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Soil Reflectance, Temperature, and Fallow Water Storage on Exposed Subsoils of a Brown Soil¹

ABSTRACT

The topsoil of a Weld soil on an 0.84% slope was removed, giving an increasing depth of subsoil exposure ranging from 0 to 38.1 cm over a horizontal distance of 45.7 m. Five subranges of subsoil exposure—0 to 7.6, 7.6 to 15.2, 15.2 to 22.8, 22.8 to 30.4, and 30.4 to 38.1 cm—were formed with each subrange corresponding to a horizontal distance of 9.14 m. The exposed surface 5 cm of these soil removal treatments differed in texture, structure, reflectance, clod bulk density, aggregate stability, and wind-erodible soil fraction.

Over a 5-year period, mean fallow efficiency for all five soil removal treatments ranged from 25.6 to 38.5%. Reflectance of the exposed surface 5 cm of soil of each soil removal treatment varied considerably among treatments. Mean soil temperatures in fallow were negatively correlated with visual efficiency (P = .05) which was used as an indirect value of soil reflectance. Average soil water gained in fallow was negatively correlated (P = .05) with the mean fallow soil temperature measured at a depth of 7.6 cm. The negative correlation between soil water gained and mean soil temperature was significant (P = .01) in a dry year (1960) and nonsignificant (P = .05) in a year of above-average precipitation (1957). A positive correlation was obtained between soil water gained during fallow and visual efficiency (P = .10).

Soil water storage in fallow and depth to seedbed water were influenced by soil texture and aggregation in some years. No significant relationship was found between soil water storage at the end of fallow and subsequent crop production because of interactions involving soil temperatures and fertility levels.

¹ Contribution from the Northern Plains Branch, Soil and Water Conserv. Res. Div., ARS, USDA, in cooperation with Colorado Agr. Exp. Sta., Journal Series no. 1196.

² Soil Scientists, USDA, Sidney, Mont., and Akron, Colo., respectively.

Received for publication June 7, 1967. Accepted for publication September 11, 1967.