The Behavior Of Residue Nitrate And Its Utilization By Plants In Agro-ecosystem

Development of intensive agriculture is usually company with increase in agrochemical input, high input of nitrogenous fertilizer result in continuous nitrogen surplus in agro-ecosystem. There were large amount of residue NO-3-N in soil profile after crop harvest in irrigation agricultural system of North China, nevertheless, it was not seen clearly that how much the residue NOVN would supply to succession crops and how they would move into subsoil and leach into shallow groundwater. This study set up field micro-plot experiments and soil column experiments by technique of external injection of labeled 15NO-3-N to investigate of the behavior of residue nitrate and its utilization by plants in agro-ecosystem, and main conclusion was as follows.Under conventional water and nitrogen management condition, the recovery of labeled NO-3-N in different soil layers by spinach was significantly higher than that by wheat; the recovery of labeled NOVN in 15cm, 45cm and 75cm soil profile by spinach were 28.2%, 22.3% and 16.3% respectively. Those by Xiaoyan54 in corresponding positions were 21.8%, 17.4% and 11.5%, while those by Jing411 were 21.8%, 11.6% and 7.4% respectively, furthermore, the recovery of labeled NOVN by Xiaoyan54 were significantly higher as compared with Jing41 l.The similar conclusion was obtained in soil column experiment, but the recovery of labeled NOVN in corresponding layers of soil profile by all crops were higher in soil column experiment than in field micro-plot experiment due to root systems was restricted in narrow area in soil column pipe. There was significant positive correlation between the root length density of two types of wheat and the recovery of labeled NOVN in corresponding soil layers; but root length density of spinach and its recovery of labeled NOVN in corresponding soil layers were positively correlated in trend, however, not reached to significant level. The root length densities of spinach in different soil layers were all lower than those of two wheat varieties, whereas its root architecture and relative higher growth speed of aboveground contributed to spinach capable of acquiring more nitrogen.Under N fertilizer application or not in 0-20cm soil layer, the recovery of labeled NO-3-N injected at 110cm soil horizon by maize were 11.9% and 6.7% respectively; nitrogen fertilizer application in upper soil layer contributed to growth of maize roots in the middle or lower layers and improved its recovery of labeled NOVN in subsoil; it was possible to avoid NOVN further moving into shallow groundwater through plants utilizing residue NO-3-N in subsoil.Under the condition of artificial controlling water supply in soil column experiment, acquisition and recovery of labeled NOVN in different depths by wheat decreased with soil depth at four stages of shooting- earring- flowering- maturating, thereinto the recovery of labeled NO-3-N in 10-20cm, 40-50cm and 70-80cm soil depth were 15.7%, 3.4%, 1.2% at shooting stage, and 30.6%, 10.7%, 3.9% at earring stage, and 33.1%, 13.1%, 5.1% at flowering stage, and 32.5%, 12.4%, 4.7% at maturating stage respectively; the experiment results indicated the depth of soil NOVN acquired at different growth stages by wheat, and could offer theoretical basis for idea of "simultaneous nitrogen supply " in nitrogen fertilizer recommendation.In high residue NOVN soil profile made in advance, summer crop of Sorghum hybridSudangrass could acquire more residual nitrate in upper soil layers than maize, and residue NOVN in root zone in Sorghum hybrid Sudangrass treatment was lower as compared with maize treatment. Sorghum hybrid Sudangrass was able to capture more residue NOVN than maize and prevent them to move downward, consequently showed "safe net" function of plant uptake. Land fallow in summer season increased the risk of NO-3-N leaching.Under the condition of water and nitrogen management in these experiments, there was not apparent free water flow to pass through 100cm depth soil horizon, therefore, nor was there NOVN to be leached i...