Soil chemical and microbiological responses to irrigation with diluted winery wastewater in a Shiraz vineyard in Stellenbosch, Western Cape

Abstract

There is an increase in the shortage and demand for irrigation water in the farming system, especially in the Western Cape, South Africa. To reduce the pressure on the demand for clean water and meet the irrigation demand, the practice of supplementing available clean water with urban/industrial wastewater including winery wastewater (WWW) is becoming popular. Hence, a field study was conducted over three seasons (2018-2020) in a Shiraz/110 Richter vineyard at the Agricultural Research Council (ARC), Infruitec-Nietvoorbij, Stellenbosch, South Africa. The study assessed (i) the effect of diluted WWW and raw water on soil chemical parameters: pH, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), Carbon (C), Soluble-s, electrical conductivity (ECe), exchangeable potassium percentage (EPP’) and exchangeable sodium percentage (ESP’)) and soil enzyme activities (β-glucosidase, phosphatase and urease) where different cover crops and catch crops were cultivated (ii) the effect of the diluted WWW and raw water on the element content of the different catch and cover crops in the vineyard (iii) the performance of the summer growing catch crops and winter cover crops in the vineyard after irrigation with diluted WWW and raw water in the vineyard (iv) the effect of diluted WWW, raw water, summer catch crops and winter cover crops on the grapevine performance. Species cultivated as winter cover crops were oats (Avena sativa L.) and N-fixing whereas species cultivated as summer catch crops were pearl millet (Pennisetum glaucum), Dolichos beans (Lablab purpureus), chicory (Cichorium intybus) and a control (no cover crop). The experimental design was a randomized complete block design (RCBD) with 3 replications. Soils were sampled after irrigation with diluted WWW (after harvesting of catch crops) and after winter rainfall (after harvesting of cover crops) for soil chemical and soil enzyme activities. Catch and cover crops were sampled after irrigation with diluted WWW and after winter rainfall. Throughout the study period, irrigation with either diluted WWW or raw water had no significant effect on soil β-glucosidase, phosphatase, and urease activities. After application of diluted WWW and raw water over three seasons, there was a significant difference in soil pH, P, EPP’ and soluble in the 0-15 cm soil layer. In the 15-30 cm soil layer, the significant impact was on soil pH, P, K, ECe and EPP’. At 30-60 cm soil layer, only soil K differed significantly between the treatments and at 60-90 cm soil layer, soil P, K, Na, soluble-s and EPP’ differed significantly between the treatments. After three seasons of irrigation with diluted WWW, summer catch crop, Dolichos bean produced higher Dry Matter Decomposition (DMP) compared to pearl millet while N-fixing winter cover crop produced higher DMP than oats. The chemical composition of winter cover crops (N, P, K, Ca, Mg and Na) differed significantly between the treatments in the 2018 and 2020 seasons after winter rainfall. Following dilution with winery wastewater, the chemical composition of summer catch crops (N, P, K, Ca and Mg) differed significantly.