Predictability of Change in Soil Reflectance on Wetting

The loss of reflectance from the oven dry state to field capacity for 15 surface soils from Central Indiana, representative of the Mollisol and Alfisol great soil groups, is definitely related to the oven dry reflectances of the soils. A regression analysis of the relationship of the darkening effect of wetting on the reflectance of the soils when dry results in regression curves with R2 values ranging from .9914 to .9291 over the five wavelength bands used, -52-.58 µm, .71 µm, .76 - .90 µm, .90-1.22 µm and 1.50-1.73µm. Furthermore, striking evidence of the predictability of soil moisture tensions from reflectance data was noted when the regression curves at .71 µm were run for the reflectance values of the 15 soils at 15 bar and 1/3 bar against their reflectances when oven dry. When the reflectance at 15 bar were plotted against those of the same samples when oven dry an R2 of 0.95 was found. The equation for predicting the reflectances at 15 bar from the reflectance values when oven dry was found to be: 15 bar = 1.685 + 1.067 oven dry Similarly, when data for reflectances of the 15 soils at 1/3 bar were plotted against the oven dry reflectances, an R2 of .96 was computed and the formula for estimating reflectances of the samples at 1/3 bar on the basis of their oven dry reflectance was: 1/3 bar = 0.709 + 0.487 oven dry This evidence strongly supports the thesis that moisture tensions of soils can be predicted from reflectance measurements