Claassen 145-152

Soil disturbance of wildlands sites during construction or erosion often results in loss of nutrientrich topsoils and decreased plant available nitrogen (N). When soil organic matter is removed, the content, decomposition and cycling of organic N within soils is also decreased, reducing long-term sources of plant available N. Yard waste composts are a potential resource for replacement of depleted soil organic matter on disturbed sites because they increase the soil’s organic matter content, increase N released by microbial decomposition (mineralization) and provide other beneficial plant growth responses (Stolt et al. 2001, Noyd et al. 1996). Yard waste composts have been used as soil amendments in agricultural and horticultural systems (Grobe and Buchanan 1993; Hartz et al. 1996) and for erosion control on roadway embankments (Ettlin and Stewart 1993; Storey et al. 1995; Metro 1994). Increased plant available N is a common objective of compost amendment, but N release from composts has previously been found to be variable or negative depending on process and source material (Hartz et al. 1998). Because soluble N can be lost from the soil by ammonia volatilization, denitrification or nitrification and leaching after it is mineralized from organic forms, compost products are expected to be variable depending on source, age and weather conditions during production. This variability influences field behavior of compost by changing the N available for revegetation, the type of residual organic material added to the soil and the associated microbial activity during decomposition. Product variability makes appropriate amendment of compost in field situations difficult, contributing to poor plant establishment if N release is low, or to weedy invasion if N release is excessive. Compost Science & Utilization, (2004), Vol. 12, No. 2, 145-152