A Study On Combined Pollution Effects Of Cadmium And Nitrate In Vegetable-Soil System

Cadmium pollution of vegetable soil can seriously affect the quality of vegetables, and application of a large number of nitrogen fertilizer which could lead to high nitrate accumulation in vegetables can also pose a threat to quality of the vegetables. It has an important practical significance to study the interactions between the cadmium pollution and the nitrogen fertilizer application and its impacts on the quality of vegetables. In this paper, a pot experiment (three kinds of design), using popular vegetable amaranth and brassica chinensis, was carried out to study the nitrogen-cadmium interactiions on the quality and growth of amaranth and brassica chinensis, the transferences of cadmium and nitrate in soil and vegetables, and the impacts on soil enzyme activities. The main results are as follows:1. The effects of binary completely orthogonal of high concentrations of cadmium (0; 20; 50 mg/kg soil) and nitrogen (0; 0.1; 0.2 g/kg) on quality and growth of amaranth and brassica chinensis:the results showed that N and Cd interaction promoted Cd accumulation in amaranth and nitrate accumulation in brassica chinensis, reduced the growth of brassica chinensis and amaranth, increased the chlorophyll contents of brassica chinensis and amaranth, and inhibited the synthesis of amaranth Vc.2.The effects of binary completely orthogonal of low concentrations of cadmium (0; 0.5; 1.0; 1.5 mg/kg soil)and nitrogen(0; 0.2; 0.4; 0.6g/kg soil) on quality and growth of amaranth and brassica chinensis:the results showed that N and Cd interaction inhibited the accumulation of nitrate in amaranth and brassica chinensis and the accumulation of Cd in amaranth, promoted the accumulation of Cd in brassica chinensis and the growth of amaranth, inhibited the growth of brassica chinensis; and reduced the amount of soluble sugar, soluble protein and Vc in amaranth and brassica chinensis and the chlorophyll content in brassica chinensis.3. The effects of binary completely orthogonal of low concentrations (0; 0.5; 1.0; 1.5 mg/kg soil)of cadmium and nitrogen (0; 0.2; 0.4; 0.6 g/kg soil) to the absorption of amaranth and brassica chinensis on cadmium and the transformation of nitrate and cadmium and nitrate in the soil:the results showed that soil cadmium pollution levels were positively related to cadmium absorption by amaranth and brassica chinensis,soil cadmium pollution significantly inhibited nitrate accumulations in amaranth and brassica chinensis,and nitrogen content in soils had a very significantly positive correlation to nitrate contents in amaranth and brassica chinensis.4.The effects of binary completely orthogonal of low concentrations of cadmium (0; 0.5; 1.0; 1.5 mg/kg soil)and nitrogen (0; 0.2; 0.4; 0.6 g/kg soil) to soil enzyme activities of amaranth and brassica chinensis:the results showed that N and Cd interaction promoted the soil enzyme activity of sucrose and urease,but inhibited the activities of soil proteases and the activities of acid phosphatase in amaranth, and promoted the activities of acid phosphatase.5. At low concentration of cadmium (1.0 mg/kg soil) pollution, the effects of different species of nitrogen fertilizers (urea, ammonium sulfate, ammonium bicarbonate, ammonium chloride) on the quality and growth amount of amaranth and brassica chinensis were evaluated so as to give the priority application order of nitrogen fertilizers under the contamination of cadmium (1.0 mg/kg soil) as ammonium sulphate, ammonium bicarbonate, ammonium chloride, urea.With the above analysis, the application of nitrogen fertilizers increased the pollution of high concentration cadmium to amaranth and brassica chinensis, reduced output of amaranth and brassica chinensis with high cadmium pollution,and increased the yield of amaranth and reduced that of brassica chinensis with low cadmium pollution.