Graduation Year

2018

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Mahmood Nachabe, Ph.D.

Committee Member

Manjriker Gunaratne, Ph.D.

Committee Member

Kenneth Trout, Ph.D.

Committee Member

Jiangfeng Zhou, Ph.D.

Committee Member

Ajit Mujumdar, Ph.D.

Keywords

Microscopic Capillary Length, Pressure Gradient, Soil Water Content

Abstract

Field Capacity (FC) is a key parameter to quantify in agricultural engineering, irrigation controlling, and soil physics studies. For instance, irrigation studies focuses on determining the optimal amount of water needed by plants to grow following an irrigation system and therefore relies on determining FC. Likewise, the value of FC is a good indicator of soil textures, structures and pore size distributions. For example, loamy soils have a wider distribution of pores leading to high FC values. FC depends on multiple physically-grounded variables which include matric potential value (ψ_FC ), water content at FC (θ_FC ), specific drainage time to reach FC (t_FC )and drainage flux (q_FC ).

Previous definitions of FC have many limitations. Among these limitations, FC was rarely defined in the context of its soil properties as prior studies failed to include all soil parameters when quantifying FC, hence, to this day, the use of models is the sole way to normalize water content at FC (e.g., using Van genuchen and Brooks and Corey models). This study fills in these gaps by setting up a practical approach to determining FC via soil properties and developing a generalized FC solution to the case of drainage from a deeply wetted profile and a non-zero flux flow at the surface (upward flux when Evaporation (EV) is taken into account) or a zero flux at the surface (when EV is considered negligible), hence, an analytical solution to the attainment of field capacity in space and time and universal FC curves are presented.

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