Submitted to: Iowa Manure Matters Odor and Nutrition Management Newsletter
Publication Type: Popular Publication
Publication Acceptance Date: August 17, 2007
Publication Date: September 4, 2007
Citation: Cambardella, C.A., Singer, J.W., Moorman, T.B. 2007. Soil and cover crop responses to liquid swine manure application. Iowa Manure Matters Odor and Nutrient Management Newsletter. 10(3).Available: http://www.extension.iastate.edu/pages/communications/EPC/Fall07/soilcovercrop.html. Technical Abstract: Large-scale pork production is a major agricultural enterprise in the Midwest. Large numbers of confined hogs produce about 50 million tons per year of swine manure in Iowa alone. The most commonly used manure management practice in the Midwest involves fall application to land where corn will be grown in the subsequent growing season. Fall planted annual cover crops can capture manure nutrients and immobilize them in plant biomass, subsequently reducing the potential for nutrient loss through run-off or leaching. Decomposition of cover crop residue the following spring may help synchronize manure nitrogen (N) availability and corn N uptake, improving nutrient-use efficiency within the crop rotation. We conducted experiments to evaluate the effects of integrating a rye/oat cover crop with liquid swine manure application on retention of manure N in a corn-soybean cropping system. Our objectives were to compare soil N changes after manure application with and without a cover crop and to evaluate cover crop and soil N response for three manure N rates (0, 100, 200, or 300 lb N/ac). Liquid swine manure was injected about six to eight weeks after a 70% rye/30% oat cover crop mixture was drop-seeded in soybean. Manure was injected to a depth of five inches using a narrow-profile knife designed to minimize soil disturbance. We measured cover crop shoot biomass and N and phosphorus (P) uptake in mid-November and mid-April following manure injection. Surface soil (0-8 in) inorganic N in the manure injection band was quantified every week for up to six weeks after manure application and in the following spring before and up to six weeks after killing the cover crop prior to corn planting. Soil profile (to 48 inches in 8 inch increments) inorganic N was also quantified before manure application in the fall and before the cover crop was killed the following spring. We demonstrated that a rye/oat cover crop reduces soil inorganic N after liquid swine manure injection. Cover crop impacts on soil N are observed within a month after application and persist into the following spring. Cover crop nutrient uptake was higher than the control in the spring when at least 200 lb manure N/acre was applied. These results quantify the potential for cover crops to enhance plant nutrient uptake and reduce N leaching potential in farming systems utilizing manure.