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Canopy Shading Effects on Soil Heat and Water Flow

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011

* Corresponding author.

ABSTRACT

A method to model two-dimensional heat and water flow in soil as influenced by shading from a row crop is developed. The numerical method predicts the surface energy partitioning, soil temperature, and the water content as influenced by soil surface evaporation in the absence of water uptake by roots. Standard weather information, canopy shape factors, and soil thermal and hydraulic properties are the inputs required to make predictions. Although the present model does not include water uptake by roots, this feature can be added. The methods of prediction are compared with analytical methods in verification and benchmarking test problems. Predictions of soil surface temperature and subsurface temperature in a verification test scenario closely agree with analytical solution values. Predicted soil water contents during an infiltration event agree closely with analytical values predicted by a quasi-analytic simulator (used in a benchmarking test), and also with experimental data (used in a validation test). A 10-d simulation is performed to show the ability of the method to describe surface energy partitioning and soil profile conditions. The method is shown to provide reasonable results. For the specific scenario of this simulation, the diurnal time variation of surface energy partitioning, soil water content, and soil temperature exhibited a radical change when the soil located between plant rows dried to residual water content. Large spatial variations in soil energy fluxes, temperature, and water content are predicted when soil located between plant rows becomes drier than soil below the canopy. The method can predict these fluxes, which are very difficult to obtain by direct measurement. Thus, this method should have a wide range of applications in soil and crop sciences.

Journal Paper no. J12879 of the Iowa Agriculture and Home Economics Exp. Stn., Ames, IA. Project no. 2556 and 2715.

Received for publication March 1, 1988.

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