Theses and Dissertations

Date of Award

5-1-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Bradley Christoffersen

Second Advisor

Alexis Racelis

Third Advisor

Pushpa Soti

Abstract

In the Lower Rio Grande Valley of South Texas, water scarcity and drought pose ongoing challenges for farmers. Although cover crops are promoted for improving soil health and moisture, their effects on soil hydraulic properties in this region remain understudied. This thesis addresses both long-term (Chapter 2) and short-term (Chapter 3) impacts of cover crops on soil hydraulic properties and soil moisture. Long-term effects were evaluated through a three-year participatory field trial across four farms using a BACI design, while short terms were evaluated using a complete randomized block design. Soil hydraulic properties (residual water content θr, saturated water content θs, field capacity θfc, plant available water θPAW, Alpha α, pore size distribution parameter n) were characterized using the van Genuchten equation. Results showed no significant trend in impact ratios (cover/control) of residual water content θr, saturated water content θs, and plant available water θPAW over time. In contrast, marginally significant temporal trends in impact ratios of field capacity θfc, alpha and n were observed over 3 years of cover crop adoption, suggesting that cover crops may promote beneficial changes in soil hydraulic properties related to pore size and pore distribution. Results for chapter 3 showed that fallow (weed-free control) plots showed higher levels of soil moisture than the naturally sprouted (weed) cover crop plots. Contrary to expectation, termination times (60 versus 90 days) had no effect on soil moisture at all depths, total stored soil water, or water use efficiency of the weed cover crops. Overall, this thesis highlights the importance of assessing cover crop induced changes in both instantaneous and longer-term effects on soil moisture and soil hydraulic properties, respectively. Moreover, future studies on cover crops effects on soil hydraulic properties should be evaluated in tandem with management factors to mitigate negative short-term impacts on soil moisture.

Comments

Copyright 2025 Fabrizio Javier Pilco. https://proquest.com/docview/3240623845

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