Effects Of Different Tillage Methods On Soil Structure And CH₄ And N₂O Emissions In Paddy Field Rotated With Wheat Cropping Under Straw Incorporation

China is a country with high rice production and a large quantity of straw resources.Straw incorporation can increase soil organic matter,improve soil properties,crop yield,carbon sequestration and emission reduction,which is the main way to utilize straw resources.Tillage is an important agricultural production process that affects greenhouse gas emissions.The effects of different tillage on soil physic-chemical properties,soil structure and CH₄ and N₂O emissions under the condition of straw incorporation are still unclear.Therefore,field experiments were carried out in the rice-wheat rotation system to study the effects of different tillage on soil physic-chemical properties,CH₄ emission process,N₂O emission process and comprehensive warming potential under straw return.The experiment was conducted in the fifth branch of Huanghai farm,Yancheng City,Jiangsu Province（119°87’E,34°29’N）.Liangeng 7 and Huai mai 22 were used as seasonal experiment material.In the split-split plot experiment,the main plot was the treatment methods of straw,the sub-plot was the soil preparation methods in paddy field,and the split-plot was the tillage method in wheat field.There are two levels of straw treatment,i.e.no straw incorporation（NS）and straw incorporation with full amounts（S）;two levels of paddy soil preparation treatment,i.e.wet field rotary tillage（P）and dry field rotary tillage（H）;two levels of wheat field tillage,i.e.rotary after ploughing tillage（FR）and rotary tillage（R）.Each treatment was repeated 3 times.The straw was not returned to the field within 10 meters near the cement road.The main results are as follows:1.Effects of different tillage on soil aggregation,physic-chemical properties in paddy field rotated with wheat cropping under straw incorporationS treatment could regulate soil water content,increased soil water content under the condition of H,but decreased it under the condition of P treatment.Compared with P treatment,H treatment could protect soil structure and reduce soil water content.The results showed that H treatment improves soil water infiltration and drainage performance,and reduces p H value of R-S treatment significantly,also increases Eh of R treatment.S treatment could significantly increase nutrient content at jointing stage and maturity stage of rice field.R treatment could increase soil organic carbon content at maturity stage after P treatment,but it decreased soil organic carbon content at maturity stage after H treatment.S treatment decreased the proportion of soil aggregates with particle size>5 mm,mean mass diameter（MMD）and geometric mean diameter（GMD）,but had no significant effect on SOC content of soil aggregates.After R treatment,S treatment could increase the soil aggregates with particle size>5 mm.Under the condition of S treatment,R treatment increased MMD and GMD,decreased the fractal dimension（D）,increased the SOC content of soil aggregates with particle size between 0.25 and 5 mm.It indicated that the P-R treatment could help to protect the stability of soil aggregates.2.Effects of different tillage methods on CH₄ and N₂O emissions in paddy field rotated with wheat cropping under straw incorporationIn the rice-wheat rotation system,S treatment significantly increased CH₄ emission during rice growth period.Under the condition of NS treatment,H treatment increased CH₄emission,while P treatment decreased CH₄ emission.S treatment increased N₂O emission except for H-R treatment,R treatment decreased N₂O emission of paddy field for two years under the condition of S treatment.The results showed that H-R treatment had the best effect of reducing emissions while ensuring stable yield under the condition of S treatment.3.Effects of different tillage methods on CH₄ metabolism in paddy field rotated with wheat cropping under straw incorporationS treatment significantly increased CH₄ emission during rice growth period.Under the condition of NS treatment,H treatment increased CH₄ emission;while under the condition of S treatment,H treatment reduced soil water content,reduced decomposition of soil organic carbon,inhibited CH₄ production activity and improved CH₄ oxidation activity in the second year,thus reduced CH₄ emission.Under the condition of NS treatment,R treatment could reduce CH₄ emission.Under the condition of S treatment,R treatment could reduce soil water content,increase the gene abundance of pmo A and CH₄ oxidation activity,but organic matter content and gene abundance of mcr A increased,which promoted the growth and reproduction of methanogens,increased production activity and emission of CH₄.4.Effects of different tillage methods on N₂O metabolism in paddy field rotated with wheat cropping under straw incorporationS treatment promoted nitrification at maturity stages except for H-FR treatment in2018,resulting in a significant increase in N₂O emission.Under the condition of NS treatment in 2018,H treatment increased the gene abundance of nir K and nir S and denitrification activity at jointing stage,increased the（nir K+nir S/nos Z）value at booting stage and NH₄⁺-N content at maturity stage,promoted the nitrification activity at maturity stage,and thus increased N₂O emission.Under the condition of S treatment,although the contents of NH₄⁺-N and NO₃^--N were increased by R treatment,the AOB gene abundances and nir K gene abundances were decreased by microbial competition for nitrogen,which inhibited nitrification and denitrification,thus reducing N₂O emissions in two years.