Influence of temperature and moisture on nitrogen mineralizationin vegetable fields of central China

The processes of nitrogen (N) mineralization was determined in order to establish reasonable N application in vegetable fields in central China. The study researched the influence of temperature and water on N mineralization in two typical vegetable soils (yellow-brown and fluvo-aquic soils) in an indoor cultivation experiment. The results indicated that mineralization and am-monification rates in yellow-brown soils increased with increasing temperature. While nitrification rate at 15% and 25% water con-tents increased with increasing temperature, it decreased with increasing temperature at 35% water content. At 15% water content, mineralization rate of fluvo-aquic soil increased with increasing temperature. At 25% and 35% water contents, however, mineraliza-tion rate initially increased and then decreased. Nitrification rate in fluvo-aquic soil increased with increasing temperature at 15% and 35% water content. At 25% water content, however, it initially increased then decreased. Ammonification rate generally decreased with increasing temperature. At 25% water content and 35 ℃, mineralization rate in yellow-brown soil was 34.9 mg·kg^-1. Also at 25% water content and 25 ℃, mineralization in the same soil was 63.9 mg·kg^-1. Under different temperature conditions, mineraliza-tion rate of fluvo-aquic soil was higher than that of yellow-brown soil. While ammonification rate of yellow-brown soil increased with increasing water content, the reverse was true for nitrification rate. The maximum mineralization rate was at 25% water content. Variations in ammonification, nitrification and mineralization rate with water content in fluvo-aquic soil were not so evident. It was noted that the critical moisture content for microbial activity in yellow-brown soil was 25%, and that in fluvo-aquic soil was not evi-dent. The functional relationship of nitrogen mineralization rate with water content and temperature condition in yellow-brown soil was more significant than that in fluvo-aquic soil.