Submitted to: American Journal of Alternative Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/1995
Publication Date: N/A
Interpretive Summary: Grass seed production fields in Oregon's Willamette Valley have traditionally been burned after harvest to dispose of straw residue and to destroy the next season's potential pests and diseases. The practice of open field burning may be entirely eliminated within the next few years. Low-input, in-the-field composting could provide an alternative for grass seed straw utilization but was not thought possible because of high C:N ratios of grass straw. Composting of grass seed straw into an easily spread soil amendment has been shown to be possible without the addition of a high-nitrogen component such as inorganic nitrogen or manure. The objective of this research was to develop on-farm, low-input composting technology. Field studies included replicated trials of grass seed straw residue were formed in windrows and turned 0, 2, 4, 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 of 80% were achieved with as few as 2 turns. 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.
Technical Abstract: A method for low-input, on-farm composting of grass straw was developed. The composting methodology was developed by forming windrows of perennial ryegrass (Lolium perenne) straw & turning either 0, 2, 4, or 6 times throughout the year with a commercial straddle-type compost turner. No water beyond normal rainfall or N other than that contained in the straw was added. Average volume reduction of long straw was up to a maximum of 88% of the original with 4 or 6 turns over a period of 20-24 weeks. Average internal temperature of long straw windrows reached a maximum of 54 deg C with 4 turns. Accompanying lab studies showed bacteria, actinomycetes, & fungi ranged from 10**9, 10**8, & 10**7 propagules g**-1 straw, under mesophilic conditions, respectively. Under thermophilic conditions bacteria & fungi were reduced to 10**8 & 10**6 propagules g**-1 straw, respectively, & actinomycetes remained unchanged. Microbial biomass C, during the lab incubations, represented 4% to 6% of the total straw C. The thermophilic microbial biomass degraded approximately twice as much straw C as the mesophilic biomass. The microbial N requirement was less than 4% of the total straw N. During the lab incubation, analysis of the Klason lignin fraction showed 25% & 40% of the lignin C was mineralized at mesophilic & thermophilic temperatures, respectively. Comparison of the elemental ratios of the lignin fraction indicated even more extensive lignin degradation had occurred. Conservation of N by microbial biomass & rapid delignification are the reasons the straw composts successfully. The ability to compost these residues will help the development of sustainable farming systems by providing a methodology to recycle straw waste.