Masters Degrees (Crop Science)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6577

Browse

Now showing 1 - 20 of 84

Effects of different levels of competition by Cyperus esculentus L. on the growth and surcrose yield of irrigated sugarcane (Saccharum officinarum L.) in Northern Swaziland.
(1995) Manana, Shesi Vusumuzi Innocent.; Greenfield, Peter L.
The study was undertaken to evaluate the interference of Cyperus esculentus (L.) with growth and quality of irrigated sugarcane (Saccharum officinarum (L.)) in northern Swaziland, and to quantify or characterise yield loss in relation to C. esculentus population and its control. The study comprised two field experiments on different soil types on plant, 1st, 2nd and 3rd ratoon sugarcane located at Mhlume (Swaziland) Sugar Company during the period 1988 to 1991. Three C. esculentus population levels were established at 1680 to 1833 plants m(-2) (heavy), 1110 to 1205 plants m(-2) (medium), and 550 to 582 plants m(-2) (light). Medium and light infestation treatments were instituted through thinning by hand to populations of 67% and 33% of the original populations respectively. Four weed control methods were superimposed. These comprised two controls; a) no weed control (C. esculentus was left undisturbed throughout the growth of the crop), b) complete weed control by hand weeding throughout the season; and two levels of herbicide application rates, a recommended estate level, which was a mixture of 1.6 L MCPA (a.i.) ha(-1) (2-methyl-4-chlorophenoxyacetic acid) (400 g a.i. L(-1) ) with 1.5 L ametryn (a.i.) ha(-1) (2-methylthio-4-isopropylamino-s-triazine) (500 g a.i. L(-1) ) and one-half the recommended herbicide application. A surfactant was added to the mixture at 0.5 L ha(-1). Both trials had 12 treatments arranged in a 3x4 rectangular lattice with five replications. Significant sugarcane yield responses to weed control method were obtained on plant and 3rd ratoon sugarcane. For the plant sugarcane crop, the institution of the recommended herbicide rate and complete hand weeding gave yield increases of about 14% and 24%, respectively, compared to the no control treatment. The plant crop sucrose yield was significantly affected by weed control methods with the recommended herbicide and complete hand weeding giving 15% and 26% increase in sucrose yield, respectively, compared to the no control treatment. In the 3rd ratoon crop complete hand weeding gave an increase of 26% and 28% sugarcane and sucrose yield, respectively. Indications were that 1st and 2nd ratoon sugarcane displayed the most vigorous growth, and hence was highly competitive against the C. esculentus and suffered no yield or quality loss due to weed populations. The possible reason was that the 1st ratoon sugarcane crop grows more vigorously than the plant crop and would therefore achieve canopy earlier than in the plant sugarcane crop. Even though results under the environmental conditions and time of regeneration of young ratoons used in this study indicated little, if any, benefit of weed control, this aspect would need further study at other times of the year before no weed control on young, vigorously growing ratoons could generally be recommended. As sugarcane yield and quality were not affected by C. esculentus populations, it was not possible to establish a population level for economic control of the weed. However, regeneration of C. esculentus in subsequent years was shown to be a function of previous years' populations and control method imposed on that population. Final populations in the subsequent year were lower where weed control was instigated than where there was no weed control. The conclusion reached in this study is that weed control will not only affect competitive abilities of current C. esculentus, but also reduce future population levels of the weed. The lack of sugarcane yield and quality response to different levels of C. esculentus population made it impossible to conclusively determine the economic threshold of C. esculentus which caused sugarcane yield and quality loss in irrigated agriculture on these soils.
Nutrient studies in potatoes (Solanum tuberosum)
(1997) Ahmadi, Ramtin.; Cairns, Andrew Lawrence Patrick.; Greenfield, Peter L.
One of the biggest problems facing potato (Solanum tuberosum) production in Kwazulu-Natal is acidic soils with high a aluminium content. Traditionally, such soils were ameliorated using lime, thus increasing soil pH, Ca and Mg availability, and reducing Al availability. This study aims to determine the extent to which lime could be replaced by Calmag+B (a Ca source with little ameliorative capacity). The Calmag+B fertiliser increases the soil's Ca content appreciably, but does not alter soil pH and Al availability to the same extent as lime. Pot trials were carried out to determine the effects of liming a highly acid soil, resulting in four levels of amelioration. At each level of amelioration, three levels of Calmag+B were applied to determine whether an optimised yield response would be attained through these applications. Plant emergence and subsequent development was shown to be poor, and in extreme cases absent, under highly acidic soil conditions. Soil amelioration using lime greatly improved plant emergence, development and tuber yield, whereas Calmag+B applications were unable to improve plant emergence, development or tuber yield. The effect of both applications of substantial quantities of Calmag+B to a highly acid soil, and of the dipping of mother tubers in a nutrient solution prior to planting was investigated. The Calmag+B soil applications were unable to improve plant emergence and development. The dipping of the mother tubers in nutrient solution, however, resulted in greatly increased seedling emergence and plant development. This was due to increased nutrient uptake from the mother tuber, and not through increased root development and subsequent nutrient uptake. There were unsubstantiated claims by the manufacturers of Calmag+B that the Mg, NO(3) and B components of the fertiliser would give rise to increased uptake of the Ca component, thus enhancing the efficacy of the fertiliser. Pot trials using a sand medium were employed to test this claim. The trial consisted of interactions of different levels of Ca(2+), Mg(2+), NO(3-), and BO3(2-) applied to the sand medium in the form of a nutrient solution. None of the treatments (barring Ca itself) led to increased Ca uptake by the potato tubers. This would indicate that the claim that the Mg, NO(3) and B components of Calmag+B fertiliser would enhance the uptake of the Ca component are unfounded. It has been suggested that one of the main factors limiting potato production in Kwazulu-Natal has been inadequate mineral nutrition. Certain fertiliser distributors claim that fertiliser application over and above the levels recommended by the Kwazulu-Natal Department of Agriculture Fertiliser Advisory (KDAFA) is the solution to the problem of below potential yield and tuber quality in the province. A field trial was carried out in New Hanover (Kwazulu-Natal), using different levels of Calmag+B and Agrifos, as well as one level of application of KNO(3). All treatments were applied after KDAFA fertiliser recommendations had been fulfilled. At the 95% level of significance, the treatments did not give rise to increased yield and tuber quality. At the 80% level of significance, however, the results indicated that applications of 100kg ha -1 of Calmag+B and KNO(3) would give rise to increased tuber yield.
