Effects Of Different Ways Of Straw Returning On Soil Greenhouse Gas Emissions In Sloping Cropland

In recent years,global warming,rising of sea levels and extreme weather caused by greenhouse effect,has been increasingly threaten human survival and development.Greenhouse gas（GHG）emission was one of the important factors causing the greenhouse effect.Farmland soil is an important source of GHG emission and at the same time agricultural ecosystem is the terrestrial ecosystems that strongest affected by human disturbance,so every agricultural strategies could have important impacts on GHG emissions.Straw return as one of the most important agricultural protective measures,has been more and more used in agricultural production,and now there are many researches about the effect of conservation tillage on greenhouse gas emissions,but the researches of GHG emissions in sloping farmland are not enough,especially lack of the research about the effect of straw returned and soil active carbon and nitrogen on spatial heterogeneity of greenhouse gas emissions.Soil respiration as an important component of terrestrial ecosystem carbon cycle,released about800 Pg CO₂ each year,and was the second largest carbon flux just only less than the production of photosynthesis.Soil respiration of farmland ecosystem is one of the most important parts of soil carbon emissions,so deeply investigating the influence of soil respiration of agriculture and its effect mechanism played an important role for us to accurate estimation of carbon balance and reasonable strategies for reducing greenhouse gas emissions.Chinese Loess plateau is one of the most serious soil erosion areas,and is also the regions thatowing longest agriculture history in our country.This region was mainly rainfed agriculture,and the precipitation is uneven,soil is loose,and the product is low.Conservation tillage technology is a new technology of water-saving and maintaining soil fertility.Straw mulching could change soil temperature,soil moisture and soil microbial activity,and then affect soil CO₂ emissions and soil organisms.In this paper,we selected typical sloping farmland in the Loess Plateau of west Henan,using the method of field in situ monitoring combing with simulative experiments in laboratory,analyzed the effect of different straw mulching method on soil temperature,soil moisture,soil respiration and N₂O emissions and soil organic carbon,and provided academic support for reducing GHGs emissions and establishing a suitable straw mulching strategy.The main results were as follows:（1）The influence of different methods of straw returning on soil respirationDifferent ways of straw counters-field processing had large influences on soil respiration.Compared with conventional tillage treatment,straw incorporation was significantly promoted soil respiration,especially in the periods of high soil temperature and moisture.There was no significant difference between straw mulching and conventional tillage treatment on accumulation of soil CO₂ emissions throughout the year.However,among different slope positions,there existed obvious differences in soil respiration among different straw returning treatments and showed she same tendency,lower slope >middle slope>upper slope.The difference in straw returning treatment was larger than control,which indicated that straw input increased the spatial heterogeneity of soil respiration.There was significantly exponential correlation between soil temperature and soil respiration,and there wassignificantly linear correlation between soil moisture and soil respiration,and the correlative index was higher under straw mulching treatments.Compared with straw incorporation and conventional tillage treatments,straw mulching has dual function of promotion and suppression on soil temperature.Soil organic carbon content under different straw returning treatments was different,straw returning significantly increased active organic carbon,especially in high soil temperature and moisture period.The content of soil active organic carbon under different slope position are spatial heterogeneity,showing the tendency as below: lower slope >middle slope>upper slope.（2）The effect of different components of straw adding on soil N₂O emissionThe effects of different corn litter components and mixture addition on soil N₂O emission was investigated via laboratory incubation in the present study.Five treatments were set in this experiment: soil with no litter addition（CK）;soil with stalk litter addition（CKS）;soil with leaf litter addition（CKL）;soil with leaf sheath litter addition（CKLS）;soil with mixed litter（stalk: leaf: leaf sheath = 5:3:2）addition（CKM）.The results showed that litter addition had a priming effect on N₂O emission at the beginning of the incubation.N₂O emission from the samples with litter addition was stable since the sixth day of the incubation period and was greater than that from CK samples.The cumulative N₂O emission from samples with litter addition was significantly higher than that from CK samples（p <0.05）,further,cumulative N₂O emissions of CKS and CKM were significantly greater than that of CKL and CKLS（p<0.05）.Litter mixing accelerated soil N₂O emission to a certain extent in the first stage of incubation（10-28d）,however,there was no interaction among different kinds of litter in the last stage of the incubation.The total N contents ofall residues in the end of the incubation were significantly greater than the initial contents;on the contrast,the ratio of C/N of the incubated residues was significantly smaller than the initial ratios（p < 0.05）.For the incubated samples of CKM,the mass were smaller than that predicted,the total N content was greater than that predicted;while the C/N ratio was smaller than that predicted.However,there was no significant difference between observed and predicted soil cumulative N₂O emissions.These results indicated that litter mixing accelerated the processes of litter decomposition and N accumulation,but had no significant effect on N₂O emission.（3）Effects of different corn litter component on soil organic carbon mineralization and content of active organic carbonLitter addition significantly promoted SOC mineralization,the amount of soil accumulative carbon mineralization was 2.88（CKS）,2.13（CKL）,2.84（CKLS）,3.04（CKM）times as compared with CK treatment.The SOC mineralization rates of litter addition treatments overall divided two stages: fast decomposition stage（1-28d）and slow decomposition stage（28d to the end of experiment）.Litter mixture significantly promoted SOC mineralization,the amount of observed soil accumulative carbon mineralization significant higher than that of predicted value in the end of experiment and the promotion was happened in the fast decomposition stage.In the end of experiment,the content of litter carbon was not visible changed compared with initial content,but content of total nitrogen was significantly increased,the content of stem,leaf and leaf sheath and mixed litter was 42%,41% 108% and 80% higher than initial content.The carbon-nitrogen ratio decreased significantly,the value of stem,leaf and leaf sheath and mixedlitter was 72%,68%,47% and 39% compared with initial value.The predicted mass remaining and carbon-nitrogen ratio were higher than observed values;the predicted content of soil total nitrogen was lower than observed value.In the end of experiment,the content of microbial carbon（MBC）was higher under CKS treatment,and the different was not visible under other treatments.The content of microbial nitrogen（MBN）had the tendency to decrease and the MBC/MBN accordingly increase under litter addition treatments.The difference of CKS,CKL and CKM treatments was significant compared with CK treatment.The content of dissolved organic carbon（DOC）was higher under CKLS and CKM treatments than other three treatments,and the difference under CKS and CKL treatments was not significant.