Effect Of Freezing-Thawing On Nitrogen Mineralization In The Cultivated Black Soil

The black soil area of Northeast China is one of the three biggest black soil area all the world, and is an important commodity grain base of China, providing 35 billion kilograms commodity grain which accounts for one-third of the whole country every year. Due to the effects of geographic location and climate characteristics, the black soil area of Northeast Chin undergo freezing-thawing cycles frequently during late autumn and early spring periods, having deep influence on agro-ecosystems of black soil. However, However, the study of freezing-thawing on nitrogen (N) mineralization of cultivated black soil hasn’t not been paied more attention. With cultivated black soil as the research object, the characteristics of N mineralization were investigated in cultivated black soil by laboratory incubation, in order to deeply understand the process of N minaralization in black soil of Northeast China during the non-growing season. The results are as follows:(1) Freezing-thawing had significantly influence on the ammonium N content of cultivated black soil (p< 0.05), and its dynamics were multiply affected by freezng-thawing intensity (freezing temparatue and thawing temperature), freezing-thawing frequency and soil moisture content. With freezing temperature decreased and thawing temperature increased, soil ammonium N content increased significantly. With the increase of freezing-thawing frequency, soil ammonium N content first increased then decreased, reaching the highest value at 3 cycles of freezing-thawing. With increasing of moisture content, soil ammonium N content increased significantly under freezing and thawing conditions.(2) Freezing-thawing had significantly influence on the nitrate N content of of cultivated black soil (p< 0.05), and its dynamics were multiply affected by freezng-thawing intensity (freezing temparatue and thawing temperature), freezing-thawing frequency and soil moisture content. With freezing temperature decreased and thawing temperature increased, soil nitrate N content increased significantly. With the increase of freezing-thawing frequency, soil nitrate N content first increased and then decreased, reaching the highest value at 3 cycles of freezing-thawing. With increasing of moisture content, soil nitrate N content decreased significantly under freezing and thawing conditions.(3) Freezing-thawing had significantly influence on N mineralization rate of cultivated black soil(p< 0.05), and its.dynamics were multiply affected by freezng-thawing intensity (freezing temparatue and thawing temperature), freezing-thawing frequency and soil moisture content. With freezing temperature decreased and thawing temperature increased, soil N mineralization rate increased significantly. With the increase of freezing-thawing frequency, soil N mineralization rate decreased significantly. With increasing of moisture content, soil N mineralization rate changed little under freezing and thawing conditions.(4) Freezing-thawing had significantly influence on the DON content of cultivated black soil (p<0.05), and its dynamics were multiply affected by freezng-thawing intensity (freezing temparatue and thawing temperature), freezing-thawing frequency and soil moisture content. With the increase of freezing-thawing frequency, soil DON content first increased and then decreased, reaching the highest value at 6 cycles of freezing-thawing. With increasing of moisture content, soil DON content increased significantly under freezing and thawing conditions.(5) Freezing-thawing had significantly influence on the MBN content of cultivated black soil (p<0.05), and its dynamics were multiply affected by freezng-thawing intensity (freezing temparatue and thawing temperature), freezing-thawing frequency and soil moisture content. With freezing temperature and thawing temperature decreased, soil MBN content decreased significantly. With the increase of freezing-thawing frequency, soil MBN content first increased and then decreased, reaching the highest value at 6 cycles of freezing-thawing. After 6 freezing-thawing cycles, freezing-thawing increase soil MBN content from then on comparing with controls. With increasing of moisture content, soil MBN content first increased and then decreased under freezing and thawing conditions.In this paper, the content of ammonium N, nitrate N, DON, MBN and N mineralization rate as evaluation index, investigate the variation of nitrogen mineralization characteristic of cultivated black soil under different freezing-thawing intensity, freezing-thawing frequency and soil moisture content conditions, providing a data reference for nitrogen application of northeastern cultivated black soil, and theoretical and practical support for maintenance of nitrogen fertility and improvement of soil nitrogen supplying capacity.