Catherine N. Gacengo1, C Wesley Wood1, Joey N. Shaw1, Kipling Balkcom2, Andrew J. Price2, Randy L. Raper2, and Brenda H. Wood1. (1) Auburn University, Department of Agronomy and Soils, 202 Funchess Hall, Auburn, AL 36849-5412, (2) USDA-ARS, 411 S Donahue, Auburn, AL 36832
Decomposition patterns of cover crops determine availability of nutrients to subsequent crops. Decomposition and mineralization patterns of Lupinus albus L. (white lupin), Avena strigosa Shreb (black oat), Trifolium incarnatum L. (crimson clover) and Brassica napus L. (rape) were studied under field conditions at the E.V. Smith Research Center in Macon County, Alabama. Air dried materials in nylon litterbags were surface placed or buried on three landscape positions: drainageway, sideslope and summit. Litterbags were retrieved at 1, 2, 4, 6, 10, 14, 18, 22 and 26 weeks for mass and nutrient determination. Buried material decomposed and released nutrients significantly faster than surface placed material. When buried, 65-75% of material loss occurred within the first month of the study period. During the same period, only 17-38% of mass was lost on surface placed materials. Dry matter decline and nitrogen (N), phosphorus (P) potassium (K) and carbon (C) losses were statistically similar across the three landscape positions. Nitrogen loss was in the order black oat > clover > rape >lupin, and black oat > clover = rape > lupin for buried and surface placed materials, respectively. Although there were no significant cover crop N loss differences among landscape positions, buried lupin on summit and sideslope positions immobilized N during the first week while, it lost 34% of its initial N within the same time period in the drainageway. All surface placed materials initially immobilized N for varying time periods except black oat. Surface placement of cover crops may result in N immobilization lasting between one to six weeks compared to a maximum of one week period when cover crops are buried.
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