Effects of Continuous Nitrogen Application on Grain Yield and Nitrogen Uptake and Utilization in Winter Wheat-Summer Maize Rotation System

[Objective] This study aimed to achieve high yield and stable yield of win- ter wheat-summer maize rotation system and provide basis for rational application of nitrogen fertilizer. [Method] Effects of continuous nitrogen application on grain yield, economic profit, nitrogen uptake and utilization efficiency, and soil inorganic nitrogen accumulation in winter wheat-summer maize rotation system were investigated. [Re- sult] Nitrogen application could significantly increase the y（eld of the winter wheat- summer maize rotation system, which increased by 17.76%-30.32% and 22.24%- 46.63% in two rotation cycles, respectively. The yield of the winter wheat-summer maize rotation system was the maximum in two rotation cycles with nitrogen appli- cation amount of 660.0 kg/hm2, which reached respectively 23 391.19 and 23 444.35 kg/hm2, the yield and economic benefit were the highest, the nitrogen fertilizer use efficiency was 22.2% and 30.7%, the agronomic efficiency was 8.3 and 11.3 kg/kg. However, the nitrogen fertilizer use efficiency and agronomic efficiency between ni- trogen application amount of 540.0 and 660.0 kg/hm2 showed no significant differ- ence. After two rotation cycles, inorganic nitrogen accumulation in 0-40 cm soil with nitrogen application amount of 540.0 kg/hm2 was almost equal to that before experi- ment. [Conclusion] Under the experimental conditions, comprehensively considering the grain yield, economic profit, nitrogen fertilizer efficiency and soil inorganic nitro- gen balance, the optimal nitrogen application amount was 625.3-660.0 kg/hm2 in high-yield winter wheat-summer maize rotation system.

Fate of ^(15)N-Labeled Urea Under a Winter Wheat-Summer Maize Rotation on the North China Plain

A field experiment was conducted to investigate the fate of ^15N-labeled urea and its residual effect under the winter wheat （Triticum aestivum L.） and summer maize （Zea mays L.） rotation system on the North China Plain. Compared to a conventional application rate of 360 kg N ha^-1 （N360）, a reduced rate of 120 kg N ha^-1 （N120） led to a significant increase （P 〈 0.05） in wheat yield and no significant differences were found for maize. However, in the 0-100 cm soil profile at harvest, compared with N360, N120 led to significant decreases （P 〈 0.05） of percent residual N and percent unaccounted-for N, which possibly reflected losses from the managed system. Of the residual fertilizer N in the soil profile, 25.6%-44.7% and 20.7%-38.2% for N120 and N360, respectively, were in the organic N pool, whereas 0.3%-3.0% and 11.2%-24.4%, correspondingly, were in the nitrate pool, indicating a higher potential for leaching loss associated with application at the conventional rate. Recovery of residual N in the soil profile by succeeding crops was less than 7.5% of the applied N. For N120, total soil N balance was negative; however, there was still considerable mineral N （NH4^＋-N and NO3^--N） in the soil profile after harvest. Therefore, N120 could be considered ngronomically acceptable in the short run, but for long-term sustainability, the N rate should be recommended based on a soil mineral N test and a plant tissue nitrate test to maintain the soil fertility.

Effects of Different Nutrient Management Systems and Cultivation Methods on Crop Yield and Soil Fertility

[Objective] The aim was to provide scientific basis for improving the middle and low yielding fields fertility and farmland productivity. [Method] A field experiment was carried out to study the effects of different management practices （including nutrient management systems and cultivation methods） on crop yield and soil fertility in winter wheat/summer maize rotation system. [Result] The crop yield in the treatment of the high yield and high efficiency system was remarkably higher than farmer conventional management practice. After five crop seasons experiment, the contents of soil organic matter for high yield and high efficiency system increased 2.72-3.01 g/kg, and that of soil total nitrogen increased 0.12-0.16 g/kg, the soil Olsen-P increased 5.2 mg/kg and the soil available K （NH4OAC-K） increased about 37.8 mg/kg. [Conclusion] Considering the yield and soil fertility comprehensively, the management system of high yield and high efficiency could effectively increase the crop yield and improve the soil fertility.

长期定位施用化肥对作物氮素吸收利用的影响

基于连续进行33年的长期定位试验,利用15 N示踪,研究长期施用化肥对冬小麦-夏玉米轮作中氮吸收利用的影响。结果表明,长期氮磷肥配施氮素利用率最高,为55.63%,与对照相比较提高了13.2%;其次为氮磷钾肥配施,氮素利用率为55.21%;氮磷钾肥配施处理氮素损失率最低,为8.71%。长期单施氮肥和氮钾肥配施的处理氮素利用率最低,分别为36.21%、34.53%,损失率高达38.63%、38.31%。