华北平原夏玉米季化肥氮去向及土壤氮库盈亏定量化探索

为提高华北平原夏玉米种植体系的氮肥利用率、减少氮肥对环境的污染，对前人的15N示踪试验数据进行整理核算，分析肥料氮、作物氮、土壤氮三者之间的关系，探明夏玉米季化肥氮的去向及土壤氮库的盈亏情况。结果表明：华北平原地区玉米产量最高时施氮量平均为190 kg·hm-2；秸杆吸氮量高于籽粒，且吸氮量随施氮量增加而升高，土壤残留量和损失量有随施氮量增加而增加的趋势；土壤氮库盈亏量与施氮量之间呈现线性极显著正相关，在秸秆50%和100%还田的两种条件下，施氮量为198 kg·hm-2和137 kg·hm-2时，土壤氮库达到平衡；推荐施氮条件下夏玉米对氮肥的吸收利用率远高于传统施氮，过量施氮会引起作物产量和氮肥利用率降低的负效应，增加土壤氮素残留和损失；施氮量在40~360 kg·hm-2范围内时，3种秸秆处理方式下，氮肥各去向绝对量与施氮量之间均呈显著线性相关关系；而氮肥各去向比率与施氮量之间只有地上部吸收率和籽粒吸收率与施氮量之间呈显著线性相关关系。由此，明确了华北平原夏玉米合理施氮量：秸秆50%还田时，为198 kg·hm-2；秸秆100%还田时，为137 kg·hm-2，揭示了华北平原夏玉米施氮量与土壤氮库盈亏量呈线性极显著正相关。这为确定华北平原夏玉米合理施氮量，提高氮肥利用率，避免肥料浪费及其对环境的危害提供了理论依据。

Exploration of N Fertilizer Fate and Quantitative Soil Nitrogen Pool Budget in Growing Season of Summer Maize in North China Plain

In order to increase the utilization rate of nitrogen fertilizer and decrease the environmental pollution from fertilizer nitrogen in planting system of summer maize in North China plain, the original data were collected from the previous studies of 15N-microplot experiments to investigate the relationships of fertilizer-nitrogen, crop-nitrogen and soil nitrogen, and to explore the fate of fertilizer nitrogen and the situation of profit and loss of soil nitrogen pool in summer maize cropping system. The results showed that the average nitrogen application was 190 kg·hm-2 with the highest yield of thesummer maize in North China plain; the nitrogen uptake of straw was higher than that of N uptake of grain, and the N uptake by maize plants was increased with the increase of N fertilizer application rates,soil N residues and loss tended to increase with the increase of N fertilizer application. In the two conditions of 50% and 100% straw returning to field, there were the significantly positive linear correlations between the nitrogen uptake of plants and balance of soil N, and the soil nitrogen pool reached the balance when nitrogen fertilizer rates were N 198 kg·hm-2and N 137 kg·hm-2. The N utilization efficiency with nitrogen rate recommended was much higher than that with the traditional nitrogen rate applied. Excessive application of N fertilizer caused negative effect of reducing the crop yield and nitrogen utilization rate, and increased N loss and N accumulation in soil. In the conditions of 0%, 50% and 100% straw returning to field, there were the significant linear relations between the amounts of different N fates and nitrogen application rates with the range of N 40~360 kg·hm-2. In composition of the whereabouts of the N fertilizer, the absorption ratios of grain and total plants above the ground showed significant linear relations with the amount of nitrogen application. Thus, the reasonable N application rates of summer maize was defined in North China plain： when the straw was returned 50% and 10