亚热带丘陵小流域氮平衡及调控对策

以位于湖南省长沙县的两个亚热带丘陵小流域(约50 km2)为目标区域,综合2012—2014连续3年的野外定位观测、入户调查及统计数据资料,建立氮素收支框架模型,定量分析了农区和森林-农区小流域氮素的输入、输出特征及主要影响因素。结果表明:农区小流域氮素的输入、输出以及盈余强度平均分别为312.0、165.1、146.9 kg·hm~(-2)·a~(-1);森林-农区小流域氮素的输入、输出以及盈余强度平均分别为160.2、83.3、76.9 kg·hm~(-2)·a~(-1)。两个小流域具有较为类似的输入输出结构:饲料与肥料是亚热带小流域N输入的主要来源,合计占73.4%(农区)和63.9%(森林-农区);氨挥发与反硝化等N的气态损失是流域N输出的主要形式,平均占50%以上,而产品输出仅占N输出的1/4~1/3。减少化肥投入与适当控制畜禽养殖规模是控制小流域氮输入的主要途径,采取相应的技术措施减少N气态损失及增强N的流域内循环是提高小流域N利用效率和防控农业面源污染的主要措施。

N balance analysis and adjusting countermeasures of small watershed in subtropical hilly area

Two small watersheds(about 50 km²) were selected as the study region in subtropical hilly area in Changsha County, Hunan Province. By establishing N budget framework model and using data of in situ observation, door to door survey, and governmental statistical yearbooks, the input and output characteristics of nitrogen(N) and the main influencing factors were quantitatively analyzed during the 3-year period from 2012 to 2014. The results showed that N input, output, and surplus intensities in the small watersheds were averagely 312.0, 165.1, and 146.9 kg·hm^-2·a^-1 for the agro-watershed(AW), while 160.2, 83.3, and 76.9 kg·hm^-2·a^-1 for the forest-agro-watershed (FAW), respectively. A similar input and output structure were found in the two small watersheds, the dominant N input were feed and fertilizer, which accounted for 73.4% in AW and for 63.9% in FAW, respectively. The gaseous loss, which included ammonia volatilization and denitrification, was an important pattern of N output, contributed more than 50%. However, the N output of products accounted for just 1/4-1/3 of the total. Therefore, reduction of fertilizer application and moderate livestock and poultry breeding scale are the major approaches of controlling N input in a subtropical watershed. Correspondingly, reducing the gaseous loss of N through technical measures and strengthening the N recycling use in a watershed are the primary measures in increasing N use efficiency and controlling agricultural non-point source pollution.