RUNOFF FROM COTTON FIELDS FERTILIZED WITH POULTRY LITTER

Broiler litter is a valuable soil amendment for crop production, with litter typically applied to land areas used for grazing and/or hay production. Historically, farmers have based litter application rates on the nitrogen (N) needs of the receiving crop; however, this results in over–application of phosphorus (P). To alleviate the tendency to accumulate P in nearby watersheds, export of litter to other regions has been proposed. A field study was conducted at the University of Arkansas Northeast Research and Extension Center at Keiser, Arkansas, to quantify the impact of poultry litter on runoff water quality from cotton (Gossypium hirsutum L.) cropland in the Mississippi River Delta. Six 0.6–ha fields were fertilized with either commercial fertilizer (annually 140 kg N ha –1 yr –1 in a split application) or poultry litter (7,200 to 9,200 kg litter ha –1 yr –1 ). Runoff from each field was diverted through an H–flume, where water samples were collected. Stage was recorded and used to compute runoff flow. Concentration and mass loss of eight water–quality analytes were measured from 21 individual runoff events over a three–year monitoring period. Seedcotton yield was lower from the litter–fertilized plots, suggesting a need for refinements in the production system. Three–year total mass losses of total suspended solids (TSS) and nitrate nitrogen (NO3–N), as well as total runoff volume, were reduced from fields receiving poultry litter compared to fields receiving commercial fertilizer. Differences associated with the two fertilizer treatments did not clearly exhibit a systematic change over three years, as would be expected if soil structure were changing as a result of the organic amendments. Although total TSS mass loss was reduced, concentrations of nutrients associated with the solid fraction of chicken litter increased periodically in runoff events that immediately followed litter application. Moreover, total loss of orthophosphate P from litter–treated fields was four times greater than from fields fertilized conventionally. Additional research is needed to ensure that poultry litter exported to the Mississippi River Delta region can be applied as part of an integrated crop fertility program that results in the desired agronomic performance while protecting and enhancing water quality.