Home » Journal Entries » Effect of Irrigation with Diluted Winery Wastewater on Phosphorus in Four Differently Textured Soils

Effect of Irrigation with Diluted Winery Wastewater on Phosphorus in Four Differently Textured Soils

A.R. Mulidzi, C.E. Clarke, P.A. Myburgh

The wine industry needs solutions for wastewater treatment, as environmental legislation for its disposal is
increasingly being enforced due to non-compliance. The feasibility of re-using diluted winery wastewater
was assessed in a pot experiment under a rain shelter over four simulated irrigation seasons. Four soils
varying in parent material and clay content, viz. aeolic sand from Lutzville containing 0.4% clay, alluvial
sand from Rawsonville containing 3.3% clay, granite-derived soil from Stellenbosch containing 13% clay,
and shale-derived soil from Stellenbosch containing 20% clay, were irrigated with wastewater diluted to
3 000 mg/L COD (chemical oxygen demand), whereas the control received municipal water. Irrigation with
diluted winery wastewater increased the pH(KCl) in the shale- and granite-derived soils into the optimum
range for P availability. Although pH(KCl) in the aeolic sand was initially above the optimum range, relatively
high Na+ levels also caused available P to increase as the pH(KCl) increased. The pH(KCl) in the alluvial sand
increased beyond the optimum range, thereby causing a reduction in the available P. This indicates that
irrigation with diluted winery wastewater may only enhance P absorption if the pH(KCl) shift is towards the
optimum. It must be noted that the results represent a worst-case scenario, i.e. in the absence of rainfall
or crops.

Chemical oxygen demand, pot experiment, solubility, soil pH, water quality

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