不同降雨和灌溉模式对作物产量及农田氮素淋失的影响

【目的】定量化不同降雨和灌溉条件下农田氮素的淋失和作物产量，为不同降雨量年份的灌溉决策提供科学依据。【方法】在中国农业大学河北曲周实验站，依据该地40年（1966—2005）的气象资料，结合当地农民的习惯，设定了5种灌溉方式，即冬小麦季灌水3次，分别在越冬期、起身到拔节期和灌浆期，灌水量分别为：（A）无灌溉，（B）50 mm +50 mm +50 mm，（C）70 mm +70 mm +70 mm，（D）90 mm +90 mm +90 mm，（E）120 mm+ 120 mm +90 mm；夏玉米季灌水2次，分别在苗期和乳熟期，灌水量分别为：（A′）无灌溉，（B′）80 mm +0 mm，（C′）80 mm +70 mm，（D′）90 mm +80 mm，（E′）100 mm +100 mm。利用校验后的水氮管理模型，分析了不同降雨量和灌溉对氮素淋失和作物产量的影响。【结果】冬小麦产量随降雨和灌溉量的增加而增加。在综合考虑氮素淋失风险和作物产量的条件下，当降雨量＜200 mm（发生概率87.2%）时，可采用D灌溉方式，相应氮淋失量为0—30.9 kg N•hm-2；当降雨量＞200 mm（发生概率12.8%），可采用C灌溉方式，相应氮素淋失量为0.06—41.2 kg N•hm-2。夏玉米产量也随灌水量的增加而增加，但降雨和灌溉总量超过600 mm时，产量下降；按降雨量可分为＜250 mm（发生概率17.9%）、250—450 mm（发生概率64.2%）、＞450 mm（发生概率17.9%），分别采用D′、C′和B′的灌溉模式，相应的氮素淋失为0—7.3 kg N•hm-2，0—82.2 kg N•hm-2（其中84.2%的淋失水平为I级，淋失水平III级只有5.3%）和0—61.6 kg N•hm-2（其中I级概率为86.8%，III级只有2.6%）。【结论】不同降雨量采用不同的灌溉模式，既可以保证产量，又可以减少氮淋失。普通年份冬小麦季建议采用越冬期、起身到拔节期和灌浆期3次灌溉，每次灌水90 mm的模式。夏玉米季采用苗期和乳熟期灌溉，分别灌水80 mm和70 mm的模式。

Modeling the Effect of Rainfall and Irrigation on Nitrate Leaching and Crop Yield in Wheat-Maize Cropping System in North China Plain

【Objective】The objectives of the study are to quantify nitrate leaching and crop yield under different rainfall-year and irrigation methods and to provide information for improving farmer’ s practice under different types of rainfall-year. 【Method】Rainfall and irrigation is very important for water and nitrogen movement and crop yield in North China Plain. Therefore, 40-year (1966-2005) real climate data combined with the validated water and nitrogen management model were used to predict nitate leaching and crop yield under five irrigation methods, i.e. three times of irrigation (during winter, stem elongation and grain filling) in winter wheat season with amount of (A) no irrigation, (B) (50+50+50) mm, (C) (70+70+70) mm, (D) (90+90+90) mm,(E) (120+120+90) mm, and two times (seedling and milk-ripe stage) for summer maize with amount of (A′) no irrigation, (B′) (80+0) mm, (C′) (80+70) mm, (D′) (90+80) mm, (E′) (100+100) mm. 【Result】The simulated results showed that the grain yield increased with the enhancement of irrigation or rainfall during wheat season. About 87.2% of rainfall in all years was less than 200 mm, and the amount of nitrate leaching with irrigation method (D) was in the range of 0-30.9 kg N•hm-2. When rainfall was over 200 mm (12.8% of all years), irrigation method (C) was better as the level of nitrate leaching was low (0.06-41.2 kg N•hm-2) and crop yield was high. During summer maize season, crop yield also increased with the increase of rainfall until 600 mm. The irrigation methods (D’, C’ and B’) could be used based on the range of rainfall ＜250 mm (probability 17.9%), 250-450 mm (64.2% of all years) and ＞450 mm (17.9% of all years), respectively. The amount of nitrate leaching was in the range of 0-7.3 kg N•hm-2, 0-82.2 kg N•hm-2 (probability of N leaching belongs to grade I was 84.2%, and grade III was only 5.3%) and 0-61.6 kg N•hm-2 (probability of N leaching belongs to grade I was 86.8%, and grade III was only 2.6%), respectively. 【Conclusion】 Stochastic rainfall and its distribution in different seasons must be taken into farmer’s irrigation practices for keeping crop yields and mitigating N leaching in North China Plain. In normal-rainfall year, (D) and (C’) irrigation methods should be recommended in wheat and maize season, respectively.