Fertilization effects of compost produced from maize, sewage sludge and biochar on soil water retention and chemical properties

Composting is a technique recommended for sewage sludge stabilization. Recently, it has been recognized that sewage sludge co-composted with bulking material and biochar can avoid environmental risk and improve compost quality. The impact of composting process parameters, feedstock type and particle size on soil properties is not well understood. The aim of this study was to investigate the effects of different compost particle sizes and the feedstock types on the physical and chemical characteristics of a sandy soil. The following mixtures of feedstocks in the composting process were used in this study: i) maize straw, ii) maize straw with sewage sludge and iii) maize straw, sewage sludge and biochar. Biochar was produced from a willow (Salix viminalis L.). The plant material was pyrolyzed at a temperature of 350 degrees C for 2 h. Four compost size classes were used: 0-250 mu m, 250-500 mu m, 500-1000 mu m, and 1000-2000 mu m. Compost application improved the water retention characteristics of the soil depending on the compost particle size and feedstock type. The lowest value of the available water content was obtained for the soil with maize straw compost. When sewage sludge or biochar was added during the composting process, it resulted in an increase in the soil available water content. The available water content decreased when large compost particles were used. Both experimental factors (feedstock type and particle size) significantly affected the water repellency. It was also observed that with a decrease in the compost particle size, the water repellency rapidly increased. The results for the chemical compositions of compost and feedstocks suggest that small compost particles have a relatively higher content of sewage sludge.