Effects of returning crop straw into Vertisol on the physical and chemical prope rties and availability of manganese, zinc, copper

Field trials and laboratory incubation experiments were carried out to study the effects of returning crop straw into Vertisol on its physical and chemical properties and availability of Cu, Zn and Mn. The results show that returning crop straw can decrease the soil bulk density and increase the soil porosity,especially the soil capillary porosity. The contents of humic acid and fulic acid in soil are also increased obviously. The increasing content of humic acid has a good effect on the activity increase of soil organic matter and on the soil fertility improvement. It is found that compared with applying chemical fertilizer alone, returning crop straw with applying chemical fertilizers raises the contents of exchangeable form of manganese, zinc and copper in soil by 11%, 21% and 41%,respectively; the contents of organic matter bound forms of manganese and copper are increased by 19% and 103%, respectively.Soil incubation experiment results show that when the powder straws is incubated with Vertisol for 3 months, the contents of available manganese and copper are increased by 21% and 27%, respectively.