Effects Of Fertilization And Irrigation On Nitrogen Migration Characteristics In Paddy Field Of Black Soil Region

As an important exogenous nitrogen supplement to soil nitrogen, nitrogen fertilizer has played a very important role in maintaining and stabilizing rice yields, but excessive nitrogen fertilizer may lead to paddy agriculture non-point source pollution. Irrigation is important to ensure rice water requirement, appropriate irrigation methods contribute to increasing food production, protecting water resources and reducing emissions of agriculture non-point source pollutants. In this paper, proceed with the joint part of the agriculture water cycle, five nitrogen level N1～N5 (195,180,165,150 and 135 kg·hm-2) and three irrigation methods G1, G2 and G3 (normal irrigation, control irrigation and wet-shallow irrigation) was set, the migration characteristics of nitrogen in paddy fields with water circulation system at different nitrogen rates and irrigation methods was been studied through two-factor interaction field experiments in the study area, the amount of nitrogen leaching was estimated based on the rice paddy water balance equation, the suitable and reasonable fertilizer application with irrigation methods was selected for the region. Moreover, based on the use of Source-Sink model, the nitrogen non-point source pollution load of the irrigation area was been estimated.The main results of this study show that, the incremental fertilization increased the concentration of three nitrogen fertilization in the surface water, recommended fertilization and decrement fertilization are conducive to the reduction of nitrogen concentration in surface water oppositely. Different nitrogen levels had significant influence on three nitrogen concentration in the surface water and the seepage. Control irrigation and wet-shallow irrigation can reduce the concentration of ammonium and nitrate nitrogen in the seepage. Control irrigation was the least in the total quantity of nitrogen leaching in the whole stages of rice. Different irrigation methods had no significant influence on three nitrogen concentration in the surface water and the seepage.The highest mean incremental total nitrogen content in the upper soil (0～20 cm) was accured in wet-shallow irrigation, reached to 0.71 g/kg. As a result, wet-shallow irrigation could be better maintaining the total nitrogen content of the upper soil. The average yield of wet-shallow irrigation was 112% and 108% of control irrigation and regular irrigation, respectively. The proportion of the rice cumulative absorption of nitrogen to fertilizer showed the highest in wet-shallow irrigation. The relative optimal nitrogen rate should be 123.36 kg·hm-2,128.12 kg·hm-2 and 137.13 kg·hm-2 for regular irrigation, control irrigation and wet-shallow irrigation for economical, production and environment concerns.The simulation results of Source-Sink model in the irrigation area was good, the calculate results showed that the total nitrogen producing pollution load of regular irrigation was about 2.84 times of that of control irrigation, and 1.97 times of that of wet-shallow irrigation, and the total nitrogen producing pollution load was higher with higher fertilization level.