Thermal Stability Of Soil Organic Matter In Different Fractions Under Long-term No-till Farming

The stability of soil organic matter(SOM)is related to the turnover of soil organic carbon and soil fertility.The quantity and stability of SOM may be altered by the changing of tillage treatments.The combined thermal analysis techniques such as thermogravimetric analysis(TG)and differential scanning calorimetry(DSC)are widely utilized to rapidly and quantitatively analyze the SOM thermal stability.In this study,we investigated the thermal stability of SOM in the bulk soils and different fractions sampled from the different tillage treatments at the Luancheng Agroecosystem Experimental Station of the Chinese Academy of Sciences.The experiment was established in the winter wheat season in 2001.There were four tillage systems:moldboard plow without corn residue(CK),moldboard plow with corn residue(CT),rotary tillage with corn residues(RT)and no-till with corn residue(NT).Soil samples were collected from the 0-10 and 10-20 cm layer in June of 2017 We separated the bulk soil(<2 mm)into three classes(i.e.,>53 ?m,53-2 ?m,and<2?m).Few paramenters are applied in thermal stability,i.e.,%Exo1(percentage of labile organic matter in total organic matter),TG-T50(temperature when the organic matter mass is reduced by half),DSC-T50(temperature corresponding to half the energy released by the organic matter),and ED(amount of energy reduction divided by the weight loss of SOM in the corresponding temperature range).At the same time,solid-state 13C nuclear magnetic resonance spectrum technology(NMR)measures the components of organic matter,and provide a indicator called Alkyl C/O-alkyl C(the ratio of alkyl C to O-alkyl C+di-O-alkyl C)to represent soil organic carbon stability.What's more,build a correlation between thermal parameters and functional groups.The main results include the following(1)For the bulk soil,thermal stability of soil organic matter in 0-10 cm soil layer is lower than that in 10-20 cm layer;Straw mulching can effectively improve the quantity of SOM,especially the labile components.Compared with other treatments,thermal stability was decreasd under NT and RT treatments(2)For different aggregates,more soil organic matter with different types increase in sand and clay fraction.With sand aggregates,thermal stability shows lower than other aggregates in 0-10 and 10-20 cm layers.NT and RT significantly decrease the thermal stability with sand fraction.There is a certain correlation between the quality index and the energy index,but the quality index shows a better regularity than energy index in thermal stability(3)NMR indicates a reduction of recalcitrant functional groups in the bulk soil of 0-10 and 10-20 cm layers.Compared with other treatments,NT decreases the relative content of labile groups but increses the recalcitrant.13C NMR serves as a complementary technology of thermal analysis to reflect the stability of soil organic matter under tillage treatments.Several functional groups shows significant correlation with thermal pamametersThus,long-term no-till decreases the thermal stability in bulk soil with the depth of 0-10 and 10-20 cm soil layers,reduce the thermal stability in sand fraction,promote the conversion from labile functional groups to recalcitrant functional groups,and improve the stability of soil organic matter,which is a essential tillage treatment to improve the "quality" of soil organic matter.