Intercropping of maize and dry beans for the Vulindlela district of KwaZulu-Natal.
(1997) Liebenberg, Benjamin Christiaan.; Cairns, Andrew Lawrence Patrick.
The use of a maize/bean intercropping system to improve land productivity was investigated after limited land availability had been identified (Liebenberg, 1993) as a major constraint to crop production in the Vulindlela area of the KwaZulu-Natal province of South Africa. The objective of this study was to develop an intercropping system that would: a) Give an intercrop bean yield approximately equal to that of the sole crop yield, b) Give a maize yield acceptable to the farmer (needed mainly for green maize). c) Produce a land equivalent ratio (LER) greater than one. In order to ensure high bean yields, maize dominance was reduced by lowering the normal maize population of the intercrop by 50% and by using a tramline row arrangement instead of evenly spaced rows. Two bean cultivars namely Mkuzi (carioca) and Umlazi (speckled sugar) and two maize cultivars namely Kalahari Early Pearl (KEP) (an open pollinated cultivar) and SR 52 (a hybrid) were used. Single trials were planted at four localities spread over three seasons i.e. Vulindlela and Ukulinga (1992/93), Cedara (1995/96) and Makhathini (1996). The treatments included varying bean densities, bean planting times and maize harvesting stages. These treatments were compared to maize and bean sole crop controls. High maize yields led to low bean intercrop yields. However, there was little or no difference between sole bean yield and intercrop bean yields associated with lower maize yields. Intercrop maize yields were 50% of the sole maize yields at all the sites. The mean LER's for the Vulindlela and Ukulinga trials were 1.04 and 0.96 respectively while the mean LER's for the Cedara and Makhathini trials were 1.34 and 1.31 respectively. Only the latter two trials displayed significant improvements in land productivity. Mkuzi was more affected by intercropping than Umlazi while KEP competed less with the beans than SR 52 and gave higher yields under less favourable growing conditions. Yield component studies indicated that stress during the vegetative, pod formation, and pod filling stages led to yield reduction in the dry bean crops. Light and leaf nutrient level studies suggested that the yield reduction resulted from competition for nitrogen and light. There was no competition for phosphate and potassium. The study indicates that the intercropping system did meet the desired requirements under conditions that are less than ideal for maize production, such as low soil fertility, water stress and cool temperatures.
Towards the achievement of environmental standards in the South African sugar industry : the role of GIS.
(1999) Wallace, Michael Grant.; Breen, Charles Mackie.
The South African Sugar Industry is a major land user in the South African provinces of KwaZulu-Natal and Mpumalanga. Although offering substantial economic benefits in these regions, monocultural sugarcane production has had a fundamental impact on the natural environment in which sugarcane is produced. Attention was focused on the growing sector of the industry after flood events during the previous decade resulted in major soil erosion of sugarcane land. Widespread intentional cane burning is attracting increasing societal and regulatory pressure. New national environmental legislation in the spirit of the United Nations Conference on Environment and Development (UNCED) Agenda 21 and various other international agreements, demand that industries - including agriculture - demonstrate sustainability in their use of environmental resources. National law now more rigorously addresses biodiversity and wetland environmental issues. New water laws will fundamentally alter the existing water-use paradigm in sugarcane production. These issues are not unique to South Africa, having much in common with those faced by other major sugar producing countries. In order to effectively manage the impacts of production processes on the environment, organisations are turning to internationally accepted environmental management standards, such as the ISO 14000 series, in order to demonstrate their environmental responsibility to government and society, whilst promoting their acceptability to consumers. The SA Sugar Industry is in the early stages of investigating appropriate environmental management systems. The natural resources required for - and impacted upon - by sugarcane production are variable in space and over time. Effective and responsible environmental management must make optimum use of appropriate technology to effectively utilise the large volumes of often complex data pertaining to these resources and associated environmental processes. Geographic Information Systems (GIS) are computer systems designed for the capture, analysis, storage and display of spatial data and attribute data related to location. Whilst not a new development, recent advances indicate that GIS has substantially matured as a decision support technology and as such is being used successfully by many organisations involved in environmental management, where its use offers unique benefits at a variety of decision levels and spatial scales. GIS is applied at many complexity levels, from simple thematic map production to complex spatial analysis. The major advantage of GIS is considered by some to be its ability to spatially model environmental scenarios, producing graphic results (usually maps). As such, GIS has considerable value in formal Decision Support Systems. The major environmental issues facing South African sugarcane producers are fundamentally spatial in nature. The development and incorporation of environmental GIS capacity into their proposed environmental management system is indispensable in addressing these issues and moving towards achieving and maintaining acceptable environmental standards in the SA sugar growing sector.
Modelling the production potential of land for sugarcane in the KwaZulu-Natal Midlands sugarcane belt.
(2000) Brüggemann, Edgar Alfred.; Klug, John R.; Greenfield, Peter L.; Dicks, Harvey M.
Commercial sugarcane records for 19 seasons from 146 fields were obtained from selected estates in the KwaZulu-Natal Midlands. The estates, located at Kranskop, Umvoti and Richmond, are representative of the higher-potential rainfed sugarcane production region of the Midlands sugarcane belt. Extensive editing and cleaning of the agronomic records was required. Regression models were developed to determine which parameters of the field records were consistently associated with sugarcane yield (TCH) and could be used for yield predictions. Depending on the predictor variables selected, the best models based on 535 crop cycles accounted for 55% and 43% ofthe observed yield variation respectively. Linear regression was an appropriate analytical technique since the assumptions of normality and homoscedasticity were upheld and multicollinearity was not a problem in the models. The models were validated using an independent data set of 47 observations and satisfactory performances were confirmed. The 95% confidence limits of yield predictions for the population mean lie within 10% of long-term mean yields. These predictions could be useful for estate resource allocation and harvest planning. Key physical field attributes associated with sugarcane yield were locality, aspect, altitude, soil type and effective rooting depth. Season and rainfall were important climatic variables. Ofthe factors influenced by management, sugarcane variety, plant / ratoon status, crop cycle, N and K nutrition and the topsoil Ca:Mg ratio were important yield predictors, depending on the equation used. The relative importance of individual predictors varies with the specific combination of resources for a particular observation. The models were linked to a geographic information system to demonstrate an application ofthe models for yield prediction in response to spatial variables. These predictions showed that the models could be used at a general scale within estates to identify areas of differing production potential. Reliable yield predictions could not be made for individual fields and within-field resource variations could not be adequately accounted for.
