Regulatory Effects Of Straw Return And Tillage Methods On Soil Properties,Winter Wheat-Summer Maize Yield And Carbon Footprint

The Huanghuaihai Plain is the main production area of winter wheat-summer maize in China,and poor soil quality and low fertility are the fundamental reasons that restrict the improvement of crop yield in this area.Straw return,soil tillage and nitrogen（N）application,as important technical measures in agricultural production,are important ways to improve soil fertility and promote sustainable production of crop systems.This experiment was conducted in Huangjiazhuang Village,Taishan District,Tai’an City,Shandong Province from October2017 to June 2021,with Jimai 22（winter wheat）and Zhengdan 958（summer maize）as the test materials,and set up an annual straw return method trial and a tillage method with different N application rate trial.The annual straw return experiment was conducted in a one-way completely randomized group design with four experimental treatments:no straw return（CK）,single maize straw return（W1M0）,single wheat straw return（W0M1）and both wheat-maize straw return（W1M1）.A two-factor randomized group design was used to set up three tillage methods（continuous rotary tillage,RS;continuous deep tillage,DS;RS applied annually with a DS interval of two years,TS）and three N application rates(165 kg N ha^-1,N165;225 kg N ha^-1,N225;300 kg N ha^-1,N300)for the tillage method and N application trial.The purpose of this study was to explore the effects of straw return and tillage combined with N fertilizer on annual straw carbon input,soil physical and chemical properties and the structure and function of rhizosphere microbial community of winter wheat,and to clarify the effects of soil properties and rhizosphere microbial community changes on the growth and development of winter wheat and the physiological mechanism of increasing yield of winter wheat.To study the effects of different tillage methods and N application on agricultural production inputs,greenhouse gas emissions and carbon sequestration,and to evaluate their environmental effects using total production carbon footprint and yield carbon footprint,and to clarify the effects of tillage methods and N application rates on the environmental effects of annual production of winter wheat-summer maize,which will help to promote annual high-yield,high-efficiency and sustainable production of winter wheat-summer maize.The main results are as follows:1 Effect of annual straw return method on soil properties and yield of winter wheat-summer maizeThe cumulative carbon input under different straw return methods was 11.87-36.51 Mg ha^-1,resulting in a change in SOC storage of-1.30-2.16 Mg ha^-1.Straw return significantly reduced the proportion of soil solid phase,improved the ratio of soil macroaggregate and the stability of aggregate;enhance the carbon sequestration capacity of macroaggregate,thereby increasing the level of soil carbon pool,and significantly increasing soil available nutrient content;it significantly increased soil enzyme activity and microbial diversity,and finally increased the total annual yield by 7.4%-12.95%on average compared with no straw return.W1M1 had the highest yield,but it caused more carbon loss.W0M1 increased soil fertility and annual yield year by year and reduced farmland carbon loss and promoted the multiple utilization of wheat straw.2 Effects of tillage methods and N application rates on soil propertiesTS and DS improved straw input in the 10-30 cm soil layer and reduced the percentage of soil solid phase compared with RS,and TS optimized the soil three-phase ratio in the 0-30 cm soil layer,which significantly reduced the R value,and optimized the structure;RS and TS significantly improved macroaggregate ratio in the 0-10 cm soil layer compared with DS,while in the 10-30 cm soil layer,DS and TS significantly improved the macroaggregate ratio compared with RS;RS and TS significantly increased soil inorganic N,available phosphorus,and available potassium content in the 0-10 cm soil layer compared with DS,while DS and TS significantly increased soil available nutrient content in the 10-30 cm soil layer compared with RS;in the 0-10 cm soil layer,the enzyme activity was higher under RS and TS,while in the 10-30 cm soil layer,the enzyme activity of DS and TS was higher;RS preferentially accumulated45.3-46.3%of SOC in the 0-10 cm soil layer,which was significantly higher than DS and TS treatments,respectively;on the contrary,DS and TS significantly increased the percentage of SOC in the 10-20 cm and 20-30 cm soil layers,resulting in a more balanced vertical distribution of SOC,and TS balanced and optimized the SOC storage increment in the 0-30 cm soil layer during the experimental period.N225 and N300 significantly increased soil carbon sequestration,available nutrient content and enzyme activity compared with N165,but there was no significant difference between N225 and N300.3 Effects of tillage methods and N application rates on the structure and