Submitted to: American Society of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: August 2, 2004
Publication Date: October 31, 2004
Citation: Griffin, T.S. 2004. Gross transformation rates of manure n using 15 n pool dilution. American Society of Agronomy Meetings. Technical Abstract: Transformations of manure nitrogen (N) in soils are controlled not only by the interaction of environmental and soil factors, but also by the composition or quality of the substrate. In a micro-scale aerobic incubation experiment, gross N transformation rates were estimated for four dairy manures with markedly different net N transformation characteristics, using 15N pool dilution methodology. At 7 and 56 d after manure application to a sandy loam soil, gross transformation rates were estimated over a 48 hr period on paired samples following injection of 15N-ammonium or 15N-nitrate. The dilution of these two 15N pools is used to estimate gross mineralization and nitrification, respectively. Gross N mineralization of unamended soil was 1.6 and 1.0 mg N/kg soil/d, at 7 and 56 d after application, respectively. Seven days after incorporation of manure, gross mineralization was 50 to 225% greater (up to 2.8 mg N/kg soil/d) in amended soil, with few significant differences between manures. Even 56 d after incorporation, manure increased gross mineralization rates 50 to 90%, compared to unamended soil. Gross N immobilization, however, was strongly affected by manure composition, especially early in the incubation; manures which were low in fibrous carbon had immobilization rates of 1.0 mg N/kg soil/d, while those high in fibrous carbon immobilized 2.1 to 3.3 mg N/kg soil/d. These results are in agreement with net N transformation data for these same manures, and clearly demonstrate the impact of manure composition on gross N transformation.