Fig. 4 Soil color parameters of field burned soil after recombustion at 550°C for 8 h as a function of the amount of citrate-bicarbonate-dithionite-extractable Fe. Alphanumerical Munsell hues were converted to numerical values by using a Munsell hue circle (Chamberlin and Chamberlin, 1980). With this conversion 5YR = 15 and 10YR = 20