Distribution and severity of herbicide resistance in the Republic of South Africa.
(2001) Smit, J. J.
No abstract available.
Effect of irrigation water regimes applied via subsurface drippers on soil water distribution and on sugarcane (Saccharum officinarum L.) growth.
(2002) Gama, Mandla Ernest.; Greenfield, Peter L.
The effects of different water regimes on sugarcane growth were investigated for subsurface drip irrigation over three seasons. Arbitrary factors (0.5, 0.75, 1.0 and 1.2 of ETc), were applied to adjust the daily estimates of Penman Monteith evapotranspiration (Et). These drip treatments were compared to an overhead sprinkler irrigated (1.0 ETc) block of sugarcane. In the plant and first ratoon crops, the drip plots were irrigated to field capacity, by replenishing an allowable deficit of 10 mm. In the second ratoon however, the soil was irrigated to a 50% total available moisture (TAM) level. Soil water movement and root distribution adjacent and below emitters was measured. There was an increase in vertical and lateral soil water movement with increase in irrigation water regime. The rooting density increased with increase in soil water content. However, the root density decreased slightly in the 1.2 ETc treatment below the emitters in the wetter season. There were no differences in cane growth among the drip treatments in the first two seasons, mainly due to the wet weather conditions. In the second ratoon the 1.2 ETc treatment had the tallest stalks, which resulted in the highest cane and sucrose yields (t ha-1). There were no differences in cane and sucrose yields among the other treatments. There were no consistent differences in the plant canopy cover among the drip treatments. The cane growth in the sprinkler block was poor in the plant and first ratoon crops, probably due to the leaching of N, and it was comparable to the drip block in the second ratoon. The crop water use efficiency (CWUE) decreased with an increase in irrigation water regimes, and all drip CWUE treatments were better than that of the sprinkler block in all years. The study has shown that, a) the estimated daily ETc could be reduced by 50 % while still achieving the Mhlume estate average cane yield of 95 t ha-1, b) rainfall use efficiency, cane and sucrose yields could be increased by using 1.2 ETc at the 50% TAM level, c) there is a need to re-examine N applications under drip irrigation, particularly where heavy rains occur after leaf samples have been taken.
Nitrogen in the soil-plant system of successive rainfed wheat crops under conventional cultivation.
(2002) Otto, Willem Morkel.; Haynes, Richard John.; Greenfield, Peter L.
Soil mineral N and soil water content at planting, biomass accumulation, yield and grain quality parameters (hectolitermass and protein percentage) were measured on an unfertilized and recommended-N-application treatment during two consecutive growing seasons (1997-1998). The trials were planted in a fallow-wheat-wheat cropping system at three representative localities in the summer rainfall region of South Africa. High levels of available soil water and mineral N were measured following the fallow period preceding the start of the trials in 1997. For example, soil water content was 81.7%, 69.6%, and 78.2% of DUL at Bethlehem, Kroonstad and Petrusburg respectively. Although comparable total soil profile water contents to 1997 were measured in 1998 at all three sites, the cultivation zone (0-400 mm) had a substantially lower soil water content. This was due to erratic rainfall distribution during the fallow period, which prevented effective soil cultivation management, subsequent soil water conservation and residue decomposition. Undecomposed residue in the cultivation layer at planting appeared to affect availability of soil mineral N to the growing crop. At planting in 1998, undecomposed crop residue amounted to 53.6% at Bethlehem, 32.5% at Kroonstad and 46.9% at Petrusburg of that added at harvest in 1997. Soil mineral N was lower at planting in 1998 compared to 1997 due to decomposing residue (C:N ratio of above 73) in the cultivation zone immobilizing soil mineral N. This reduced initial growth, N accumulation, yield, and grain protein percentage without additional fertilizer N. Distribution of soil mineral N showed notable amounts in the 600-1200 mm soil layers, with limited changes over the trial period. This was linked to low root exploration of these soil layers (10-15% of total root distribution). The ratios of soil mineral NH(4+):N0(3)- for the different soil layers indicated similar values over the trial period. Climatic data for the localities indicated differences in the amount and distribution of rainfall and temperatures during the study period, which influenced crop development, yield and grain protein percentage. At Bethlehem above average in-season rainfall was measured during 1997, at Kroonstad average rainfall and at Petrusburg below average in-season rainfall. Response to applied N at the localities varied in magnitude during 1997. Nitrogen application significantly increased N concentrations of plant components, N uptake, yield and grain protein percentage, although values for all these parameters were lower in 1998 than in 1997. Indeed higher yields were produced in 1997 (mean=1.838 t ha(-1)) compared to 1998 (mean=0.980 t ha(-1)). A significant yield response to applied N was measured at the two higher yielding localities in both cropping years, but there was no significant response at the lower yielding locality. The limiting factors appeared to be the availability of soil water and residual soil mineral N. From the calculated response functions, the variables soil water content at planting, soil mineral N content at planting, in-season rainfall, and added fertilizer N explained the bulk of the variations in grain protein percentage, plant N uptake, and yields. It was concluded that the present fertilizer N recommendation system for dryland wheat production, which is based on fertilizer response curves for specific yield potentials, should be augmented by using initial soil mineral N and water contents in the profile measured prior to planting.
Comparative responses of fodder and grain teff (Eragrostis tef (Zucc.) Trotter) cultivars to spatial, temporal and nutritional management.
(2002) Kassier, Sigrun Barbara.; Greenfield, Peter L.
