Stability Of Soil Aggregates Under Different Land Use Patterns And Its Relationships With Organic Matter And Iron-aluminum Oxides

In red soil on China southern region, due to the strong human intervention and soil tillage intensity, soil structure stability drops quickly, which brings about other proplems such as soil erosion, fertility reduction and soil harden sclerosis. Soil aggregates play an important role in soil structure stability. In order to find out factors influencing stability and destruction of soil aggregates, to achieve purpose of reducing soil erosion process and inhibiting the deterioration of cropland environmental ecology system, this research using Quaternary red soil collected in Hunan, Hubei and Jiangxi provinces from different land uses, studied distribution and stability of soil aggregates, mean weight diameter (MWD) and percentage of aggregate destruction (PAD) by dry sieving and wet sieving, analyzed the relationships between distribution and stability of soil aggregates with organic matter under different land uses, chosed the typical samples (paddy, forestland and dry land) on the basis of the characteristics of soil samples composition of humus and iorn-aluminum oxide from their relationships with stability of aggregates basis on this charcteristical of soil samples. The results indicated that:(1)At different land use patterns, soil aggregates was almost size of>5mm with dry sieving, with a proportion of55%, and the proportion was highest(75.4%) in the paddy use pattern, the MWD was paddy>forestland>tea garden> dry land> orchard. While it was dominated of <0.25mm size by wet sieving, but for paddy and forestland size of>5mm was the most (46.0%and42.8%, respectively),39.2%and36.1%higher than that for dry land, the MWD was forestland>paddy>tea garden> dry land> orchard.(2)The PAD at different land use patterns followed by dry land>orchard>paddy>tea garden>forestland. Except orchard and paddy, PAD at other land uses was negatively correlated with organic matter content and MWD by wet sieving.(3)Different land use patterns affected soil organic matter content greatly, and the order of organic matter content was followed as below:paddy>forestland>tea garden>dry land>orchard. Soil aggregates MWD of different land use patterns was positively correlative with organic matter content no matter by dry sieving or wet sieving. The soil organic matter content was extremely positively correlative with aggregates with>5mm, negatively correlated with1-0.5mm and0.5～0.25mm sizes at different land uses, while it didn’t correlated with water-stable aggregates with5～2mm、2～1mm sizes.(4)Humus C in all sizes’ aggregates was positively correlated with the MWD by dry sieving, and the MWD by wet sieving only correlated with humus C in aggregates with>5mm and <0.25mm sizes, while PAD was not significantly correlated with humus C in all sizes. MWD by dry sieving was only correlated with humic acid C in0.5～0.25mm size significantly and PAD had no significant relationship with humic acid C in all sizes. Fulvic acid C was significantly correlated with dry sieving MWD in all sizes expect5～2mm, while correlated with wet sieving MWD only in size of0.25mm, and PAD also was not significant correlated with fulvic acid C in all sizes. The effect of land uses on the concents and distributions of humus, humic acid and fulvic acid were significant, with a order of paddy>forestland>dry land.(5)Free-stuff and amporphous iron-aluminum oxides both had no significantly relationship with MWD and PAD in all sizes’aggregates. This indicated that the effect of iron-aluminum oxides on the formation and stabilization of macroaggregets was negligible and its effect maight be just on the microaggregates. Moreover, land use patterns also did not affect the distribution of different iron-aluminum oxides significantly.