Mingchu Zhang, University of Alaska-Fairbanks, Fairbanks, AK, Robert Harmel, USDA-ARS, Grassland Soil and Water Research Laboratory, Temple, TX, Zhongqi He, 1100 Robert E Lee Blvd, USDA-ARS, New Orleans, LA, Heidi M. Waldrip, PO Drawer 10, USDA-ARS, Bushland, TX and Paulo H. Pagliari, University of Minnesota-Twin Cities, Lamberton, MN
Nutrient runoff from manured land can cause water quality problems; however, properly managing application rate in combination with tillage and crop system may reduce water soluble organic C (WEOC) and N (WEON), and decrease the risk of nutrient runoff. The objective of this research was to determine the effects of poultry litter on WEOC and WEON in a Vertisol-dominated Texas Blackland Prairie soil under different crops, tillage regimes, and grazing managements. Since 2001, poultry litter was applied at rates of 0, 4.5, 6.7, 9.0, 11.2, and 13.4 Mg/ha (i.e. 0, 2, 3, 4, 5 and 6 t/ac) to fields under a corn/oat/wheat rotation that received annual tillage. In addition, a control field was included that received inorganic fertilizer. For comparison, poultry litter (6.7 and 13.4 Mg/ha) was also applied to pasture with or without cattle grazing. Cumulatively, manure was applied for 12 years. Soil samples (0-15 cm) were taken and analyzed for KCl-mineral N, WEOC and WEON, and the UV-Vis spectral properties of WEOC were analyzed. Results showed that soil mineral N concentration was higher (p<0.05) in cultivated soils that received the 13.4 Mg/ha rate of poultry litter than soils that received inorganic fertilizer or a lower litter application rate, or when litter was applied to pasture. The concentration of WEOC was higher (p< 0.05) in pasture soils than in cultivated soils, indicating that decomposition was promoted by tillage. The concentration of WEON was increased with the higher rates of poultry litter application, while C:N ratios decreased as the litter application rate increased. However, the soil from pasture which received litter appeared to have a greater C:N ratios than cultivated soils that received the same rate of litter. The spectral analysis indicated that properties of soil WEOC differed under different management and rate of litter applications.