Nitrogen Transformations in Broiler Litter-Amended Soils

Nitrogen mineralization rates in ten surface soils amended with (200？μg N g？1 soil) or without broiler litter were investigated. The soil-broiler litter mixture was incubated at for 28 weeks. A nonlinear regression approach for N mineralization was used to estimate the readily mineralizable organic N pools ( ) and the first-order rate constant (k). The cumulative N mineralized in the nonamended soils did not exceed 80？mg N kg？1 soil. However, in Decatur soil amended with broiler litter 2, it exceeded 320？mg N kg？1 soil. The greatest calculated of the native soils was observed in Sucarnoochee soil alone (123？mg kg？1 soil) which when amended with broiler litter 1 reached 596？mg N kg？1 soil. The added broiler litter mineralized initially at a fast rate (k1) followed by a slow rate (k2) of the most resistant fraction. Half-life of organic N remaining in the soils alone varied from 33 to 75 weeks and from 43 to 15 weeks in the amended soils. When was regressed against soil organic N ( ) and C ( ), positive linear relationships were obtained. The pools increased with sand but decreased with silt and clay contents. 1. Introduction In general, nitrogen (N) is said to be the most difficult nutrient to manage in agriculture because of challenges in estimating the amount of N available for plant uptake and synchronizing N release from sources to meet a specific crop demand [1]. Even though the Earth’s atmosphere contains 78% N in the form of dinitrogen (N2) gas, most of this N is unavailable for plant uptake [2] with the exception of leguminous plants which can fix N. In the plant root zone, N is present in organic forms, including plant and microbial protein and amino acids, all together forming soil organic matter [3] from which the N is slowly converted into plant-available forms. During mineralization, organic N is converted into plant-useable inorganic forms ( –N and, –N) that are released into soil and subjected to various fates. For farmers in general and organic farmers in particular, N mineralization is an important process to understand because several environmental conditions govern this process [3]. Presently, there is an array of commercial inorganic N fertilizers available; however, their costs are prohibitory and out of range for many limited resource farmers. Thus, a careful management of organic N sources is one of the most important priorities for farmers; this in turn will limit unfavorable N losses into the environment. Because of the rapid growth of the organic farming segment of the United States agriculture, there is a high demand for