Teff has its origin in Ethiopia as grain crop, while in South Africa it is primarily a forage crop for hay and recently as summer grazing pasture. The response of teff herbage and grain production to planting date, growth stage at cutting, seeding rate and N fertilizer application was studied. Previously limited research data were available for teff production in South Africa. Spring plantings (September to October) are required to maximise total herbage yield with 9.40, 8.48 and 7.64 t DM ha -1) recorded for 1996/97, 1997/98 and 1998/99 respectively. Summer plantings (November to December) give maximum herbage yield from the first cut, yielding 4.42, 4.72 and 3.78 t DM ha -1) for 1996/97, 1997/98 and 1998/99 respectively. The exact planting date is season dependent. Temperature and rainfall determine the beginning of the growth season regarding favourable conditions for teff germination and growth. Herbage yield of cut 1 increases with advancement in growth stage at cutting. Cutting at the vegetative and piping stages gives most number of cuts , up to five yielding 7.45 t DM ha -1) (1996) while the full flowering stage gives the least (one or two cuts , 4.75 and 7.72 t DM ha -1 in 1996 and 1997 respectively). Yield is also affected by environmental conditions influencing germination, biomass accummulation and regrowth after cutting and by lodging. A trade-off results between herbage quantity and quality. Yield increases while quality decreases with advancing phenological stage, resulting in reduced digestibilty and CP and increased fibre content. Seeding rate differences were manifested primarily in weed infestation level, which varied between cultivars depending on leafiness and associated sward density. Nitrogen application levels gave maximum response between 75 and 150 kg N ha -1, with some cultivar differences. Split N application according to expected yield distribution related to planting date is recommended. Grain yield response to seeding rate and N fertilization levels could not be established. Heavy grain losses through thunderstorms and wet conditions at grain maturity precluded yield measurements. Teff yield responses are influenced by day length, environmental factors, such as temperature and rainfall. and phenological stage at cutting. These variables influence biomass accumulation and regrowth.
The effect of different furrow irrigation regimes on infiltration and sugarcane (Saccharum officinarum L.) yield at Ubombo Swaziland.
(2003) Mazibuko, Njabulo W.; Greenfield, Peter L.
In surface irrigation, the soil serves as a medium for infiltration and for conveying water from the upstream to the downstream end of a field. Soil infiltration characteristics are therefore extremely important for surface irrigation design and management. In this study, the infiltration characteristics of the Sibaya (Si) soil type (Glenrosa, in the South African soil classification system) was determined by a volume balance method using a two-point approach technique. The infiltration model adopted was that of Kostiakov. The purpose of the study was to examine the effect of different irrigation scheduling on infiltration characteristics, and on irrigation performance. A trial was conducted on a field with predominately Rondspring and Sibaya soils from 1999 to 2001. The five irrigation treatments were the Ubombo method, Penman-Monteith (PM) derived irrigation scheduling factors of 1.25, 1.00 and 0.75, and alternate row irrigation using Ubombo scheduling and 1.00 x PM on plant and first ratoon cane, respectively. Treatments were arranged in a randomised complete block design with five replication. The Ubombo scheduling method had the highest number of irrigation events followed by the 1.25 x PM, whilst the 0.75 x PM had the least. The infiltration variables indicated that, for the Ubombo and 1.25 x PM treatments, irrigation often occurred when the soil water content was still less than 50% depleted plant available water (DPAW). This was in agreement with the tensiometer and neutron probe data. The tensiometer readings ranged from -55 to -75 kPa, -50 to -65 kPa, and -8 to -12 kPa at 0.15 m, 0.30 m, 0.45 m soil depth respectively. Likewise, 0.75 x PM was irrigated when the soil water content was greater than 50% (DPAW). Tensiometer readings would nearly always read above -80 kPa at both 0.15 m and 0.30 m, and above -75 kPa at 0.45 m. Further examination of the tensiometer and neutron probe data suggested that irrigation scheduling determined the preferential depth of water uptake by the crop. Frequent irrigation resulted in the crop depleting soil water predominately at the 0.15-0.30 m soil depth and hardly any at 0.45 m and below, particularly when the crop was young. There were no significant differences in yield among any of the treatments in the plant or ratoon crops. The plant crop consistently recorded higher yields than the first ratoon in all the treatments. Ubombo scheduling recorded the highest sugarcane yield in both seasons at 84 tha(-1) for the plant and 82 tha(-1) for the first ratoon cane. The 0.75 x PM had the lowest yield (78.3 tha(-1)) in the plant crop as well as in the first ratoon (74 tha(-1)). The volume balance approach provided a reliable and convenient way of assessing surface inigation systems to identify alternatives that may be effective in improving the system performance, and in assessing different irrigation schedules. Sound management which comes about by selecting the most efficient stream size, length of field, and set time, and also a suitable irrigation schedule for that soil type depends on detailed knowledge of the infiltration rate of a particular soil. Information on infiltration constitutes the basis for establishing the necessary design, evaluation criteria and operational management system in irrigation.
Alleviation of cotyledonal cracking in green beans (Phaseolus vulgaris L.) by calcium seed treatment.
(2003) Mazibuko, Tholakele Gladness.; Modi, Albert Thembinkosi.
Cotyledonal cracking is a physiological disorder of common beans, and rarely, soybeans that occurs as transverse fissures across the cotyledons. The phenomenon is generally referred to as transverse cotyledonal cracking (TVC). Although TVC has been known for decades now, factors contributing to its occurrence, and how the disorder can be alleviated, are still not well understood. The objective of this study was to investigate the effect calcium seed treatment on cotyledonal cracking in green bean (Phaseolus vulgaris L.) seeds. Six cultivars (Imbali, Sodwana, Outeniqua, Elangeni, Tokai and Tongati) were examined for water absorption patterns during a 6-h imbibition in distilled water. Cultivars were categorised according to the rates of water absorption, in the presence of seed coat, and there was a significant correlation between seed size and water absorption rate. To examine seed predisposition to TVC, seeds were imbibed with and without seed coats and TVC was scored every hour for the 6-h duration of imbibition. There was a significant positive correlation between water absorption rate and TVC. Genetic analysis of the cultivars using SDS-PAGE revealed that there are possible differences between the resistant cultivars and sensitive cultivars, with respect to protein patterns. Imbali, one of the small cultivars (-1.5 g seed -1) that imbibed water uniformly, was resistant to cotyledonal cracking compared to the largest cultivar (Sodwana -2.5 g seed -1), which also had a high rate of water absorption. Priming seeds with calcium (CaS04, Ca(N03)2 and CaCl2) osmolarities (0, 1, 10, 50, 100, and 100 mM) increased seed calcium content and reduced susceptibility to TVC. Comparison of priming and seed coating with respect to field emergence, TVC, stand establishment and seed yield showed that coating was better than priming. However, greenhouse studies showed that the effect of priming in the progeny of treated seeds was significantly better than that of coating, with respect to TVC reduction. In both laboratory and field studies, it was clear that applying calcium concentrations greater than 50 mM was not necessary to alleviate TVC and improve seed performance. Seed germination and emergence were reduced at calcium concentrations greater than 50 mM. It is concluded that calcium is effective in controlling TVC under both laboratory and field conditions. The effect of calcium is associated with regulation of imbibition and improvement of seed calcium content. Enhanced seed calcium content likely improved cell wall integrity.
