冻融作用对农田黑土有机氮组分的调控效应

为深入了解非生长季农田土壤有机氮库组成及转化特征,采用Bremner氮素分级法研究了室内模拟冻融条件下(冻融温度、冻融频数、水分含量)农田黑土有机氮组分含量的变化行为。结果表明:冻融作用对农田黑土有机氮组分及其转化过程影响显著,氨态氮和氨基酸氮是土壤酸解有机氮的主要组分。随着冻结温度降低,土壤氨基酸氮含量显著增加,氨态氮和未知氮含量均显著降低,而氨基糖氮含量变化行为因融化温度而异。随着融化温度升高,土壤酸解有机氮组分无规律性变化。随着冻融频数增加,冻融土壤氨基酸氮含量显著降低,未知氮含量显著增加,氨态氮含量先增加后降低,而氨基糖氮含量则无显著性变化。随着水分含量增加,冻融土壤氨态氮和未知氮含量均显著增加,这与氨基酸氮的变化趋势正好相反,而氨基糖氮含量则无显著性变化。可见,较大的冻融温差、适宜的冻融频数和水分含量是影响土壤有机氮库转化的主要驱动因子。冻融作用能够提高土壤酸解有机氮中氨态氮和氨基酸氮的含量及其分配比例,增加土壤可矿化氮量,促进土壤氮素转化,有利于土壤有效氮的累积,为春季作物生长提供足够的氮素。

Regulation Effects of Freezing-Thawing Cycles on Farmland Black Soil Organic Nitrogen Components

In order to deeply understand organic nitrogen (N) components and transformation properties of farmland soil during non-growing season, with a laboratory simulation experiment, the dynamics of organic N components in the cultivated black soil were investigated under different freezing-thawing conditions (freezing-thawing intensity, freezing-thawing frequency, water content) by the Bremner N classification method. The results showed that freezing-thawing cycles (FTCs) has significant influence on organic N fractions and transformation process of cultivated black soil. With freezing temperature decreasing, amino acid N content significantly increased, ammonia N and unknown N contents significantly decreased, and the changes of amino sugar N content differed from thawing temperature. With thawing temperature increasing, the fractions of acid-hydolyzable organic N changed with no rule. With freezing-thawing frequency increasing, amino acid N content significantly decreased, unknown N content significantly increased, ammonia N content first increased then decreased, and amino sugar N content changed with no rule. With water content increasing, the contents of ammonia N and unknown N in the FTCs-treated soil both increased significantly being contrary to the changes of amino acid N, and amino sugar N content changed in a no rule. Therefore, it is preliminarily concluded that larger freezing-thawing amplitude, suitable freezing-thawing frequency and water content were the major factors affecting organic N transformation of farmland black soil with potential influence on soil N cyclic process and N supply capacity.