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Simulation of Surface Energy Balance and Soil Temperature under Strip Tillage: II. Field Test

Land Resource Research Center, Central Experimental Farm, Ottawa, ON, Canada K1A 0C6

Michael D. Novak^*

M.D. Novak, Dep. of Soil Science, Univ. of British Columbia, 2357 Main Mall, Suite 248, Vancouver, BC, Canada V6T 1Z4

ABSTRACT

Strip tillage may be a viable management technique for annual crops in northern latitudes, since the mulch strip should conserve soil and water while higher temperatures in the bare strip should yield good germination. The object of our research was to identify the processes that determine surface energy-balance components and soil temperatures under strip tillage and simulate them using a physically based numerical model. We tested the model with micrometeorological data collected at Vancouver, BC. Soil temperatures and evaporation rates in bare and uniformly covered straw-mulch plots were predicted reasonably well, except for the bare plot when evaporation was soil limited. The disagreement was attributed to variability associated with patchy soil drying and inadequacy of the simple surface-resistance model used to calculate evaporation. Good agreement for evaporation rates under 10 and 20 t ha^-1 mulches was achieved by enhancing transfer rates within the mulch layers by at least a factor of 4.5 above molecular diffusion rates. For the strip-tillage plots, the model underestimated (energy-limited) evaporation rates and soil temperatures in 0.1-m-wide bare strips separated by 0.3-m-wide mulch strips. This disagreement was attributed to micro-scale advection of warmer and drier air from the mulch strips to the bare strips, a phenomenon neglected in the model (and in all such models in the literature). The measurements showed that springtime soil temperatures in bare strips oriented in various directions were nearly equal to those in an adjacent bare plot. Therefore, considerable erosion protection should be possible without deleterious soil thermal regimes for seed germination.

^* Corresponding author.

Received for publication August 30, 1990.