Influence of Manure Application Rates and Continuous Corn on Soil-N
1978
Magdoff, F. R.
Manure application to continuous corn (Zea mays L.) should provide some or all of the crop N needs and help maintain or increase soil organic matter. This should be done without damaging the environment by adding excess nutrients to ground or surface waters. A range of factors may influence manure decomposition, and hence N availability to crops. However, application recommendations are usually not site specific. To attempt to deal with site specific considerations, a comparison was made of the effect of manure on soil-N and crop response to inorganic-N between similar continuous corn experiments at two different sites. The manure-N experiments with continuous corn were conducted on both a somewhat poorly drained Panton clay (Typic Ochraqualf) and a well-drained Calais loam (Typic Fragiorthod). Manure rates of 0, 22, 44, and 66 metric tons/ha/year were combined in factorial arrangement with ammonium nitrate rates of 0, 112, and 224 kg N/ha/year. Comparison of calculated theoretical soil-N with experimentally determined levels after 5 years and the response of corn to fertializer-N indicate that mineralization of manure organic-N, when applied to the Panton clay, was less than when applied to the Calais loam. Thus, manure-N was less available to the growing crop on the clay and accumulated in the soil at a greater rate than in the loam. The annual manure application rates required to maintain initial soil N levels in Panton clay and Calais loam under continuous corn production were calculated to be 40 to 52 tons/ha respectively. Two mineralization models were examined: Model 1 assumed only the first year manure mineralization rate above native soil organic matter decomposition rate; Model 2 assumed a 5-year mineralization decay series. Both were effective in predicting final soil-N levels.
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