Carbon and nitrogen mineralization during co-utilization of biosolids and composts

Increasing the consumer value of organic wastes through co-utilization or mixing is directly related to organic carbon (C) and nitrogen (N) mineralization when the mixture is used as a soil amendment. The objective of this study was to put forward a protocol that can be used to estimate the behavior of a mixture of biosolids and composts in a co-utilization program from the perspective of decomposability and release of plant available nitrogen (PAN) over time. Published literature suggested that the components of such mixtures would decompose in similar manner whether alone or in combination, and that net N immobilization characteristics of components with high C:N ratios could be overcome. Using the proper ratio of the components was essential to the development of a soil amendment which was more valuable than its components. Three mixtures for co-utilization of organic wastes were assessed using the computer simulation model, DECOMPOSITION. Municipal biosolids was mixed with paper mill sludge, leaf litter, and municipal solid waste (MSW) compost. Weather at Baltimore, MD, was selected for these simulations, with mixtures being applied in April. In each case a ratio was found to make a product with good N availability, but each mixture was sufficiently decomposable to limit its ability to increase soil organic matter(OM). The organic wastes most resistant to decomposition, very stable composts, were evaluated for potential to increase soil organic matter. Simulation of very stable compost decomposition showed that they would increase soil organic matter if applied annually for an extended period. These composts were also a good source of PAN after several years of application to soil.