Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2005
Publication Date: 8/9/2005
Citation: Ferguson, R.B., Nienaber, J.A., Eigenberg, R.A., Woodbury, B.L. 2005. Long-term effects of sustained beef feedlot manure application on soil nutrients, corn silage yield and nutrient uptake. Journal of Environmental Quality 34:1672-1681. Interpretive Summary: This is a final report of a 10-year study designed to find the impact of manure and composted manure compared to commercial fertilizer on corn production. We set up treatments of two levels of manure or composted manure to be spread on cropland. Irrigated corn used for silage was the crop used for this entire study. We applied enough material to satisfy the estimated nutrient needs of the corn in terms of nitrogen or phosphorus each year, using an equivalent amount of nitrogen on each treatment. We also planted winter wheat on half of the field to test the effect of a winter cover crop on nitrogen that might be subject to moving deeper into the soil if the crop didn't use it. After six years, there was too much unused phosphorus on the phosphorus treatment plots and we did not apply any more manure or compost to those plots. After 10 years we found that the nitrogen used by the crop could be equally used from any source: manure, compost or commercial fertilizer. This told us that the prediction for nitrogen value of the manure or compost was good and that it was a good method for using the nutrients. We did find slightly less nitrogen in the soil below the roots where we planted a winter cover crop which told us that the cover crop was successful in holding the nitrogen near the surface. We found an excessive amount of phosphorus in the soil that received the high yearly application of manure or compost. However, the phosphorus did not move beyond the root zone. The yields were generally as good or better where we used manure or compost instead of commercial fertilizer. The only time that less corn silage was harvested was during very dry years where the cover crop was used. That was probably caused by the cover crop removing more soil moisture before the corn was planted. The final conclusions were that manure or composted manure were equally beneficial to commercial fertilizer with respect to nitrogen. However, phosphorus is the limiting fact. Soil phosphorus content will be exceeded if repeated applications are made to satisfy the nitrogen needs of corn. Both phosphorus and nitrogen can be used safely with annual soil checks.
Technical Abstract: A field study was initiated in 1992 to investigate the long-term impacts of beef feedlot manure application (composted and uncomposted) on nutrient accumulation and movement in soil, corn silage yield and nutrient uptake. Two application strategies were compared—providing the annual crop nitrogen (N) requirement (N-based rate) or crop phosphorus (P) removal (P-based rate), as well as a comparison to inorganic fertilizer. Additionally, effects of a winter cover crop were evaluated. Irrigated corn (Zea mays L.) was produced annually from 1993 through 2002. Average silage yield and crop nutrient removal were highest with N-based manure treatments, intermediate with P-based manure treatments, and least with inorganic N fertilizer. Use of a winter cover crop resulted in silage yield reductions in 4 of 10 years, most likely due to soil moisture depletion in the spring by the cover crop. However, the cover crop did significantly reduce NO3-N accumulation in the shallow vadose zone, particularly in latter years of the study. The composted manure N-based treatment resulted in significantly greater soil profile NO3-N concentration and higher soil P concentration near the soil surface. The accounting procedure used to calculate N-based treatment application rates resulted in acceptable soil profile NO3-N concentrations over the short term. While repeated annual manure application to supply the total crop N requirement may be acceptable for this soil for several years, sustained application over many years carries the risk of unacceptable soil P concentrations.