Nitric nitrogen in soils of vegetable garden in Shanghai city

Based on the samples from the surface soil layers of vegetable garden in the suburbs of Shanghai city and measurement of soil NO3--N content in different management modes, this article contrasts it with ripe soil to learn the current situation of NO3--N in soils of vegetable garden in the city and provides scientific gist for reasonable fertilization. Experiment results showed that contents of NO3--N in the soils were greatly different among different management modes. The results indicated that there was much more nitric nitrogen in soils of vegetable garden in greenhouse, followed by the soils of opened vegetable garden, and then by the soils of traditional vegetable garden. Accumulation of soil NO3--N was in all profile, not merely in the surface layer. For instance, in the depth of 80~100 cm, NO3--N content in soils in greenhouse was several times as many as that of the field. Furthermore, salinization of soils in vegetable garden in greenhouse was evident, and one of the main characteristics was NO3--N accumulation. The more salt in soil, the more NO3--N in soil. Moreover, the excessive nitrogen fertilizers resulted in decrease in soil pH. Statistical analysis showed that there was a significant negative correlation between soil pH and contents of nitric nitrogen.