On-Farm Evaluation of Liquid Swine Manure as a Nitrogen Source for Corn Production

Liquid swine (Sus scrofa) manure (LSM) is a substantial crop nutrient resource in Iowa. An on-farm study was conducted in 2000-2003 at 16 sites to evaluate corn (Zea mays L.) response to LSM N. Replicated field-length strips were a control and two LSM rates, fall or spring applied, and four fertilizer N (FN) rates applied aft er planting in subplots. Average corn grain yield (GY) in the strips was 7.8, 9.6, and 10.4 Mg ha(-1) for the control, low, and high LSM rates, respectively. Plant and soil tests also increased with LSM application, indicating corn response. With the low LSM rate, GY increased with FN at many sites, but less frequent and smaller increase with the high LSM rate. Despite the average 82% fraction of LSM total-N as NH4-N, FN equivalence based on GY was only 61 to 64%. This indicates potential N losses, not unexpected due to application time and large springtime precipitation at some sites. Critical values for the late spring soil NO3-N (LSNT) and lower corn stalk NO3-N (CSNT) were 27 and 1820 mg NO3-N kg(-1), respectively; and the tests consistently indicated excess N but had poor relationship to N response at low values. Relative chlorophyll meter (RCM) values did not differentiate excess to slight N deficiency. The LSM was able to supply N for corn production, but like fertilizer, must be managed carefully. If additional N may be needed to achieve optimal yield, application must be based on well-calibrated soil or plant tests.