function of rhizosphere bacterial communityTS reduced the number of rhizosphere bacteria OUTs compared with RS and DS,and N165 increased the number of OUTs compared with N225 and N300.However,tillage methods and N application rates had no significant effects on Chao1,ace,Shannon,and Simpson.Tillage methods and N application rates led to significant differences inβdiversity of rhizosphere bacterial communities,and the bacterial community structure was more stable under TS.The abundance of Bacteroidetes and Gemmatimonadetes was the highest under RS;the abundance of Actinobacteria and Myxobacteria was the highest under TS;and the abundance of Acidobacteria and Verrucomicrobia was higher under DS.N165 mainly increased the abundance of Actinobacteria,Acidobacteria and Bacillus;N225 mainly increased the abundance of Trichoderma and Mucor;and N300 mainly increased the abundance of Bacteroidetes.The changes of soil physical and chemical properties caused by tillage and N application significantly affected the relative abundance of dominant bacteria in rhizosphere.Compared with RS and DS,TS significantly increased the abundance of cellulose hydrolysis,photoheterotrophic and chemoheterotrophic functional bacteria genera.DS significantly increased the abundance of nitrifying bacteria and plant pathogen.RS significantly increased the abundance of urea decomposition,nitrogen respiration,ammonia volatilization and aromatic compound degradation functional bacteria.Under N225,nitrification,urea decomposition and aerobic ammonia oxidation related to rhizosphere nitrogen cycle were significantly enhanced,and cellulose hydrolysis,methanol oxidation and methylation were also significantly enhanced.The abundance of aromatic compounds degradation,intracellular parasites and photoautotrophic bacteria was significantly increased under N165.4 Effects of tillage methods and N application rates on growth traits of winter wheatRS and TS significantly increased the root length density and surface area density of wheat roots in 0-10 cm soil layer compared with DS,while DS and TS significantly increased the root distribution in 10-30 cm soil layer compared with RS.The small population size under RS resulted in the smallest leaf area index and thus produced the maximum canopy photosynthetic effective radiation and cumulative daily radiation,while the oversized population under DS had the largest leaf area index and resulted in the lowest photosynthetic effective radiation and cumulative daily radiation.However,the appropriate population structure under TS led to a good canopy structure.Increased N application significantly increased the quality of wheat population,resulting in higher leaf area index and lower photosynthetically active radiation and cumulative daily radiation.RS and TS significantly increased the net photosynthetic rate of wheat flag leaf compared to DS,and N165 and N225 significantly increased the net photosynthetic rate compared to N300.Finally,DS and TS significantly increased dry matter accumulation and grain yield compared to RS.The dry matter accumulation and grain yield increased significantly with the increase of N application rate from N165 to N225,but the effect of increasing yield from N225 to N300 was not significant.5 Effects of tillage methods and N application rates on carbon footprint of winter wheat-summer maize productionAppropriate tillage method can reduce greenhouse gas emission（GHG）on the basis of increasing soil carbon sequestration and grain yield.Compared with RS and TS,DS increased mechanical oil consumption,significantly increased soil direct and indirect N₂O emission and reduced CH₄ absorption,resulting in the highest total GHG emission.N fertilizer production and transport,direct and indirect GHG emission increased significantly with higher N application,resulting in a significant increase in total GHG emission.TS and DS significantly increased soil carbon sequestration compared to RS,which in turn significantly reduced total production carbon footprint（CF）.There was no significant change in total CF from N165 to N225 with additional N fertilizer application,but a significant increase in total CF from N225to N300 with additional N fertilizer application.Compared to RS,TS with comparable or less N application met the synergistic enhancement of yield and environmental benefits.In addition,the CF（including SOC sequestration）under TS was significantly lower than that under RS,indicating a relative net carbon sink.With comparable annual grain yields,TS-N225 reduced the CF of the agricultural system compared to the conventional management model（RS-N300）by two ways:（1）more SOC stock in the 0-30 cm soil layer,which implied a reduction in CO₂emission or an increase in CO₂ sequestration;（2）a reduction of 75 kg ha^-1 of N application combined with tillage,resulting in a decrease in GHG emissions by 0.85 Mg CO₂ eq ha^-1 year^-1.Under TS-N225,the final CF was significantly lower by 1.87 Mg CO₂ eq ha^-1 year^-1 and the yield CF was only 0.24 kg CO₂ eq kg^-1.