冻融作用对农田土壤可溶性氮组分的影响

为了解非生长季农田土壤氮素转化过程,采用室内冻融模拟培养试验研究了不同冻融温度和冻融循环次数对东北4种典型农田土壤(棕壤、褐土、草甸土、黑土)可溶性氮组分含量的影响。结果表明:随着冻结温度降低,4种农田土壤可溶性无机氮(DIN,NO_3~–-N+NH_4~+-N)、可溶性有机氮(DON)和可溶性全氮(DTN)含量均显著增加。随着融化温度升高,除NH_4~+-N含量显著升高外,4种农田土壤NO_3~–-N、DON和DTN含量的变化行为受冻结温度和土壤类型的协同影响。随着冻融循环次数增加,棕壤和褐土NO_3~–-N、NH_4~+-N、DON和DTN含量均显著增加;草甸土NO_3~–-N、DON和DTN含量均显著增加,而NH_4~+-N含量显著降低;黑土NO_3~–-N和NH_4~+-N含量均显著降低,而DON和DTN含量则先升高后降低。不同类型土壤受冻融作用影响的响应能力不同,其大小顺序为褐土棕壤、草甸土黑土。可见,冻融作用促进了土壤氮素转化,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,但同时也增加了土壤氮素流失风险。

Effects of Freezing-Thawing on Dissolved Nitrogen Components of Farmland Soils

In order to deeply understand nitrogen (N) transformation process in farmland soil during non-growing season, with a laboratory simulation experiment, the effects of different freezing and thawing temperatures and freezing-thawing cycling frequencies on the contents of soil dissolved N components were investigated in four typical farmland soils (brown soil, cinnamon soil, meadow soil and black soil). The results showed that with freezing temperature decreasing, the contents of nitrate N (NO– 3-N), ammonium N (NH4+-N), dissolved organic N (DON) and dissolved total N (DTN) all increased significantly in four farmland soils. With thawing temperature increasing, the dynamics of soil NO– 3-N, DON and DTN in four farmland soils were synergistically affected by freezing temperature and soil type, except for NH4+-N content increasing significantly. With freezing-thawing cycling increasing, the contents of NO– 3-N, NH4+-N, DON and DTN all increased significantly in brown soil and cinnamon soil; the contents of NO– 3-N, DON and DTN all increased significantly, and NH4+-N content decreased significantly in meadow soil; the contents of NO– 3-N and NH4+-N both increased significantly, and DON and DTN contents both first increased then decreased in black soil. As affected by freezing-thawing, the response capacity of tested soils differed from soil type, with following as cinnamon soil>brown soil, meadow soil>black soil. Therefore, it is preliminarily concluded that freezing-thawing cycling could promote soil N transformation, and was beneficial to the accumulation of soil available N, which could provide abundant nutrients for crop growth in spring but might also increase the risk of soil N loss at the same time.