanthoplus discoidalis prevalence (P < 0.05). The lowest prevalence of amoured cricket was found in Mutale irrigated system (9.52%). All municipalities showed that they highly depended on chemical control for pest management. All municipalities except Makhado dryland system, mentioned that chemicals were effective for insect pest management. The percentage of farmers who agreed that chemicals were effective was significantly different from farmers who did not agree that chemicals were effective (P < 0.05). The overall study showed that climatic factors increased the prevalence of insect pests in Limpopo Province. High temperatures could have influenced the population and distribution of insect pests. New insect pests observed seemed to have quickly adapted to climatic factors in Limpopo Province and therefore, resulted to severe damage on host crops. The study also emphasized that chemical control was effective for insect pest management. However, farmers were over applying pesticides to kill insect pests. This resulted in high levels of pesticide resistance. Frequent application of pesticides can be harmful to the environment and to human health, and can also increase the level of pesticide residues on vegetables. More studies need to be conducted on the biology of new and emerging insect pests in Limpopo Province. Awareness on new and emerging insect pests must be raised to assist farmers in preparedness on how to manage insect pests. Farmers need to be trained more on chemical control measures and other control measures such as integrated pest management and biological control for pest management. The government should also train extension officers on climate change and insect pests, climate smart agriculture and effects of pesticides in order to deliver relevant advisory services to farmers.
Evaluating seed quality and performance of low and high phytic acid maize (Zea mays L.) under varying phosphorus rates and water regimes in dryland conditions.
Bakhite, Mohammed Abdalla Elgorashi.; Odindo, Alfred Oduor.; Magwaza, Lembe Samukelo.
Maize (Zea mays) being the staple crop for many communities in Sub-Saharan Africa and also used for animal feeding, a considerable effort has been made to improve quality and yield. In recent times plant breeders have focused on reducing phytic acid (PA) on maize seeds to improve grain nutritional quality. Although studies of low phytic acid genes have been reported in temperate maize, the current research was based on the tropical genetic background which was screened for low phytic acid. This is the first report for applied breeding of the trait in the tropical maize. Little is known on the agronomy and responses of tropical maize specifically to water stress and its response to phosphorus application. No studies provided on the seed quality performance and response of low phytic acid maize to water stress and phosphorus application. Reducing Phytic acid of tropical maize could have negative effects on seed quality and yield. The primary objective of this study was to compare the performance of low phytic acid (LPA) maize seeds of tropical origin with three other varieties i.e. high phytic acid (HPA) of tropical origin, SC701 and LS8520 based on seed quality and water stress. The study consisted of two maize synthetic populations differing in phytic acid (PA) content (from the African Center of Crop Improvement (ACCI)); namely, LPA and HPA synthetic populations. Both the LPA and HPA synthetic populations were derived from a tropical second generation (F2) population and were selected based on their phytic acid (PA) content. They were produced at the Ukulinga Research Farm, University of KwaZulu-Natal (29°40'05.7"S 30°24'20.9"E), in Pietermaritzburg, South Africa. These two maize synthetic populations were compared with two commercial maize varieties (from McDonald Seeds), white maize (SC701) and yellow maize LS 8520 R (484) which in this study was coded LS8520. All seeds used in this study were produced under identical production conditions and in the same growing season, thereby ensuring that the seeds were of the same physiological age. The first experiment investigated the characterisation of LPA maize varieties for seed germination and vigour. Seed quality was evaluated using the standard germination test and accelerate aging test together with electric conductivity test (EC). The second experiment was conducted as a pot trial to investigate the effect of exogenous phosphorus application on seed quality and yield of low phytic acid maize varieties. In third experiment, a field study over two seasons (2015/2016 and 2016/2017) was conducted at Ukulinga Research Farm in Pietermaritzburg, under dryland conditions. The objective of the experiment was to evaluate the newly produced ACCI’s two genetically synthetic maize populations of LPA and HPA under dryland field condition and compare them with the commercial white and yellow tropical maize varieties their germination, growth, yield and yield components. Lastly, an experiment under controlled conditions on photosynthetic efficiency and yield responses of LPA and HPA maize tropical lines to deficit irrigation. The study was carried out under controlled environment conditions. The objective was to evaluate the photosynthetic efficiency of low phytic acid (LPA) and high phytic acid (HPA) tropical maize varieties grown under water-stressed conditions. The results of the first experiment indicated that the performance of LPA varieties was comparable to those of commercially produced varieties. This study suggests that the combination of LPA lines of tropical origin used in this study was satisfactory to meet the minimum seed quality parameters particularly seed germination and vigour. The results for phosphorus application showed that the application of phosphorus improved the growth, flowering and yield of LPA and other varieties as well. The mean germination time (MGT), germination vigour index (GVI), electrical conductivity (EC) (μS g-1), root length, shoot length and the root-shoot ratio of the harvested seeds after phosphorus application were also improved. When the LPA and HPA tropical maize exposed to dryland environments the results revealed that the SC701 variety outperformed the other three varietiess in growth and yield. It was concluded that the LPA maize performed lower under field conditions. In the water stress trial, results showed that LPA maize varieties recorded higher values of stomatal conductance (gs) and transpiration rate (T) compared to HPA and SC701 for both normal and water stress conditions. HPA showed a significantly (P< 0.001) higher value of photosynthetic rate (A) than LPA and SC701 for all the water stress treatments. HPA and SC701 were comparable in most of chlorophyll fluorescence parameters. With regard to yield, HPA showed increased performance in terms of overall yield and seed weight, and this suggests that HPA varieties are less sensitive to water stress than LPA maize varieties. The results from this study have proven that LPA maize varieties are sensitive to limited conditions and further research under a wide range of environmental conditions is required. Overall, the results indicated that the seed germination of LPA was comparable to other varieties but the yield remains low. There is a need to conduct more experiments to demonstrate the performance of LPA under field conditions in response to phosphorus application and water stress. These differences between the traits could help breed programs. The selection for LPA and HPA tropical maize should be based on their physiological performance to be planted in temperate zones to grant higher yield performance.
