Fraction distribution and availability of soil manganese as affected by landforms in the Loessial Gully Region

Landform is a major factor influencing the availability of manganese (Mn) in soils because of its effects on soil properties and soil water conditions. This study was therefore conducted to investigate the relationship between landforms and Mn fraction and availability in a loessial gully region. The results showed that available Mn in soils varied greatly with landforms in the study area. Available Mn decreased with depth in soil profile. The highest available Mn was observed in plateau land while the lowest available Mn was observed in gully bottom. The content of exchangeable Mn was higher in sloping land and gully bottom than in plateau and terrace lands. Compared with gully bottom, plateau, terrace and sloping lands led to higher Mn in carbonate and organic matter bound fractions but lower Mn in oxide bound fraction. The mineral bound Mn was higher in gully bottom and terrace land than in plateau land. In spite of the direct source of available Mn, exchangeable Mn contributed little to Mn availability due to its low content in soils. Organic matter bound Mn, however, acted as the main source of available Mn and contributed largely to Mn availability.