Effects Of Rice Straw Returning On Soil Nitrogen Fractions And Related Enzyme Activities In Cold Region

Heilongjiang province is an important main japonica rice producing area in cold regions of China.In 2020,the yield of rice in Heilongjiang province was 28.962 million tons.According to the ratio of grain and grass 1:1.1,the amount of rice straw reached 31.858 million tons.Therefore,the "14th Five-year Plan" for circular Economy development and the no.1 Central document in2021 clearly required to increase the intensity of straw returning and implement the black soil protection project.Soil nitrogen is an essential nutrient for plant growth and an important factor for the survival and activity of soil microorganisms.The nitrogen in soil mainly exists in the form of organic nitrogen,which needs to be mineralized by soil microorganisms and converted into inorganic nitrogen to be absorbed and utilized by rice.Soil enzymes play an essential role in the process of organic nitrogen mineralization,which can indirectly reflect the status of nitrogen surplus and deficiency in soil.Straw is rich in organic matter and nutrients,straw returning can increase soil nitrogen content,improve soil enzyme activity,and then affect the growth and yield of rice.Studying the effects of rice straw returning on soil nitrogen components,related enzyme activities and rice yield in cold region has great significance to promote the efficient production and sustainable development of japonica rice.This experiment was conducted in the campus experiment base and the Xiangyang experiment and practice base of Northeast Agricultural University from 2019 to 2021,and the long-term location experiment and pot experiment was used in this study.Five treatments were set up in the long-term location plot experiment,which were no rice straw returning(S0),continuous low amount of straw returning(CL),continuous high amount of straw returning(CH),high amount of straw returning every other year(IH)and high amount of straw returning every two years(IH2).Seven treatments were set up in pot experiment,which were no rice straw returning(S0),low amount of shearing straw returning(CS1),high amount of shearing straw returning(CS2),low amount of crushed straw returning(SS1),high amount of crushed straw return(SS2),low amount of decomposed straw returning(DS1),high amount of decomposed straw returning(DS2).The effects of rice straw returning method and amount on soil nitrogen fractions,enzyme activities,the growth and yield of rice were studied.The results showed that:(1)Straw returning affects soil nitrogen content.Long-term straw returning significantly increased the contents of total nitrogen,total acidolysable nitrogen,acidolysable ammonium nitrogen,acidolysable unknown nitrogen and ammonium nitrogen,but significantly decreased the contents of non-acidolysable nitrogen,acidolysable amino acid nitrogen,acidolysable amino sugar nitrogen,available nitrogen and nitrate nitrogen in soil.(2)Straw returning affected soil nitrogen cycling related enzyme activities.Straw returning significantly increased soil urease,nitrate reductase and N-acetyl-β-D-glucosidase activities,but had no significant effect on soil leucine aminopeptidase activities.Straw returning for 4 years had no significant effect on soil nitrite reductase activity,while straw returning 10 years significantly increased soil nitrite reductase activity.(3)Straw returning affected dry matter weight of rice.The dry matter weight of rice plants decreased in the first year of straw returning,but significantly increased after 4 consecutive years of shearing straw return(CS1 and CS2),and increased after 10 consecutive years of straw returning.(4)Straw returning affects nutrient accumulation of rice.The nitrogen and phosphorus accumulation of rice plants were decreased in the first year of straw returning,and the nitrogen,phosphorus and potassium accumulation of rice plants was significantly increased after four consecutive years shearing straw return(CS1 and CS2).After 10 consecutive years of straw returning,high amount of straw returning(CH)significantly increased the accumulation of nitrogen and potassium in rice plants,the accumulation of phosphorus in rice plants showed no consistent regularity under straw returning treatment.(5)Straw returning affects rice yield.In the first year,straw returning tended to reduce rice yield.Compared with no straw returning,low amount of shearing straw returning(CS1),high amount of shearing straw returning(CS2),high amount of crushed straw(SS2)and high amount of decomposed straw(DS2)significantly reduced rice yield,while the difference between low amount of crushed straw(SS1)and low amount of decomposed straw(DS1)did not reach a significant level.Rice yield was significantly increased under high amount of crushed(CS2)after4 consecutive years,and increased after 10 consecutive years of straw returning.