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Dynamic Simulation of Water Storage in Fallow Soil as Affected by Mulch of Hydrophobic Aggregates¹

ABSTRACT

A mechanistic numerical model, based on fundamental physical principles and written in IBM S/360 CSMP language, was designed to compute the dynamic balance of water in a fallow soil through repeated cycles of infiltration and evaporation. The necessary inputs are: (i) hydraulic characteristics of the soil and of the surface crust or mulch layer; (ii) duration and intensity characteristics of rainstorms or irrigations; and (iii) the potential evaporation rate as it varies diurnally and from day to day. The output provides time-dependent rates and cumulative quantities of infiltration, runoff, surface detention, evaporation, internal drainage, and changes in water content of different layers and of the profile as a whole. Computations carried out for a 4-day simulation (including two rainstorms and four evaporation cycles) illustrate the use of the model for uniform, crusted, or mulched soil; and predict that the presence of a mulch of hydrophobic aggregates, several centimeters thick, can greatly increase the quantity of water absorbed and retained in the profile. This finding accords with previously-published experimental results and indicates a promising approach to soil management for water conservation in dryland and irrigated farming.

¹ Contribution from the Dep. of Soil & Crop Sciences, Texas Agric. Exp. Sta., Texas A&M Univ., College Station, Tex. 77843.

² Visiting Professor, Dep. of Soil & Crop Sciences, Texas Agric. Exp. Sta., Texas A&M Univ., College Station, Texas; on leave from the Department of Soil & Water Science, Hebrew University of Jerusalem, Rehovot, Israel.

³ Professor, Dep. of Soil & Crop Sciences, Texas Agric. Exp. Sta., Texas A&M Univ.

⁴ Assistant Professor, Dep. of Agric. Econ., Texas Agric. Exp. Sta., Texas A&M Univ.

Received for publication January 21, 1975. Accepted for publication May 5, 1975.