South Africa Wine Technical Yearbook 2025

AUGUST

Winery wastewater irrigation (Part 7): Effect on soil enzyme activities By Reckson Mulidzi & Carolyn Howell

Introduction Irrigation with wastewater, amongst other management practices, 1 could change the internal soil environment in ways that affect the activities and functioning of microorganisms responsible for the breakdown of soil organic matter (OM), and for the mineralisation of nutrients. 2 Enzyme activity may be stimulated through the change that might be due to stimulation of enzyme-producing soil microorganisms and, hence, enzyme activity, through the supply of easily decomposable organic material in wastewater, a process known as priming. 3 Where enzymes are associated with and protected by soil colloids,

Abstract Although the effects of winery wastewater (WWW) on soil chemical properties have been the focus of some research, little is known about the effect of WWW on soil enzyme activity. Therefore, soils from four potential vineyard areas were irrigated, in pots, over four successive simulated seasons (SS), each consisting of six irrigation events, with municipal water and with WWW diluted to a chemical oxygen demand of 3 000 ml/L. Urease, β-glucosidase and phosphatase activities were determined in the 0-10 and 10-20 cm soil layers after the third and fourth SS. Compared with municipal water, irrigation with WWW increased the average activities of urease and β-glucosidase, but suppressed that of phosphatase. Using diluted WWW for irrigation increased urease and β-glucosidase activities in all four soils, increased β-glucosidase in the Stellenbosch shale and granite soils and decreased β-glucosidase activity in the Rawsonville sand. Compared with uncontaminated water from dams, rivers or boreholes, the effects of WWW on enzyme activity are therefore likely to differ from soil to soil and from enzyme to enzyme.

41

TECHNICAL YEARBOOK 2025