Effects of Corn Stover, Manure, and Nitrogen on Soil Properties and Crop Yield

Residues and farmyard manures are considered important in determining the N fertilizer requirement of crops. This relationship was studied in a 10-year field experiment on a Typic Hapludalf soil (pH 7.8). Five levels of fertilizer N were applied annually with three management treatments which included 1) returning the stover produced by the preceding corn (L.) crop, 2) poultry manure equivalent to 112 kg N/ha/year and 3) no stover returned or manure applied. Dry matter yields and N in grain and stover were measured each year.In general, the manure treatment without N fertilizer gave yields comparable with any other treatment. Where fertilizer N was not applied, stover depressed yields; but where N was applied, stover resulted in slightly higher fields than where stover was removed. Stover returned to the soil did not increase fertilizer N requirements at nomal rates of application. Fertilizer N narrowed the C/N ratio of the stover residue, but this additional N was not reflected in the total N content of the grain or the soil. Regression equations for yields of grain and N on N applied indicated that a single term, the square root of N applied, would fit the response pattern for the majority of treatments, not including manure in most years. Treatments including manure required terms with the square and cube of applied fertilizer N levels to describe the response pattern. Yields from residual N were higher on plots where stover had not been applied than where applied and, at the highest level of applied N, equalled those from residual manure. Soil organic matter (OM) declined during the experiment, but stover residues and manure gave a smaller decline than without residues. Applied N did not help to conserve OM, but increased inorganic N (NO + NH) in the soil. The degree of water-stable aggregation was increased by stover and manure treatments. It was concluded that corn stover residue did not affect the N fertilizer requirement of this soil for grain corn production. Annual applications of liquid poultry manure, containing N equivalent to 112 kg/ha, precluded a requirement for fertilizer N.