Nitrogen and potassium mineralization from winery solid waste composts in sandy and sandy loam soils

This study aimed at quantifying nitrogen (N) and potassium (K) released from winery solid waste (WSW) composts during laboratory incubation to address deficiency in two texturally distinct soils. Composts had 4, 10, 20, 30, 40% (w/w) of filter materials (FMs) mixed with grape marc and pruning canes. The composts were mixed with the soils at equivalent rate of 200kg N ha(-1) and incubated for 42days. Quantitatively higher (p<0.05) ammonium N content was recorded in sandy than sandy loam soil during the incubation duration while exchangeable K was increased in K-deficient sandy soil. Cumulative total mineralized N (TMN) measured during the incubation duration ranged from 59mg kg(-1) to 672mg kg(-1) depending on compost type and soil texture while a 10-fold increase in compost FMs content resulted in 144% and 139% increases in cumulative mineralized K in sandy and sandy loam textured soil, respectively. Percent N mineralized from the composts relative to the amount applied during the incubation duration was less than 54% reflecting the composts and soils inherent characteristics. The high ammonium N and K mineralized suggests that farmers must be cautious in utilizing these composts for field crops production due to the potential environmental risks.