Abstract:
The majority of mine-affected waters contain large quantities of calcium and magnesium sulphate, with some dominated by sodium sulphate or bicarbonate. The availability of large volumes of mine impacted waters and large tracts of unfarmed land owned by mines, creates an opportunity to utilise these waters for irrigation. Not only will this drastically reduce mine water treatment costs, it will create sustainable livelihoods and food production, particularly post-mine closure. The aims of this study were to monitor and model field scale water and salt balances for a small scale mine water irrigation scheme in Mpumalanga, in order to predict the long-term impact and sustainability of gypsiferous mine water irrigation, as well as determining the effect of sulphate salinity on crop response of various temperate annual cereal grain crops. A field trial was established at Mafube Colliery outside Middelburg (Mpumalanga, South Africa) during 2016-2018. White maize was irrigated for one of the two seasons on virgin, unmined land. Regular monitoring was carried out to collect atmospheric, crop and soil data for detailed validation of the soil water balance (SWB) model. For the first season, it has shown that crops (specifically maize) grow well with these mine impacted waters, with minimal environmental impacts in the short term and proved to be more profitable than dryland production. The grain produced is safe for human consumption, which makes this a feasible practice. Pot trials were carried out at the UP Experimental Farm where crops were grown in water culture at five levels of salinity with an EC range of 120 to 2000 mS m-1. A combination of a nutrient solution, gypsum (CaSO4.2H2O) and Epsom salts (MgSO4.7H2O) was used to make up each treatment. The effect of salinity on germination, seedling establishment and vegetative growth was investigated. Increasing sulphate salinity negatively affects germination, seedling and vegetative growth of annual temperate crops, especially when dominated by Mg. After exceeding the threshold for salt stress, a linear reduction in relative growth was found for both seedling establishment and vegetative growth, as well as a decline in germination percentage. In general, annual temperate cereal crops are more sensitive to sulphate salinity during the vegetative growth stage compared to the seedling stage at the same sulphate salinity concentrations. Irrigation with mine water is viable, sustainable and feasible, if the appropriate management practices are in place and if some environmental impact is acceptable. Crop and cultivar selection, climatic conditions, irrigation method, soil and water quality are but a few of the parameters that need to be considered when irrigating with saline sulphate waters. Another important aspect to look at it, is nutritional requirements and possible imbalances.
