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Title: Cover crop effects on nitrogen mineralization and availability in conservation tillage cotton

item Schomberg, Harry
item Endale, Dinku

Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2004
Publication Date: 1/10/2005
Citation: Schomberg, H.H., Endale, D.M. 2005. Cover crop effects on nitrogen mineralization and availability in conservation tillage cotton. Biology and Fertility of Soils. 40(6):398-405.

Interpretive Summary: Producers want to increase efficiency in crop production. Optimumizing fertilizer use can help reduce costs and improve returns on investment. Residues from crops grown to reduce erosion in the wintertime (cover crops), can increase or decrease nitrogen availability to the following crop. Scientists at the J. Phil Campbell, Natural Resource Conservation Center in Watkinsville, GA measured the amount of nitrogen available to cotton following crimson clover and rye cover crops. More nitrogen was available to cotton following crimson clover because, as a legume, the clover can capture atmospheric nitrogen and make it available for plant growth. However, this did not result in greater cotton yield, probably because the extra nitrogen resulted in excessive vegetative growth of the cotton. The best yield of cotton fiber resulted with the rye cover crop due primarily to appropriate levels of nitrogen and more water availability compared to clover. The rate at which nitrogen became available in the cotton-rye system was slower, compared to the cotton-clover system, and probably more closely matched the requirements for good cotton growth. The rate at which nitrogen becomes available during the growing season can be predicted based on soil temperature. Using this system could help reduce costs on the 13 million acres of cotton grown in the US where nitrogen applications average 80 lb / ac.

Technical Abstract: Cover crops influence N availability to subsequent crops. We evaluated the magnitude of this effect in cotton (Gossypium hirsutum L.) by comparing cereal rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.) influences on N availability and cotton production in a Typic Kanhapludult at Watkinsville, GA. Seed cotton yields following clover and rye were 882 and 1205 kg ha-1 respectively, in 1997 and 1561 and 2352 kg ha-1 respectively, in 1998. In 1997, cotton biomass, leaf area index, and N were greater following crimson clover than following rye on some dates but not in 1998. Net N mineralization rates following crimson clover and rye averaged, respectively, 0.58 and 0.34 kg N ha-1 d-1 in 1997 and 0.58 and 0.23 kg N ha-1 d-1 in 1998. Total N mineralized ranged from 60 to 80 kg ha-1 following crimson clover and 30 to 50 kg ha-1 following rye. Heat units and cumulative heat units were positively correlated with N mineralized in both systems. Net N mineralization rates were 0.023 kg ha-1 heat unit-1 once net N mineralization began. Nearly 40 % of the rye and 60 % of the clover biomass decomposed during the 6 weeks prior to cotton planting in 1998. Soil heat units appeared to be a useful tool for evaluating N mineralization potential.