Influence of cover crops on potential nitrogen availability to succeeding crops in a Southern Piedmont soil

Abstract

Winter cover crops are essential in conservation tillage systems to protect soils from erosion and for improv- ing soil productivity. Black oat (Avena strigosa Schreb) and oilseed radish (Raphanus sativus L.) could be useful cover crops in the southeastern USA, but successful adop- tion requires understanding their influence on N availabil- ity in conservation tillage systems. Black oat and oilseed radish were compared to crimson clover (Trifolium incar- natum L.) and rye (Secale cereale L.) for biomass pro- duction and effects on N mineralization during the summer crop growing season from fall 1998 through summer 2002 near Watkinsville, GA. Rye produced 40 to 60% more biomass, although N contents were less than the other cover crops. Oilseed radish and black oat N contents were similar to crimson clover. Black oat, oilseed radish, and crimson clover C/N ratios were less than 30, whereas rye averaged 39. Amount of N mineralized in 90 days (Nmin90) measured with in situ soil cores was 1.3 to 2.2 times greater following black oat, crimson clover, and oilseed radish than following rye. No differences in Nmin90 were found between black oats, crimson clover, and oilseed radish in 1999 and 2000. The amount of potentially mineralizable N( N0) was not different due to cover crop, but was 1.5 times greater in 2000 and 2002 than in 1999. The rate of N mineralization (k) was 20 to 50% slower following rye than the other three cover crops. Black oat and oilseed radish biomass production and soil N mineralization dy- namics were more similar to crimson clover than to rye, which indicates that they could be used as cover crops in the southeast without significant changes in N recom- mendations for most crops.