Integrated Residue Management Systems for Sustained Seed Yield of Kentucky
Bluegrass Without Burning
John Holman, Grass Seed Cropping Systems; Donn Thill, Professor Weed Science
Introduction
Sustained bluegrass seed productivity has historically relied on open-field burning
of post-harvest residues. Field burning maintains stand longevity by reducing thatch
accumulation, weed seed number and viability, and disease and insect pressure, and by
returning phosphorus and potassium to the soil profile. However, field burning has been
associated with significant air quality issues and public health impacts. In order to
sustain bluegrass seed production, an important source of income for producers in
northern Idaho and eastern Washington, the goal must be to encourage in situ
decomposition and/or non-thermal removal of straw residue. In the absence of burning
and without enhanced straw decomposition or efficient straw removal methods, bluegrass
acreage in this area will likely decrease. Furthermore, reduced bluegrass production will
result in increased annual crop production, which would likely increase soil erosion and
decrease water quality.
In 2001, the Department of Plant, Soil, and Entomological Sciences organized a
team of researchers, extension personnel, industry and grower advisors and cooperators,
and representatives from state and federal agencies, to develop alternative residue
management systems that eliminate or substantially reduce the need to burn bluegrass
residue yet sustain productivity and economical seed yield. University of Idaho team
members are listed below.
Research Projects
High Intensity Grazing
A large-scale, long-term, on-farm experiment will be established in a growercooperator field at Craigmont, ID. The research area will be about 30 acres in size. The
experiment will consist of eight main post-harvest residue removal treatments replicated
four times [open field burn (current practice); bale and burn; mechanical removal – bale +
mow; “alternate year cropping system”; and two levels of cattle grazing intensity (high
and moderate) at two grazing times (immediately after grass seed harvest and one month
after harvest)].
Mechanical forces applied through ruminant animal utilization of grass seed
residue include disruption of the sod via hoof action and physical particle size reduction
via mastication during ingestion and rumination (feed particulate is commonly reduced to
less than eight mm for transit through the digestive tract). Grass seed residue is further
reduced via microbial fermentation in the rumen and other fermentative organs of the
hind gut. These mechanical and fermentative forces imposed by the ruminant animal
may be managed to have the same net effect as open field burning of the crop residue.
Successful integration of the livestock and grass seed enterprises therefore, could serve to
eliminate air quality problems associated with grass seed burning while securing an
economic value from the grass seed residue
Cattle will be allowed to graze the high intensity grazed plot until 90% of the
biomass is removed. At the termination of each grazing treatment, the amount of residue
biomass remaining will be determined. At the beginning and at the end of each grazing
period, weights of the cattle will be obtained on two consecutive days. Total mega
calories of metabolizable energy harvested will be determined based on body weight and
on weight gain or loss of the animals during the grazing period. An economic value of
the grazed residue will be estimated based on the fair-market value of mega calories from
locally produced conventional forages and grains. As an additional appraisal of energy
harvested by the cattle, an estimate of digestibility of the grazed forage will be
determined. Available forage (tillers plus residue) will be sampled along with fecal
samples from random droppings. Forage and fecal samples will be examined for an
internal digestibility marker (such as indigestible acid detergent fiber) to determine
organic matter digestibility.
Microbial Residue Decomposition
Microbial biotechnology treatments will be evaluated at Craigmont, ID.
Treatments include bale plus microbiological amendment, and microbiological
amendment following cattle grazing. The parameters monitored will include grass seed
production, residue decomposition rate/biomass turnover, total microbial and
actinomycete counts, and the number of fungal propogules and pathogens. It is
hypothesized that the soil disruption caused by intensive cattle grazing will mix
remaining residues into the surface layers of the soil, which will significantly enhance
their decomposition rate by the actinomycetes. Previous research at the University of
Idaho found two strains of naturally occurring, nonpathogenic residue-degrading bacteria,
and are currently used to decompose thatch and control some fungal diseases in turf.
They decompose highly resistant thatch and grassy residues while also inhibiting the
growth of plant pathogenic fungi.