Effects of long-term fertilizer management regimes on availability of soil micronutrient elements

The effects of fertilizer management regimes on contents of soil available iron, manganese, zinc and copper in the ploughed layer (0-20 cm) and soil profile (0-60 cm) were investigated based on the 28-year long-term experiment on Lou soil in Guanzhong Plain, Shaanxi province, China. The fertilizer management regimes included: control without applying any fertilizers (CK), application of organic manure (M2), application of chemical nitrogen and phosphorus fertilizers (N2P2), and application of nitrogen and phosphorus chemical fertilizers plus dairy manure (M2N1P1 and M2N2P2). The results show that in the ploughed layer the contents of soil available Fe, Mn, Cu and Zn under the CK and the contents of available Fe, Cu and Zn under the N2P2 are close to be deficient, while in the M2, M2N1P1 and M2N2P2 treatments, trace elements are in abundance. In term of the spatial variation in the soil profile, compared to the CK, the M2, M2N1P1 and M2N2P2 can significantly increase the contents of iron, manganese, zinc, copper in 0-10 cm layer and also have the increasing tends in soil available contents of Fe, Mn, Cu and Zn at layers below 10 cm. The N2P2 application could increase available contents of Fe and Mn in 0-10 cm layer, and has no effects on the soil available Zn, and decrease the content of available Cu relative to the CK. However, the effects of the N2P2 treatment on soil available Fe, Mn, Cu and Zn at deeper layers are not significant. According to the results, it is suggests that without applied any fertilizer or only applying N、P fertilizers，micro-element fertilizers should be appropriately applied to meet the need of crop growing, while only applying organic manure as this experiment, certain iron and manganese should be applied. The application of nitrogen and phosphorus chemical fertilizers plus dairy manure could meet requirement of micronutrients under winter wheat-summer maize cropping system on Lou soil.