Research On Utilization And Fate Of Nitrogen In Vegetable Protected Soils

The environmental problems that resulted from excessive inputs of nitrogen (N) in planting vegetables in protected soils were more and more important. Rational management ways and strategy of N need to be researched and developed. However, foundation questions still need be deeper researched. This study targeted at vegetable production of protected soils in representative intensive agricultural zone in Beijing, main research on the dynamics of accumulation and distribution of N in soils, N use efficiency, distribution and apparent balance of N in soil～plant systems. The results showed as following:(1) There was not effect of N application increased on yield of radish (Raphanus stativus L.) and economic profits planting in high degree fertility soils. The conic model described the relationship between tomato yield and the rate of N application during the second vegetable growing, when the rate of N application was more than 647.7 kg/hm2, the margin of increasing production , production vale and economic profits begin reduce. The liner～plateau model described the relationship between celery yield and the rate of N application during the fourth season vegetable growing, when the rate of N application was more than 617.7 kg/hm2, the production value and economic profits were significant decreased . With the increasing of N rate, profits of inputting fertilizer N and output～input ratio were decreased in one year. The nitrate content of radish, rape and celery increased significantly due to the rate of N application increased, but the nitrate content of tomato little response on higher rate of N application. However, there was not effect significant of the rate of N application increased on the contents of Vc, soluble sugar and protein in vegetables.(2) With the continuations of vegetables growing seasons, the N application rates impacted significantly on accumulative amounts of nitrate in 0～100cm soil profiles. The nitrate storage was decreased under the condition of no N application. Accumulative amounts of nitrate in soils were not significant changed with organic fertilizer application alone. There was a wave trend in the treatments with lower, recommendation and higher N application rate during the first and second seasons. When N rates were more than 617.7kg/hm2, the nitrate storage of soil body was reduced during the beginning of celery, was increased during the ending. The changes were a single apex curve during radish and celery planting, and double apex curve during tomato growing. The supply of N nutrition and demand of vegetables were changed in Synchronization with the recommendation rate of N application. The nitrate storages in soil body were significantly increased with farmers'traditional N application rates during the middle and ending period of vegetables growing season,it was resulted to excessive supply of N nutrition.(3) After four season vegetables planting, the nitrate storage in 0～400cm soil body were significantly decreased as the N rate was lower than the higher N application rate in every season , there was increased by 1652 kg/hm2 significantly in farmers tradition N application rate. There was a net lost of nitrate in 0～200cm soil body without N fertilizer application. The nitrate storages in 0～60cm soil body was not significant changed in lower and recommended N application rate. Input of N impacted significantly on accumulation nitrate in 0～200cm soil body, but little response to soils below 200cm. Nitrate content decreased in root zoon soil without N added in first season. However, nitrate content in 0～100cm soil body was great accumulation with farmers'tradition N application rate. After continuous two seasons, nitrate content decreased in 0～200cm soil body without N application, but increased significantly in farmers'tradition N application rate treatments. After continuous applying three times of farmers tradition N application rate, nitrate content rapid increased in 0～200cm soil profiles, accumulated in top soil layer moved down along soil profiles, and accumulated in 100～200cm soil profiles. The effect was not obvious through rape planting to decrease nitrate content in catch season.(4) Nitrate～N is the mostly forms of Inorganic nitrogen leaching, that 96.4%～99.2% accounts in total Inorganic nitrogen leached. There was not significant effect of N application on the concentration of nitrate in leaching liquid of soils in the first vegetable planted. The concentration of nitrate in leaching liquid of soils increased significantly in higher and farmers tradition N application rate from the second season. There was not significant change of the concentration of nitrate in leaching liquid in treatments that the rate of N application less than that of higher N application rate. Leaching amount of ammonium～N was low and little response to N application. The soil leaching amount of inorganic N was 23.3～46.8 kg/hm2 during whole rotation period. The coefficient of soil leaching amount of inorganic N was 0.2～0.6%, there was difference significant among treatments. The mean concentration of nitrate in leaching liquid of soils was 35.9 mg/L which great exceeded the standard of drinking water (10mg/L). The leaching amount of N in spring～summer was higher significantly than that of in autumn～winter, that 60.0%～73.1% accounts for whole year.(5) With the increasing of N rate, recovery efficiency of N fertilizer reduced, residual rate of inorganic N fertilizer in soil and losses increased. The total N uptake of radish (Raphanus stativus L.) increased significantly with rate of N application increased, but the amounts of fertilizer N uptake was not significant changed. The 7.2%～51.1%, 40.7%～69.9% and 8.2%～22.9% of total inorganic N application was taken up by plants, left in soil and lose, respectively. When rate of N application was higher than 647.7kg/hm2, the total N uptake of tomato plant was decreased significantly. The 3.2～14.3%, 58.6～79.1% and 13.5～30.6% of total seasonal fertilizer N application was taken up by plants, left in soils and lose, respectively. The total N uptake of celery will not increased significantly when the N rate was more than 617.7 kg/hm2. The 3.7～30.8%, 65.3～72.0% and 11.3～32.7% of total seasonal inorganic N application was taken up by plants, left in soils and lose, respectively. Residual N of the first season has significant after～effect on the growth of tomato in second season, but there was not significant residual effect on celery yield in fourth season. The total recovery efficiency of fertilizer N was 66.7% with lower N application rate. (6) The main N was from the input of N fertilizer and residual Nmin in the beginning stage in the seasonal N balance of soil～vegetable. The total N input increased significantly with the increases of N fertilizer application. The main N output was residual Nmin in soils in this system. The apparent balance of seasonal N was not change significantly in soils with organic fertilizer alone and lower N application during the first season. The apparent balance values decreased in soils with recommendation and higher N application rate. The apparent balance values increased significantly in the treatments with traditional N application rates was not change significantly in the other treatments in the phase system. The apparent balance of season N and of phase increased significantly with the increases of N application rate during the second and fourth seasons. In spare season, the N apparent balance still increased significantly in soils with traditional N application rate in last season. The annual input of N was the second main resources in the N balance system of soil～vegetable. The residual Nmin before seeding and mineralization N from initial soils self were the second N resources. When annual N application rate was less than 2171.5kg/hm2, the radio of crop N uptake to total N output was relative high; When annual N application rate was more than 2171.5kg/hm2, the radio of residual Nmin in soils to total N output was high. There was a positive relationship between apparent balance of system N and annual N application rate (r0.01 = 0.917).According to the native conditions, on the base of mixing organic fertilizer and phosphor (P) fertilizer and potassium (K) fertilizer together, the annual rate of N fertilizer should control in 370-740 kg/hm2. The upper limit of N rate in every season should be at the recommendation N application rate in current stage., the lower limit be at 0.5 times of the recommendation N application rate. The nitrate storage in 0～60cm soil layer should be looked as a index, and focusing on aftereffect of N fertilizer and regulation of N during the fastigium of crop take up nutrients. Benefit to increase N use efficiency, gain high crop yields and economic benefit, ensure vegetables sanitation and quality safety, decrease the risk of N leaching and losing.