Effect of poultry litter application method on ammonia volatilization from a conservation tillage system

Abstract

Ammonia (NH₃) volatilization from agricultural fields is important economically as a direct loss of the valuable crop nutrient nitrogen (N), but it can also be a significant environmental concern for soil, air, and water quality of nearby ecosystems. As poultry production has expanded in cropland areas of the southeastern United States, poultry litter has become a major source of crop nutrients for farmers using conservation tillage systems. However, the conventional application method of broadcasting poultry litter on the soil surface can allow as much as 60% of the applied litter N to volatilize as NH₃. To provide management options that can prevent NH₃ losses and help farmers use poultry litter nutrients more efficiently, a research team at USDA's Agricultural Research Service developed a prototype tractor-drawn implement for subsurface application of dry poultry litter in perennial pasture and conservation tillage systems. When compared to surface broadcasting, previous research showed that subsurface application of poultry litter decreased odor problems, increased crop yields, prevented more than 90% of nutrient losses in runoff, and prevented NH₃ volatilization from perennial pasture systems. The current study was conducted to expand our knowledge regarding the effect of this litter application method on NH₃ volatilization from row-crop conservation tillage systems. For two consecutive summers, field plots with a uniform high-residue surface cover of chopped wheat straw received about 5,000 kg ha⁻¹ (4,500 lb ac⁻¹) of poultry litter applied by surface spreading with no incorporation, surface spreading followed by light disking, or subsurface banding using the prototype USDA ARS applicator. Small mobile wind tunnels monitored NH₃ volatilization for at least five days after each litter treatment. Results for both years showed that NH₃ losses were consistently affected by diurnal variations that were closely related to the vapor pressure deficit. Compared to conventional surface spreading of poultry litter, NH₃ volatilization decreased an average of 67% when the litter application was followed by light disking, and decreased an average of 88% when the litter was applied below the soil surface using the prototype applicator. These data show that subsurface injection of dry poultry litter can preserve adequate surface cover for conservation needs while constraining NH₃ losses to minimal levels, thus conserving N for row crops and reducing potential nitrogen losses to the environment.