Taro [Colocasia esculenta (L.) Schott] production by small-scale farmers in KwaZulu-Natal : farmer practices and performance of propagule types under wetland and dryland conditions.
(2004) Shange, Lindiwe Princess.; Modi, Albert Thembinkosi.
Ethno-archaeological evidence shows that taro [Colocasia esculenta (L.) Schott] originated in Asia. It may have been brought into South Africa a few hundred years after 300 BC from Madagascar, where Malaysian settlers introduced it about 300 BC. The crop is grown in the tropical and subtropical regions of the world, largely for subsistence on farms. In South Africa, taro is mainly produced in the subtropical coastal belt, stretching from Bizana in the Eastern Cape to the KwaZulu-Natal north coast. Although it is a staple crop for the subsistence farmers who grow it, there are no data on taro agronomy in South Africa. The hypothesis of this study was that traditional knowledge about taro production practices is not adequate to form a basis for agronomic and extension interventions to promote the status of the crop to that of a commercial commodity. A survey was conducted at two districts in KwaZulu-Natal, Umbumbulu and Ndwedwe, where taro is a staple crop. The objective of the survey was to determine the cultural practices associated with taro production, including knowledge about varieties, agronomy, plant protection, storage and marketing. Qualitative data obtained from the survey was used to plan an investigation into the agronomy of taro. The survey showed that subsistence farmers at Ndwedwe and Umbumbulu used traditional methods for taro production that had very small influence from the extension services from the Department of Agriculture. The farmers identified three varieties of taro, which they designated as the "red", "white" and "Zulu" types. The "red" and "white" designations were based on consistent crop morphological characteristics. This finding confirmed the reliability of indigenous knowledge for crop classification.The survey also revealed that wetland and dryland conditions are used to produce taro. At Umbumbulu, production occurred predominantly under dryland conditions, whereas at Ndwedwe there was an almost even utilisation of both wetlands and drylands. At both locations, the farmers estimated plant spacing using their feet, which showed that the plant populations would be about 18400 plants ha(-1). Full corms were a predominant type of propagation material. In the light of the survey findings about site types (wetland or dryland), propagation material and plant spacing for taro production, field experiments were designed to 1) determine the effect of site type on taro production, 2) compare three propagule types (full corm, full corm with a shoot and half corm) in taro production and 3) examine the effect of planting density (18400, 24600 and 37000 plants ha(-1) on the performance of propagules with respect to production under wetland and dryland conditions. Field experiments showed that wetland cultivation improved taro yield by 40% compared with dryland production. However, in each of the two site categories, there were significant differences between sites. Using full corms with shoots also enhanced taro yield (42% > full corms without shoots and 66% > half corms), when means were determined across all sites and planting densities. Increasing planting density also caused an increase in taro production (4.9 t ha (-1), 6.8 t ha (-1) and 11.5 t ha (-1), for 18400,24600 and 37000 plants ha,(-1), respectively; LSD (0.05) = 1.4 t ha,1). The enhanced performance of taro under wetland conditions, where corms with a shoot were used and at high planting densities may have been associated with photosynthetic efficiency. Wetland conditions and corms with shoots improved plant emergence and plant growth, which are essential agronomic conditions for efficient capture of the sun's energy for photosynthesis. It is proposed that using propagules with shoots and high plant populations under dryland conditions could enhance taro production. Although wetland cultivation enhanced yield, the survey showed that the total area of land that could be used for wetland cultivation at Ndwedwe and Umbumbulu was too small to warrant sustainable wetland production.
Investigating the role of polygalacturonase in cotyledonal cracking of green beans (Phaseolus vulgaris L.)
(2005) Tshazi, Thabani Xolani.; Modi, Albert Thembinkosi.
Transverse cotyledonal cracking (TVC) was characterised at physiological, biochemical and molecular levels in three common bean (Phaseolus vulgaris L.) cultivars: Imbali, Tongaat and Tokai. The incidence of TVC was determined visually on ten-day old seedlings and was expressed as the number of cracks per plant. The effect of Ca++ on TVC incidence was examined by enhancing the calcium content of seed cotyledons using calcium salts in seed priming and coating. EDAX was used to quantify the cotyledonal calcium content. Activities of the pectinolytic enzymes polygalacturonase (PG) and pectin methylesterase (PME) were assayed at dry seed, VC, R4 and R6 phenophases of the bean plant, and zymogram electrophoresis was used to identify the two enzymes. The results showed that cultivars Imbali, Tongaat, and Tokai were susceptible resistant and intermediate, respectively, with respect to TVC incidence. Calcium uptake was higher in Tongaat cultivar (P= 0.05) compared with Imbali and Tokai, irrespective of calcium salt enhancement. Vigour was significantly reduced (P< 0.01) by both coating and priming. TVC significantly lowered yield (P= 0.05) in the susceptible Imbali cultivar. Zymogram analysis identified lytic bands at ~45kDa (PG gel) and ~30kDa (PME gel). The activity profile of PME was similar for all cultivars. However, PG activity of susceptible Imbali was high in dry seeds and at the R4 and R6 stages of plant development, whereas the more resistant cultivars displayed high activity at the VC stage only. It is concluded that high PG activity at R4 stage is a more reliable determinant of green bean propensity to cotyledonal cracking.
Agronomic performance of wild mustard in an intercropping with green beans.
(2005) Phiri, Nathan.; Modi, Albert Thembinkosi.
