Proper recycling of manure nutrients is a major issue on livestock farms in the U.S. and other developed countries. Animal manure provides nutrient-rich organic matter that can serve as a valuable fertilizer resource for crop production. In a well-managed production system, manure nutrients are returned to the soil where they are used to produce feed crops for animal production. The problem in this recycling of nutrients is that losses occur, and these losses can adversely affect the environment and production costs. Nutrient losses of greatest concern are gaseous emissions of ammonia, nitrate leaching to ground water, and surface runoff of phosphorus.
Farmers need management strategies that minimize nutrient losses to the environment and maximize nutrient use in crop production without adversely affecting their profit. To be most beneficial to the environment, manure must be applied with little disturbance of the soil surface to minimize soil erosion.
Scientists at USDA-ARS and the Pennsylvania State University used computer simulation of farms, supported by field research, to evaluate and compare the performance, environmental impact, and economics of alternative manure application methods in farming systems. In this study, broadcast spreading with and without incorporation by tillage, band application with soil aeration, and shallow disk injection were compared. Results were published as part of a special section on novel manure management techniques in the March–April 2011 issue of the Journal of Environmental Quality.
The model was first evaluated by comparing predicted ammonia emissions, nitrate leaching, and phosphorus runoff losses with those measured over four years of field trials, and good agreement was found. Then in the simulation of farms over many years of Pennsylvania weather, reductions in ammonia emission and phosphorus runoff losses were obtained through improved incorporation of manure.
Use of a shallow-disk injection device for applying manure below the soil surface generally provided the lowest nutrient losses of the techniques studied without substantially reducing farm profitability. In some farming systems, the improvement in crop production provided through reduced nutrient losses improved farm profit. Use of band application of manure along with soil aeration provided less environmental benefit, and the increased costs of production were generally greater than the economic benefit received. The study authors say this information will help animal producers choose manure application equipment that reduces their impact on the environment while maintaining farm profitability.
“Shallow injection of manure appears to be the best option for reducing nutrient losses to the environment,” says Al Rotz, lead author of the study. “Although this additional equipment and the management required increases the cost of manure handling, the annual improvement in nutrient use can often offset this cost and, in some cases, may even improve farm profitability.”
Research is ongoing in Pennsylvania and other locations in the mid-Atlantic area to further evaluate different methods for subsurface injection of manure in both liquid and solid forms. Refinement and adoption of this manure application technique is one of many potential strategies for reducing nutrient runoff into the Chesapeake Bay, Rotz says. Reduction in nutrient loading is needed to help clean and improve the aquatic life in the Bay.
Adapted from Rotz, C.A., P.J.A. Kleinman, C.J. Dell, T.L. Veith, and D.B. Beegle. 2011. Environmental and
economic comparisons of manure application methods in farming systems. J. Environ. Qual. 40:438–448.
View online at www.crops.org/publications/jeq/ tocs/40/2