Nutrient Source and Tillage Impact On Corn Grain Yield and Soil Properties.

Large amounts of animal manure, particularly poultry litter and dairy manure are generated in the southeastern USA where corn (Zea mays L.) is also extensively grown.  However, little information is available about the use of poultry and dairy manure as an alternative source of nutrients for corn production and the long-term impact on soil properties.  This study examined corn crop yields, soil nutrients, and organic carbon content under two rates (low or high) of inorganic fertilizer (134 and 403 Kg N ha^-1) and poultry litter and dairy manure (each applied at 4.5 and 13.5 Mg ha^-1) compared to a non-treated control under two tillage practices (no-till and incorporated systems). Treatments were replicated four times in a split plot design. Poultry litter, dairy manure, and chemical fertilizer were applied on the same plots and corn was planted each year from 2004 to 2007.  Soil samples were taken annually in the spring prior to treatment application to evaluate the status of the residual nutrients in soil. No significant differences in corn grain yield between the two tillage practices were observed in all four years.  The high rate of poultry litter application produced similar grain yield as chemical fertilizer application in all four years. Dairy manure produced significantly smaller grain yield than poultry litter and chemical fertilizer treatments except for the high rate of dairy manure in 2006. After four years of poultry litter application, Mehlich-3 P increased from an initial 31.4 mg kg^-1 to 63.0 mg kg^-1 for 4.5 Mg ha^-1 rate and to 178 mg kg^-1 for 13.5 Mg ha^-1 rate. More specifically, 8.3 kg ha^-1 of P applied as poultry litter increased soil Mehlich-3 P by 1 mg kg^-1 after four years of application. The increase was smaller for dairy manure and negligible for chemical fertilizer compared to poultry litter. Results indicated that poultry litter as a primary fertilizer at the rate of 13.5 Mg ha^-1 applied in four consecutive years on a silt loam soil produced corn grain yields similar to inorganic fertilizer under both no-till and incorporated systems and did not result in residual soil test P, Cu and Zn levels considered to be harmful to surface water or cropping systems.