Submitted to: European Commission International Symposium: The Science of Composting
Publication Type: Proceedings
Publication Acceptance Date: 5/31/1995
Publication Date: N/A
Interpretive Summary: Oregon's Willamette Valley Grass seed production growers have traditionally burned the fields after harvest to dispose of straw residue and to destroy the next season's potential pests and diseases. Open field burning may be entirely eliminated within the next few years and low- input, in-the-field composting could provide an alternative for grass seed straw residue. Since composting of grass seed straw does not generate uniform high temperatures, the survival of weed seed and pathogen propagules contained in the compost is a concern. The objective of this research was to develop low-input, on-farm composting technology. Replicated field studies included trials of grass seed straw residue formed into windrows and turned 0, 2, 4, and 6 times from October 1992 to June 1993. Timing of windrow turns was based on site access and on having at least three weeks between consecutive turns. Volume reductions were as high as 88% over 32 weeks. Laboratory studies identified mechanisms regulating the composting processes and related microbial activities involved in the decomposition of high C:N ratio substrates. These studies provide an approach for developing low-cost grass seed straw compost for utilization in the cropping system. If composting of waste grass straw and its amendment to soils used to produce grass seed crops is to gain acceptance, it is important that the presence of viable weed seed and pathogen propagules be reduced.
Technical Abstract: The field straw windrow composting study showed that a minimum of two turns and natural rainfall was required to reduce straw residue volume by 80% or greater in 16 to 21 wk. The decomposition of the high C:N ratio straw residue is contrary to established composting methodology where a C:N ratio of 30:1 or less is thought to be required to compost grass straw. The microbial biomass required more C and less N to function in the thermophilic treatment compared to the LT treatment. The microbial biomass N requirement was less than 4% of total straw residue N in both treatments. The low N requirement of the decomposer biomass indicates that the form or compartmentalization of N is more indicative of substrate quality than the concept of combined substrate C:N ratio. The increased requirement of the thermophilic biomass for C resulted in an increase in the decomposition of the lignin fraction compared to the LT treatment. The increased lignin fraction decomposition was detected through changes in the element composition of this fraction. For these reasons, the composting of grass straw residue is feasible without initially lowering the C:N ratio. Composting has value both as an avenue of straw disposal and for its potential for utilization in the cropping system. Volume reductions of straw windrows in this study were as high as 88% over 32 wk making in-field composting a viable straw disposal alternative to open field burning.