Submitted to: Compost Science and Utilization
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/1995
Publication Date: N/A
Interpretive Summary: The composting of high C to N ratio grass straw is an alternative straw residue management approach that can upgrade the negative value of on-farm waste such as grass straw. The high C to N ratio straw residue is composted without the addition of N to lower the C to N ratio making composting of straw economical. Extensive lignin degradation showed why grass straw composts readily without additional N. When applied to cropping systems, the upgraded waste can be reutilized to promote the development of sustainable agricultural through the recycling of nutrients.
Technical Abstract: Utilization of high C:N ratio farm residues is difficult because of low value and bulk. Composting is an ideal method for upgrading the residue, however, it was not thought possible without co-composting. We have successfully composted grass straw with a C:N ratio of 50 to 1 by establishing ideal bulk density and moisture regimes. After turning and densification in the field, composting conditions are achieved with the rapid growth of thermophilic microorganisms. During laboratory incubations of the grass straw, bacteria ranged from 10**8-10**9 g**-1 grass straw. Actinomycetes numbered 10**8 g**-1 grass straw. Fungi ranged from 10**6- 10**7 propagules g**-1 grass straw. Microbial biomass C during composting represented 4-6% of total grass straw C. A significant amount of lignin C, 25%, was degraded during mesophilic decomposition while 39% was degraded during thermophilic decomposition. The acid insoluble lignin fraction became highly oxidized and accumulated N. The decomposed lignin C, N, H, and O concentrations were similar to humic substances in soil. These data indicate that extensive lignin degradation occurred. A simulation of microbial production indicated that the microbial biomass was more efficient at mesophilic than at thermophilic temperatures.