Effect of cropping system on the manganese in lime concretion fluvo-aquaic soils

The influences of cropping system changing from upland farming to the rotation of rice and upland farming on the total content, morphology and availability of manganese in lime concretion fluvo-aquic soils were studied. The results show that the contents of manganese in the residual, crystalline iron oxide bound, amorphous iron oxide bound, manganese oxide, organically bound and carbonate bound account for 27.19%～46.26%, 10.48%～21.65%, 2.76%～12.28%, 17.39%～26.53%, 10.61%～24.57%and 0.16%～8.35%of the total manganese content in soils,respectively. With the change of cropping system from upland farming to the rotation of rice and upland farming, manganese is released from crystalline iron oxide, and further transferred into organic matter and amorphous iron oxide or exists solely as manganese oxide. These result in the increase of the movability and availability of manganese for crops, leading to the decrease of the total content of manganese and the decreasing range that is 8.77%in the tilled layer of soils for rotation of rice and upland crops.