Fall 2002
Project demonstrates crop nutritive value of liquid swine manure
John Lundvall, Iowa State University Extension, and John E. Sawyer, Department of Agronomy
The Iowa State University (ISU) Swine Manure Nutrient Utilization Project, part of the Integrated Farm/Livestock Management (IFLM) Demonstration Program, receives funding from the Iowa Department of Agriculture and Land Stewardship, Division of Soil Conservation, USDA Natural Resources Conservation Service, and the Leopold Center for Sustainable Agriculture. The project goal is to learn more about liquid swine manure nitrogen (N) and phosphorus (P) availability to crops and compare crop yield with manure versus commercial fertilizer in a series of systematic demonstrations across Iowa.
Weighing equipment to document application rates.
Study leaders John Sawyer and Antonio Mallarino recognize that swine manure is an important nutrient source for corn and soybean in Iowa. However, environmental concerns arise when manure N and P are not adequately accounted for or used by crops. A goal of the project is to increase producer confidence in swine manure’s nutrient availability and consistency relative to commercial fertilizers by encouraging soil testing, manure nutrient analysis, equipment calibration, proper rate application, and use of best-management practices to reduce applications of additional commercial fertilizer when appropriate. Project objectives include the following:
1) Compare corn yield
response between manure and commercial fertilizer
2) Estimate manure N and P crop availability.
3) Address producers’ uncertainty about applying additional N and
P after manure application
4) Document soybean yield response to direct manure application
5) Monitor soil and plant nutrient responses to manure and fertilizer
application
6) Provide education opportunities for farmers and ag business personnel
through summer field days, winter meetings, promotional literature, and
Web-based information.
Since 2000, the project has had 39 on-farm demonstrations with 16 cooperators in 12 Iowa counties. At each field site, preliminary soil samples are collected to monitor baseline soil P, potassium (K), pH, and organic matter levels. Cooperators collect surface or probed samples of stored liquid manure (finishing facilities with under-building pit or concrete tank storage) 2–3 weeks before land application. Samples are analyzed at the ISU Analytical Services Laboratory for solids, total-N, -P, and -K, as well as ammonia-N.
Using a cooperator’s presample total-N analysis, targeted manure application rates are calculated. Manure is applied at zero (check), half, and full rates of total-N (target of 0, 75, and 150 lb of total-N per acre before corn in a corn–soybean rotation; 0, 100, and 200 lb of total-N per acre in continuous corn or before soybean). Field-length manure treatment strips are randomized and replicated three times at each field site. When manure is applied, portable scales are used to weigh application equipment for rate calibration. Multiple manure samples are collected during application and analyzed like the presamples to document total-N, -P, and -K nutrients applied in treatment strips. These data are collected to evaluate both the application process and manure nutrient content and consistency.
To
address producer uncertainty about applying additional N and P fertilizer
after manure application, four rates of fertilizer are hand-applied to
replicated small plots in each control and manure application strip. At
field sites featuring corn after soybean, supplemental N fertilizer rates
of 0, 40, 80, and 120 lb of N per acre are evaluated; at continuous corn
field sites N fertilizer rates are adjusted to 0, 60, 120, and 180 lb
of N per acre. In corn and soybean fields with a history of soil P testing
in the high or lower soil test category, P fertilizer rates of 0, 20,
40, and 60 lb of P2O5 are evaluated in separate small plots. Crop-removal
rates of K fertilizer are hand-applied to all small plots, with N fertilizer
blanket-applied to P small plots and P fertilizer blanket-applied to N
small plots.
Several methods are used to monitor crop nutrient status during the growing season. Early-season and post-tassel aerial photos of each corn field site provide a visual assessment of soil and plant characteristics. Late-spring soil nitrate test samples are collected within small plots and throughout manure treatment strips. Crop P uptake during early vegetative growth is monitored by collecting aboveground plant samples from small P plots near the V5 (vegetative stage with 5 leaf collars showing) growth stage. Corn leaf N status is monitored near the R1 (silking) growth stage with a Minolta (SPAD) chlorophyll meter. Lower SPAD values mean “less green” leaf tissue, suggesting that the corn plant is not receiving adequate N for optimum growth. End-of-season cornstalk test samples are collected from small plots to evaluate N status at crop maturity.
Corn and soybean yield is determined by hand-harvest from the interior of each small plot. Cooperators combine-harvest the manure application strips by using yield monitors or weigh wagons to measure grain yields. After harvest, soil samples are collected from P small plots for routine agronomic and potential environmental P tests. Soil profile nitrate is monitored at several N rates within each manure application strip.
New cooperators and field sites are being identified for the 2003 crop year. Producers interested in cooperating in this project should contact the project coordinator before fall manure or commercial fertilizer application. If you are interested in participating in the project, please contact project coordinator John Lundvall at 2104 Agronomy Hall, ISU, Ames, IA 50011; phone (515) 294-5429; E-mail jlundval@iastate.edu.
This is first in a series of newsletter articles highlighting the ISU Swine and Manure Nutrient Utilization Project. Future articles will highlight manure sampling results and demonstration results.
