Effects Of Water Tillage Maturity Years On Organic Carbon Components And Humus In Paddy Soils Of Different Parent Soils In Cold Region

In order to explore the effects of water tillage ripening years on the content of soil organic carbon components and humus content and structural characteristics.Three soil types of meadow soil parent paddy soil,meadow black soil parent paddy soil and gleyed albic soil parent paddy soil in Sanjiang Plain were studied,and the same type of upland soil was used as control.By studying the changes in the content of soil organic carbon components and the contents of humic acid（HA）,fulvic acid（FA）,humin（Hu）and the structural characteristics of HA and FA under different ripening years after the conversion of dry land to paddy field,the changes in soil fertility characteristics of paddy fields with different soil types in cold regions were explored.The main findings are as follows:1.After reclamation from dry land to paddy field,the content of easily oxidized organic carbon in paddy soil of meadow soil parent soil and meadow black soil parent soil decreased with the extension of paddy field maturity.In the meadow soil parent soil paddy soil,the content of easily oxidized organic carbon in each layer of soil was the highest at 6a;the content of soil readily oxidizable organic carbon in the soil core of the parent soil paddy soil increased with the increase of ripening years,and the rate of increase slowed down in the later stage of soil ripening.2.After reclamation from dry land to paddy field,the content of soluble organic carbon in meadow soil parent soil paddy soil and gleyed albic soil parent soil paddy soil decreased first and then increased with the increase of ripening years;the content of particulate organic carbon in paddy soil of meadow soil parent soil and gleyed albic soil parent soil decreased with the extension of maturation years.Except for the gleyed albic soil parent soil paddy soil,the soil microbial biomass carbon content of each layer decreased first and then equilibrated with the extension of maturation years,and the meadow black soil parent soil paddy soil decreased the most.The soil microbial biomass carbon content of the three soil types was lower than that of the control upland soil.The meadow soil parent soil paddy soil,the gleyed albic soil parent soil paddy soil,and the meadow black soil parent soil paddy soil decreased by 6.0%,4.1%and8.6%at 23a,25a and 35a,respectively.3.After reclamation from dry land to paddy field,the content of light and heavy organic carbon in topsoil,meadow black soil paddy soil and gleyed albic soil paddy soil decreased with the increase of soil ripening years.The soil heavy organic carbon in meadow soil parent soil paddy soil has been in equilibrium since it was changed to water tillage,and the range of change is 0.05 to 0.18g·kg^-1.4.Among the three soil types,the contents of HA,FA and Hu in each layer of soil decreased first and then increased with the extension of curing years.From the perspective of soil profile,the change of topsoil is the largest,and the change of subsoil is not obvious,mainly to reduce;from the perspective of different components,HA changed most obviously,and FA changed slowly.From the perspective of different soil ripening years,the main changes are within 6～20a.The degree of humification of paddy soil was lower than that of dry land soil.The PQ value of topsoil increased first and then decreased with the increase of ripening years.The degree of soil humification in the plough layer of paddy field was greater than that in the plow layer and the subsoil layer.The degree of soil humification was the highest at 10a,10a and35a.5.During the gradual ripening of paddy soil,the contents of carboxyl,carbonyl and phenolic hydroxyl groups of HA in various soils increased year by year,the degree of oxidation and aromatization increased,the structure of HA was complicated.TheΔlg K value of FA decreased with the increase of soil maturation years,and the internal structure of FA was simpler than that of HA.In the early stage of ripening,the condensation degree of HA and FA molecules in the paddy soil of meadow soil parent soil was faster and the aromaticity was stronger,while in the early stage of ripening,the condensation degree of HA and FA molecules in the paddy soil of meadow black soil parent soil and the paddy soil of gleyed albic soil parent soil was the highest,and the oxidation degree was the highest.The E4 values of HA in all types of soils increased with the extension of curing years,and the molecular complexity and condensation degree increased.With the extension of water tillage maturity,the humification process of soil accelerated,and the oxidation degree and aromaticity increased.Theδ¹³C value of HA in the central soil layer of different profiles was the highest,theδ¹³C value of HA in the subsoil was the highest and significantly lower than that of FA.