Composting cattle slurry solid fraction with Italian ryegrass straw (Lo­lium multiflorum Lam.) or gorse (Ulex europaeus L.)

Abstract

Cattle slurry solid fraction (SF) was col­lected from a dairy farm (SF) and com­posted with increasing rates of Italian rye-grass straw or gorse, in static piles turned only three times. Temperatures increased to a maximum of 65 ºC after the first turn in the pile only with SF. In contrast, higher temperatures were registered much sooner in piles mixed with straw or gorse. The ad­dition of these bulking agents to SF in­creased temperatures and also the initial rates of organic matter (OM) mineralisation. In contrast, potential OM mineralisation and organic N content decreased.

The C/N ratio declined following a similar pattern for all compost treatments, from 32–38 at the beginning of the proc­ess, to a value of 13–17 towards the end of composting. Stabilized compost was obtained from raw SF feedstock as indi­cated by the low compost temperature, low C/N ratio and the small content of NH4⁺ combined with increased concentra­tions of NO3^-. The high concentration of OM (784-832 g kg^-1) and total N (28-35 g kg^-1) in final composts in addition to a low electrical conductivity (0.72-1.16 dS m^-1) suggests that SF composts may be ef­fective as soil amendments. The use of straw or gorse contributed to guarantee compost sanitation.