CALCULATION OF NET NITROGEN MINERALIZATION FROM THE DECOMPOSABLE SOIL ORGANIC MATTER POOL
The calculation of Net Nitrogen Mineralization (NNM) presented in this paper was based on the assumption that soil organic matter carbon may be divided into a stable, texture dependent pool (Cstab) and a labile, decomposable pool (Cdec). Because the Cstab pool is biologically inert due to its interaction with fine-grained mineral soil particles, only the Cdec pool reflects man made changes in the soil organic matter content. Consequently, to estimate the rate constant of soil organic matter carbon, the CO2-C production of soils was related to the corresponding amounts of Cdec. Because this rate constant kdec was derived from incubation experiments, the influence of actual decomposition conditions in the field was calculated according to the concept of “Effective Mineralization Time” (EMT). Setting the C/N ratio of Cdec = 10, the NNM from the Cdec pool was calculated according to the Equation: NNM = 0.1 * Cdec * kdec* EMT. To evaluate the calculation method of NNM, the nitrogen uptake of plants was related to nitrogen supply. It was estimated that the mean recovery of N by different vegetable crops grown on plots without mineral nitrogen fertilizer was about 70% of the total nitrogen supply (including the NNM and the Nmin values at the start and the end of the cultivation period).
Rühlmann, J. (1999). CALCULATION OF NET NITROGEN MINERALIZATION FROM THE DECOMPOSABLE SOIL ORGANIC MATTER POOL. Acta Hortic. 506, 167-174
carbon, fertilizer, fraction, rate constant, recommendation, texture