Effects of Annual Turkey Litter Application on Surface Soil Quality of a Texas Blackland Vertisol

Proper application management is essential to minimize adverse environmental effects and maximize agronomic benefits of land applying poultry litter as a nutrient source and soil amendment. In this study, turkey (Meleagris gallopavo) litter was applied to five cultivated fields (target rates 4.5, 6.7, 9.0, 11.2, 13.4 Mg ha(-1)) and to two pasture fields (target rates 6.7, 13.4 Mg ha(-1)) to evaluate the effects on surface soil quality in the Vertisol-dominated Texas Blackland Prairie. A cultivated field that received only inorganic fertilizer and two pasture fields (one native prairie and one grazed pasture) served as "controls." Despite the annual variability in litter composition, actual application rates, and weather conditions, 7 years of litter application produced several significant differences in surface soil properties. Litter application produced significant increasing trends in soil organic C and extractable P for several cultivated and pasture fields. Similarly, after seven annual litter applications, litter rate was significantly related to total N, total P, extractable P, Zn, and Cu in the cultivated fields and to total P, extractable P, Zn, and Cu in the pasture fields. These observations coupled with previous findings indicate that annual litter application rates should be within 2.2 to 4.5 Mg ha(-1) for cropland and 4.5 to 6.7 Mg ha(-1) for pasture to limit the buildup of extractable P, Zn, and Cu in the soil. Although these target rates appear to be appropriate, the annual variability in litter composition (both nutrients and moisture) can, if not accounted for, make it difficult to determine proper application rates. Therefore, preapplication soil and litter testing and spreader calibration is strongly recommended so that litter application supplies only crop nutrient requirements (typically P) and balances agronomic and environmental concerns.