Wp De Clercq

The role of wild vegetable species in household food security in maize based subsistence cropping systems

Wild vegetables (WV) are an important source of food in the maize based subsistence farming sector of rural South Africa. Their main role is as relish as they are used as an accompaniment for staple cereal based diets. They are generally reported to be rich in micronutrients. Although they may be consumed in small quantities, they influence the intake of cereal staples, manage hunger and play a central role in household food security for the poorer rural groups. Mixing several WV species in one meal contributes to dietary diversity in terms of more vegetable types as well as in terms of choice of relish. For some very poor families WV are substitutes for some food crops. The seasonal occurrence of these vegetables leaves many families without a food source during the off-season. Wild vegetables increase agro-biodiversity at the household level. This agro-biodiversity helps in buffering against the accumulation and multiplication of pests and diseases and provides important cover for the soil. Further research on agronomic, social and economic dimensions is required to understand the roles of WV in subsistence farming systems in South Africa.

Model-Based Integrated Methods for Quantitative Estimation of Soil Salinity from Hyperspectral Remote Sensing Data： A Case Study of Selected South African Soils

Abstract Soil salinization is a land degradation process that leads to reduced agricultural yields. This study investigated the method that can best predict electrical conductivity (EC) in dry soils using individual bands, a normalized difference salinity index (NDSI), partial least squares regression (PLSR), and bagging PLSR. Soil spectral reflectance of dried, ground, and sieved soil samples containing varying amounts of EC was measured using an ASD FieldSpec spectrometer in a darkroom. Predictive models were computed using a training dataset. An independent validation dataset was used to validate the models. The results showed that good predictions could be made based on bagging PLSR using first derivative reflectance (validation R 2 = 0.85), PLSR using untransformed reflectance (validation R 2 = 0.70), NDSI (validation R 2 = 0.65), and the untransformed individual band at 2 257 nm (validation R 2 = 0.60) predictive models. These suggested the potential of mapping soil salinity using airborne and/or satellite hyperspectral data during dry seasons.

Nutrient fluxes in rainfall, throughfall and stemflow in Eucalyptus stands on the Zululand coastal plain, South Africa

Atmospheric deposition was assessed at two sites over a four-year period in post-canopy-closure (mature) Eucalyptus stands in the northern Dukuduku and southern KwaMbonambi commercial plantation forestry areas of Zululand, South Africa. The aim of this study was to determine the magnitude and relevance of nutrient addition with rainfall, throughfall and stemflow to commercial forestry in this region. Canopy cation exchange was used with rainfall and canopy drainage to derive wet, dry and total atmospheric deposition. Nutrient concentrations measured in the rainfall, throughfall and stemflow varied widely throughout the study period, and between sources and sites. Rainfall was slightly acidic at both sides, but became less acidic upon passing through the tree canopies. Canopy exchange and collection of dry deposition resulted in increased cation concentrations under the tree canopy, while the canopy generally absorbed nitrogen (N), from the rainfall, reducing the below canopy concentrations. Atmospheric deposition was shown to be responsible for large quantities of nutrients added to the eucalypt stands at each site. Annualised deposition averaged across all years at each site amounted to N, calcium, magnesium, and potassium (K) fluxes of 11.0, 6.0, 2.7 and 10.2 kg ha−1 y−1 at Dukuduku and 10, 10.6, 7.5 and 18.8 kg ha−1 y−1 at KwaMbonambi, respectively. Organic N fluxes contributed a further 8.1 kg ha−1 y−1 at Dukuduku and 7.1 kg ha−1 y−1 at KwaMbonambi to the total N deposition. Although K deposition values were high, additions of all other nutrients, although also high, were within the ranges reported in local and international research. Over the course of a full rotation, the atmospheric deposition levels recorded at these sites may have potential to supply a large proportion of the nutrients that are lost during stem-wood harvesting. This study adds value to understanding of nutritional sustainability of fast-growing plantation forests, demonstrating the importance of atmospheric deposition as a nutrient addition source to plantation-grown eucalypts along the Zululand coastal plain.

Hydrosalinity fluxes in a small scale catchment of the Berg River (South Africa).

The occurrence of dryland salinity is widespread throughout semi-arid regions of the world. The sources of salts may be either rock weathering or rain deposition. Clearing of natural scrubland to make way for cultivated crops and pastures may also change the water balance, trigger salt mobilization and increase the salinity of water resources. These processes are suspected to be the main cause for salinization of the Berg river catchment (South Africa). The objective of this study was to determine the hydrosalinity fluxes associated with overland and subsurface (vadose zone) flow for different soils and land uses. For this purpose, the following data were collected during 2006 in a typical small scale catchment (~40 ha) located near the town of Riebeek West: weather data, hydrological and water quality measurements, soil water contents and chemistry. The climate of the area is Mediterranean with winter rainfall of about 350 mm a. The chemical speciation of water and soil solution in the catchment is conservative, with Na and Cl being the dominant ions. Soil water and salt contents varied seasonally. Due to the typical low intensity of rainfall, the fluxes of salts during individual runoff events were steady. Fluctuations in salinity due to local processes were buffered at a catchment scale. Uncultivated (bare) soil produced more runoff and higher salinity compared to pasture land. Overland flow varied between 3 and 18% of rainfall, mobilizing up to 24 g m of salts during 2006, depending on soil properties, slopes, rainfall intensity and duration, and antecedent moisture conditions. Subsurface fluxes of water and salts were estimated with the HYDRUS-2D model. Management practices at farm scale are required in order to reduce salt mobilization and salinization at catchment scale.

Regional sustainability in table grape production on saline soils

A study was done in South Africa to investigate the state of the soil salt content and its effect on plant growth on a regional rather than a point basis. The study site went through a development phase since 1996 of establishing new vineyards each year. This provided an excellent opportunity to investigate soil characteristics, plant vigour and their relationship since the start of development. Soil samples were taken and trunk circumferences were measured. The soil properties included in the investigation were soil clay percentage, ECe, soil pH value and time since initial irrigation. Exploratory data analyses were done and variograms were drawn for all data. Kriging was used to map the variables and multiple regression analysis was used to investigate their relationships on a regional basis. A number of useful observations were made. Trunk circumference as an index of growth showed a negative correlation with ECe and a positive correlation with soil pH. Trunk circumference reflected a positive growth c...A study was done in South Africa to investigate the state of the soil salt content and its effect on plant growth on a regional rather than a point basis. The study site went through a development phase since 1996 of establishing new vineyards each year. This provided an excellent opportunity to investigate soil characteristics, plant vigour and their relationship since the start of development. Soil samples were taken and trunk circumferences were measured. The soil properties included in the investigation were soil clay percentage, ECe, soil pH value and time since initial irrigation. Exploratory data analyses were done and variograms were drawn for all data. Kriging was used to map the variables and multiple regression analysis was used to investigate their relationships on a regional basis. A number of useful observations were made. Trunk circumference as an index of growth showed a negative correlation with ECe and a positive correlation with soil pH. Trunk circumference reflected a positive growth cycle when compared with time since development. Regression analysis showed that trunk circumference as an indicator of vigour could be confidently predicted through knowledge of the vine age, soil pH and ECe and reflected upon measurement and prediction of sustainability in grape production. This approach has widespread applications for agriculture in terms of dealing with variation in a landscape and dealing with water supply problems. Methodology that uses a regional approach rather than a point approach in management could enhance the ability to increase profitability and ultimately improve water management.