Effects Of Soybean Continuous Cropping On Soil Combined State Of Humus And Composition In Black Soil

In this plot experiment, soil humus components and combined states of humus were measured fromdifferent size fractions mechanical stability and water-stable aggregates in different soybean continuouscropping years. Results showed that:1.After soybean continuous cropping, soil nutrients, microbial and enzyme activity changed as follows:black soil available nitrogen and total nitrogen content increased, potassium content decreased; total nitrogencontent increased. The number of bacteria significantly reduced after soybean continuous cropping, on thecontrary, the changes in the number of fungi the performance of cropping process is higher than the number ofpositive fungal crop, this change with the diffirent change in the number of actinomycetes. After soybeancontinuous cropping, soil urease, invertase, phosphatase, hydrogen peroxide activity decreased; whilecellulase, polyphenol oxidase and protease activity was gradually increased. Soybean continuous croppingaccelerated the decomposition and transformation of organic matter. with increasing soybean continuouscropping years,the humus (HS), humic acid (HA) and humic acid/fulvic acid ratios (H/F) decreased in theorder of rotation> continuous1> continuous3. While the fulvic acid (FA) increased in the order ofcontinuous1<rotation <continuous3.Heavy fraction organic matter and complex organic matter decreasedwith increasing soybean continuous cropping years, while heavy fraction content and complex degreedecreased in the order of continuous3> rotation>continuous1. Soil pH decreased with increasing soybeancontinuous cropping years. The E4/E6of soil humic acid decreased with increasing soybean continuouscropping years. In summary, soybean continuous cropping is not conducive to the accumulation and updatingof soil humus components.2.The loosely combined-HA and stably combined-HA increased with the increased continuous cropping.While the stably combined-HA decreased with the increased continuous cropping. HS proportion of totalcarbon in loosely combined humus and stably combined humus decreased in the order of continuous3>continuous1>rotation, respectively. While the unitedly combined humus and tightly combined humusdecreased in the order of rotation>continuous1>continuous3, respectively. The HA, FA and H/F increasedwith the increased continuous cropping in loosely combined humus. No difference between the unitedlycombined HS and continuous cropping appeared. While the HA and H/F increased with the increasecontinuous cropping in stably combined HS. With respect to continuous3, the loosely combined-HA ofrotation resulted in significant increase of E4/E6.While the E4/E6of stably combined-HA from continuous3showed higher than rotation. In summary, continuous3could improve the ratios of loosely to stably combinedHS and stably to tightly combined HS. The unitedly combined HS transformed into loosely combined HS and stably combined HS with the increased continuous cropping and therefore decreased soil fertility.3.>5mm size fraction particles of soil mechanical stability of aggregates decreased with increasingsoybean continuous cropping years. With increasing soybean continuous cropping years, the looselycombined HS of>5mm size fraction and <0.25mm size fraction increased The loosely combined HA of>5mm size fraction increased, the loosely combined FA of>5mm size fraction and2~0.25mm size fractionincreased. With increasing soybean continuous cropping years, the unitedly combined HS mainly distributedin>5mm and5~2mm size fraction.The unitedly combined HS of5～2mm and2～0.25mm size fractiondecreased,the content of <0.25mm size fraction first increased and then decreased. The unitedly combined HAof>5mm size fraction first decreased and then increased. With increasing soybean continuous cropping years,The unitedly combined FA of2~0.25mm decreased. The stably combined HS of>5mm size fraction and5~2mm size fraction first increased and then decreased. The stably combined HS of2~0.25mm size fractiondecreased. The stably combined HA of>5mm size fraction and5~2mm size fraction first increased and thendecreased. The stably HA of2~0.25mm size fraction decreased. There are some differences change incombined HS of between various size aggregates.4.Water-stable aggregates content of2~0.25mm size fraction in rotation was higher than soybeancontinuous cropping, continuous1than continuous3. Organic carbon content of various size aggregatesdecreased in the order of2～0.25mm size fraction>0.25~0.035mm size fraction>(<0.053mm sizefraction)>(>2mm size fraction). With increasing soybean continuous cropping years, the loosely combinedHS of>2mm size fraction and <0.053mm size fraction decreased. The loosely combined HS of2~0.25mmsize fraction increased. The loosely combined HA of>2mm size fraction and <0.053mm size fractiondecreased. The loosely combined FA of2~0.25mm size fraction increased. The unitedly combined humuscontent of2~0.25mm size fraction was higher than other size fracions. The content of <0.053mm sizefraction was the lowest. With increasing soybean continuous cropping years, the unitedly combined humicacid content of2~0.25mm size fraction and0.25~0.053mm size fraction decreased. The unitedly combinedFA of0.25~0.053mm size fraction also decreased. With increasing soybean continuous cropping years, thestably combined HS of>2mm size fraction decreased. The stably combined HA of0.25~0.053mm sizefraction decreased. The stably combined FA of>2mm size fraction and0.25~0.053mm size fraction decreased.The tightly combined HS of>2mm size fraction and2~0.25mm size fraction also decreased with increasingsoybean continuous cropping years.5. Elemental analysis results show that with increasing soybean continuous cropping years, the O/C ratioof humic acid decreased, the oxidation degree of soil humic acid reducted. The C/H of soil fulvic acid washigher in continuous cropping than rotation; while O/C ratio, on the contrast, are higher than continuouscropping,the condensation degree of continuous cropping increased, but the degree of oxidation decreased. Onthe contrary, the changes of C/H, O/C ratio was different in humin. the condensation degree of continuous cropping decreased, but the degree of oxidation increased. Differential thermal analysis showed that thealiphatic compounds began decompose after continuous3in soil humic acid. The condensation degree of soilhumic acid was higher in continuous1,while the condensation degree of soil humic acid was lower incontinuous3.The aliphatic compounds of fulvic acid begans to decompose after continuous3, aliphaticstructures decreased. The condensation degree of humin increased, the change was same with fulvic acid.