Effect Of Conservation Tillage On Soil Organic Carbon Distribution Characteristics With Aggregates Stability In Yellow Soil Of The Central Guizhou

Guizhou Province is a typical agricultural province in the Karst mountainous region with fragile ecology.Conservation tillage is the main tillage measure to prevent and control farmland soil erosion and protect farmland ecological environment.This paper depends on the long-term fertilization field experiment primarly,and selects maize monoculture system（MM）,wheat（intercropping green manure）-maize rotation（WMR）and rape-maize rotation（RMR）on soil aggregate stability and organic carbon content were investigated in order to further study the conventional tillage（FT1）,no tillage（FT2）,minimal tillage（FT3）,conventional tillage+light simplified fertilization（FT4）,no tillage+light simplified fertilization（FT5）,downslope conventional tillage（ST1）,cross ridge tillage（ST2）,cross ridge tillage+straw mulching（ST3）,cross ridge tillage+straw mulching+contour hedgerow（ST4）to analyze the differences in soil physical and chemical properties.The agglomerate dry sieving and wet sieving grouping method was used to screen out the mechanically stable agglomerates and water-stable agglomerates of different treatments,Calculate their mean weight diameter（MWD）,geometric mean diameter（GMD）,percentage of aggregates>0.25 mm(R_0.25),percentage of aggregate destruction（PAD）,unstable aggregate index(E_LT),fractal dimension（D）,measuring the organic carbon content of different aggregates with different particle sizes and calculating contribution ratio,and proving the response of different protective farming measures to flat land and slope land,respectively.Provide theoretical basis for the efficient use of nutrient resources in karst areas and sustainable development of dryland agriculture.The main conclusions are summarized as follows:（1）Rotation can improve soil physical and chemical properties,increase the content of macroaggregates and their stability,and increase the content of organic carbon in soil aggregates.Compared with maize monoculture,the soil bulk density in different rotations was significantly reduced by4.56%～7.20%,soil porosity and saturated water holding capacity were significantly increased by 5.41%～13.60%,3.42%～8.43%,and organic carbon and total nitrogen were increased significantly by 24.01%～36.05%,10.40%～10.52%;the percentage aggregate destruction rate is significantly reduced by 25.97%～31.32%,the unstable aggregate index is significantly reduced by 30.65%～35.90%,and the fractal dimension is significantly reduced by 0.36%～0.71%;The organic carbon content of water stable aggregates of>0.25mm increased by 17.60%～41.32%,which is conducive to increasing the organic carbon contribution rate in macroaggregates,especially aggregates of>5 mm.（2）No tillage,minimal tillage,no tillage+light simplified fertilization can effectively increase its soil pores and improve soil fertility in flat land with rape-corn rotation..Compared with conventional tillage,soil bulk density of different conservation tillage measures decreased by 3.03%to 7.45%,soil porosity and saturated water holding capacity increased by 2.29%～5.62%,6.18%～13.98%,and organic carbon and total nitrogen increased significantly by 7.94%～22.07%,6.72%～17.16%.Under the no tillage+light simplified fertilization,the aggregates have the best stability.Compared with other treatments,the mean weight diameter,the geometric mean diameter and the percentage of aggregates>0.25 mm can significantly increase by 19.95%,31.58%,0.32.%and 26.39%,19.16%,5.55%,and the aggregate destruction rate,unstable aggregate index,and fractal dimension can be reduced by68.87%,60.84%,0.22%at the maximum;>5 mm,5-2 mm,2-1 mm,1-0.5 mm of the waterstable aggregates also had the highest organic carbon content,which were 39.29%～107.145%,15.91%～56.03%,36.37%～46.67%and 7.69%～27.18%higher than other treatments,respectively.（3）Cross ridge tillage,cross ridge tillage+straw mulching and cross ridge tillage+straw mulching+contour hedgerow can maintain and enhance soil nutrients in slope land with rape-maize rotation,effectively.Compared with the downslope conventional tillage,the soil bulk density of different conservation tillage measures decreased by 3.38%～6.60%,and the soil porosity and saturated water holding capacity increased by 1.91%～3.71%,5.54%～11.13%.Compared with other treatments,the cross ridge tillage+straw mulching had the highest organic carbon content and total nitrogen content,and the ratio of carbon to nitrogen was the largest.Compared with other treatments,the percentage of aggregate destruction and the unstable aggregate index of t cross ridge tillage+straw mulching+contour hedgerow decreased the most.The stability of aggregate of the cross ridge tillage+straw mulching is better,which the mean weight diameter,the geometric mean diameter and the percentage of aggregates>0.25 are 1.95%,2.34%,and 2.19%higher than those of downslope conventional tillage.5 mm,5-2 mm,2-1 mm,1-0.5 mm of water stable aggregates have the highest organic carbon compared to other treatments,which were 6.24%～16.92%,4.47%～12.13%,14.73%～24.68%,0.80%～9.55%.（4）The mechanically stable aggregates and water stable aggregates are dominated by aggregates of>5mm which implement different protective tillage in flat land and slope land,and the water stable macroaggregates organic carbon of aggregates of>0.25 pairs to the total organic carbon contribution rate of the soils under different treatments was over 89%.