Abstract
An estimation for the nitrogen (N) mineralization of organic materials incorporated into the soil is useful for minimizing the overuse of organic materials, which causes environmental pollution. The applicability of a kinetic method for the estimation of the progress of crop residue-N mineralization in soil was examined. The amount of inorganic N started to increase with lag-time when the soils with ground crop residues were incubated for 140 d. The lag-times were longer for Gleyic Cumulic Andosol (GCA) (FAO/Unesco : Fluvisols) and Brown Andosol (BA) (Andosols) than Brown Lowland soil (BLs) (Fluvisols). Lag-times were also longer in soils with wheat (Triticum aestivum L.) residue than corn (Zea mays L.) residue. The soils with sugar beet (Beta vulgaris L.) residue had the shortest lag-time. The time courses of the accumulated inorganic N in soils with crop residues fitted well to the first-order kinetic model proposed by Sugihara et al. The progress of residue-N mineralization under field conditions was estimated by a kinetic method using the data of daily average soil temperature during two crop growing seasons (April 1993-August 1994). The estimated progress was compared with the progress of residue-N absorbed by the plants, which was reported in a previous paper using ^<15>N-crop residues. In the case of BLs with corn and wheat residues, and BA and GCA with sugar beet residue, the estimated progress of N mineralization was similar to the progress of N uptake in the plants. However, there was an overestimation in the case of BLs with sugar beet residue and underestimations in the cases of two Andosols with corn and wheat residues. We considered that three reactions caused the over- and underestimations: 1) The faster decomposition of crop residue in the incubation experiment using ground residues; 2) The faster release of N from crop residues with high C/N ratio in the field experiment using basal N fertilizer; and 3) The uptake of ^<15>N by plants from ^<15>N-crop residue followed the gross N mineralization of crop residue and not net N mineralization.
