Study On Bioavailability Of Residual Nitrate Nitrogen In Vagetable Soil

Development of intensive agriculture is usually company with increase in agrochemical input,high input of nitrogenous fertilizer result in continuous nitrogen surplus in vagetable ecosystem.there were large amount of residue NO3--N in soil profile after crop harvest in irrigation agricultural system of Center China,between Changjiang Reviver and Huaihe Reviver,nevertheless,it was not seen clearly that how much the residue NO3--N 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 15NO3--N to investigate of the behavior of residue nitrate and its utilization by plants in vagetable ecosystem,and main conclusion was as follows:(1) The use of 15N micro-injection of the field test to study the system of vegetable growing spinach, cabbage vegetables on soil nitrate at different levels make use of marked differences. Tests showed that in N0, N1, N2, N3 conditions, spinach of 30 cm and 15 cm, respectively, marking the utilization of nitrate as follows: 20.71%, 13.31%, 20.54%, 25.95% and 20.25%, 9.59% , 14.98%, 30.65%, the average utilization rate were 20.48%, 11.45%, 17.76%, 28.30%, which under the conditions of spinach in the N3 marker 30㎝ the highest utilization of nitrate, which would indicate that the traditional basis of nitrogen application rate reduce the amount of nitrogen fertilizer plants in favor of mining the deep markings on the nitrate absorption. Spinach in the N3 has the highest utilization of nitrate feitilizer. In N0, N1, N2, N3 conditions, the after cabbage crop of 30 cm and 15 cm, respectively, marking the utilization of nitrate as follows: 15.12%, 7.61%, 11.88%, 9.16% and 11.58%, 5.55%, 9.67% , 8.98%, the average utilization rate were: 13.35%, 6.58%, 10.78%, 9.07%. Cabbage in the N0 which under the conditions of tags to 15 cm has the highest utilization of nitrate.(2) Post-harvest spinach, 15N tag to deal with all of the soil profile nitrate accumulation, there is a clear peak, and then post-harvest crop cabbage, 15N tag to deal with none of the soil profile nitrate accumulation, there is a clear peak.(3) Soil profile Whether the upper or lower part of the accumulated nitrate accumulated nitrate in the soil under water, have taken place in the vertical and horizontal movement, and nitrate showed marked movement away from the upper length, the lower short-distance rule. In this test under the condition of water and nitrogen management, cabbage is not obvious during the growth of free flow through the soil profile 90 cm deep, and therefore also in the cabbage growing season there were no strong nitrate leaching.(4) the use of 15N labeled method to clear out plants on soil profile labeled nitrate utilization at different levels, is to examine the soil profile at different levels of residual nitrate-N and plant where the effectiveness of a better way; plants through the absorption of the rich set to reduce nitrate in the soil profile of the residues, residues in the soil excavation nitrogen, but also to achieve a serious accumulation of nitrate in soil restoration purposes.