Influences on compositions of clay minerals in soil aggregates by the long-term returning to the field of Chinese milk vetch and the combined application of chemical fertilizer
Based on the experiment of long-term application of Chinese milk vetch-double cropping rice rotation in Nanxian County,Hunan Province,an experiment was conducted in this paper to investigate types,contents and distribution characteristics of clay minerals in various clay fractions(100-2000nm,25-100 nm)within four kinds of soil aggregates including the large aggregates(＞250 μm),small aggregates(53-250 μm),silty.clay aggregates(2-53 μm),and micron aggregates(＜2 μm)in soils which were respectively treated by using the single application of Chinese milk vetch(MV),single application of chemical fertilizer(Fl00),and combined application of the MV and chemical fertilizer(MV+F100).Results show that there are similar mineral compositions in different sized aggregates within soils which were treated by using three treatments.They are mainly illite and kaolinite,with a small amount of vermiculite and 1.4 nm sized transition minerals.Compared with the micron aggregates(＜2 μm)in treated soils by using the MV and the MV+F100,the 100-2000 nm sized kaolinite contents of large aggregates(＞250 μm),small aggregates(53-250 μm)and silty clay aggregates(2-53 μm)in those treated soils are relatively low,while vermiculite contents of those respective aggregates are relatively high.Compared with the soil treated by using the MV,the relative content of illite in the micron aggregates(＜2 μm)in the soil treated by using the MV+F100 is obviously increased,and the relative contents of vermiculite in various sized aggregates of soils treated by using the MV+F100 are obviously increased.With the decrease of particle sizes of clay minerals from 100-2000 nm to 25-100 nm and the decrease of types of clay minerals,the relative contents of illite are increased significantly,but those of kaolinite are decreased and the crystallinities of kaolinite are more poorer.Compared with treated soils by using the F100,the silica-alumina ratios of 100-2000 nm sized particles within various sized aggregates in treated soils by using the MV+F100 are significantly reduced,with the appeared phenomenon of desiliconization and alumina-enrichment.
Chinese milk vetch returning to the fieldchemical fertilizeraggregates in the soilclay mineralparticle
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