Effects And Mechanisms Of Raw And Carbonized Straw Returning On Dryland Plastic-mulching Maize Productivity And Carbon Emission

China has relatively abundant straw resources.The annual output of straw exceeds 1 billion tons.Rational utilization of straw resources is an inevitable requirement for sustainable development of agriculture in China.Straw returning has multiple benefits such as carbon sequestration and carbon emission reduction,improvement of soil fertility,reduction of pollution and improvement of soil water retention capacity.The impact of straw returning on dryland corn productivity and soil carbon emissions will vary depending on the amount of return,plastic film mulching,and straw treatment methods,that is,different application amounts,straw raw material and carbonization returning to the field were different and which were affected by film mulching.At present,the production and environmental effects of different gradients straw raw material and carbonization under different film mulching still lacks systematic observation and analysis.There are few reports on carbon sink and carbon emission reduction potential of farmland ecosystems in arid areas.The effect of straw returning on soil respiration,soil quality and maize yield and its mechanism need to be further explored.The research object is dryland maize ecosystem,two independent experiments were carried out.They are straw carbonization（biochar）return experiment and straw raw material（maize stover）return experiment.1)In the experiment of biochar returning to the field,four gradients were set under the condition of film mulching（M）and no film mulching（N）respectively:no returning（CK）,10 t/ha biochar（Bio-1）,20t/ha biochar（Bio-2）,30 t/ha biochar（Bio-3）.2)In the experiment of maize stover returning to the field,four gradients were set under the condition of film mulching（M）and no film mulching（N）respectively:no returning（CK）,1/3 maize stover 3.75 t/ha（Sto-1）,1/2 maize stover 5.625 t/ha（Sto-2）,total amount of maize stover 11.25 t/ha（Sto-3）.Fixed field positioning experiments were carried out at the Yuzhong Agro-Ecological Experimental Station of Lanzhou University from 2019 to 2020.The main results were as follows:1.Effects of biochar returning with film mulching on maize productivity,soil quality and carbon emission1)The return of biochar had no significant effect on soil water content in 0-100cm soil layer,film mulching improved soil water content.In the 0-20 cm soil layer of maturing stage in 2019,there was no significant difference among all treatments.In2020,the soil water content of 0-20 cm soil layer under film mulching was significantly higher than that under no film mulching.The return of biochar had no significant effect on the soil temperature of 0-10 cm.However,from May to June,the soil temperature under film mulching treatments was higher than that under no plastic film mulching treatments,and the temperature difference gradually decreased in the later period.Compared with the control,MBio-1、MBio-2、MBio-3 and NBio-3treatments significantly increased maize yield in 2019-2020.In 2019 and 2020,compared with MCK and NCK,the maize yield of different gradients of biochar returning increased by 5%-7.8%,4%-7.4%and 4.9%-10.4%,2.6%-6.4%respectively.The growth rate of maize yield increased with the increase of biochar returning amount,and film mulching also significantly increased maize yield.2)The single application of biochar reduced the soil bulk density during the two-year experiment,while film mulching didn’t have significant effect on the change of soil bulk density,and there was no significant interaction between the return treatments and film mulching.At the harvest stage of 2020,compared to the MCK（1.13 g/cm~3）and NCK（1.12 g/cm~3）before sowing in 2019,the return of different gradients biochar reduced the soil bulk density to 1.09-1.13 g/cm~3 and 1.09-1.12g/cm~3,respectively.At the harvest stage of 2020,soil p H decreased,and there was no significant difference between treatments.At the same time,film mulching significantly reduced soil p H,and there was no significant interaction between the return of biochar and film mulching.3)The single application of biochar increased the soil organic carbon content significantly,and reduced soil nitrogen loss,but film mulching had no significant effect on it.At the end of the fallow period in 2021,in the treatments of biochar returning treatments,the SOC content increased to 7.48-8.4 g/kg and 7.4-8.44 g/kg compared with MCK（7.37 g/kg）and NCK（7.38 g/kg）at jointing stage of 2019.The return of biochar increased the soil total nitrogen content and reduced the loss of soil nitrogen at the end of the fallow period in 2021.At the end of fallow period in 2021,compared with MCK and NCK at jointing stage in 2019,TN content decreased by2.2%-4.08%and 3.12%-6.2%respectively.The decrease of soil TN content in returning treatments was lower than that in MCK（5%）and NCK（7.15%）.The results show that the improvement effect of biochar on SOC and TN content increased with the increase of returning amount,but film mulching had no significant effect on it.4)The returning of biochar increased soil EOC and MBC content,film mulching increased this trend.At the maturing stage of 2020,compared with MCK and NCK of the jointing stage in 2019,soil EOC content increased by 27.1%-53.2%and 14.0%-26.8%.The soil MBC content increased by 4.8%-23.8%and 3.0%-17.8%under different gradient biochar returning treatments.The results showed that the single return of biochar increased soil EOC and MBC contents,and film mulching treatment increased soil microbial activity by increasing soil temperature and water content,so the combination of biochar returning and film mulching was more beneficial to improve soil EOC and MBC contents.5)The returning of biochar with film mulching reduced the total CO₂ emission during the growing season of 2019;there was no