Effect Of Different Straw Returning Modes On Soil Organic Carbon And Its Fractions In Guan Zhong Plain

As global temperature continuously increases, greenhouse gas reduction and carbonsequestration have been receiving increasing attention in environmental and soil science in therecent decades. The study of soil organic dynamics has become the hot point of global soilorganic caron research. Labile soil carbon fractions (e.g. soil microbial biomass carbon,particulate organic carbon, readily oxidized carbon, easily mineralizable organic carbon,extractable carbon and other carbonhydrates), which make up a relatively small proportion oftotal soil organic matter, are typically more sensitive to changes in soil management practicesor environmental conditions than total soil organic matter, and consequently they arewell-established as early indicators of the change caused by crop residue incorporation, soiluse or pollution. Guan zhong Plain, as the main production area of crops in shann’xi province,has been positively popularizing conservational tillage in line with the nationwidepopularization of conservational tillage. Straw returning, as the one of the core technologiesof consevational tillage, could improve soil condition thereby increasing the crop yield,resulting in positive effect on dynamics of soil organic matter, carbon sequestration, andenvironment conservation. However, information about the effect of crop straw returning onsoil organic carbon in Guan Zhou Plain is not enough. Therefore, this research took the fieldexperiment of crop straw returning as an object to study the change of soil organic carbon andits fractions under nine modes of crop straw returning in Guan Zhou Plain. The main resultsare as follows:(1) Crop straw returning could increase the content of particulate organic carbon andnitrogen, but there was no significant effect on the content of mineral-associated carbon,nitrogen and C/N of particulate organic matter as well. Different crop straw returning modesaffected the content of particulate organic carbon and nitrogen differently. Among the ninemodes of crop straw returning, the mode of wheat straw pulverization+rotary tillage+maizestraw pulverization+subsoiling or rotary tillage had better effect. The percentage of particulateorganic carbon was47%~57%with an average of51%. The percentage of particulate organiccarbon was41%~50%with an average of45%. However, the difference of nine crop strawreturning modes was not significant. The mode of wheat straw pulverization+rotarytillage+maize straw pulverization+subsoiling was observed with the highest value of particulate organic carbon to total organic carbon, and the mode of wheat straw pulverization+rotary+no maize straw returning saw a highest value of particulate nitrogen to total nitrogen.(2) Crop straw returning is beneficial to improve the content of aggregate organic carbon,especially increase the larger size aggregates. Different straw returning modes affectedaggregate organic carbon differently. Among the nine modes of crop straw returning, themodes of crop straw pulverization+rotary tillage were better to increase the content ofaggregate organic carbon. In the short-term experiment period, crop straw returning caused nosignificant effect on stability of aggregate. Crop straw returning is beneficial to improve theoxidation stability of larger aggregate organic carbon and decrease the oxidation stability ofsmaller aggregate organic carbon.(3) The content of salt extractable organic carbon is greater than water extracter organiccarbon under crop straw returning modes. Crop straw returning could improve the content ofmicrobial biomass organic carbon, salt extractable organic carbon, and water extractableorganic carbon. However, the effect of different crop straw returning modes differentiated.Among the nine modes of crop straw returning, the mode of wheat straw pulverization wascapable of increasing the discussed fractions of soil organic carbon. Labile organic carbonfractions were sensitive to the change of soil organic carbon caused by different crop strawreturning modes. And water extractable organic carbon was observed with the highestsensitivity to different crop straw returning modes. Thus, water extractable could be an earlysentitive indicator to the change of soil organic carbon under crop straw returning condition.(4) Different crop straw returning modes affected the fractions of soil organic carbonseparated by physical fractionation. In general, crop straw returning is helpful to increase thecontent of free light fraction and occluded fraction, and also increase their percentage to totalorganic carbon. In regard to humified organic caron, several modes of crop straw returningslightly increase the content of heavy fraction and humified fraction, but there was nosignificant change of the percentage of humified fraction. Occluded fraction was moresensitive to different crop straw returning modes.(5) Crop straw returning in the form of pulverization+rotary caused the greatest effect onthe mineralization characteristics (accumulated mineralization, mineralization rate, and ratioof mineralization) of aggregate organic carbon. Specifically, crop straw returning had greatereffect on the ratio of mineralization of0.25~0.05mm size aggregates. The modes of wheatstraw stubble+maize straw pulverization (Ws|Mp), No wheat straw+maize strawpulverization (Wn|Mp), wheat straw stubble+No wheat straw (Ws|Mn) and wheat strawpulverization+No maize straw (Wp|Mn) increased the ratio of mineralization of0.25~0.05mm size aggregates. The effect of crop straw returning on soil organic carbon mainly by way of affecting0.25~0.05mm size aggregates organic carbon.