Abstract: Clarifying the differences in soil selenium and zinc forms of wheat growing areas can provide theoretical basis for improving wheat quality and production efficiency and facilitate functional agriculture development. In this study, soil samples with high, medium and low levels of selenium and zinc were collected from typical wheat planting areas in Shanxi Province. The contents of soil selenium and zinc, soil organic matter (SOM), cation exchange capacity (CEC) and soil mineral composition were measured, and the differences of selenium and zinc forms in different levels and the influencing factors were further analyzed. The results showed that the sequence of different selenium forms was organically bound state (39.1%-53.8%) > residue state (33.5%-48.9%) > exchange + carbonate bound state (5.2%-5.9%) > Fe-Mn oxide-bound state (3.4%-4.5%) > water soluble state (1.0%-3.1%). The zinc content of different forms in all samples was residue state (81.0%-86.3%) > organically bound state (6.5%-8.1%) > Fe-Mn oxide-bound state (6.2%-7.5%) > carbonate-bound state (0.7%-1.9%) >exchange state (0.3%-1.5%). Organically bound selenium and residual selenium caused the difference of soil total selenium content, with contribution rate of 55.2% and 32.2%, respectively. Residual zinc was the main form causing the difference of soil total zinc, with a contribution rate of 77.4%. With the increases of total selenium content, the proportion of residual selenium decreased obviously, and the proportion of organically bound selenium increased obviously. With the increases of total zinc content, the proportion of residual zinc decreased, and the other forms of zinc increased slightly. Except for residual selenium, SOM was positively correlated with different forms of selenium and zinc (r=0.74-0.93), while CEC was not correlated with different selenium and zinc levels. The correlation between all selenium and zinc forms and corresponding total selenium and zinc was the highest (r> 0.95). The mineral composition analysis showed that the contents of pyrite, hornblende, talc and clay minerals in soil with high selenium level were significantly higher than those in soil with medium or low selenium level. The content of dolomite, pyrite and hornblende in soil with high zinc level was significantly higher than that in soil with medium or low zinc level. In general, the differences in the contents of different forms of selenium and zinc in the soil under different selenium and zinc levels were determined by the differences in total content of selenium and zinc in wheat growing area of Shanxi Province. Soil mineral composition was the material basis of the differences in selenium and zinc contents, while organic matter was the driving force for the changes in soil selenium and zinc forms.

Key words: wheat growing area, soil selenium form, soil zinc form, mineral composition