Pan ShuZheng;Pan SZ

;Institute of Soil Science, Academia Sinica, Nanjing 210008, China.

ferrous ions;characterization redox potential;horizons soil types anthropogenic;paddy soils;soil formation;gleyification china

The gleyization of representative paddy soils in the middle reaches of the Yangtze River was characterized, taking oxidation-reduction potential(Eh), the amount of active reducing substances and the forms of iron and manganese as the parameters. TheEh value was linearly related with the logarithm of the amount of active reducing substances, 83% of which was ferrous iron. The degree of gleyization of different horizons was graded as ungleyed, slightly gleyed, mildly gleyed and gleyed. The Eh of thefour grades was >500, 300-500, 100-300 and <100 mV, respectively, and the corresponding amount of active reducing substances was <1, 1-7, 7-30 and >30 mmolc/kg, respectively. The amount of ferrous iron of the four grades was <0.5, 0.5-5, 5-25 and >25 mmol/kg, respectively. The extent of gleyization of a soil was classified as upper-gleyed, middle-gleyed and lower-gleyed, depending on whether the depth of the gley horizon was <30 cm, 30-60 cm or >60 cm.