季节性冻融区农业土壤矿质氮有效性变化规律原位试验

为了更好地认识冻融过程对季节性冻融农业区土壤矿质氮有效性的影响,以吉林省长春市黑顶子河流域为研究对象,采用改进的树脂芯法开展了自然状态下表层土壤氮素原位培养试验。结果表明:土壤冻结过程使各下垫面土壤铵态氮含量增加了170%,硝态氮含量减少了19%,进而增加了土壤矿质氮含量及铵态氮所占比例,同时使各下垫面土壤铵态氮含量变异系数减小36%,硝态氮含量变异系数增加了250%。冻土融化过程中,土壤铵态氮含量无显著变化,硝态氮含量显著增加后趋于稳定;冻土融化初期,积雪融化和积雪融化与冻土融化的叠加过程使各下垫面土壤铵态氮含量变异系数分别增加了39%和48%,硝态氮含量变异系数减小了65%和40%,但大部分阶段硝态氮变异系数大于铵态氮。冻融过程中,土壤含水率的变化并未对土壤中铵态氮和硝态氮含量产生显著影响。

In situ experiment on change law of soil mineral nitrogen availability in seasonal freezing agricultural areas

Abstract: Northeast China is one of the most important grain production areas in China and it is the most typical area affected by seasonal freezing and thawing. The freeze-thaw process is a key driving force for soil nitrogen migration and transformation in cold regions, as it changes the physical structure (soil aggregates, hydrothermal conditions) and biological characteristics (microbial community, biological characteristics) of soil and greatly affects the mineral nitrogen availability. However, most studies on the effects of freeze-thaw process on soil nitrogen conversion had just used soil column freezing test using homogeneous soil at the specified freezing and thawing temperature and frequency, or in watersheds with natural underlying surface conditions, such as forest watersheds and arctic alpine regions, thus the nitrogen conversion in the farmland soil affected by agricultural activities could not be well reflected. Therefore, studying the impact of freeze-thaw process on farmland nitrogen conversion and availability is necessary and of great significance for guiding fertilizer management in seasonal freeze-thaw agriculture areas. In order to better understand the effects of freezing-thawing processes on soil mineral nitrogen availability in seasonal freezing and thawing agricultural areas, modified resin core method was used to develop in situ nitrogen cultivation of surface soil in a seasonal freezing agricultural watershed in northeast China. The in situ nitrogen cultivation experiments were carried out in 5 fields with different underling surface during the 2015?2016 freezing-thawing period, and the test devices were taken out in 6 batches before and during the freezing-thawing period for comparative analysis. Results showed that the soil freezing process increased the ammonium nitrogen content of the surface soil by 1.7 times and reduced the nitrate nitrogen content by 19%, which in turn increased the soil mineral nitrogen content and the proportion of ammonium nitrogen. In addition, it also reduced the difference coefficient of soil ammonium nitrogen content among different underlying surfaces by 36%, and increased that of nitrate nitrogen content by 2.5 times. During the melting process of frozen soil, the ammonium nitrogen content of soil did not change significantly, and the nitrate nitrogen content rapidly increased and then tended to be stable. At the beginning of soil melting period, the accumulation of snow and the melting of frozen soil increased the difference coefficient of ammonium nitrogen content by 39% and 30%, and reduced the difference coefficient of nitrate nitrogen content 65% and 40%, respectively. However, the difference coefficient of nitrate nitrogen content was greater than that of ammonium nitrogen in most stages. The melting of snow significantly increased the soil moisture content, which promoted the formation of ammonium nitrogen in the soil and reduced the formation of nitrate nitrogen, but the effect was not significant.