Nz Jovanovic’s research while affiliated with University of Pretoria and other places

Irrigation of agricultural crops is one of the most cost-effective options for the utilisation of gypsiferous mine wastewater. In addition, it creates the opportunity to produce crops during the dry season. Gypsum is a slightly soluble salt and concen-trating the gypsiferous soil solution through crop evapotranspiration precipitates gypsum in the soil profile, removing it from the water system and reducing the potential for groundwater pollution. In previous research, it was found that crops can be commercially produced under irrigation with gypsiferous mine-water with no obvious impact on groundwater in the short term (3 years). It was, however, recommended that monitoring should continue to confirm findings over a longer period and for different conditions. A research project was therefore initiated in 2001 to determine the impact of irrigation with several gypsiferous water/soil combinations on crop performance, soil properties and groundwater quality. Field trials were carried out in South Africa on three mines: Kleinkopjé and New Vaal Collieries (Anglo Coal), and at Syferfontein (Sasol). Dif-ferent crop and pasture species were grown on different soil types under centre-pivot irrigation with different mine-water qualities. Intensive monitoring systems were established in each irrigated field to determine the components of the soil-water and salt balance. Boreholes were also installed to monitor groundwater level and quality. Field water and salt balance data were used for calibration and validation of the mechanistic, generic crop, Soil-Water Balance (SWB) Model. The results of the field trials indicated that high crop and pasture yields can be obtained, provided site selection, land preparation, fertilisation and irrigation water management are appropriate. The results of the soil-water and salt balance studies indicated that con-siderable volumes of mine-water can be used and substantial amounts of salts can be removed from the water system through precipitation of gypsum in the soil profile. The groundwater impact was limited based on borehole measurements, indicating the presence of a zone of attenuation between the cropped soil profile and groundwater, but this should be monitored over a longer period. With appropriate management, water and salt runoff, and under specific conditions, drainage and salts leached can be intercepted, thereby minimising unwanted impacts on groundwater. Thirty-year scenario simulations were run with SWB and the generated salt loads from this model were used as input into a separate groundwater model in order to predict the likely long-term effects of irrigation with gypsiferous mine-water on groundwater. The results of these simulations showed that while salts reached the groundwater, there was a drop in concentration of the plume as it moved away from the irrigated area. This was due largely to dilution by infiltration from rainfall recharge and the dispersive characteristics of the aquifer. The simulations also showed the importance of matching the amount of drainage from an irrigated site with the transmissivity and storage properties of the aquifer below. These results suggest that large-scale irrigation with gypsiferous water could be viable if irrigated fields are carefully sited to prevent waterlogging and are well managed. A site-specific approach is essen-tial.

The use of gypsiferous mine water for irrigation of agricultural crops is a promising technology that could add value through agricultural production and utilise mine effluent. Crop response to irrigation with gypsiferous mine water, as well as the impact on soil and groundwater resources were investigated in a three-year field trial set up at Kleinkopje Colliery (Witbank, Mpumalanga Province, South Africa). Sugar-beans, maize and wheat were irrigated with four centre pivots on virgin and rehabilitated land, under three irrigation management regimes using two qualities of mine water. Good crop yields were obtained compared to dry-land cropping. Waterlogging in certain areas of the fields indicated that especially rehabilitated land should be properly prepared and, where necessary, waterways built to prevent yield reduction. Soil salinity increased over the duration of the trial due to high concentrations of Ca2+, SO42- and Mg2+ in the irrigation water, but this never reached levels critical to yields of most crops. Exchangeable Ca2+ and Mg2+ in the soil increased with time, whilst K+ decreased. Plant analyses indicated possible nutrient deficiencies, which should be easily managed through corrective fertilisation. The groundwater impact was limited based on borehole measurements, indicating the presence of a buffer zone between the cropped soil profile and groundwater, but this should be monitored over a longer period. Commercial production of crops under irrigation with gypsiferous mine water is feasible and the resulting environmental impact is limited, but further research is required to confirm these findings over a longer period. WaterSA Vol.28(4) 2002: 413-422

Mechanistic, generic crop, irrigation scheduling models require crop-specific growth parameters which are not readily available for many crops and conditions. The objective of this work was to determine growth parameters for 19 summer vegetable cultivars, and to calibrate the SWB (soil-water balance) model. These vegetable crops were grown in a field trial at Roodeplaat (Gauteng, South Africa) during the 1996/97 summer rainy season. Weather data were recorded with an automatic weather station, phenological stages monitored and growth analyses carried out weekly. Fractional interception of radiation was measured with a sunfleck ceptometer and soil water content was monitored with a neutron water meter. Field measurements were used to generate a database of crop water and radiation use efficiencies, specific leaf areas, stem-leaf partitioning parameters, canopy extinction coefficients, maximum rooting depths and crop heights, as well as thermal time requirements for crop development. These data are invaluable for generating the parameters required to accurately simulate the soil-water balance with mechanistic crop models.