| The experiments were conducted from 2002 to 2003 on a loamy soil of long-term straw incorporation at Qianzhuliu experiment site, Longkou, Shandong Province, P. R. China. YN15 and JM20, two typical cultivars of winter wheat used in local production were chosen in this study. The 15N isotope technique was applied in the experiment. From soil-winter wheat plant system of view, the effects of different nitrogen application amount (6 nitrogen rates from 0 to 450kgN/hm2 in 90kg increments for winter wheat) on the fate, transport, compartmentalization and losses of nitrogen in the system, the yield and quality of wheat and the distribution of NO3--N in 0-100cm soil profile were studied. The main results were as follows:Nitrogen utilization of different nitrogen treatmentsOn the farmland of wheat yield 8500-9000kg/hm2, with the increment of nitrogen fertilizer dosage, the nitrogen fertilizer use efficiency and the fertilizer nitrogen total recovery efficiency obviously dropped and nitrogen fertilizer losses increased significantly. As the treatment of 90kgN/hm2, nitrogen fertilizer use efficiency was tallest, amounting to 50%.From rising to jointing period of winter wheat, both rate and amount of nitrogen absorbed by plant were the highest in the life of wheat. When the nitrogen application amount over 90kg/hm2, nitrogen accumulation amount in wheat plant at maturity lowered clearly. Looking at the source of the nitrogen recovered by wheat plant, the decline of the nitrogen fertilizer dosage properly from 0 to 450kgN/hm2, could increase nitrogenous proportion in plant from soil nitrogen and enhance available nitrogen to be absorbed by wheat. Addition, the proportion of nitrogen derived from topdressing fertilizer was higher than nitrogen from base fertilizer in wheat plant. At maturity, the proportion of nitrogen distribution in plant parts manifested grain>culm>leaf>chaff. The proportion of kernel nitrogen was three times of the rest. The plant at lower nitrogen treatments had a relatively large proportion of nitrogen in wheat grain. Additions of nitrogen fertilizer decreased the nitrogen transportation quantity from vegetative organs to wheat kernel.Range from 0 to 450kgN/hm2, the increase of nitrogen application lowered the apparent nitrogen use efficiency. There was not a obvious effect of applied nitrogen on nitrogen physiologic efficiency. The nitrogen harvest index of 90kgN/hm2 was the tallest, about 80%. However, there was not a significant difference among other treatments. In the condition of higher wheat grain yield, nitrogen border benefit was low, and declined obviously with addition of nitrogen application amount.Dynamics of soil nutrient and soil URE In 0-100cm soil profile, the content of total N lowered gradually from topsoil to depth (1.2g/kg in 0-20cm soil layer, 0.4g/kg in 80-100cm). Comparison after-wheat-harvest with before-sowing, application of nitrogen fertilizer could increase content of total nitrogen in 0-100cm soil profile and content of organ matter in 0-20cm soil layer, but had no obvious difference among different nitrogen treatments. The increment of nitrogen fertilizer dosage from 0kgN/hm2 to 450kg/hm2 could raised the URE activity, available phosphorus content in 0-20cm soil layer at forepart of wheat growing stage and the content of available nitrogen in 0-60cm soil profile at the latter of wheat growth stage obviously. Changes of NO3--N content in 0-100cm soil profile with time and spaceNO3--N leaching to groundwater would cause the decline of drinking water quality. NO3--N content in 0-100cm soil profile rose with addition of nitrogen fertilizer application amount in wheat growing period. After harvest, NO3--N accumulation amount of high nitrogen treatments (270 kgN/hm2, 360 kgN/hm2, 450 kgN/hm2) in 60-100cm soil layers is low nitrogen treatments (90 kgN/hm2, 180 kgN/hm2) of 3-5 times. In the condition of high wheat yield, the possibility of NO3--N leaching to groundwater would fall significantly when the nitrogen fertilizer application amount was le...
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