Effects Of Exogenous Carbon Addition On Organic Carbon Mineralization,Humification And Enzyme Activities In Agricultural Soils

The transformation of soil organic carbon is an important biochemical process in soil,and it is also an important driving factor of soil organic carbon,nitrogen,phosphorus and sulfur cycle.In the past,it was found that the addition of carbon source could increase the content of soil organic carbon,the quantity of soil microorganism and enzyme activities,and play a positive role in soil fertility.However,in the black agricultural soil of Northeast China,the research on the carbon transformation of agricultural soil by different exogenous carbon addition was relatively less.Therefore,three kinds of exogenous carbon,i.e.nano carbon,straw and biochar,were used as materials to study the mineralization process,humification process and the change rule of carbon metabolism related enzyme activities in agricultural soil within two years after exogenous carbon addition,and to explore the influence mechanism of different exogenous carbon on the transformation process of soil organic carbon,so as to provide scientific basis for the maintenance of agricultural productivity in the black soil area.The results were as follows:1.After the three kinds of exogenous carbon addition,the soil properties and nutrient characteristics changed with the growth period of crops.and were mostly higher in spring or summer.Compared with no carbon addition,the soil pH did not change and the soil bulk density decreased after three kinds of exogenous carbon addition,soil temperature increased after nano carbon and biochar addition,soil water content increased after straw addition in last two years.Compared with no carbon addition,the nano carbon application improved the content of soil organic carbon,total nitrogen,carbon storage,nitrogen storage and reduced the ratio of C:P,N:P,while the straw application increased the content of nutrients,carbon storage,nitrogen storage,phosphorus storage.Meanwhile,the biochar application grew the content of soil organic carbon and carbon storage.Straw and biochar addition increased soil ecological stoichiometric characteristics comparatively no carbon addition.Principal component analysis showed that the proportion of nitrogen and phosphorus in fertility factors increased after three kinds of exogenous carbon addition.2.After the three kinds of exogenous carbon addition,the contents of labile organic carbon,non-labile organic carbon,dissolved organic carbon,soil respiration rateand mineralization rate of organic carbon changed with the growth period of crops,which was consistent with the seasonal dynamic law of no carbon addition in last two years.Compared with no carbon addition,the content of soil labile organic carbon,dissolved organic carbon decreased and soil respiration rate and mineralization rate of organic carbon increased after three kinds of exogenous carbon addition,while the straw and biochar application increased the content of non-labile organic carbon.The results of principal component analysis showed that the soil dissolved organic carbon became the main factor affecting soil mineralization after the addition of three kinds of exogenous carbon,and the proportion of soil respiration rate and soil organic carbon mineralization rate increased after the addition of straw and biochar.3.The humic components and the optical properties of humic acid changed with the growth period of crops after three kinds of exogenous carbon addition,which were higher in the first autumn(lower humic acid and fulvic acid),and lower in the second year.Compared with no carbon addition,three kinds of exogenous carbon application improved the content of humin,but had no significant effect on fulvic acid,the ratios of humic acid to fulvic acid,PQ value,humic optical properties.Meanwhile,the nano carbon application decreased the content of humic acid content,but increased after straw addition.Principal component analysis showed that the proportion of optical properties of humic acid increased after three kinds of exogenous carbon addition.4.After the three kinds of exogenous carbon addition,the activities of soil carbon metabolizing enzyme activities all changed with the growth period of crops.Among them,the activities of soil cellulase,amylase,catalase and soil total enzyme index were higher in spring,while the activities of soil invertase reached the maximum in the autumn of the second year.Compared with no carbon addition,after the three kinds of exogenous carbon addition had no significant effect on soil cellulase activity and decreased catalase activity,while the nano carbon application decreased soil invertase activity and total enzyme index.Meanwhile,the biochar application increased soil amylase activity,invertase activity,total enzyme index.Principal component analysis showed that the proportion of cellulase activity increased after addition three kinds of exogenous carbon.5.The results of correlation analysis showed that compared with no carbon addition,the mineralization process of soil organic carbon had little correlation with soil properties,ecostoichiometric characteristics,carbon storage,nitrogen storage phosphorus storage after the three kinds of exogenous carbon addition in last two years.After three kinds of exogenous carbon addition,the humification process of soil organic carbon had significant correlation with soil water content and organic carbon content,but had no regularity with ecostoichiometric characteristics,carbon storage,nitrogen storage,phosphorus storage comparatively no carbon addition.Meanwhile,the activities of soil carbon metabolizing enzymes were significantly correlated with soil nutrient content,but not with soil ecological stoichiometric characteristics and carbon storage,nitrogen storage and phosphorus storage.According to the above result,three kinds of exogenous carbon addition can promote the carbon metabolism of soil to some extent,among which straw and biochar addition are more significant than nano carbon addition.After carbon source addition,the carbon metabolism of soil is still controlled by soil properties,soil mineralization process,soil humification process and soil enzyme activities.