Abstract
To promote appropriate nitrogen (N) fertilization for summer and autumn tomato cultivation in the Hida region of Gifu Prefecture (Japan), the amount of N mineralized in upland topsoils during the cultivation period was estimated using a kinetic analytical method. N mineralization was determined in moist soils collected from upland fields in the study area and incubated at 10°C, 20°C, and 30°C for 16–24 weeks. In most soil samples, N mineralization increased linearly across all temperatures. The amount of mineralized N during incubation can be described by a first-order reaction model. Moreover, even when the N mineralization parameters k (mineralization rate constant) and Ea (apparent activation energy) were treated as regionally common values to simplify estimation, the model fit remained high. The mineralization rate of N0 (N mineralization potential), estimated based on soil temperature during the cultivation period, was as low as 23％. Under these conditions, the amount of mineralized N was considered to fit well to a model assuming a linear increase over time, and therefore, could also be described by a zero-order reaction model. Furthermore, even when Ea was treated as a regionally common parameter, the model still showed a good fit. In addition, N25, another N mineralization parameter corresponding to the amount of N mineralized per day at 25°C, positively correlated with the chemical oxygen demand (COD) of an extract solution measured using the simplified hot-water method for estimating the available N. This finding suggests that N25 can be estimated using COD. Based on these findings, we developed a zero-order reaction model capable of estimating N mineralization easily during the cultivation period without the need for incubation tests. In this model, a common Ea value of 64.1 kJ mol−1 and N25 estimated via COD were used as N mineralization parameters.
