Study On The Status Of Organo-Mineral Complexes And Character Of Fertility In Dryland Of Purple Soils

The soil organo-mineral complexes, formed by intimate association of organic matters or humic substances and mineral, is one of the fundamental features that distinguishes soils from their geological parent materials, and effects on the nature of soil aggregate, and the amounts and characters of soil particle aggregation is closely related to soil fertility. By way of collecting soil samples outdoors and analysis indoors and using the dry land soils developed from purple soils as research materials, this paper investigated status of organo-mineral complexion, Characters of aggregation and soil fertility for discussing the relationship among them under different land treatments, and the factors that influencing the amounts and characters of organo-mineral complexion and soil aggregation and restricting status of soil fertility, the main results were as follows:There were remarkable differences of status and activity of Fe oxide and aluminum oxide in dry land soils developed from different parent soils and under different utilizations. The effect of free iron on soil complexion differed with soil types, and there was no notable correlativity between free Fe and amorphous Fe. But it was controlled by soil pH. And differences of free and amorphous Fe were distinct. The distributions of composed iron were consistent with that of free iron. Both contents of amorphous aluminium and composed aluminium were very low, and changed a little. The content of organic matter was positively related with degree of organo-mineral complexing, which showed that there was direct affiliation between them. There was notable relation between content of organo-mineral complexing and degree of organo-mineral complexing, which implicated the high degree of complexion of organic matter in soils, most of the organic matter composed organo-mineral complexes by combing the mineral colloids. The loosely and tightly combined humus accounted for most of organic matter in complexes, and the ratio of loosely and tightly combined humus changed with type of parent rocks and land utilizations. The different status of organo-mineral complexion sufficiently reflected the differences of aggregating conditions of organic matter in purple soils. The structure of activity of humic was affected by utilization and soil forming mother rock. As the human behavior frequently disturbed the soil, humicmolecules weight became less; polycondensation degree and aromatility of soil humic deceased, and its activity became intense.Utilization methods influenced aggregation degree of microaggregate of purple soil, the aggregation degree were in such order: grassland>forestland>garden plot>cropland, aggregation degree of microaggregate in soil developed from Jas group was least, and that of J3S group was maximal. There were evident differences of distribution of soil particle aggregation in soils developed from purple soils. The big soil particle aggregation occupied most of soil particle aggregation and they represented better character of aggregation. The water-stability of soil particle aggregation changed a lot because of different parent materials. The organic matter influenced >0.25 mm soil particle aggregation and >0.5 mm water-stable soil particle aggregation slightly and played an important role in the aggregation of >5 mm water-stable soil particles. The percentage of aggregates destruction were remarkably negatively related with content of >5 mm water-stable soil particle aggregate, and ultimately negatively related with >0.25 mm water-stable soil particle aggregate, which meant the content of water-stable soil particle aggregate dropped as the rise of percentage of aggregates destruction, the loosely Fe took a role in increasing content of water-stable soil particle aggregate. The main factor that affecting content of >0.5 mm water-stable soil particle aggregate was percentage of aggregates destruction, whereas organic matter and percentage of aggregates destruction were the dominating matters that influencing content of >0.25 mm water-stable soil...