Effects of nitrogen fertilization on nitrate content of radish (Raphanus sativus L. ) and soil nitrate leaching

Massive N fertilizer application on vegetable fields has caused international awareness. It is widely accepted that extraordinarily accumulation of nitrate in vegetable does harm to health of human beings and would also arose a lot of nitrate leaching to rivers and groundwater. A lysimeter experiment with undisturbed soil layers was carried out to study the effects of N rates on radish (Raphanus sativus L) yield, nitrate content and nitrate leaching in a cinnamon soils under the condition of greenhouse in the suburb of Beijing from Oct. 2007 to Mar. 2008. Residual soil NO3--N, yields, and content of nitrate in radish were also measured. There were six treatments (N fertilization levels) in the study, namely: no fertilizers (N0); chicken manure 6570 kg/ha (N1); chicken manure 6570 kg/ha+N100 kg/ha(N2); chicken manure 6570 kg/ha+N 200 kg/ha(N3); chicken manure 6570 kg+N300 kg/ha(N4); chicken manure 6570 kg+N 1015 kg/ha (N5). The N5 is farmers’ conventional level of using N. The results show that the yields of radish are only increased by 6.04%–10.92% in the fertilized soil comparing to unfertilized soil. Increasing extent of radish yield would decrease when the urea-N rate exceeds 100 kg/ha. The yields of radish in different N rates have not significance difference each other. So we can conclude when N is fertilized on fertile soils, the yield of radish is not increased remarkably. Nitrate content in radish is about 196.86 mg/kg when the organic fertilizer is only applied, and the content is decreased by 5.08% comparing to the condition of unfertilized N. When dry chicken manure in combination with urea are fertilized on the soil, the content of nitrate significantly is increased with the increase of N rates (P0.05). The residual nitrate-N contents in depths of 0–100 cm soil profile are increased with the increase of the N rates and significantly correlated with the rates (r=0.993, r0.01=0.917). Nitrate-N concentrations in groundwater is high, reaches to 32.88 mg/L averagely. The leached amount of Nitrate-N is 4.42–6.14 kg/ha during the growth of radish and there are not any significant differences between the different treatments.