Soil Science
Permanent URI for this communityhttps://hdl.handle.net/10413/6548
Browse
Browsing Soil Science by Author "Chaplot, Vincent A. M."
Now showing 1 - 5 of 5
- Results Per Page
- Sort Options
Item Analysis of global gully characteristics and the impacts of gabions and grass on sediments and carbon storage.(2018) Dube, Hastings Bangani.; Muchaonyerwa, Pardon.; Chaplot, Vincent A. M.Abstract available in PDF file.Item Assessing decomposition and soil carbon sequestration potential of sorghum residues from different cultivars.(2022) Ntonta, Sipho.; Zengeni, Rebecca.; Muchaonyerwa, Pardon.; Chaplot, Vincent A. M.Abstract available in PDF.Item Grassland degradation and rehabilitation of soil organic carbon and nitrogen stocks.(2014) Dlamini, Phesheya.; Chaplot, Vincent A. M.; Chivenge, Pauline.Land degradation is widely considered to adversely affect soil fertility, soil quality, constrain productivity, subsequently leading to a decline in soil organic carbon (SOC) and nutrients in soils, yet little is known about the stocks, environmental controls, destabilization mechanisms and carbon sequestration potential of degraded grassland soils. The aim of this dissertation was to evaluate (1) the impact of land degradation on SOC and nitrogen (N) stocks, distribution and SOC quality, to elucidate the environmental controls, in a communal rangeland with varying intensities of degradation, (2) to examine the rehabilitation potential of the same rangeland (3) to assess the spatial variability and replenishment potential of SOC and N stocks in a typically degraded grassland catchment. A meta-analysis was conducted to provide a quantitative review of the impact of land degradation on SOC stocks in grassland soils, worldwide. Subsequently, the impact of degradation on SOC and N stocks and organic matter quality was investigated in a communal rangeland in the KwaZulu-Natal province, South Africa with varying intensities of degradation. Thereafter, different rehabilitation techniques were applied in the same communal rangeland to replenish SOC and N stocks. Advantage was also taken of 23 ha degraded grassland catchment to assess the spatial variability, carbon replenishment potential of SOC and N and to elucidate the main environmental controls. Degradation resulted in a significant depletion of SOC stocks in grassland soils, both in the meta-analysis and field experiment. The meta-analysis indicated that the depletion of SOC stocks as a result of degradation was more pronounced in sandy acidic soils under dry climate than clayey soils under wet climate. The field experiment showed that degradation significantly depleted SOC stocks by 89% and N stocks by 76% in sandy acidic soils at the study site. The reduction of the stocks due to degradation was accompanied by an increase in soil bulk density, a decrease in soil aggregate stability and concomitant decrease of macro and micronutrients (e.g, Ca by 67%; Mn, 77%; Cu, 66% and Zn, 82%). SOC and N stocks decreased sigmodially with a linear decrease in grass aerial cover. After two years, the “Savory and fertilization techniques increased SOC stocks by 6.5% and 3.9%, respectively. At catchment level, degradation led to high spatial variability of SOC and N stocks controlled primarily by soil surface characteristics, including grass cover, soil surface crusting and secondarily by topography. The carbon replenishment potential of degraded grassland catchment was estimated to be 4.6 t C ha-1, with clay-rich Acrisols having a greater capacity to replenish SOC stocks than sandy Luvisols and Gleysols. In conclusion, the results of this dissertation indicate that degradation results in high depletion of SOC and N stocks. However, rehabilitation has the potential for carbon sequestration and can lead to more sustainable grassland ecosystems.Item Identification of the principal mechanisms driving soil organic carbon erosion across different spatial scales.(2013) Müller-Nedebock, Daniel.; Chaplot, Vincent A. M.; Chivenge, Pauline.Soil water erosion is recognized as the principal mechanisms behind soil organic carbon (SOC) losses from soils, a soil constituent essential for ecosystem functions. SOC erosion can thus be far-reaching, affecting the future human welfare and the sustainability of ecosystems. Little research has yet been done to investigate the main mechanisms involved in the lateral translocation of SOC on the landscape. Understanding the effects of the different water erosion mechanisms, which control SOC losses (SOC[L]) at the hillslope level, creates scope for further scientific studies. Empirical data from 357 plots, with a range in slope length from 1 (n=117) to 22.1m (n=240) were analysed to estimate the global variations of particulate organic carbon content (POC[C]), POC losses (POC[L]) and sediment POC enrichment ratio (ER). The global average POC[L] rate was calculated to be 12.1 g C m⁻² y¯¹. Tropical clayey soil environments revealed the highest POC[L] (POC[L]=18.0 g C m⁻² y¯¹), followed by semi-arid sandy (POC[L]=16.2 g C m⁻² y¯¹) and temperate clayey soil environments (POC[L]=2.9 g C m⁻² y¯¹). The global net amount of SOC displaced from its original bulk soil on an annual basis was calculated to be 0.59±0.09 Gt C, making up an approximated 6.5% of the net annual fossil fuel induced C emissions (9 Gt C). POC[L] data for different spatial scales revealed that up to 83% of the eroded POC re-deposits near its origin in hillslopes, and is not exported out of the catchment. The low organic carbon sediment ER obtained from the data of clayey soils (ER of 1.1) suggests that most of the eroded POC remains protected within soil aggregates. Consequently, erosion-induced carbon dioxide (CO₂) emissions in tropical areas with clayey soils are likely to be limited (less than 10%), as the process of POC re-burial in hillslopes is likely to decrease the rate of organic matter (OM) decomposition and thus serve as a potential carbon sink. Water erosion in sandy and silty soils revealed organic carbon sediment ER as high as 3.0 and 5.0, suggesting that in these soils the eroded POC is not re-buried, but is made vulnerable to micro-decomposers, thus adding to the atmospheric CO₂ influx. The results obtained in the review study only reaffirm that large variations of POC[L] are evident across the different pedo-climatic regions of the world, making it a scientific imperative to conduct further studies investigating the link between SOC erosion by water and the global carbon cycle. A field study was designed to quantify the POC exported in the eroded sediments from 1x1m² and 2x5m² erosion plots, installed at different hillslope aspects, and to further identify the main erosion mechanisms involved in SOC erosion and the pertaining factors of control. The erosion plots were installed on five topographic positions under different soil types, varying vegetation cover, and geology in the foothills of the Drakensberg mountain range of South Africa. Soil loss (SL), sediment concentration (SC), runoff water (R) and POCL data were obtained for every rainfall event from November 2010 up to February 2013. Scale ratios were calculated to determine which erosion mechanism, rain-impacted flow versus raindrop erosion, dominates R, SL and POC[L]. Averaged out across the 32 rainfall events, there were no significant differences in R and POC[L] between the two plot sizes but SL were markedly higher on the 5m compared to the 1m erosion plots (174.5 vs 27g m¯¹). This demonstrates that the sheet erosion mechanism has a greater efficiency on longer as opposed to shorter slopes. Rain-impacted flow was least effective where soils displayed high vegetation coverage (P < 0.05) and most efficient on steep slopes with a high prevalence of soil surface crusting. By investigating the role of scale in erosion, it was possible to single out the controlling in situ (soil surface related conditions) and ex situ (rainfall characteristics) involved in the export of SOC from soils. This information will in future contribute toward generating SOC specific models and thus further inform erosion mitigation.Item Land use and land management impact on CO2 emissions from soils in selected smallholder farming systems.(2016) Adam, El-Khatab Mohamed Abdalla.; Chivenge, Pauline.; Chaplot, Vincent A. M.; Everson, Colin.Abstract available in PDF file.