Graduate Thesis Or Dissertation
 

Water and solute transport : modeling and application to water conservation in layered soil

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cf95jf09t

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  • Sandy soils are among the least productive soils because of their inability to store adequate water for plant growth. Their high percolation rate not only allows water to move quickly beyond the root zone, but also washes nutrients below the reach of plant roots. High evaporation occurs from the soil surface. Many acres of these soils around the world are left out of crop production. This study is a contribution to bring these soils into production by increasing their ability to hold more water in the root zone. Several promising methods of enhancing these soils were simulated, surface mulch, buried barrier layer, and a combination of both. The effects of varying texture and thickness of these layers and varying evaporative demand were investigated. The impact of such modifications on solute distribution in the soil was also simulated. A simulation model of water and solute transport in layered soils was developed for this purpose. The Richards equation for one-dimensional water transport in unsaturated soils was modified to account for the water jump between the layers. The solute transport equation was also modified by implementing the same theory of water infiltration in layered soil to the solute convective transport. The Crank-Nicolson scheme was used to solve the transport equations with the help of the Newton-Raphson iteration method. The results of the simulation show that the proposed methods increase water content in the sandy soil by up to 45%. The combination of barriers, which decreases leaching and evaporation was the most effective in conserving water. Most of the contribution came from the influence of the mulch layer in suppressing water losses by evaporation. The combination method traps solute in the root zone, and this decreased solute leaching from the soil may limit plant growth in saline soils.
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