Wild mustard (Brassica spp.) is used as an edible wild leafy vegetable by indigenous people in South Africa. The potential of wild leafy vegetables in agriculture is not well understood, because there is generally no agronomic research on their production practices. The objective of this study was to examine the performance of three wild mustard species (herein referred to as I, K and M) over four cropping seasons in an intercropping system with green beans (Phaseolus vulgaris L. cv. Imbali). The crops were grown with and without organic fertiliser under dryland conditions at two sites (The University of KwaZulu-Natal Research Farm, Ukulinga and in a rural area of Umbumbulu, KwaZulu-Natal within the farmers' locality) during autumn, winter, spring and summer of 2004 to 2005. Plant development (leaf number, plant height and fresh biomass) during the first six weeks after sowing and seed yield were used to determine agronomic performance of each species. Nutrient status of the rhizosphere soil was determined at 42 days after sowing for each species to determine what effect growing the species would have on mineral availability. Wild mustard production significantly (P < 0.01) performed better at Ukulinga than Umbumbulu. Polyculture was beneficial for wild mustard leaf accumulation and green bean production as determined by land equivalent ratios greater than one for all species combinations, regardless of fertiliser application. Cool environmental conditions occurring in autumn and spring were more favourable (P < 0.05) for wild mustard and green bean biomass accumulation than summer and winter conditions. However, wild mustard seed yield was highest in winter compared with autumn and spring, and there was no measurable seed production in summer. Soil analysis results at 42 days after sowing showed an increase in P, K, Cu and Mg in the rhizosphere of wild mustard without organic fertiliser. Polyculture improved Zn, Cu, Mn and K in wild mustard leaf tissue. It is concluded that wild mustard can be grown as a leafy vegetable throughout the year, but it requires cool environmental conditions to enhance seed yield. Species M significantly yielded better biomass and seeds than species I and K during all the seasons. However, species K performed the least in all aspects.
Pepper and tomato seed performance in response to imbibition and dehydration.
(2005) Nemakanga, Rendani.; Modi, Albert Thembinkosi.
The International Seed Testing Association and the Association of Official Seed analysts define seed vigour as the ability of a seed lot to perform during the germination process and crop stand establishment under a wide range of environmental conditions. There are many ways to determine seed vigour, but few satisfy the requirements of being simple, inexpensive and reproducible, among others, to permit the seed industry to adopt seed vigour as an indicator of seed quality when they sell seeds. Hence, the standard germination test, which is performed under uniform and favourable conditions, is generally used to indicate seed quality when seeds are marketed. The objective of this study was to determine the performance of tomato and pepper seeds in response to pre-germination hydration and dehydration relative humidities (12%, 49% and 75% RH). Before hydration, seeds were hydrated at three temperatures (10°C, 20°C and 30°C). Hydration was performed by imbibing pre-weighed pepper ('Santarini' and 'California Wonder'), Chilli and tomato ('Heinz', 'Marondera' and 'Roma') seeds for 2 h in 10 ml of distilled H(2)0 per 100 seeds at 10°C, 20°C and 30°C. Dehydration was performed by change in seed mass determined during a 72-hour dehydration at 12%, 49% and 75% RH. Seed performance in response to imbibition and dehydration was determined by leakage of electrolytes from seeds during imbibition, laboratory germination capacity and seedling emergence under simulated shadehouse nursery conditions. A pot experiment was conducted to determine the effects of seed treatments on yield. Seed mass increased by about 50% during the 2-hour of hydration. Dehydration was hastened by decreasing the RH, and 12% RH significantly (P < 0.05) reduced the post-imbibition seed moisture content compared with 49% and 75% RH. The latter two relative humidities reduced the seed moisture content to about 10% and 15%, respectively, for all cultivars, irrespective of imbibition temperature. Low imbibition temperature (10°C) significantly (P < 0.01) increased electrolyte leakage, compared with high imbibition temperatures (20°C and 30°C), which were not significantly different from each other. At all hydration temperatures, low RH (12%) caused a significant (P < 0.01) decrease in seed germination whereas 49% RH and 75% RH apparently had a priming effect on seeds. There was no significant difference between imbibition temperatures, with respect to seed germination, but 100G caused a significant decrease in germination index, a measure of seed vigour. Seedling emergence was significantly (P < 0.01) reduced by both low imbibition temperature (10oG) and low dehydration relative humidity (12% RH). The negative effects of low imbibition temperature and rapid dehydration at 12% RH were also observed as stunted seedling growth. Principal component analysis and linear regression were used to determine a statistical model to predict seedling emergence from germination percentage. The model predicted emergence consistently, but it overestimated it by about 2% to 3%. It is concluded that low imbibition temperature and rapid dehydration can be used to simulate stress to determine seed performance in pepper and tomato.
Moderation of growth and sucrose flux in sugarcane by temperature.
(2005) Ngomane, Dambuza.; Greenfield, Peter L.; Smit, Michiel.
Sugarcane plants (cultivar NCo376) were studied to assess the effects of temperature and season (spring and autumn equinox) on the morphological and physiological response of stalk components. Plants were grown from single-eyed setts for ca. five months and then placed into three temperature controlled glasshouses (22/12°C (C), 27/17°C (W) and 32/22°C (H) day/night temperatures). The plants were sampled twice weekly over a one month period., and intemodes 4, 6 and 10 of the primary haulms of each plant sampled for growth and sugar analysis. During spring, the leaf emergence rates were 0.0303, 0.1095 and 0.1682 leaves d(-1) at temperatures C, W and H, respectively; and 0.0327, 0.0824 and 0.113 leaves d(-1) in autumn. The phyllochron intervals were 114°Cd in spring and 147°Cd in autumn. Highest green leaf blade area of the primary haulms was achieved at H (438.0 and 511.7 cm2 in spring and autumn, respectively). The stalk extension rates were 1.22, 1.02, 0.38 cm d(-1) (spring) and 1.35, 0.98, 0.45 cm d(-1) (autumn), respectively, in descending order of temperature. Total biomass and stalk biomass per plant were not affected by temperature, despite the differences in stem elongation. Internodes of plants at C were shorter but thicker and heavier than the comparable internodes of plants at W and H. In autumn, the mature internode sucrose concentrations were 35.5, 29.2 and 25.5% at C, W and H, respectively; corresponding to mean RS% of 5.7, 9.8 and 13.3%, and fibre % of 58.8, 61.1 and 61.3%, at the respective ascending order of temperature. Sucrose % in the mature internodes in spring were 27.8, 20.9 and 19.9% at C, W and H, respectively; corresponding to RS% of 5.9, 9.76 and 10.9% and fibre % of 66.3, 69.4 and 69.2% at the respective ascending order of temperature. Temperature effect on the concentration of the stalk components of the immature internodes was in general not significant. Sucrose partitioning coefficients in the mature internodes were 0.25, 0.21 and 0.20 in spring and 0.50, 0.32 and 0.21 in autumn (at C, W and H, respectively). Data that resulted from this study, which is isolated to temperature and cultivar NCo376 can be used in models of sugarcane that simulate leaf appearance and senescence, assimilate partitioning between leaf and stalk and assimilate partitioning between the stalk components namely sucrose, reducing sugars and fibre.
