Tillage Effects On Cover Crop Decomposition and Nutrient Cycling In Cotton.

Conservation tillage and cover cropping are commonly-used practices for reducing soil erosion losses in cotton (Gossypium hirsutum L.) production systems in the southeastern U.S.  The rate at which cover crops decompose and release nutrients back to soil may vary based on tillage system.  The objectives of this experiment were to measure the decomposition and nutrient release of rye (Secale cereale L.) and wheat (Triticum aestivum L.) cover crops in a conventional- versus strip-tillage cotton system and evaluate their impact on the subsequent cotton crop.  Field trials were conducted in 2009 and 2010 in Tifton, GA, where cotton was grown in conventional- and strip-tillage following a rye or wheat cover.  Mesh litterbags containing cover crop residues were buried in conventional-tillage plots prior to planting cotton to simulate incorporated residues.  Cover crop and cotton plant samples were collected periodically over the growing season and analyzed for biomass and plant nutrients.  Cover crop biomass decline was analyzed by non-linear regression and plotted using an exponential decay model.  Conventional-tillage resulted in more rapid biomass decline than strip-tillage both years.  Total nutrient release was not different between tillage treatments (P ≤ 0.05), however it was much less in 2010 because of poor cover crop stands.  In 2009, strip-tillage resulted in greater total N, P, K, Ca, Mg, B, and Mn uptake by cotton (P ≤ 0.10), but tillage effects were insignificant in 2010.  Cotton lint yields ranged from 1248 kg ha^-1 to 1678 kg ha^-1, but tillage had few effects on lint yield and fiber quality both years.  These results suggest that tillage can significantly affect cover crop decomposition and nutrient uptake by a subsequent cotton crop, but has only minimal impact on lint yield or quality.