Use of Anaerobically Digested Swine Manure as a Nitrogen Source in Corn Production

Swine (Sus scrofa) manure is an important source of N for crop production. The processing of manure in an anaerobic digester for biogas production is only a partial manure treatment process and is not designed as a disposal method. However, digestion will alter manure characteristics, and this may affect nutrient availability to crops. The objective of this study was to evaluate the N supply to corn (Zea mays L.) from swine manure before and after anaerobic digestion for biogas production. Raw and digested swine manure were late-fall applied as main plots, with three manure N rates as subplots, and six fertilizer N rates as sub-subplots. Response to manure and fertilizer N was determined through soil inorganic N, plant N status and uptake, and grain yield. After 3 yr of study, results indicated no difference between raw and digested swine manure as a source of N for plant use in the year of application or in the residual year. Equivalence to fertilizer N was the same with both raw and digested swine manure, and varied between years with 100% in 2000, 44% in 2001, and 60% in 2002. These differences are attributed to varying growing seasons and N loss potential from time of late fall manure application compared with the spring-applied fertilizer N. Late fall and early spring soil sampling indicated rapid conversion to NO3(-) with both sources. Results of this work indicate that digested liquid swine manure can readily supply plant-available N and management for corn production should be the same as with raw swine manure.