Effects Of Long-Term Fertiizer Management On Micronutrient Status Of Soiland Crops On Lou Soil In Guanzhong Plain

The effects of fertilizer management regimes on status of iron, manganese, copper and zinc in soil and crops were investigated based on the 18-year and 28-year long-term experiments on Lou soil in Guanzhong Plain, Shaanxi province, China. The 18-year fertilizer management regimes included: (1) control without appling any fertilizer (CK), (2) application of chemical nitrogen(N), phosphorus(P) and potassium(K) fertilizers (NPK), (3) application of NPK chemical fertilizers plus corn stalk (SNPK) and (4) application of NPK chemical fertilizers plus dairy manure (MNPK). The 28-year fertilizer management regimes included (1) control without appling any fertilizer (CK), (2) application of organic manure (M2), (3) application of chemical nitrogen and phosphorus fertilizers (N2P2), (4) application of nitrogen and phosphorus chemical fertilizers plus dairy manure (M2N1P1 and M2N2P2). The main results obtained were as follows:1. Soil available iron, manganese, copper and zinc contents in ploughed layer (0-20 cm) were significantly affected by fertilizer management regimes. It showed that the contents of soil available Fe, Mn, Cu and Zn under CK, Fe, Cu and Zn under NP and Fe, Mn and Zn under NPK were close to be deficient. While on M, SNPK, MNPK and MNP treatments, above trace elements were in abundance. In term of the spatial variation in the soil profile, compared to CK, application of SNPK, M, MNP and MNPK can significantly increase the contents of iron, manganese, zinc, copper at 0-10cm layer and also had the tendency to increase at layers below 10 cm. Application of chemical fertilizers (NP and NPK) also increased available contents of Fe and Mn, and had no effect on soil available Cu and Zn at 0-10cm layer, soil available Fe, Mn, Cu and Zn at deeper layers were similar between treatments.2. Compared to CK, the contents of iron and zinc in wheat and maize seedlings were more or less reduced under 28-year application of NP, M and MNP, but in all treatments, the contents of iron, manganese, copper and zinc in crops were in the rational range. The contents of copper in wheat flag leaf and the one below under M and MNP were lower than the critical concentration. The contents of zinc in wheat flag leaf and the one below in all treatments were also below the critical concentration, as well as in cob leaf of maize under NP,M and MNP. The contents of iron, zinc, copper in wheat and maize grain were decreased in fertilized treatments except under M2N2P2 relative to CK treatment. Based on above results, M2N2P2 was the best one among the tested fertilizer management regimes for wheat-maize rotation system.3. The contents of iron, manganese, zinc and copper in wheat and maize seedlings were affected by 18-year different fertilizer management regimes. The contents of iron, manganese and copper in seedlings were in the rational range, except Zn in wheat seedlings under NPK, and in maize seedlings under NPK, SNPK and MNPK, which was in deficient. Similar to seedling stage, the contents of iron, manganese and copper in wheat flag leaf and the one below and cob leaf of maize in all treatments were in abundance. However, the contents of zinc in those leaves showed Zn deficiency. As a result, the contents of zinc in wheat and maize grain were also low, especially in fertilized treatments. The apparent balance sheet indicated that input of manganese, copper and zinc did not compensate the uptake by wheat and maize, which led to depletion of those elements under NPK, except for iron; the input of iron, manganese and copper were higher than the output by crops under SNPK, except zinc which gave the negative budget value. On MNPK treatment, all four elements showed positive budget values.. Based on soil analysis and crop micronutrients'status, we suggested that micronutrient, such as Zn, should be applied in wheat-maize cropping system when chemical fertilizers and/or combination with crop straw/stalk applied. Although organic manure combined with chemical fertilizers did significantly increased levels of soil micronutrients, Cu in wheat and Zn in maize were still in deficiency. Therefore, it needs further study to optimize combination of organic manure and chemical fertilizers to improve crop's micronutrient status.