Field‐Scale Evaluation of Poultry Manure as a Combined Nutrient Resource for Corn Production

An on‐farm study was conducted in Iowa from 2004 to 2006 at 18 sites to evaluate corn ( Zea mays L.) grain yield (GY) and soil‐ and plant‐test responses to poultry manure (PM) nutrient application at the field scale. A control and two target PM rates based on total N (PM‐N) were applied in randomized field‐length strips with three replications. Corn GY responded positively to PM applications. While N, P, and K plant and soil tests were related to PM nutrient rates, there was considerable variation, and relationships were probably influenced by the multiple applied nutrients. Soil‐test P and soil‐test K across sites increased linearly with increasing PM total P and K rates and with large increases from the high rates. This confirms high P and K crop availability. Grain yield responses to PM decreased linearly with increasing leaf chlorophyll meter (CM) and late spring soil NO 3 –N test (LSNT) values but were not related to end‐of‐season lower corn stalk NO 3 –N test values. No N test had a plateau relationship with GY, suggesting no excess N supply despite large PM‐N rates. This confirms low first‐year PM‐N availability. The relationship between CM and LSNT indicated a critical LSNT value at 24 mg kg −1 , similar to that from previous small‐plot research. This field‐scale study showed that PM is a valuable nutrient resource. However, due to PM multinutrient content and differences in availability, the nutrient causing GY and plant‐ or soil‐test results often cannot be clearly identified and results need careful interpretation for reliable use.