The effect of daylength and temperature on growth and 'onset of bulbing' in tropical cultivars of onion.
(2005) Tesfay, Samson Zeray.; Greenfield, Peter L.
Onions are widely produced within the tropics, but little scientific research has been done specifically on the Eritrean cultivars, like Hagaz Red 1 and 2 (HR I, and HR 2). Many onion cultivars are limited in their range of adaptation due to the combined effects of photoperiod and temperature. A priority for research on the crop was to elucidate the local crop's growth response to environmental conditions, particularly temperature and daylength. The Eritrean cultivars HR I and 2 and an American (Louisiana) cultivar Red Creole (RC) grown in South Africa were grown in growth rooms under all combinations of three daylengths (11.5h, 12h, 12.5h) and three day/night temperatures (25/12°C, 30/15°C and 35/18°C). Growth responses were determined at 108 days and by using a growing degree day (GDD) base. A broken-stick regression model was used to determine the points of inflection, indicating the initiation of bulbing. Based on leaf area and plant height data, mathematical differentiation equations and coefficient of determination (R2) were applied to determine the base temperature (6.4°C) for these particular cultivars. All three cultivars needed at least 12 h daylength for bulb initiation when assessed by a bulbing ratio >=2.0. A bulbing ratio >=2.0 characterizes the onset of bulbing. Under a 11.5 h daylength, a temperature higher than 25/12°C decreased vegetative growth. Temperature in this region may be a supra-optimal condition for the growth of these cultivars at this daylength. However, the 25/12°C and 30/15°C temperatures were found to be ideal for onion bulb production under 12 hand 12.5 h daylengths. The three cultivars (HR I, HR 2 and RC) showed very similar growth response to the daylength and temperature interactions. The thermal presentation of plant growth indicated that there were relationships between bulb initiation and rate of leaf area growth under inductive conditions (12 hand 12.5 h). Under the 12 h daylength, cultivars needed 343, 482, and 597 GDD units before bulb initiation and 405, 432, and 431 GDD to increase the rate of leaf area development at 25/12°C, 30/15°C, and 35/18°C, respectively. Under a 12.5 h daylength, these cultivars needed 344, 423, and 432.2 GDDs to initiate bulbing and 140, 411, and 579 GDDs to increase leaf growth rates at 25/12°C, 30/15°C, and 35/18°C, respectively. In the 12 h daylength, bulbing was initiated and followed by an increased rate of growth of leaf area. However, the reverse happened for the 12.5 h daylength. Overall, where plant response to temperature can be expressed as the rate of progress towards a morphogenetic change, GDD values can be used to predict a plant developmental stage at a particular temperature. It must be concluded that temperatures induced significant variations in growth components (leaf number, plant height, leaf area), and affected bulbing response. The findings in this study confirmed that the cultivars require only a certain fixed amount of thermal time for their development at a particular temperature, and that, if anything, the slow growth rate at the higher temperature must be due to supra-optimal temperatures. They also require a minimum 12 h photoperiod for bulb formation.
The effects of chlormequat chloride and ethephon on selected small grain cereals in South Africa.
(2006) Ramburan, Sanesh.; Greenfield, Peter L.
Lodging poses a serious limitation to successful economic production of small grain cereals and can lead to extensive yield and quality losses. Plant growth regulators (PGR's) that reduce plant height and lodging have been employed in management systems in Europe and the United States, however, these compounds have not been evaluated on commercial cultivars of wheat, barley and oats in South Africa. Current recommendations to reduce lodging include limiting N inputs, seeding rates and critical irrigations, all of which may also limit yield potential and grain quality. The objectives of this study were to assess the effects of two common stem-elongation-inhibiting PGR's (chlormequat chloride and ethephon) on the growth, development, and agronomic characteristics of wheat, barley and oats. The aim of the study was to introduce an additional component of intensive cereal management in the form of PGR's, and to allow producers to implement intensive production practices without incurring losses due to lodging. Field trials were conducted with each of the three cereal crops in the 2003 and 2004 seasons at Vaalharts and Bethlehem. The PGR's were applied separately and in combination with each other to lodging-tolerant and -susceptible cultivars (wheat and oats) at different stages of development (tillering, elongation, flag leaf stage). The PGR's were also tested in combination with different levels of N (barley) applied at the haulm elongation stage, the flag leaf stage, or both. The PGR chlormequat produced negligible effects on plant height, lodging, yield, or quality components in all of the tested cultivars . Ethephon and the PGR combination successfully reduced plant height (by 120 to 150mm) and lodging (by 25 to 94%) when applied to the lodging susceptible cultivars of wheat and oats at the flag leaf stage or as a split application to the barley cultivar "Puma" (plant height and lodging reduced by 180 to 230mm and 83 to 92% respectively). Effects on grain yield were variable, ranging from occasional reductions (by 3 t ha(-1) and improvements (by 1 t ha(-1) with the barley, and no effects with the wheat and oats. Wheat quality parameters such as protein content and hectolitre mass were improved by 2 and 4% respectively. However, the nature of the responses was highly dependent on the times of application with later applications producing the greatest positive effects on quality, yield and lodging reductions. Additionally, ethephon and the PGR combination allowed higher levels of N to be employed without increases in lodging of barley. Generally, ethephon and the PGR combination applied at the flag leaf stage of growth are suitable anti-lodging tools for small grain cereal production and should be employed as an insurance measure against lodging in intensive management systems.
Phytotron and field performance of Taro [Colocasia Esculenta (L.) Schott] landraces from Umbumbulu.
(2006) Mare, Rorisang 'Maphoka.; Modi, Albert Thembinkosi.
