Submitted to: Perspectives on Chesapeake Bay Advances in Estuarine Sciences
Publication Type: Proceedings
Publication Acceptance Date: October 1, 2000
Publication Date: N/A
Currently most nutrient management plans incorporate a fixed percentage when accounting for available organic N in the first year of manure application and a variable percentage for ammonium availability. The latter number is adjusted depending on spreading or incorporation strategies but the availability of organic N and ammonium N are considered independent of each other. We conducted a study to determine the variability in N mineralization of dairy manures and to determine if compositional parameters can be used to predict the available organic N. Dairy manures (n=107) were collected from farms in MD, VA, PA, NY, and CT. Manure compositions ranged from 14 to 38.6 g/kg dry matter, 0.9 to 9.5 kg/cubic meter total N, and 0.3 to 4.7 kg/cubic meter ammonium-N. Manure-amended soil was aerobically incubated at 25 C and concentrations of ammonium N and nitrate N were determined at day 2 and day 56. The manures were highly variable in their N mineralization characteristics, ranging from a net mineralization of 55% to a net immobilization of 29% of the organic N. When compositional parameters such as total N, ammonium N, organic N, total C, DM, lignin, neutral detergent fiber, acid detergent fiber, hemicellulose, C/N ratio, and pH were individually regressed against mineralizable organic N, the highest coefficient of determination (r2) was 0.14. These results suggest that the availability of dairy manure organic N is highly variable and that the availability cannot be predicted by simple compositional parameters. It is also clear that the availability of manure ammonium-N can be impacted by the mineralization characteristics of the organic N fraction.