Study On The Fate And Input Threshold Of Nitrogen Of Open-field Cabbage In Chongqing

With the changes of the structure of people’s diet, the proportion of consumption of vegetables is rapidly increasing, and the vegetable-grown land is rapidly expanding. Chinese cabbage is one of leafy vegetables which is widely planted in a lot of places in China, and Nitrogen fertilizer is an important measure to improve the leafy vegetables production. Due to that its planting density is big. planting time is short.and its root are very shallow, fertilization of Cabbage and other leafy vegetables is generally higher than grain crops.In actual production, farmers in order to obtain a higher vegetable production, a large number of fertilizer (especially nitrogen) are input. Because of lower utilization of N in vegetables, a lot of nitrogen fertilizer must contribute to an higher environment risk.There were many researches on Nitrogen fertilizer for vegetable production, quality and vegetable fertilization impacting on the environment, but those researches focused on one of them, most of those research were about Protected Vegetable in north of China, and less were on nitrogen fertilizer applied on Nutrient of Soil vegetable system utilization, production efficiency and environmental quantitative risks in south China. Therefore, this paper through the leakage pool facilities and a large area of micro vegetables in open field experiment plot is to study the winter cabbage in different nitrogen middleweight cabbage yield, quality, N uptake, residual soil nitrogen leaching, gaseous losses in Chongqing, to give the regional winter cabbage nitrogen input threshold to mention the basis for the Winter cabbage production and environmental protection. The main findings are as follows:Nitrogen fertilization could effectively improve the yield of cabbage and farmers’ income. Mix organic Nitrogen and chemical Nitrogen could improve the yield of the vegetables, Agronomic efficiency, and reduce nitrogen content of cabbage to improve to quality of Chinese cabbage. In field trials, Nitrogen application rate and yield of Chinese cabbage, economic benefits were in compliance to linear-platform model. When nitrogen application were422.9kg·hm-2and421.1kg·hm-2, yield of cabbage and famer income have achieved the maximum. Nitrogen fertilization could effectively improve nitrogen content of cabbage, and between the two was positively correlated. When nitrogen application was492.5kg·hm-2. Cabbage nitrate content was below to quality threshold of nitrate(785mg·kg-1)The fate of nitrogen including plant absorption, soil residues leaching and gaseous losses. The results of Nitrogen Leaching trials have showed that, in the conditions of this experiment, nitrogen absorbed by cabbage, remained in soil, leached with water and Volatilized as gas were respectively30.8%,32.9%,8.5%and27.9%. Among nitrogen absorbed by cabbage, remained in soil, and Volatilized as gas were about1/3of total input of nitrogen.Nitrogen fertilization could effectively affect the fate of Nitrogen in cabbage-soil system. Cabbage absorption and utilization of nitrogen were from10%to50%in different Nitrogen Levels. With the increase of nitrogen fertilizer. Nitrogen utilization fell, between in line with the secondary curve the relationship, y0.0005x2·0.4332x+105.53(R2=0.856). With the increase of the amount of nitrogen application, samples with nitrate concentration of water leakage reached a good situation wre reducing, while numbers of excessive samples wre increasing. When nitrogen application was more than326.0kg·hm-2, concentration of nitrate of leakage water exceeds safety standards. Nitrogen leaching losses of wre mainly inorganic nitrogen losses, accounting for more than66%of the total nitrogen leaching. Nitrogen Leaching and rainfall were positively correlated.Nitrogen leaching increase with the in the increase of the amount of nitrogen input, performing from slopes of two straight lines, and the inflection point of302kg· hm-2. Balance method was used to infer losses of gaseous nitrogen of22%～49%. With the increase of the amount of nitrogen application, losses of nitrogen gaseous increase, and both of them show follow a quadratic variation.Soil nitrogen residual of vegetable land was mainly from nitrate and ammonium nitrogen was relatively small. Both of the two are left in the soil layer of0to20cm. A certain accumulation of nitrate in the lower soil, but the amount was low. Organic fertilizer can reduce the nitrate content of the soil, but can improve the ammonium nitrogen. Residual of inorganic nitrogen in soil and nitrogen application were in accordance with the exponential equation y=29.726e0.0044x (R2=0.88*). When the residual of soil nitrate was150kg·hm-2could make pollution to shallow groundwater. So taking this value as a soil residual environmental threshold was appropriate, and the amount of nitrogen input was442.3kg·hm-2.Considering factors of farmers’incomes, the quality of the vegetables, the residual of nitrate in soil and its impact on the groundwater, taking lower threshold of nitrogen input as inflection point of farmers’ incomes, that was421.1kg·hm-2, and making the upper limit of the maximum residual nitrate in soil (150kg·hm-2) corresponding to the amount of nitrogen application was442.3kg·hm-2. Within the scope of this threshold of application of nitrogen fertilizer, we could get multiple objectives containing high-yield, high-quality, and high-efficiency of cabbage, environmental protection.