Extractable Soil Phosphorus and Inorganic Nitrogen following Application of Raw and Anaerobically Digested Swine Manure

fectof anaerobicdigestionon nutrientcontent andplant nutrient availability. Processing of swine (Sus scrofa domestica) manure in an anaerobic Due to a potential increase in the use of anaerobic digester for biogas production is not a complete waste treatment process. Therefore, digested manure must be utilized in some manner, digestion systems for energy production, there is need most likely as a source of plant nutrients. The objective of this study for a reliable estimate of plant-available N and P in diwas to compare the effect of raw and digested liquid swine manure gested swine manure. Evaluation of digested manure as application on soil test P (STP) and inorganic N. A laboratory incuba- a crop nutrient source requires determination of the eftion study was conducted for 112 d, with a factorial combination of fects of digestion on nutrient content and the ability to raw manure, digested manure, and inorganic fertilizer at five nutrient provide plant-available nutrients when the material is rates (0, 12.5, 25, 37.5, and 50 mg total P kg 1 and 0, 50, 100, 150, applied to land. and 200 mg total N kg 1 ). Raw and digested swine manure produced Nutrient release from manure at a time when crops the same NH4–N disappearance, NO3–N formation, net inorganic N, are not actively assimilating nutrients can cause low nuand increase in STP. Routine STP methods estimated similar P recovtrient use and poor crop response. Binder et al. (1996) erywith bothmanuresources, averaging21% attheend ofincubation. Forthefirst28dofincubation,theSTPlevelswerehigherforfertilizer state the importance of synchronizing manure nutrient than manure; STP levels were similar for all P sources after 28 d. mineralization with crop use. Also, environmental loss Nitrification of manure NH4 was rapid, reaching background concen- of nutrients can occur when supply exceeds crop detrations by 14 d, with conversion rate similar to fertilizer NH4–N. By mand. One problem in manure management is the unthe end of incubation, maximum net extractable inorganic N, pre- certainty of organic matter mineralization rate. Specific dominantly NO3–N, averaged 20% less than total applied N for both animal digestion processes (monogastric or ruminant), raw and digested manure. Anaerobic digestion did not substantially feed preferences, and rations of different species and affect manure nutrient supply, and we conclude that anaerobically overall handling of the manure are responsible for difdigested liquid swine manure can provide similar plant-available N ferences in manure nutrient concentrations and effects and P as expected from raw swine manure. on availability to plants (Bailey and Buckley, 2001). To evaluate anaerobically digested swine manure as a plant-available source of N and P, it is important to