| As one of the important sources of soil organic carbon,the decomposition process of crop residues has a great influence on the accumulation of soil organic carbon.Due to the difference of growing environment,the content of each component in crop residues is very different,which not only appears in different crop residues,but also in different organs of the same crop.Crop residues in different parts will decompose to different degrees due to different carbon-containing components.These differences will have different effects on decomposition mineralization and fixed accumulation of soil organic carbon.Therefore,in order to clarify the decomposition characteristics of maize residues from different parts and the effects of returning maize residues on carbon turnover in black soil,In this experiment,7 components of maize plant leaf residues(LB),leaf sheath residues(LS),bract residues(PB),stem bark residues(SB),stem pulp residues(SP),root stubble residues(R)and whole stalk residues(mixture of leaves and stems)(WS)with different characteristics were selected as decomposition materials.The decomposition characteristics of maize plant residues in different parts were studied through indoor culture and outdoor decomposition tests,and the differences of maize residues in different parts during decomposition were clarified.Taking black soil as the research object,different parts of corn plant residues were added to the soil for pot experiment.Through analyzing the dynamic changes of soil basic physical and chemical properties,soil active organic carbon component content and soil humus component content changes of different parts of corn plant residues.The effect of decomposition of different parts of maize on soil organic carbon mineralization and fixation was studied.The results show that:(1)Laboratory culture experiment was conducted to explore the decomposition transformation characteristics of maize plant residues from different parts by dynamically monitoring the dynamic changes of total organic carbon content,cellulose and hemicelluellulost content,hum-like composition and structural changes in the process of decomposition.The results showed as follows: with the prolongation of decomposition time,the content of organic carbon in the residues of different parts of maize plant was significantly reduced,the content of carbon in the residues of stem bark and root stubble was significantly higher than that in other parts,and the content of organic carbon in the residues of leaves decreased the most,and the carbon release rate was 23.41%.From the content of organic components,the content of cellulose and hemicellulose in the stubble residue was the lowest,and the decomposition was the slowest.The content of cellulose and hemicellulose in stem skin residues was the largest,but the decomposition rate of cellulose and hemicellulose before and after decomposition was second only to stubble residues.In addition,the cellulose and hemicellulose contents of the three leaf residues were low,but the decomposition rate of cellulose and hemicellulose of the three leaf residues was the highest compared with other residues,and the decomposition rate of cellulose and hemicellulose of the whole straw residues was between stem residues and leaf residues.The relative content of humus component WSS in maize residues from different parts increased significantly,while the relative content of HLM showed a downward trend.However,due to the differences in the structure and chemical components of residues in different parts,the promotion time of humus synthesis is different.The decomposition degree of HAL and FAL was higher in the early stage of decomposition than in the more difficult parts,and the decomposition and conversion between Hal and FAL occurred earlier under the action of microorganisms.At 120 days after the end of the test,the PQ values of residues in different parts increased,and the straw residues increased the most,by 17.25%.Therefore,there are differences in the formation sequence of HA and FA in different parts of residual humus,as well as their respective characteristics and content changes in the further humification process.In addition,the composition of functional groups in maize residues from different parts of the plant is similar.During the whole process of decomposition of crop residues,carbohydrates,amides and sugars gradually decrease,the contents of hydroxyl,ketone carbonyl,methyl,methylene and methylate gradually decrease,carboxyl groups increase,and carboxyl salts are formed.The aliphatic properties of compounds in different parts of residues decrease and aromatic properties increase.(2)The mass loss rate of maize residues in different parts showed a trend of rapid increase in the early stage and slow increase in the late stage.0-60 d is the rapid decay period,and the cumulative mass loss rate is up to 48.40%.Leaf residues were the most easily decomposed,followed by stem pulp residues.Leaf sheathing surrounded the base of stem and leaf,and the mass loss rate of straw residues was significantly lower than that of leaf residues and bracts.The mass loss rate of whole stalk residues was higher than that of root stubble residues and stem peel residues,which were the most difficult to decompose.The structure and chemical components of residues in different parts of maize plant were different,and the characteristics of nutrient release were different.The more nutrient content was,the more nutrient was released,and the release rate of nutrients in different parts of maize plant was K>P>N.Among them,the release rates of nitrogen,phosphorus and potassium of three leaf residues were significantly higher than those of other parts at different decomposition time nodes,and the release rates of root stubble residues were the lowest,followed by stem bark residues.(3)Compared with CK treatment without straw residue returning,soil electrical conductivity and p H value were significantly increased under different parts of corn residue returning treatments.The return of residues from different parts of maize plant increased the contents of soil alkali-hydrolyzed nitrogen,available phosphorus and available potassium.However,due to the differences in the composition of residues from different parts,the effects of residues from different parts on the content of soil available nutrients were different.Among them,leaf residues of maize plant had a greater effect on the content of soil available nutrients than residues from other parts.The contents of soil alkali-hydrolyzed nitrogen were significantly affected by stubble residues and stem bark residues,while the contents of available potassium were not significantly increased.At the later stage of decomposition,the effects of different parts of residues returning to the field on soil nutrients gradually did not differ.(4)Compared with CK treatment without straw residue returning,the contents of soil organic carbon,microbial biomass carbon,easily oxidized organic carbon and particulate organic carbon were significantly increased by all treatments with different parts of corn residue returning to field.During the decomposition period,the treatment with straw residues was always higher than that with root stubble.The leaf residues were higher than stem residues in the first 90 days,and lower than stem residues in the later period,and the straw residues were between stem and leaf.At the end of culture,the content of active organic carbon components in each treatment was significantly increased compared with that at the beginning(0 d).The dynamic change of active carbon components in soil during decomposition mainly depended on the difference of chemical components in different organs.The residues in the easily decomposed parts were more conducive to supplement the amount of active carbon in soil,and were the most sensitive to the change of soil organic matter.Redundancy analysis showed that soil SOC was positively correlated with CPI and CPMI.Soil EOC,POC,MBC were positively correlated with soil CPMI.There was a significant negative correlation between soil Kos and soil organic carbon.(5)Compared with CK treatment without straw residue returning to field,soil humic acid,fulvic acid and humin carbon contents of soil were effectively and significantly increased by different parts of corn residue returning to field,and humus composition was improved to simplify its structure.Among them,the processing of SB,R and WS has the best effect compared with other processing.The soil PQ value was significantly increased by various treatments,and the highest value was obtained by R treatment.Compared with perishable leaf residues,stem residues and root stubble which were difficult to decompose were more likely to accumulate in soil,and the degree of humification was higher.The ΔlgK values of humic acid and fulvic acid were higher than those of CK in all treatments.The decomposition of corn residues could promote the activation of soil humic acid and fulvic acid,and the molecular structure of humic acid and fulvic acid in soil tended to be simplified and rejuvenated. |
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