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.