On Variation of the Distribution and Forms of Cu,Zn,Ni,and Mn in Soil Profile

Variations of the forms of Cu,Zn,Ni and Mn in calcic concretion black soil profile and farming practices on its effects were studied by using a seven-step sequential extraction procedure.The results showed that relative amounts of exchangeble,organic bound and amorphous iron oxide bound Cu,Zn,Ni and Mu decreased and of manganese oxide bound and residual Cu,Zn,Ni and Mu increased with the deepenning of the soil profile.The distribution of relative amounts of carbonate bound Zn,Cu,Ni and Nu in the soil profile was not consistent,some increased and some decreased with the deepenning of the soil profile,and were also affected by farming practices.Crystalline iron oxide bound Cu,Zn,Ni and Mu could be divided into two types,relative amounts of Cu and Ni were comparative stable,however the Zn and Mu were remarkably changeable.Cultivation and rotation of rice and upland farming enable the less available fractions of those microelements transformed into more available fractions to crops.