Dynamics and model fitting of nitrogen transformations in pig slurry amended soils

To optimize the efficient use of nutrients in pig slurry by crops and to reduce the pollution risks to surface and groundwater, a full knowledge of the fate of nitrogen (N) in amended soils is needed. A 120 day laboratory incubation experiment was conducted to study the effects of pig slurry application on soil N transformations. Pig slurry was added at the rates of 50 and 100gkg(-1). A nonamended soil was used as a control treatment. Soil samples were taken after 0, 7, 14, 30, 45, 60, and 120 days of incubation and analyzed for NH4+-N and NO3--N. Initially, the application of pig slurry produced significant increases in NH4+-N, especially at the highest application rate, whereas NO3--N content was not affected. Nitrification processes were active during the entire incubation time in the three treatments. In the control soil, the net N mineralization rate was highest during the 1st week (5.7 mg kg(-1) d(-1)), followed by a low-steady phase. Initially, net N mineralization rate was slower in soil with the lowest slurry rate (2.7 mg kg(-1) d(-1)), whereas in the treatment with the highest slurry rate, a net N immobilization was observed during the 1st week (4.8mgkg(-1)d(-1)). Mineral-N concentrations after 120 days were 180, 310, and 475 mg kg(-1) in soils amended with 0, 50, and 100 g kg(-1) of pig slurry, respectively. However, when results were expressed as net mineralized N, the opposite trend was observed: 74, 65, and 44 mg kg(-1). Of the six kinetic models tested to describe the mineralization process, a two-component, first exponential model (double model) offered the best results for all treatments.