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Radiation Balance of Ridge-Tillage with Modeling Strategies for Slope and Aspect in the Subarctic

USDA-ARS, 309 O'Neill, UAF, Fairbanks, AK 99775

M. J. Schwarzer and G. S. Campbell

Dep. of Agronomy and Soils

R. I. Papendick

USDA-ARS, Johnson Hall, Washington State Univ., Pullman, WA 99164

* Corresponding author.

ABSTRACT

Radiative exchange at the soil surface can be altered by the surface configuration. Tillage methods that modify the soil surface for increased radiation absorption are needed in the subarctic, where soil temperature is a limiting factor in crop adaptation and production. The radiation climate of ridge-tillage was investigated to determine the optimum ridge aspect and slope for maximizing radiation absorption on soils in the subarctic. Comparisons of net radiation (R_n), albedo, and soil surface temperatures were made on ridge plots (6.1 by 6.1 m); with ridges oriented northeast-southwest, northwest-southeast, east-west, and north-south; and a horizontal surface during the 1988 through 1990 growing seasons at Fairbanks, AK. A radiation-balance model of ridged surfaces was developed to ascertain localized irradiance and isothermal net radiation (R_ni) effects owing to slope and aspect of ridges. Measured R_n differences were found at midday on clear days when R_n was about 30 W m^–2 higher on ridged than horizontal surfaces. The higher R_n resulted from a lower albedo and lower soil surface temperatures of the ridged surfaces. Modeled irradiance on ridges used in this study agreed well with measured values. Modeled R_nl results using four seasons of micrometeorological data suggested that southerly aspects inclined 20 to 40° offered the greatest advantage in radiation absorption at Fairbanks.

Received for publication September 12, 1991.