| Because of water movement and the changes of chemical condition, the substance deposited on the surface of soil structure (cutans) in P and W horizon. As the new growth of soil which formed in the process of soil forming and development, soil cutans is not only the mirror of the structure characteristics in process of soil forming and development but also the information carrier of elements leaching transport in soil. Soil cutans have the important genesis significance. As the most important multivalent element of soil, iron and manganese are the most sensitive to the redox condition. Both the content and form of them are important to the formation of cutan. By studying the morphological characteristics of iron and manganese could give an insight into the substance composing and formation characters of cutans on soil structual surface, it could be used as the criterion for studying the occur,process of development and correlated condition on paddy soil.The soil cutans, which sampling from the typical profile of paddy soil in Chongqing were studied. The morphological characteristics of iron and manganese, the effect of iron, manganese on phosphorus,copper and zinc in cutans were also studied to the composition and cause of formation of the soil cutans, to achieve to have a general understanding on the soil cutans in paddy soil. The main results as follows:(1)The pH of tested soil cutans is 6.0～7.8, higher than the matrix soils. The content of organic matter tested soil cutans is 7.46～26.7g/kg, they were higher than the content of tested matrix soils, and the difference reached a greatly obvious level (|t|=5.11,p＜0.0l).(2) The total iron content of tested soil cutans is 18.8～43.7g/kg, they are significantly higher than the content of the matrix soils(|t|=5.89, p＜0.01). The content of free iron, amorphous iron and organic chelated iron are 3.99～11.5g/kg, 2.15～9.44g/kg, 0.0502～1.48g/kg respectively, they are all significantly higher than the content of matrix soils(p＜0.01). Close to matrix soils, the free degree of iron in soil cutans is 14.2%～31.7%. Taking one with another, the activation degree of iron (27.4%～90.7%) is higher than matrix soils (|t|=2.18,p＞0.05).(3) Generally speaking the contents of total manganese (136～1178mg/kg), free manganese (37.0～859mg/kg), amorphous manganese (33.7～676mg/kg) and organic chelated manganese (24.3～484 mg/kg) are all higher than the content of matrix soils (p＞0.05).The the free degree of manganese is 27.3%～87.0%, and the activation degree of manganese is between 63.7% and 90.9%.The average content of total iron is 66.6 times of the total manganese in soil cutans. According to the distribution of iron and manganese, the soil cutans are classified into two types in this paper: one is iron-manganese cutans, which both the content of the total iron and total manganese higher than matrix soils. The other is iron cutan, which the the content of the total iron higher than matrix,but the total manganese lower than matrix soil or have no remarkable difference with matrix soils.(4) The content of total nitrogen, total phosphorus and total potassium in soil cutans are 0.580～1.71g/kg, 0.197～0.836g/kg, 9.35～16.6g/kg respectively, and the content of total nitrogen and total phosphorus are significantly higher than the content of the matrix soils (p＜0.01). The total copper and total zinc content of soil cutans are also higher than the content of matrix soils, and the difference of total zinc content was remarkable (|t|=2.23,p＜0.05).The content of total phosphorus is remarkable correlated with the content of total iron in tested soil cutans, while content of available phosphorus is negatively correlated with the content of total manganese. The copper content of soil cutans is remarkable correlated with the iron and manganese content. Generally speaking, the copper and manganese have the better symbiotic relationship, while the zinc and iron have the better symbiotic relationship. |
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