Cattle slurry solid fraction (FSC1 and FSC2, collected from open and closed sinkholes, respectively) was collected from two dairy farms and composted with and without straw, in static and in turned piles. Thermophilic temperatures were attained soon after separation of FSC1, which was collected at lower rate, and increased to a daily maximum temperature of 68 °C in the static pile with straw. However, the temperature in the FSC2 piles did not reach temperatures above 51 °C. Straw addition to slurry solid fraction contributed to raise temperatures in all piles, but did not increase organic matter (OM) mineralization rates. Maximum mineralizable OM was higher in the turned than in static piles but the final N compost content was higher in static piles, suggesting that revolving can increase N losses. The C/N ratio declined from over 27 to a value of 11-13 towards the end of composting and followed a similar pattern for all compost treatments. Stabilized compost was obtained from raw SF feedstock as indicated by the low compost temperature, low C/N ratio and the low NH4+ content, besides higher NO3- concentrations. The high concentration of OM (720-820 g kg-1) and total N (30-44 g kg-1) in final composts in addition to a low electrical conductivity (below 100 mS m-1) suggests that SF composts may be useful as soil amendments with agronomic and environmental advantages. However, further research is needed to assure compost hygienization since the FSC2 did not reach thermophilic temperatures during composting.
compost; dairy cattle; mineralization; organic amendments; organic fertilizer
