Effect Of Straw Returning And Rotational System On Carbon Emission Of Aggregates In Wheat-Maize Farmland

The study was conducted at the agricultural experimental station of Shandong Agricultural University from 2017 to 2018.The experiment was based on a 15-year long-term protective tillage test field.Using gas chromatograph,agglomerate analyzer and related experimental analysis techniques,the system discussed the no-tillage?NT?,rotary tillage?cultivation depth 10-15 cm?RT,subsoiling tillage?cultivation depth 35 cm?SS,no-tillage+subsoiling rotational tillage?NT+SS?,rotary tillage+subsoiling rotational tillage?RT+SS?5 kinds of tillage measures for winter wheat-summer maize farmland aggregates stability,soil carbon of aggregates,aggregates carbon mineralization,plant carbon storage and crop yieldunder the conditions of straw returning?S?and not returning to field?0?.The main conclusions are as follows:1.Soil physical properties and aggregates carbonThe increase of soil depth candecrease the soil bulk density,the number of large aggregates,and the carbon content of the aggregates,and the reduction of the aggregates size also can make reduce the carbon content of the aggregates.From the perspective of soil physical properties,straw mulching reduces the soil bulk density in the plough layer?0-20 cm?and increases the soil surface temperature and humidity.The results showed that no-tillage increased the content of large aggregates?>2 mm?in the topsoil?0-10 cm?,but the no-tillage aggregates destruction rate?PAD?was the highest,and increased the aggregates content of2⁰.25 mm in the subsoiling,but the lowest mechanical stability of aggregates.In the model of rotary tillage,the content of large aggregates and the waterstability of aggregates in the rotary tillage+subsoiling rotational tillage were both higher than that of successive years of rotary tillage.The mechanical stability of aggregates in the no-tillage+subsoiling rotation under 10 cm was highest.In terms of the carbon components of the aggregates,the SOC of aggregatesin the no-tillage,no-tillage+subsoiling rotational tillagewas better thanrotary tillage+subsoiling rotationin wheat season,and the maize season is better for rotary tillage+subsoiling rotational tillage;No-tillage+subsoiling rotational tillage,rotary tillage+subsoiling rotational tillage and subsoiling increased the ROC content of the large aggregates?>2 mm?in the plough layer.2.Soil aggregates carbon mineralizationWhen soil aggregate mineralization culture was carried out under indoor artificial control conditions,the greenhouse gas emission rate of each treatment increased at first and then decreased,reached the first peak on the 3rd day and the second peak within the 10th to 20th day;The accumulative release and accumulative mineralization rate were the trend of rapidly increased and then gradually slowed down and stabilized.Compared with no straw addition,straw addition has a significant carbon stimulation effect,and CH₄ and CO₂ emissions are large.Among them,the CH₄ emission of no-tillage+subsoiling rotational tillagein the whole soil with straw addition were significantly lower than that of other tillage measures,the lowest in rotary tillage+subsoiling rotational tillage without straw.In the aggregates with grain size of 2⁰.25mm,the rotary tillage+subsoiling rotational tillage had the lowest CH₄emissions.The CO₂ emission of no-tillage+subsoiling rotational tillage was significantly lower than that of rotary tillage+subsoiling rotational tillage,and the SOC mineralization rate was the lowest.The CO₂emissionand SOC mineralization rateof rotary tillage+subsoiling rotational tillage added with straw were lower than that of no-tillagein the aggregates with particle size<0.25 mm.According to the change of the aggregate carbon,the large aggregates ROC retention in the rotational tillage mode is greater.And the addition of straw can significantly reduce the SOC loss rate of large aggregates in rotational tillage treatment,and reduced the contribution rate of aggregates mineralization in no-tillage+subsoiling rotational tillage.3.Effects of straw and rotational tillage on crop productivityStraw returning can increased the above ground biomass of plants,slow down the premature aging of no-tillage in the late growth stage,improved the leaf area of no-tillage+subsoiling rotational tillage,the carbon content of each organs and the carbon storage of maize ear,increase the grain number per ear and annual yield.Rotary tillage+subsoiling rotational tillage mode can slow the premature senescence of continuous rotary tillage and promoted crop growth.Combining straw returning can increased the carbon content and carbon storage of various organs of wheat and increased the annual yield.In summary,the rotational tillage can reduced carbon enrichment in the topsoil of no-tillage and rotary tillage,alleviated the situation of no-tillage large aggregates?>2 mm?and low mechanical stability of subsoiling aggregates.No-tillage+subsoiling rotational tillage,rotary tillage+subsoiling rotational tillage and subsoiling significantly increased the SOC content of soil aggregates.Straw addition could reduce the SOC loss rate of large aggregates in rotational tillage and the contribution rate of aggregates mineralization in no-tillage+subsoiling rotational tillage.The soil carbon is retained,and finally the straw returning to the field reduced the premature senescence of the no-tillage and rotary tillage leaves and increased the annual yield.Therefore,the application of straw returning and subsoiling-based rotational tillage mode in conservation tillage has important practical value.