Effects Of Organic Materials Addition And Freeze-thawing Cycles On Organic Carbon Mineralization Of Chernozem

Chernozem is the main soil type for planting corn in Jilin Province,but long-term tillage caused some problems,such as soil fertility declining and organic carbon content decreasing.Therefore it is important to promote organic carbon content of the Chernozem for agricultural sustainable development.For this reason,the relative study has been carried out by our research team,it is proved that the application of straw and organic-inorganic fertilizer can increase the content of soil organic carbon significantly,but the research about the mineralization of organic carbon in the process of accumulation has not been carried out.Chernozem in Northwestern of Jilin Province was selected to study the distribution of?micro?aggregate and its organic carbon,active components of organic carbon,release characteristics of CO₂,contents of carbonate and calcium form under the condition of organic materials addition and its freeze-thawing cycle by laboratory simulative experiment.The reassignment of exogenous carbon into the soil,and the relationships with the mineralization of soil organic carbon was further analyzed.The results of this study can provide theoretical basis for the establishment of environment-friendly soil fertilization.The results of the study are summarized as follows:Firstly,with the addition of straw,organic-inorganic fertilizer and their freeze-thawing cycles conditions,the CO₂ release rate of the Chernozem was divided into three stages:the rapid raising and descending stage,the slow raising and descending stage,the steady descending stage.The cumulative amounts of CO₂ was fitted with the first-order kinetic equation?R²>0.89?,and the higher proportion of organic carbon was added,the higher release rate and potential cumulative amounts?Ci?of CO₂.Freeze-thawing cycles can inhibit the potential cumulative amounts of CO₂,and increase the peak value of CO₂ release rate.The smaller inhibition function and the greater increasing effect were presented with the higher proportion of organic carbon addition.Secondly,organic-inorganic fertilizer increased the content of carbonate and carbonate-bound calcium.The treatment without straw addition and straw addition decreased the carbonate content,and the difference was significant compared with the treatment of organic-inorganic fertilizer.There was no significant difference in the content of carbonate-bound calcium.The exchangeable calcium content of all treatments increased firstly and then decreased to the initial value with incubation time increasing,and its content of the organic-inorganic fertilizer treatment was significantly lower than that of the other treatments.Carbonate decomposition of the Chernozem is also a source of CO₂ release.The effect of freeze-thawing cycles on soil carbonate content is not obvious.Thirdly,organic materials addition can cause the large microaggregates to transform into aggregates and small microaggregates,and the proportion of large microaggregates is still dominant.Straw addition is beneficial to the formation of aggregates,and fertilizer addition is more favorable to the formation of small microaggregates.Compared with large microaggregates,aggregates and small microaggregates exhibited stronger potential ability of carbon sequestration,but due to less content in Chernozem,its sequestration contribution was lower.Exogenous carbon enters large grain-size?micro?aggregates preferentially,and the higher proportion of organic carbon was added,the more carbon content increased.The potential mineralization ability of grain size from large to small decreases gradually.Freeze-thawing cycles had some influence on the distribution and mineralization of soil microaggregates and its organic carbon,but not regularly.Forthly,the addition of straw and organic-inorganic fertilizer increased the content of active organic carbon,and reduced the stability of soil carbon.The content of easily oxidized carbon increased firstly and then decreased and tended to be stable,and had small difference with the content of initial incubation.The water soluble organic carbon was increased,and especially for organic-inorganic fertilizer addtion,while promoting effect of straw addition was smaller.The mineralization intensity of easily oxidized carbon was significantly higher than that of water soluble carbon,and the mineralization ratio of easily oxidized carbon with straw addition was higher than that of fertilizer treatment.Freeze-thawing cycles had certain influence on active organic carbon,and there was less difference.Finally,in conclusion,the addition of organic materials can increase the released amount of CO₂ significantly in a short period of time,but also increase the content of organic carbon and active organic carbon over a long period of time,or decrease the declined rate of that of the Chernozem.The structure of soil aggregates develops well and the soil environment is improved.Freeze-thawing cycles can inhibit the relaease of CO₂ of the Chernozem in a short time,but in the longterm,the inhibition function is reduced,and the soil indexes can be returned to the normal level of each treatment.