The taro landraces that are most preferred by farmers from Umbumbulu, KwaZulu-Natal were identified through focus group discussions with farmers. Farmers ranked taro landraces on the basis of preference as determined by economic value, social significance, ecological importance and food characteristics. Using pairwise ranking, the farmers' preference of taro landraces across all locations was found to be in the following order: Dumbe-dumbe, Mgingqeni, Pitshi and Dumbe-lomfula. Dumbe-dumbe was identified as the currently actively cultivated taro whereas Mgingqeni was regarded as a less desirable cultivated taro. Pitshi was regarded as an antiquated landrace and Dumbe-lomfula was generally regarded as a taro type of no economic, social or food value that grew on river banks as a wild species. Glasshouse and field studies were conducted to determine the effects of temperature and growing location [Pietermaritzburg (UKZN) and Umbumbulu] on emergence, plant growth and yield of taro. Starch and mineral composition of taro corms were determined in harvest-mature corms. Effects of three day/night temperature levels (22/12°C, 27/17°C and 33/23°C) were examined on the growth of four taro landraces Dumbe-dumbe, Mgingqeni, Pitshi and Dumbe-lomfula. Pitshi-omhlophe, an ecotype of Pitshi for which there was a limited amount of planting material, was also included in the glasshouse studies. The farmers stated that the normal growing season for the economically important landraces, Dumbe-dumbe and Mgingqeni, was six months, but in this study plants were grown in glasshouses for nine months, and in the field, for seven months before the attainment of harvest maturity. Emergence was determined daily for glasshouse experiment until all plants had emerged and it was determined monthly for the field experiment. Leaf number, plant height and leaf area were measured every month to determine growth and development, while number of corms and fresh corm weight were used at harvest to determine yield. For all landraces, time to emergence increased significantly with decrease in temperature from 33/23°C to 27/17°C, but it increased significantly for only Dumbe-dumbe and Mgingqeni from 27/17°C to 22/12°C. Mgingqeni showed the shortest time to emergence, whereas, Pitshi showed the longest delay in emergence. The locations were not significantly different in emergence. Mgingqeni displayed the highest emergence in UKZN (91.4%), whereas, Dumbe-dumbe displayed the highest emergence (95.5%) and Dumbe-lomfula displayed the lowest emergence (55.9%) in Umbumbulu. Leaf number was highest for Pitshi-omhlophe, in glasshouse experiment due to its tendency to produce multiple shoots compared with the other landraces. Plant height increased with increase in temperature for all landraces except for Pitshi, for which height decreased with an increase in temperature. Leaf area was greatest for Dumbe-lomfula at all temperatures and lowest for Pitshi at both 22/12°C and 27/17°C. Leaf number was highest for Mgingqeni and lowest for Dumbe-lomfula at both sites, although it was significantly lower only for Dumbe-lomfula in UKZN. Plant height and leaf area were significantly highest for Dumbe-lomfula at both sites. The highest total number of corms per plant was shown by Pitshi-omhlophe at 22/12°C. Total fresh corm weight was highest for Dumbe-lomfula at 27/17°C and lowest for Pitshi at 22/22°C. The field experiment results showed Pitshi and Dumbe-lomfula with significantly higher total fresh corm weight in UKZN compared with Umbumbulu. Corms were analysed for mineral elements and starch. There were significant differences in starch content between temperatures (P = 0.017) and taro landraces (P = 0.025). There was also a significant interaction of temperatures and landrace (P = 0.002). Starch content increased with temperature for all landraces except for Pitshi-omhlophe and Dumbe-lomfula which showed a decrease at 27/17°C. There were significant differences in corm mineral content between temperatures, locations and landraces (P < 005). It is concluded that the chemical composition of taro corms is influenced by growth temperature and the location (site) where the crop is grown. The results of this study also indicated that taro plant growth is enhanced by high temperatures (33/23°C). High temperatures are, however, associated with short leaf area duration and subsequently low yield. The findings of this study may also be useful in determining taro quality for processing.
Phytate related response of maize seed to phosphorus and temperature.
(2006) Asanzi, Nafabuanga Mireille.; Modi, Albert Thembinkosi.
The aim of the study was to determine the effect of day/night temperatures (22/l6°C, 2712l oC and 33/27°C) and phosphorus levels (0, 0.12 and 1.2g per 20 kg soil) on seedling establishment and seed viability during three stages of seed development (15, 22 and 33 days after flowering) for seed of normal and quality protein maize cultivars. Soluble carbohydrate accumulation and mineral element content were determined using environmental scanning electron microscopy (ESEM) in relation to seed phytate levels and seed germination capacity at different stages of development. Leaf emergence rate and plant height during seed development were significantly (P < 0.05) influenced by temperature and phosphorus nutrition. Phosphorus in seed is stored primarily in the form of phytic acid, also known as phytate. Accumulation of phytate takes place during maturation phase of seed development. Phosphorus nutrition and temperature also caused a.significant (P < 0.05) increase in seed germination at all stages of seed development. Furthermore, phosphorus nutrition and temperature influenced occurrence of soluble carbohydrates in seeds. Myo-inositol, the sugar alcohol that forms the basic structure of phytate, was increased by P nutrition and increasing growth temperature. Whereas, QPM maize was generally found to perform poorly than normal maize, with respect to phytate content, seed germination and seedling establishment, both cultivars displayed the same responses to phosphorus nutrition and temperature. In both cultivars, globoids, the sites of phytate synthesis and storage, were found only in the embryonic axis. Subsequently, there were significantly low levels of mineral elements (P, Mg and K) found in the endosperm, compared with embryonic axis. This finding suggested that the embryonic axis plays a major role in seed performance, through its effects emanating from phyate metabolism. Myo-inositol plays a role in membrane biogenesis during stress conditions such as temperature by maintaining the integrity of the cell wall and minimizes the leaching of cations essential during germination. Myo-inositol, although it occurs in small concentrations, could be used to indicate seed quality in maize, because its accumulation was found to be associated with enhanced phyate levels and better seed germination in a wide range of temperatures. Low vigour seeds are associated with high electrolyte leakage during imbibition. Mineral elements form a significant portion of the imbibition leachate, which causes seeds to lose nutrients for early seedling growth. This study provided evidence that phosphorus nutrition can alleviate poor seed vigour of maize by improving phytate levels.

Browse

Browsing Masters Degrees (Crop Science) by Issue Date