Long-term effects of poultry litter and conservation tillage on crop yields and soil phosphorus in cotton-cotton-corn rotation

Long-term field experiments are needed to fully realize positive and negative impacts of conservation tillage and poultry litter application. A study was initiated on a Decatur silt loam soil at the Tennessee Valley Research and Extension Center, Belle Mina, AL, USA 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 [100kgNha⁻¹ from ammonium nitrate (AN), and 100 and 200kgNha⁻¹ from poultry litter (PL)]. Cotton was rotated with corn (Zea mays L.) every third year. Results from 2003 to 2008 showed that all tillages gave similar cotton lint yields with AN at 100kgNha⁻¹. Application of PL at 100kgNha⁻¹ in NT plots resulted in 12 and 11% yield reductions compared to that of CT and MT, respectively. However, NT plots with higher quantity of PL (200kgNha⁻¹) gave similar yields to CT and MT at 100kgNha⁻¹. During corn years, higher residual fertility of PL, in terms of grain yields, was observed in NT plots compared to CT and MT. Long-term PL application (100kgNha⁻¹ year⁻¹) helped to maintain original soil pH in CT and MT while AN application decreased soil pH. In NT plots, PL at 100kgNha⁻¹ was not sufficient to maintain original soil pH, but 200kgNha⁻¹ maintained original pH. Although not-significant, elevated P levels were observed in all tillages compared to original P levels which indicates possibility of P build up in future with further application of PL. Application of PL at double rate (200kgNha⁻¹) in NT plots resulted in significant build up of P. Results indicate that NT gives similar yields to CT when received AN, but needs higher rate of PL application to achieve similar yields to CT.