Long-Term Effects of Conservation Tillage and Poultry Litter On Cotton and Residual Crop Corn Yields and Soil Phosphorus.

Long-term field experiments are needed to fully realize positive and negative impacts of conservation tillage and poultry litter application on cotton production. A study was initiated in north Alabama in 1996 to evaluate cotton  (Gossypium hirsutum L.) performance with long-term poultry litter (PL) application under different tillages and to study the build up of phosphorus (P) with application of PL. Treatments include incomplete factorial combinations of three tillage systems [conventional till (CT), mulch-till (MT), and no-till (NT)], two cropping systems [cotton- fallow and cotton-winter rye (Secale cereale L.)], and two nitrogen sources and rates [100 kg N ha^‑1 from ammonium nitrate (AN), and 100 and 200 kg N ha^‑1 from poultry litter (PL)]. Cotton was rotated with corn (Zea mays L.) every third year. Results from 2003-2008 showed that all tillages gave similar cotton lint yields with AN at 100 kg N ha^-1. But application of PL at 100 kg N ha^-1 in CT and MT plots gave significantly higher lint yields compared to NT. On average, PL application in NT plots resulted in 12 and 11% yield reductions compared to CT and MT, respectively. However, NT plots with PL at 200 kg N ha^-1 gave similar yields to CT and MT. During corn years, higher residual fertility of PL was observed in NT plots. Long-term PL application (100 kg N ha^-1 yr^-1) helped to maintain original soil pH in CT and MT while application of AN decreased soil pH. In NT plots, PL at 100 kg N ha^-1 was not sufficient to maintain soil pH, but 200 kg N ha^-1 maintained original pH.  However, PL application at double rate (200 kg N ha^-1) in NT plots caused build up of P.