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.
University of Idaho Kentucky Bluegrass Research and Extension Team
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Donn Thill, Weed Science/Team Leader
Janice Reed, technical support
Jodi Johnson-Maynard, Soil Science
Karl Umiker, technical support
Joe McCaffrey, Entomology
Russ Biggam, Brad Harmon, technical support
Wes Chun, Plant Pathology
Larry Van Tassell, Agricultural Economics
Bob Smathers, technical support
J.D. Wulfhorst, Ag. Econ & Rural Sociology
Stella Rweza, graduate student
John Holman, Ken Hart, David Clark, Jim Church, David Barton, Extension
Carl Hunt, Animal Science
Don Pierce, WWW Application Specialist
Bahman Shafii, Experiment Station Statistician
Don Crawford, Microbiology; Janice Strap, Postdoc
Grower Cooperators/Advisors
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Nezperce Prairie Grass Growers Association
David Mosman, Craigmont, ID
Doug Lustig Farm, Greencreek, ID
Tom Mosman, Craigmont, ID
Chris Ramsey, Rockford, WA
Paul Stearns, Rockford, WA
Herb Millhorn, Rockford, WA
CDA and Nez Perce Tribes
Jacklin Seed Division
Seeds Inc.
Dye Seed
Grassland West
EPA
Idaho State Department of Agriculture
Idaho Department of Environmental Quality
Research and Technology Transfer Objectives
1. Develop non-thermal or reduced thermal systems that optimize straw
decomposition and maintain or increase Kentucky bluegrass seed yield.
2. Determine the optimum herbicide and herbicide application time to predictably
suppress growth of Kentucky bluegrass stands.
3. Develop livestock grazing systems and/or use of emerging biotechnology
alternatives (microorganisms) that optimize biomass turnover and maintain or
increase bluegrass seed yield without burning.
4. Compare nutrient cycling efficiency and soil quality factors in burned, reduced
thermal, grazed, and non-thermal Kentucky bluegrass systems.
5. Investigate the aboveground insect pest and predator relationships in bluegrass
systems and monitor diseases and weeds associated with the different treatments.
6. Examine the economic efficiency of each bluegrass production system including
the associated production, price, and financial risk.
7. Identify potential key social and economic costs and benefits of alternative
residue management practices versus current open-burning practices.
8. Distribute information to growers, field consultants, extension educators and
scientific audiences.
Research Projects
Reduced Thermal Residue Management
A study was initiated in fall 2002 at Worley, ID on ‘Alene’ Kentucky bluegrass
following the first year of seed harvest. Study design is RCB with four replications with
plots 60ft x 300ft in size. The treatments include full load burn (historical residue
management practice); bale and burn; bale, mow, and harrow; and a “systems” residue
management treatment. The “systems” residue management treatment consists of a
rotation of all three residue management treatments, where in year one the residue is
baled and mowed, in year two the residue is baled and burned, and in year three the
residue is full load burned. Plot maintance and treatments are implemented using grower
scale field equipment and a grower cooperator. Using a grower cooperator and field
equipment minimizes small plot treatment effects, and results in research findings similar
to those of growers who implement the practice on their farm.
The objective of this study is to reduce the amount of burning required to
maintain seed production. The rake, bale, mow, and harrow treatment is a common
practice in Washington, where burning of bluegrass residue is prohibited. Grower
testimony suggests this practice maintains seed production for three to four years
compared to eight to ten years when residue is full load burned. This study is currently
in the second year of seed harvest. In the next two to three years, this study should
determine if bale and burn or the “systems” residue management treatment will maintain
seed yield and reduce the amount of burning compared to full load burn.
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.
Forage Quality
A study at Pullman, WA is evaluating forage quality of ‘Kenblue,’ ‘Touchdown,’
‘Ascot,’ and ‘Limousine’ bluegrass varieties. Treatments are under irrigation and
dryland in a RCB with three replications. Forage samples are collected at boot,
flowering, swathing, combining, and periodically for two weeks following harvest.
Samples are evaluated for protein, in-situ digestibility, stem/leaf ratio, plant height, lignin
content, and elemental nutrient composition. It is speculated that forage quality will
decrease with plant maturity and harvest date following combining. Plant physiological
parameters will be tested for correlation to forage quality.
Residue Decomposition
A study at Pullman, WA on ‘Kenblue,’ ‘Touchdown,’ ‘Ascot,’ and ‘Limousine’
and at Worley, ID on ‘Alene’ Kentucky bluegrass is evaluating residue decomposition
rate and plant physiological factors affecting residue decomposition. Treatments are
under irrigation and dryland in a RCB with three replications at Pullman, WA and under
dryland at Worley.
Residue will be collected after combing from both sites, placed in mesh bags, and
allowed to decompose in the field at Pullman, WA and in the laboratory at Moscow, ID.
Residue weight will be measured monthly to determine decomposition rates. C/N ratios
of the collected residue will be measured at combining and in the spring. Plant
physiological parameters will be measured to determine their impact on residue
decomposition. Preliminary results indicate that C/N ratio can vary by variety and/or
site. Varieties with lower C/N ratio residue will likely decompose at a faster rate and will
likely have a longer stand life under reduced thermal residue management systems.