Differences in a Composted Animal Waste and Straw Mixture as a Function of Three Compost Methods

Compost Science & Utilization, (2005), Vol. 13, No. 2, 98-107

M.J. Curtis, W.A. Kleiner, V.P. Claassen and R.A. Dahlgren
Land, Air and Water Resources, University of California, Davis, California

Spatial differences in the physical and chemical characteristics of composted organic matter are strongly influenced by the composting method. We examined a traditional turned windrow (TW) treatment and two static passively aerated treatments (uncovered (SPA-U) and covered (SPA-C)) to determine spatial and temporal differences within and between treatments during composting of an animal waste-straw mixture. Temperature, moisture content, pH, respiration rate, C:N, mineral nitrogen and 15N were measured at three depths over a period of 176 days. All treatments met composting temperature criteria established by US EPA regulation 503. Covering piles for a short period elevated temperatures and may enhance thermal destruction of pathogens on and near the surface layer. The final C:N ratio was similar (10-11) between treatments and total C loss ranged from 40-45%. Total N concentrations increased about 20% during composting and there was no measurable loss of nitrogen from any treatments. SPA treatments tended to have a greater concentration of mineral nitrogen than the turned treatment (SPA-C > SPA-U > TW). For all treatments, pH was negatively correlated with mineral nitrogen suggesting retention of volatile ammonia (as ammonium) and subsequent nitrification. A small enrichment of 15N in the SPA treatments suggests some loss of nitrogen through ammonia volatilization and denitrification with greater enrichment (or loss of volatile N) from the TW treatment. Measuring microbial respiration, as a measure of labile organic matter and compost stability, showed differences within and between compost methods and may result from differences in microbial communities and nitrogen availability. Compared to the TW treatment, compost characteristics were spatially stratified in the SPA treatments and therefore the compost would require mixing prior to application. Results from this study will assist producers in optimizing their composting operations and the quality of the compost produced.

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