Graduation Date

Spring 2023

Document Type



Master of Science degree with a major in Natural Resources, option Forestry, Watershed, & Wildland Sciences

Committee Chair Name

Susan Edinger Marshall

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Catalina Cuellar Gempeler

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Kerry Byrne

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Yoon Kim

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Natural Resources


Soil acidity is a common agricultural problem worldwide, as approximately 50% of all potentially arable soils are affected by pH limitations. At soil pH 3+) is considered to be the chemical form of aluminum in acid soil that hinders plant growth the most. Potentially, soil organic matter (SOM) can ameliorate the toxic effects of Al3+ on plants and microbes by binding with Al3+, thus preventing Al3+ (and other species of aluminum) from interacting in the rhizosphere. Increasing SOM also increases soil health indicators (i.e., microbial activity, soil water holding capacity, aggregate stability, porosity, etc.) while the management of SOM is relatively inexpensive. Wintertime cover crops (WCC) are commonly used for increasing SOM (and for other soil benefits). This study hypothesized that increased SOM from the growth of a WCC could potentially reduce Al3+ concentrations by binding Al3+ to the SOM. This study attempts to fill a knowledge gap regarding the relationship between cover crops, SOM and Al3+, as few (if any) field-scale tests on this subject have been published. In this before-after field study, a WCC of annual rye (Lolium multiflorum) was grown in a 0.4-ha field between November 2020 to July 2021 and then mowed. During this time, soil analysis was carried out for SOM percentage, Al3+ concentration, and pH. These variables were analyzed using paired t-tests and linear mixed effects regression. Random effect terms were added to the linear regression analyses to account for spatial and temporal variability in field conditions. Paired t-tests indicate a significant decrease in hydrogen (H) ion concentration (t = 2.1858, df = 16, p-value = 0.04404, n = 18), a marginally significant increase in SOM ( t = -1.8972, df = 16, p-value = 0.076, n = 18), and a marginally significant increase in Al3+ (t = -1.8741, df = 16, p-value = 0.0793). H ion concentration decreased significantly between wet (December 2020) and dry (September 2021) seasons (t = 2.1545, df = 16, p-value = 0.04678). Using linear mixed effect regression (LMER), H ion and nitrate (NO3-) were found to have significant effects on Al3+ concentrations (conditional R2=0.41), Al3+ and NO3- were found to have significant effects on H ion concentration (R2 = 0.35), and H ion and phosphorous (P) were found to have significant effects on SOM (R2 = 0.54). The fit for the last model is moderate and further inquiry could be made to predict SOM with these (and other) variables. While heterogeneity of the study site and mixed results are limitations, this study offers evidence that use of annual rye WCC may be an effective tool for maintaining SOM and pH. This study concludes that soil pH has a stronger effect on Al3+ concentration than does SOM. This concept further refines the understanding of the limitations of SOM in relation to soil pH, especially with regards to managing soil fertility and soil carbon sequestration on croplands and rangelands.

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