In-Situ Nitrogen Mineralization of Anaerobically Digested Beef Cattle Manure in Sandy Soil.

Use of anaerobic digester systems to treat livestock wastes on farms has gained momentum because of several benefits associated with it. The anaerobic digester system helps farmers meet their waste storage, energy needs, manure odor control and yields useful byproducts such as anaerobically digested solids (ADS) and anaerobically digested liquids (ADL). These byproducts have been reported to contain higher mineralized fractions of nitrogen and phosphorus as well as organic constituents which improve soil water-holding capacity and add nutrients for crop uptake.  Understanding  the N release dynamics of anaerobically digested livestock wastes (ADLW) will help farmers make decisions regarding the time, method and rate of application of the digested waste to match their crop nutrient requirement while potentially reducing the need for other sources of fertilizer. The aim of this field experiment was to model net N mineralized over a crop cycle of 90 days from ADS and ADL generated from anaerobically digestion of beef cattle manure. The treatment combinations were 2 types of ADLW (ADS and ADL), 2 application methods (surface application and incorporation at 10 cm depth),  3 application rates (30, 10 and 3 Mg ha^-1 for ADS and 152,400, 76,200, and 38,100 L/ha for ADL), and a control, sampled over 9 sampling dates at 10-day interval with 4 replications. We found significant main effects of ADWL type, application rate, and sampling dates on net N mineralized (no interactions). Application method was not significant (p=0.95). A ”two-pool” model best described the N release pattern indicating a rapid release of N within first 20 days of application followed by a slow and declining release of N thereafter for 90 days. Application timing and rate should therefore take into consideration this immediate and rapid release of N to maximize crop N uptake and minimize loss of N from the soil/crop system.