Microbial nitrogen transformations in response to treated dairy waste in agricultural soils
2004
Shi, W. | Miller, B.E. | Stark, J.M. | Norton, J.M.
Dairy wastes are commonly applied to croplands as N fertilizers, but the dynamics of N release and transformations during the growing season are difficult to predict. We compared N mineralization kinetics and examined microbial N transformations in soil receiving dairy-waste compost vs. lagoon effluent. Mineralization kinetics was examined with a 70-d laboratory incubation, and a first-order model was used to derive mineralization parameters. Measurements of N transformations were conducted with 15N pool dilution techniques in silage corn field plots that were unfertilized or fertilized with ammonium sulfate, lagoon effluent, or compost at two rates equivalent to 100 or 200 kg available N ha(-1). The N mineralization potential was higher and the first-order rate constant was lower in soil receiving compost than lagoon effluent. Approximately 6% of compost N was mineralized within 2.5 mo; in contrast, up to 90% lagoon effluent organic N was released. However, silage yield was greatest in the compost treatment, showing that synchronization of N availability is as important as the amount mineralized. The field 15N measurements indicated that microbial NO3(-) consumption was negligible despite the treatments. Microbial NH4(+) immobilization in soil receiving dairy wastes was similar to that in soil unfertilized or fertilized with inorganic N. Soil treated with the high-rate compost had the highest rates of mineralization and nitrification, which led to the highest soil NO3(-) accumulation. Our observations suggest that peak plant demand is met by the compost N; however, its high N mineralization potential makes the management of dairy compost a difficult task.
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