The Effects Of Nutrient Management On The Behavior Characteristic Of Nitrogen And Phosphorus From The Citrus Orchard Of Danjiangkou Reservoir Area

Danjiangkou Reservoir is the water resource of South-North Water Transfer Project, with the aim of satisfying the drink water supply for more than 20 cities, such as Beijing, Tianjin, Shijiazhuang and so on, so the security of water quality in this reservoir is extremely important. Hundred miles of citrus growing belt has formed arround the Danjiangkou Reservoir, and it is increasing annually 13 hm2 nowdays.It is necessary to control the non-point pollution from citrus garden while citrus planting area is raising, based on the investigation of citrus garden soil fertility and tree nutrition, the typical citrus orchards of Danjiangkou Reservoir area was selected, runoff plots experiment and soil stratified sampling method were conducted to study the effects of recommended fertilization, recommended fertilization with split-applied fertilization and recommended fertilization with planting grass on the output of runoff, nitrogen and phosphorus, form of nitrogen and phosphorus,the distribution and migration of soil nitrogen and phosphorus, the annual variation in nitrogen and phosphorus concentrations of citrus leaves, citrus yield and quality. The main conclusions are showed as follows:1)The survey of Danjiangkou Reservoir area citrus orchards showed that:the contents of soil available nitrogen and phosphorus were very low, and long-term of low level fertilization and unreasonable fertilization (partial nitrogen, less phosphorus), coupled with varying management levels of different orchards, was resulted in a larger coefficient of variation of soil nutrients, and more than half of orange trees with deficiency of nitrogen. Meanwhile, we proposed a nutrition management measures for this citrus orchard according to the survey.2) Recommendation fertilization and nutrition management significantly reduced runoff losses,with a 40.09%, compared with the conventional fertilization. Dissolved nitrogen and particle phosphorus were the main loss forms of nitrogen and phosphorus in Danjiangkou reservoir orchard, which should be controlled carefully. Fertilizer application is not the main reason for the loss of nitrogen and phosphorus in Danjiangkou Reservoir area. The loss of total nitrogen, dissolved total nitrogen and dissolved total phosphorus were deceased significantly by increasing the frequency of fertilizer application, and planting grass reduced the loss of total phosphorus, particle phosphorus and particle nitrogen effectively. The loss of 35.96% total nitrogen was decreased by increasing the frequency of fertilizer application while the loss of 59.31% total phosphorus were reduced significantly by planting grass.It is noteworthy that the loss of dissolved organic nitrogen would be increased by planting grass.3)The content of available nitrogen in 0-80 cm soil was increased by applying nitrogen fertilizer significantly, while the concentration of 20-40 cm soil was increased more than the others.The deeper in the soil, the latter the soil available nitrogen accumulation peak appeared. The content of available phosphorus in 0-40 cm soil was raised by applying phosphate fertilizer remarkably, while the concentration of 0-20 cm soil was increased more than the others.There was only a very few amount of available phosphorus move to 40-80 cm soil, that meant it was hardly for soil available phosphorus move vertically. The larger amount of nitrogen and phosphorus was accumulated in 0-80 cm soil when higher rate fertilizer(125% M0) was used, but the accumulations of nitrogen and phosphorus were declined by planting grass, while nitrogen was decreased and phosphorus was increased by more split fertilizer application. The soil nitrate of conventional fertilization treatment (CF) was moved out of root layer after 4 months. Split fertilizer application(125% M0+FT) resulted in accumulation peak of nitrate nitrogen in soil profile firstly, but planting grass treatment(125% M0+PG) had no effect on accumulation of nitrate nitrogen obviously. It was concluded that the nitrate nitrogen of 60-80 cm soil layer could be declined by more split fertilzier application and planting grass, but the most effective measurement in decreasing the risk of nitrate leaching from the soil is to reduce the application rate of nitrogen fertilizer.4) The concentrations of nitrogen and phosphorus of citrus leaves were increased by split fertilizer application more times, the content of soil available nitrogen and phosphorus determine the content of nitrogen and phosphorus in leaves and fruit of citrus. The contents of nitrogen and phosphorus of citrus leaves were declined by planting grass while high application rate fertilizer was used, but raised at the end of experiment after the grass was mowed and buried into the soil. Compared with conventional fertilization treatment, citrus fruits yield was increased by various treatments of recommended fertilization in varying degrees, the citrus yield of incremental fertilization treatment (125% M0) and planting grass treatment(125% M0+PG) increased significantly by 43.44% and 33.81% respectively, with the income increase of 6814 Yuan and 4339 Yuan Renminbi. The concentrations of fruit vitamin C,soluble solids,the ratio of solid to acid and the rate of edible were increased, but the content of total fruit acid and weight per fruit were decreased by planting grass.In a word, planting grass improved the quality of fruit, induced the flavor of fruit to taste sweet and delicious.As a consequence, combined recommendation fertilization with split fertilization and planting grass (MO+FT+PG) not only resulted in higher yield, better quality of citrus and more income, but also in lower loss of nitrogen, phosphorus and the leaching of nitrate. The nutrient management measures mentioned above possess of popularization and application value for the citrus orchard in Danjiangkou Reservoir areas.