An evaluation of source-sink relationships in three dry bean (Phaseolus vulgaris L.) cultivars.
(1989) Liebenberg, Andries Johannes.; Lea, J. D.
The effect of intensities and times of source or sink related stresses on the growth and development of a determinant (Teebus) and two indeterminant (NEP 2, Bonus) dry bean (Phaseolus vulgaris L.) cultivars was measured in a series of field experiments at Potchefstroom Research Station. Variation in stress levels was attained by defoliation, thinning, light intensity manipulation (shades and reflectors) and removal of reproductive organs. No permanent detrimental effect on vegetative or reproductive organs was observed when source was reduced or increased during the vegetative period (V1-V6f) . Flower initiation (V6f-R1) was identified as the period most sensitive to defoliation as expressed in vegetative growth and economic yield. The negative effect of shading on vegetative development was reduced by an extended growing period . Thinning during flower initiation increased the vegetative and reproductive sink. A source stress (defoliation and shading) during the flowering period (R1-R5) restricted partitioning to the reproductive organs reducing seed yield and harvest index values. Reduced interplant competition during flowering favoured partitioning to the reproductive organs. Source size had a direct relationship with economic yield during flowering. This was confirmed by the absence of a yield response to partial depodding. A lack of response to defoliation (NEP 2) and shading (Bonus) may indicate a limited sink size in these two cultivars. During seed filling (R5-R9) Bonus was very sensitive to defoliation while NEP 2 was insensitive. Bonus was less sensitive to shading than Teebus. Thus in certain cultivars the level of current photosynthesis had a significant effect on seed yield throughout seed filling. The lack of a yield response to thinning in all cultivars during this period indicated that the potential sink size was set before R5. The results provided strong evidence supporting the concepts of yield component compensation in dry beans. Pod number was most seriously affected by defoliation during flower initiation and flowering. The potential sink size was determined mainly through the number of pods per plant which was in balance with the source unless some stress factor was present. The number of seeds per pod responded to current photosynthesis as well as the previously set pod number. Seed size was the least responsive yield component and it had a consistent negative relationship with the number of pods per plant.
Farmer perceptions and the agronomic potential of provitamin A-biofortified maize on small holder farming systems of KwaZulu-Natal, South Africa
(2019) Zuma, Mthokozisi Kwazi.; Modi, Albert Thembinkosi.; Kolanisi, Unathi.
Pro-vitamin A biofortified maize (PVABM) has the potential to reduce Vitamin A deficiency (VAD) for the vulnerable groups of Sub Saharan Africa (SSA). It is therefore important to understand the willingness of farmers to incorporate PVABM into their farming systems and the agronomic potential of these varieties under different environmental conditions to motivate their introduction in smallholder farming systems. The objectives of the study were to (i) determine smallholder farmer perception of the incorporation of PVABM in in two distinctly different climatic regions of KwaZulu-Natal, South Africa, (ii) evaluate production potential and selected seed quality characteristics of PVABM compared with common maize varieties across two seasons (2015/16 and 2016/17) and (iii) access the potential acceptability of PVABM as part of traditional household diet by smallholder farmers. Results showed that farmers have positive perceptions of the incorporation of PVABM into their farming systems and there was a willingness to adopt these varieties. With respect to seed quality, although there were no significant pro-germination characteristics as determined by tetrazolium test for metabolic activity, PVABM showed better germination vigour index and final germination. Germination performance was significantly correlated with crop establishment during field trials over both seasons. This was shown by highly significant differences observed for plant growth and chlorophyll content index in both study areas across two seasons. However, the study showed no significant differences in biomass and grain yield. Sensory evaluation showed that PVABM traditional foods (green mealies and cooked maize meal) were accepted for consumption and the farmers expressed the willingness to consume PVABM in their diets. The study indicated that PVABM can be accepted by farmers into farming systems. It is recommended that plant breeding to identify genetic differences and potential to improve PVABM for a wide range of agro-ecological conditions in regions where poor smallholder farmers grow maize is performed with a view to improve food security.
