Nitrate Accumulation And Related Control Strategies In The Protected Field Of Beijing Suburb

In the vegetable production of protected field, environmental problems because of excess nitrogenous fertilizer are increasingly serious and cause great concerns. This experiment studies nitrate accumulation and related control strategies in the rotated system of tomato—catch crops(water spinach and Chinese cabbage)—radish with tomato, water spinach, Chinese cabbage and radish in the typical intensive protected field of Beijing suburb. Compared with farmers'conventional treatment, setting different nitrogenous levels for tomato and radish, researching the effect of fertilization to the yield, quality as well as nitrate accumulation and eluviations. In summer, the effect of catch crops(water spinach and Chinese cabbage) absorbing and utilizing nitrate accumulation and to the next crop compared with catch soil are as follows:1. Adding nitrogenous fertilizer in appropriate range can increase the production when the fertilizer is less than 300 kg/hm2, while the production and economy will be reduced when the fertilizer is much more than 300 kg/hm2. Nitrate in vegetable will also increase as the nitrogenous fertilizer increases, farmers'conventional treatment in particular. There is no significant effect between nitrogen and the Vc content, soluble sugar.2. The nitrate of soil profile increases as the nitrogenous fertilizer increases, there is a peak value of soil nitrate in the 100cm underground and a significant difference in the 200cm underground after the harvest of tomato, farmers'conventional treatment in particular.3. After the harvest of catch crops, the nitrate of soil profile of different levels is: catch>Chinese cabbage>water spinach, it represents that planting catch crops can reduce the nitrate of soil profile in summer. There is no fertilizer during the catch time, but farmers receive good benefits for that 50088.5 yuan/hm2 of water spinach and 17056.0 yuan/hm2 of Chinese cabbage. So planting catch crops is a method of reducing environmental risk, increasing nitrogenous fertilizer efficiency and economic benefits.4. After the harvest of radish, the nitrate of soil profile is: catch>pre-Chinese cabbage>pre-water spinach, it represents that planting catch crops can reduce the nitrate of soil profile of next crop in summer. Different pre-crop treatments in the same nitrogenous fertilizer level indicate that the nitrate accumulation in soil profile of pre-catch reaches a high. Radish output ranges from 161.33t/hm2 to 169.67t/hm2 and the benefits ranges from 20.67×104yuan to 23.12×104yuan, there is no big difference among treatments, so catch crops do not reduce productions and economic benefits.The research indicates that control of nitrogenous fertilizer and catch crops can be able to reduce the nitrate accumulation and solubility, especially planting catch crops in summer.