Incorporation Characteristics Of Rice Straw Carbon And Nitrogen Into Soil Organic Matter In Black Soil With Different Rice Planting Ages

Straw returning is an important way to improve soil organic matter.However,the climate in Northeast China is very cold,so that the paddy fields therein have a short flooding period and long non-flooding period when the soil is frozen for most of the time,little is known about the incorporation and fixation into soil organic matter and its components in the soil of different rice planting ages after rice straw returning.Therefore,using the dual-isotope-labeled(¹³C/¹⁵N)rice straw tracing technology,the effects of rice straw addition（1%of addition）on the changes of soil organic matter in black soil with different rice planting ages（0,12,35,62 and 85 a）were studied through 150-day of flooding incubation（temperature 20℃,water-flooded layer 1 cm）and 150-day of freezing incubation（temperature-15℃,saturated water state）.The main findings are as follows:（1）During flooding and freezing culture,the changes of soil dissolved organic matter and microbial biomass,as well as macroaggregates organic matter are sensitive to straw addition.Overall,straw addition significantly increased the content of soil dissolved organic matter and macroaggregates（>0.25 mm）organic matter（P<0.05）,which in turn significantly increased soil organic matter content（P<0.05）.（2）During the incubation process,7.89%-24.20%and 37.54%-76.27%of the added straw carbon and nitrogen were incorporated into soil organic carbon and total nitrogen,respectively,and the incorporation ratio is significantly affected by the rice planting ages（P<0.05）.The ratio of straw carbon incorporation increased significantly over the 12-year period of rice planting and then volatility decreased.The ratio of straw nitrogen incorporation increased significantly during the 12-year period of rice planting and then decreased year by year.（3）During the incubation process,the ratio order of added straw carbon incorporated into soil labile organic carbon were particulate organic carbon（0.72%-13.79%）>microbial biomass carbon（0.27%-5.08%）>dissolved organic carbon（0.25%-1.96%）.The ratio order of added straw nitrogen incorporated into soil labile organic nitrogen were microbial biomass nitrogen（1.55%-30.48%）>dissolved organic nitrogen（1.64%-24.68%）>particulate organic nitrogen（0.43%-9.91%）.The incorporation ratio of straw carbon and nitrogen into soil labile organic matter were significantly affected by the rice planting ages（P<0.05）,and the straw carbon incorporation ratio increased with the extension of the rice planting ages.（4）During the 150-day flooding incubation,the ratio of straw carbon and nitrogen incorporated into the soil microaggregates organic carbon and total nitrogen were the largest,which were 5.91%-10.89%and 17.46%-25.78%respectively.After the subsequent 150-day of freezing culture,the incorporation of straw carbon and nitrogen into the soil macroaggregates organic carbon and total nitrogen were the largest,which were 3.12%～13.48%and 12.29%～27.80%respectively.Overall,at the end of the 300-day culture,the ratio of straw carbon and nitrogen incorporated into soil aggregates organic matter were significantly affected by the rice planting ages（P<0.05）,and the straw carbon allocation ratio increased with the extension of the rice planting ages.