近30年中国稻区氮素平衡及氮肥偏生产力的时空变化

  【目的】  中国的稻作模式和区域条件复杂多样，研究和推荐各稻区氮肥合理施用量，为提高氮肥利用效率和维持土壤氮素平衡提供参考。  【方法】  基于1988―2017年开展的全国水稻土长期监测平台，分析主要稻区（包括东北、西南、长江中游、华南、长三角稻区，322个土壤监测点）氮肥施用水平、氮肥偏生产力、土壤氮素平衡的时空演变特征，并进一步探究各稻区氮肥的合理用量。  【结果】  近30年来，我国东北、西南、长江中游 (早稻)、华南 (双季) 和长三角稻区水稻氮肥平均施用量分别为N 159、173、179、284和279 kg/hm2，全国稻区氮肥平均施用量为N 215 kg/hm2。西南和长三角稻区氮肥施用量随施肥年限的增加而显著增加 (P < 0.05)，增加速率分别为N 0.4和2.5 kg/ (hm2·a)。整体而言，全国稻区氮肥施用量随施肥年限的增加无显著变化。30年间，各稻区之间氮素表观平衡量差异显著 (P < 0.05)。东北、西南、长江中游 (早稻)、华南 (双季) 和长三角稻区氮素年均盈余量分别为N 35、5、20、69和109 kg/hm2，氮素盈余量分别占氮肥平均施用量的22%、3%、11%、24%和39%。各稻区氮素盈余量均随着氮肥施用量的增加而显著增加 (P < 0.0001)。东北、西南、长江中游 (早稻)、华南 (双季) 和长三角各稻区水稻氮肥偏生产力分别为54、51、42、44和35 kg/kg，全国平均为45 kg/kg，仅东北和长江中游 (早稻) 稻区水稻氮肥偏生产力随施肥年限增加而显著提高 (P < 0.05)。各稻区氮肥偏生产力均随着氮素盈余量的增加而呈指数下降趋势 (P < 0.0001)。  【结论】  除西南稻区，其他稻区氮素施用量偏高。综合考虑维持土壤氮平衡和提高氮肥偏生产力，建议东北、西南、长江中游 (早稻)、华南 (双季) 和长三角稻区的适宜施氮量分别为N 131、167、156、244和151 kg/hm2。

Spatial-temporal variation of nitrogen balance and partial factor productivity of nitrogen in rice region of China over the past 30 years

  【Objectives】  There are complex and diverse rice cultivation models and regional conditions in China. Hence, it has a great importance to assess the effects of nitrogen (N) fertilizer rate on N use efficiency of rice and soil N balance in each rice growing region.  【Methods】  Based on the national paddy soil long-term monitoring platform from 1988 to 2017, the spatio-temporal variation characteristics of N fertilizer application level, partial factor productivity of N (PFPN) and soil N balance in five main rice growing regions (322 soil monitoring sites), i.e. northeast (NE), southwest (SW), middle reaches of the Yangtze River (MYR), south China (SC) and the Yangtze River delta (YRD) were analyzed, and the reasonable application rate of N fertilizer in each rice growing region was proposed.  【Results】  Over the past 30 years, the average N fertilizer inputs of rice in NE, SW, MYR (early rice season), SC (double cropping) and YRD were N 159, 173, 179, 284 and 279 kg/hm2, respectively. The average nitrogen fertilizer input across the rice area of China was N 215 kg/hm2. In SW and YRD, the fertilizer inputs were kept increasing significantly, with the increasing rates of 0.4 and 2.5 kg/(hm2·a), respectively. The apparent balance of N was significant different among the rice regions over the past 30 years (P < 0.05). The average annual N surplus in NE, SW, MYR (early rice season), SC (double cropping) and YRD rice regions were 35, 5, 20, 69 and 109 kg/hm2, respectively, which were accounted for 22%, 3%, 11%, 24% and 39% of their corresponding N application rates. The N surplus increased significantly with the increase of N fertilizer application rate (P < 0.0001). The partial factor of productivity of nitrogen in rice were 54, 51, 42, 44 and 35 kg/kg in NE, SW, MYR (early rice season), SC (double cropping) and YRD rice regions, respectively, which increased significantly with the prolonged fertilization years in the NE and MYR (early rice season) (P < 0.05), but decreased with the increasing of N surplus in the whole country (P < 0.0001).  【Conclusions】  In general, nitrogen fertilizer is over applied in all the rice production regions, except for southwest region in China. Comprehensively considering the maintenance of soil N supply and PFPN, the recommended N application rates are 131, 167, 156, 244 and 151 kg/hm2 in NE, SW, MYR (early rice season), SC (double cropping) and YRD rice region, respectively.