Subsurface Application of Poultry Litter in Pasture and No-till Soils.

Poultry litter provides a rich nutrient source for crops, but the usual practice of surface-applying litter can degrade water quality by allowing nutrients to be transported from fields in surface runoff, while much of the ammonia-N escapes into the atmosphere. Our goal is to develop improved management options that allow producers to decrease nutrient losses from poultry litter, thus protecting air and water quality while increasing soil productivity. We tested the hypothesis that nutrient losses can be decreased by using a knifing technique to apply dry poultry litter beneath the surface of pastures. Results showed that subsurface litter application decreased ammonia-N volatilization and nutrient losses in runoff more than 90% (compared to surface-applied litter), to levels statistically as low as those from control (no litter) plots. Efforts were initiated to make subsurface litter application a practical management option for producers by developing prototype implements. Two advanced tractor-drawn prototypes are now being used for subsurface application of poultry litter at the desired rate in field research. The applicator developed by USDA-ARS at Auburn, AL has trenching assemblies that apply litter in four subsurface bands simultaneously, with center-to-center lateral band spacing that is adjustable (25-102 cm) for side-dressing crops on various row spacings. The "Poultry Litter Subsurfer" developed by USDA-ARS at Booneville, AR can transport five metric tons of dry untreated litter directly from the poultry house and apply it in eight subsurface bands simultaneously, with fixed (30-cm) band spacing that is used primarily for pastures or for pre-plant applications in no-till systems. These two prototype subsurface applicators have been tested in several pasture and/or no-till experiments, and have been very effective for improving nutrient-use efficiency; increasing crop yields (possibly by retaining more nitrogen in the soil) compared to surface-applied litter, while decreasing nutrient losses to near background (control plot) levels.