Effects of long-term cultivation on soil nitrogen transformation in the coastal wetland zone of east China

Abstract

In the present study, a long-term cultivation time series soil samples (0, 3, 6, 17, 30, 60 cultivation years) were collected to study the effects of long-term cultivation on soil nitrogen transformation in the coastal wetland zone of east China using 15N dilution method. The results showed that the gross nitrification and mineralization rates significantly increased with the cultivation time in the coastal wetland zone of east China. In native coastal wetland soil, the gross nitrification and mineralization rates were 0.6 and 1.0 mg kg−1d−1, respectively. The gross nitrification and mineralization rates increased up to 5.8 and 4.3 mg kg−1d−1 in the cultivated 60 years soils, respectively. Furthermore, the ratio of gross nitrification to gross mineralization (N/M) and the ratio of nitrification to NH4+ immobilization (N/I) also significantly increased and were >1, suggesting that the increased the risk of N losses from soil through nitrate leaching with the cultivation time. The results of leaching experiment confirmed that the soils with higher gross nitrification rate had a higher nitrate peak concentration in the leachate and the amount of leaching nitrate from soil increased with the increase in gross nitrification rate. The cultivation of coastal wetland soils could increase the nitrogen losses from soil through nitrate leaching, due to gross nitrification rates was significantly stimulated in the cultivated coastal wetland soils, comparing with natural coastal wetland.