Quantitative Evaluation Of Water And Nitrogen Under Winter Wheat-Summer Maize Cropping System In Irrigative Field

Based on the field experiment documents at Quzhou County in the North China Plain spanning the time period from 1998 to 2002, soil water movement and nitrogen transport subject to crop rotation system of winter wheat-summer maize were quantitatively studied. A joint dynamic model was constructed and validated to test the field results; the effect of different bottom boundaries applied in the dynamic model upon water drainage calculation was discussed; the balances of water and nitrogen and water use efficiency (WUE) / nitrogen use efficiency (NUE) were analyzed; three different methods were used to calculate field water drainage and nitrate leaching, i.e. dynamic model, Darcy's law and water balance methods were compared. The main results are as follows:(1) According to Darcy's Law, The annual mean of water drainage, WUE, nitrate leaching and NUE are 134mm, 1.8kg m-3, 15kgN/ha and 20kg kg-1 respectively during winter wheat growth period, while 72mm, 1.1 kg m-3, 6kg N ha-1 and 33kg kg-1 respectively during summer maize growth period.(2) The results of nitrogen balance simulated by the dynamic model indicate that crop nitrogen uptaken is the main part of nitrogen loss. It is higher during winter wheat growth (147kgN ha-1) than that during summer maize (123kgN ha-1). With the constraints of light and temperature, the net mineralization during winter wheat growth (4.9-69.8kgN ha-1, 1.4-23.0% accounting for the total applied nitrogenous fertilizer) is lower than that during summer maize growth (39.5-82.1kgN ha-1, 21.2-55.4% accounting for the total applied nitrogenous fertilizer).(3) The trend of water drainage calculated by the dynamic model, with ground water level as its bottom boundary, agrees well with that by Darcy's law. And the result reflects the real conditions of experimental site.(4) The results of water drainage and nitrate leaching calculated by three methods fit well with the observed data in profile A and profile B, but not with those in profile C. This might be attributable to the lower flood irrigation mount received by profile C due to its higher topography in comparison with profile A and B.