Fluctuation of non-structural carbohydrates in the stem and ears of maize (Zea mays (L.)) during grain fill as influenced by water stress.
(1991) Shanahan, Paul Edward.; Greenfield, Peter L.
Stems of maize plants may serve as reservoirs for photosynthate produced in the leaves which may then be utilized for cell growth and maintenance requirements of the plants, and in particular for grain requirements during grain fill. Experiments were designed to ascertain the extent to which non-structural carbohydrates accumulate and are depleted in the stem and ears of locally cultivated maize hybrids during grain fill under conditions of water stress. Maize plants were grown: (i) under field conditions; (ii) under a rain-out shelter; and (iii) in pots placed inside a growth tunnel during grain fill. In the latter experiment whole maize plants were exposed to (14)C0(2) at selected intervals during grain fill. In the field trial large differences in the accumulation and depletion of total non-structural carbohydrates (TNC) were found between the six hybrids tested. The water stress conditions that prevailed from mid-grain fill (MGF) to physiological maturity (PM) resulted in TNC content levels being lower at PM than at anthesis in all hybrids except for SR 52. Total non-structural carbohydrate content in the whole stem of PNR 6427, CG 4602 and PNR 473 declined from anthesis to PM. In contrast TNC content in the whole stem of SA 60 and HL 1 declined from anthesis to MGF and then increased substantially in SA 60 and marginally in HL 1 from MGF to PM. In the rain-out shelter trial, water stress resulted in a 38 % reduction in final grain yield in SA 6 compared to 25 % in K78Y x I137TN. The greater tolerance to water stress of the more modern hybrid K78Y x I137TN compared to the obsolete hybrid SA 6 may be attributed to a number of factors, namely: (i) K78Y x I137TN recorded a higher leaf area index throughout grain fill under stress and non-stress conditions compared to SA 6; (ii) it did not partition as much non-structural carbohydrate to the stem during the first three weeks of grain fill as did SA 6 and did not markedly deplete stem non-structural carbohydrate pools to the same extent as did SA 6 under stress and non-stress conditions; and (iii) in the last week of grain fill as the leaf water potential of K78Y x I137TN increased sharply under stress conditions, it exhibited an ability to deplete stem non-structural carbohydrates to supplement the supply of current photosynthate to the grain. In the 14(C)-labelling pot trial, the maize single cross hybrid B254W X M162W generally depleted TNC in vegetative organs in the latter half of grain fill under stress conditions, while under non-stress conditions TNC continued to accumulate in vegetative organs until PM. Both stressed and non-stressed plants assimilated less 14(C) on consecutive labelling occasions during grain fill. The amount of 14(C) assimilated at six weeks after anthesis was only 12,1 and 16,3 % of that assimilated at anthesis in stressed and non-stressed plants, respectively. Stressed and non-stressed plants labelled at anthesis translocated a smaller proportion of assimilated 14(C) to the grain during grain fill than plants labelled later. Consequently, stressed and non-stressed plants labelled at anthesis recorded the highest proportion of whole plant 14(C) recovered in the whole shoot at PM compared to plants labelled on any of the other occasions. At anthesis the primary ear was not yet established as the major sink for photosynthate and much of the 14(C) assimilated at anthesis was utilized for final structural growth of the whole shoot including the cob and husks of the primary ear. Stressed and non-stressed plants assimilated similar amounts of 14(C) at anthesis and two weeks after anthesis, however, stressed plants assimilated less 14(C) than non-stressed plants at four and six weeks after anthesis. Forty-eight hours after each labelling occasion, the stressed plants had partitioned a higher proportion of assimilated 14(C) to the grain than the non-stressed plants. However, by PM the non-stressed plants had partitioned an equal or greater proportion of whole plant 14(C) recovered at PM to the grain compared to the stressed plants. Radioactivity associated with component non-structural carbohydrates, was determined using ion-exchange column chromatography and thin-layer chromatography. These procedures provided detailed data of the partitioning of 14(C) among glucose, fructose, sucrose and starch.

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