Optimization of Liquid Swine Manure Sidedress Rate and Method for Grain Corn

Abstract

Sidedressing may provide a better window of opportunity for land application of liquid swine (Sus scrofa) manure than early spring or fall application. Rates could be fine‐tuned to match crop N demand using the presidedress nitrate test (PSNT) if: (i) the yield response function to sidedress rate is consistent and (ii) yield and PSNT are positively correlated. To optimize application rate and method, we measured corn (Zea mays L.) grain yield response to in‐row injection (INJ) and topdress (TD) of liquid swine manure (LSM) sidedressed at different rates on clay loam (51‐cm rows in 1999) and silt loam (75‐cm rows from 2000–2002). Yields exceeded local long‐term averages with INJ in all but the wettest year, were variable with TD, and were 2 Mg ha−1 greater with INJ than TD at 37.4 m3 LSM ha−1. From the quadratic yield response to sidedress injection rate, optimal rate (to achieve 95% maximum yield) ranged from 38 to 63 m3 ha−1 (plot‐scale data; four 6‐m sections per plot) and 37 to 49 m3 ha−1 (field‐scale data; 0.2‐ha plots). Yields were correlated with the PSNT (r = 0.75 for no LSM sidedress; r = 0.24 for all treatments). Given the consistent yield response to sidedress INJ rate and accurate (correct 88% of the time) PSNT‐based predictions of additional N requirements (from comparisons of N fertilizer recommendation and relative yield), sidedress injection of LSM using the PSNT to fine‐tune rates according to crop N requirements can be considered as a best management practice.