Physicochemical changes and nutrient dynamics during composting of the solid fraction of dairy cattle slurry

Abstract

Cattle slurry solid fraction (SF) was collected from two dairy farms and composted in tall (1.7 m) and short (1.2 m) static piles to evaluate the physical-chemical characteristics and nutrient dynamics of SF during composting. Highest maximum temperatures (62–64 ºC) were achieved in tall piles compared to short piles (52 ºC). Therefore, tall piles enhanced compost sanitation. Final OM losses were within the range of 520-660 g kg^-1 and nutrient content gradually increased throughout the composting period, due to the net loss of OM. Linear regression between nutrient and OM contents showed highly significant correlation coefficients (P <0.001), which decreased by the following order: N, Ca, P and K. The low temperature, C/N ratio, and content of NH₄⁺-N combined with increased concentrations of NO₃^--N indicated that SF composts were stabilized. The high concentration of OM and macronutrients in the dry matter of final composts, together with a low electrical conductivity (0.6–1.4 dS m^-1), suggested that SF composts would be effective as soil organic amendments and suitable for use in agriculture.