Effect of composted mulch application on soil and wine grape potassium status

Oversupply of potassium (K) to grape vines can result in high grape berry K and pH, leading to difficulty in wine making and low wine quality. There is concern that application of mulch to grape vines may increase K supply and the associated risks. The effect of composted mulch from green wastes was investigated in a field trial involving six vineyards in New South Wales on soils commonly used for viticulture production in Australia, over three seasons (2006-08). Significant increases in extractable soil K were detected as a result of mulch application. Higher berry K and pH were also observed due to the mulch treatments, with the changes dependent on season and mulch rate. Increases in berry K were significantly related to the higher soil exchangeable K. The mean increase in berry K due to a mulch rate of 153 m(3)/ha was 123 mg/kg. The mean increase in berry pH was 0.02 units observed in two seasons. Application of mulch can increase berry K and pH, but the changes are small compared with variations observed among vineyard sites and between seasons.