Liquid Swine Manure Application to Soybean and Residual‐Year Nitrogen Supply to Corn

Liquid swine (Sus scrofa domesticus) manure (LSM) is a valuable source of plant nutrients; however, information on application to soybean [Glycine max (L.) Merr.] and subsequent potential N response in residual‐year corn (Zea mays L.) is lacking. Replicated on‐farm trials were conducted at eight sites from 2000 to 2003 in Iowa with control, low, and high LSM application rates applied to soybean. In the following year corn, four fertilizer N (FN) rates were applied within each prior‐year LSM rate. Soybean grain yield (GY) increased at 63% of sites with LSM application (mean 0.17 Mg ha−1), with no soybean GY reductions. Postsoybean harvest soil profile NO3–N increased at four sites, with mean increases across sites of 12 and 24 kg NO3–N ha−1 for the low and high LSM rates, respectively. Residual‐year corn GY increased at 71% of sites from the prior‐year low and high LSM rates (mean 0.6 and 1.1 Mg ha−1) that received no FN. The residual‐year N supply to corn was estimated at 11% of the total LSM‐N applied to soybean, the amount of postsoybean harvest profile NO3–N ha−1 increase from each LSM rate. Corn leaf relative chlorophyll meter (RCM) and end of season corn stalk NO3–N (CSNT) reflected the residual N supply, but the late spring nitrate test (LSNT) did not detect that residual N. Application of LSM to soybean can be a viable nutrient management practice; however, total‐N application should be at a rate to minimize excessive residual NO3–N and carryover to future crops.