significant difference in the total CO₂ emission of each treatment in 2020.However,under the condition of no film mulching,the total CO₂ emission increased.As the yield of biochar returned to the field increased,carbon emission efficiency increased.At the same time,the model fitting results showed that compared with the control,both the biochar return with film mulching decreased the Q₁₀.However,in the treatments without film mulching,Q₁₀ was increased.The results showed that the combination of biochar returning and film mulching reduced the total carbon emission during the growth period of maize,improved the CEE,and decreased the value of Q₁₀.2.Effects of maize stover returning with film mulching on maize productivity,soil quality and carbon emission6)Single return of maize stover had no significant effect on the soil water content.Film mulching increased soil water content.In the 0-20 cm soil layer of maturing stage in 2019,there was no significant difference among all treatments.In2020,the soil water content of 0-20 cm soil layer under film mulching was significantly higher than that under no film mulching.From 2019 to 2020,the soil temperature of 0-10 cm under film mulching treatment in May was higher than that under no film mulching treatment.In the later period,due to the shading effect of maize,the temperature difference gradually decreased,and maize stover returning had no significant effect on soil temperature.Compared with the contral,Sto-3 treatments significantly increased maize yield in 2019 and 2020.In 2019 and 2020,compared with MCK and NCK,the maize yield of different gradients of maize stover returning increased by 5.4%-9.6%,4.4%-9.1%and 4.1%-8%and 2.8%-8.8%,respectively.The growth rate of maize yield increased with the increase of maize stover returning amount.7)The single application of maize stover reduced the soil bulk density,while film mulching didn’t have significant effect on the change of soil bulk density,and there was no significant interaction between the return treatments and film mulching.At the harvest stage of 2020,compared with MCK（1.13 g/cm~3）and NCK（1.12g/cm~3）,the return of different gradients maize stover decreased the soil bulk density to1.09-1.13 g/cm~3and 1.09-1.12 g/cm~3,respectively.At the harvest stage of 2020,soil p H decreased,and there was no significant difference between treatments.At the same time,film mulching significantly reduced soil p H,and there was no significant interaction between maize stover returning and film mulching.8)The single application of maize stover increased the soil organic carbon content,reduced the loss of soil total nitrogen content,there was no significant effect of film mulching treatment on them.At the end of the fallow period in 2021,in the treatments of different gradients maize stover return,compared with the MCK（7.37g/kg）and NCK（7.38 g/kg）at jointing stage in 2019,the SOC content increased to7.48-8.3 g/kg and 7.4-8.29 g/kg,respectively.In contrast with MCK and NCK at jointing stage in 2019,TN content decreased by 4.08%-6.03%and 5.27%-6.04%respectively in the treatment of maize stover returning with different gradients.The decrease of soil TN content in returning treatments was lower than that in MCK（5%）and NCK（7.15%）.The results showed that the improvement of maize stover on SOC and TN content increased with the increase of returning amount,but film mulching had no significant effect on it.9)The returning of maize stover increased soil EOC and MBC content,film mulching increased this trend.At the maturing stage of 2020,compared with MCK and NCK of the jointing stage in 2019,soil EOC content increased by 27.1%-45.2%and 14.0%-26.7%.The soil MBC content increased by 4.8%-25.7%and 3.0%-18.9%under different gradient maize stover returning treatments.The results showed that the single return of maize stover increased soil EOC and MBC contents,and film mulching treatment increased soil microbial activity by increasing soil temperature and water content,so the combination of maize stover returning and film mulching was more beneficial to improve soil EOC and MBC contents.10)The returning of maize stover with film mulching reduced the total CO₂emission in 2019,there was no significant difference in the total CO₂ emission of each treatment in 2020 and carbon emission efficiency increased.However,under the condition of no film mulching,the total CO₂ emission increased,carbon emission efficiency decreased.At the same time,the model fitting results showed that compared with the control,maize stover return with film mulching decreased the Q₁₀,Q₁₀ was increased in the treatments without film mulching.The results showed that the combination of maize stover returning and film mulching reduced the total carbon emission during the growth period of maize,improved the CEE,and decreased the value of Q₁₀.In conclusion,in the semi-arid region of the Loess Plateau,the single return of biochar and maize stover can increase carbon sequestration,reduce nitrogen loss,reduce soil bulk density,improve soil structure,and thus increase crop yield during the two-year test period.At the same time,the combination of returning treatment and film mulching can reduce the total carbon emission during the growth period and increase the carbon emission efficiency.However,the carbon sequestration and emission reduction effect after biochar returning was more prominent.Therefore,biochar is more suitable for improving soil quality,reduce fertilizer use and reduce carbon emissions.However,it should be noted that the returning amount of biochar and maize stover was different in the two experiments,so this conclusion was preliminary.Due to the lack of comparison under the same amount of conditions,it is necessary to carry out an experiment under the same amount of carbon return measures,and further compare and evaluate the effects of biochar and maize stover on soil quality and carbon emissions.