南方典型双季稻田氮素吸收及平衡

采用田间小区试验,设置不同N肥用量N0(对照,不施N肥)、N1(早晚稻均为90 kg/hm~2)、N2(早稻120 kg/hm~2,晚稻135 kg/hm~2)、N3(早稻150 kg/hm~2,晚稻180 kg/hm~2)处理,于2017—2018连续2年定量研究双季稻田N吸收以及N肥各损失途径的情况,计算周年N收支差,初步揭示双季稻田N收支平衡特征。结果表明:在N吸收方面,水稻产量随施N量的增加显著提高,N2、N3显著高于N1,N3高于N2,但无显著差异;各处理双季稻籽粒产量为8 869.6～11 002.1 kg/hm~2,秸秆产量为8 666.2～10 744.2 kg/hm~2;水稻N积累量也随施N量增加显著增加,单季水稻平均吸N量为70.6～112.5 kg/hm~2,双季稻吸N量为140.8～226.5 kg/hm~2;各处理N肥平均吸收利用率为25.6%～28.7%,农学利用率为6.5～8.3 kg/kg,生理利用率为23.8～27.0 kg/kg,偏生产力为33.5～56.1 kg/kg, N2处理N肥吸收利用率最高;在N损失方面,N3处理各途径损失量均为最高,N2略高于N1但差异不显著,各处理单周年氨挥发损失量为20.04～111.97 kg/hm~2,损失率为22.33%～26.68%,N_2O损失量为1.38～3.15 kg/hm~2,损失率为0.49%～0.86%,淋溶淋失量为5.10～40.97 kg/hm~2,淋失率为8.63%～10.87%,径流流失量为3.78～12.98 kg/hm~2,流失率为1.67%～3.38%,单周年土壤无机N残留量为-5.70～41.53 kg/hm~2,全N残留量为-15.18～53.02 kg/hm~2;在N收支方面,各处理N盈余量随施N量的增加而增加,N3处理盈余量最高,N2略高于N1,2017年各施N处理N盈余量为13.05～32.20 kg/hm~2,2018年盈余量为29.18～39.90 kg/hm~2,周年N盈余量呈上升趋势。双季稻田N收支途径中,肥料是N素的最主要来源,N输出以作物吸收为主,且氨挥发和N淋溶损失也是N输出的重要途径;N2处理是较为合适的施N量水平,即在农民习惯施肥量(N3)的基础上减N 20%～25%,既能保证双季稻N素吸收量和利用率,也能降低N素损失量和盈余量。

Nitrogen Absorption and Balance of Typical Double Cropping Rice Fields in Southern China

This study conducted a field plot experiment, including four nitrogen application levels:N0 (no nitrogen fertilizer), N1 (90 kg/hm² of nitrogen fertilizer in both early and late rice), N2 (120 kg/hm² of nitrogen fertilizer in early rice, 135 kg/hm² in late rice) and N3 (150 kg/hm² of nitrogen fertilizer in early rice, 180 kg/hm² of nitrogen fertilizer in late rice), to study the nitrogen absorption and the loss of nitrogen in various ways of double-cropping rice for two consecutive years in 2017-2018. The annual nitrogen surplus was calculated to preliminarily reveal the characteristics of nitrogen budget in double cropping rice fields. The results showed that on the nitrogen absorption, rice yield increased significantly with the increase of nitrogen application. Yield of N2 and N3 were significantly higher than that of N1, while N3 was higher than N2 without significant difference. The grain yield of double cropping rice was 8 869.6~11 002.1 kg/hm², straw yield was 8 666.2~10 744.2 kg/hm². Nitrogen accumulation in rice also increased significantly with nitrogen application. The average nitrogen uptake of single cropping rice was 70.6~112.5 kg/hm², and 140.88~226.5 kg/hm² in double cropping rice. The average nitrogen uptake efficiency was 25.6%~28.7%, 6.5~8.3 kg/kg in agronomic, 23.8~27.0 kg/kg in physiological, and 33.5~56.1 kg/kg in partial productivity. The nitrogen uptake efficiency of N2 treatment was highest. The nitrogen loss of N3 treatment was the highest, and N2 was slightly higher than N1, but the difference was not significant. As for the nitrogen loss, the annual ammonia volatilization loss of each treatment was 20.04~111.97 kg/hm² and the loss rate was 22.33%~26.68%. The N₂O emission loss was 1.38~3.15 kg/hm² and the loss rate was 0.49%~0.86%, the nitrogen leaching loss was 5.10~40.97 kg/hm² and the loss rate was 8.63%~10.87%, the nitrogen runoff loss was 3.78~12.98 kg/hm² and the loss rate was 1.67%~3.38%, the single annual soil inorganic nitrogen residue was -5.70~41.53 kg/hm², and the total nitrogen residue was -15.18~53.02 kg/hm². As for the nitrogen budget, the nitrogen surplus in each treatment was increased with the increase of nitrogen application. The nitrogen surplus of N3 treatment was the highest, N2 was slightly higher than N1. The nitrogen surplus was 13.05~32.20 kg/hm² in the nitrogen treatment in 2017, and 29.18~39.90 kg/hm² in 2018, showing an upward trend in the annual nitrogen surplus. It showed that fertilization was the most important source of nitrogen in double cropping rice field nitrogen cycle, the nitrogen output was dominated by crop absorption, ammonia volatilization and nitrogen leaching loss were also important nitrogen output pathways. The N2 treatment was an appropriate nitrogen application, that is to reduce nitrogen by 20%~25% than the farmers conventional application amount which could not only ensure the nitrogen absorption and use efficiency of double cropping rice, but also reduce the nitrogen loss and surplus.