Soil iron fractionation and availability at selected landscape positions in a loessial gully region of northwestern China.

摘要

Soil Fe fractions and availability vary with landscape positions, because landscape position affects soil chemical properties and water conditions. In the present study, we investigated Fe fractions and availability at selected landscape positions in the loessial gully region of northwestern China. Four landscape positions, plateau, slope, terrace, and gully bottom were investigated. For each landscape position, soil samples were collected at 20-cm increments to a depth of 80 cm. Iron in the soil samples was fractionated by a modified sequential extraction method. Available Fe was assessed by diethylene thiamine pentacetic acid (DTPA) extraction procedure. The results showed that soil profile distributions of DTPA-Fe varied greatly with landscape position in the study area. The largest content of DTPA-Fe content was observed in the plateau soils, while the smallest content was observed in the gully bottom soils. Iron in soils existed mainly in the mineral bound fraction, which accounted for about 73 to 96% of the total Fe. The content of Fe in soil fractions varied greatly with landscape position. Exchangeable Fe and organic matter bound Fe were direct sources of available Fe, but exchangeable Fe contributed little to the total available Fe due to its low content in the soils. Oxides bound Fe was an indirect source of available Fe. The results of the present study indicate that landscape position strongly influences soil profile distribution and capacity of available Fe by influencing soil Fe fractions and organic matter distributions.