Study of nitrate-nitrogen leaching characteristics in the agricultural extensively planted farmland

Nitrogen loss in farmland is one of the main reasons to bring forth agricultural non-point source pollution. Furthermore, nitrogen leaching loss causing by superfluous nitrogen from farmland is the most important approach of farmland nitrogen loss. To solve the problem of nitrogen loss under the agricultural extensively planted conditions, the laboratory experiment and field monitoring was conducted to investigate the leaching characteristics. The results showed that soil nitrate nitrogen content in three typical planting areas showed a decreased tendency with the depth of soil profile, including the maximum of soil nitrate nitrogen content appearing in the 20-40 cm layer in greenhouse vine intensive planting areas. Soil nitrate concentration in the intensive planting areas did not change frequently, but change range was greater; and soil nitrate concentration in the conventional planting areas did not change frequently, but change range was greater. The average accumulation of nitrate nitrogen in the greenhouse vine intensive planting areas was the highest, which were significantly higher than that of vegetable intensive planting areas and conventional planting farmland. Monitoring results of field experiment indicated that the difference of groundwater nitrate-nitrogen content in three typical planting areas was distinct; nitrate nitrogen average content of greenhouse vine intensive planting base was the highest among three typical planting areas, being up to 11.2 mg.L^-1. However, nitrate nitrogen content of vegetable intensive planting areas and conventional planting farmland were respectively 4.02 mg.L^-1 and 1.35 mg.L^-1. It further suggested that nitrate nitrogen average content in intensive planting areas had large varied amplitude and higher over standard rate, and excessive irrigation and fertilization had caused groundwater environment pollution. The work presented in this paper is also believed to be useful in formulating ma- - nagement strategies for an extensively cropped farmland to reduce diffusive pollution from agricultural activities.