Soil nitrate accumulation and leaching to groundwater during the entire vegetable phase following conversion from paddy rice

Abstract

Large amounts of farmland have been converted from traditional cereal cropping to intensive vegetable cropping in China, creating environmental risks. Previous studies utilized several methods of estimating nitrate accumulation in soil and leaching to groundwater under intensive vegetable cultivation, such as comparing intensive cropping to non-intensive cropping, or investigating the seasonal dynamics of soil nitrates in the short term, such as 1 or 2 years. This study tried to utilize a different method, considering the effects of total nitrogen (N) input during the whole vegetable cropping phase (up to 9 years) after conversion from traditional cereal cropping on soil and groundwater. A large-scale investigation was performed in the study area. Vegetable, soil, and groundwater samples were collected from 22 fields. Results showed that soil nitrate was significantly correlated with total N input from chemical fertilizer during the whole vegetable cropping phase, and groundwater nitrate was significantly correlated with soil nitrate. Nitrate concentration in 45 % of wells exceeded the drinking water maximum contaminant level, 10 mg L−1. These results suggest that soil nitrate accumulation in the area resulted from long-term application of large amounts of N chemical fertilizer, and not from manure. Furthermore, high irrigation levels caused the accumulated nitrate in soil to leach into the groundwater, resulting in nitrate contamination of the groundwater.