Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant and Environmental Science

Committee Chair/Advisor

Juan Carlos Melgar

Committee Member

Guido Schnabel

Committee Member

Vidya Suseela

Committee Member

Lisa DeVetter


Soil disturbance from the cultivation and intensive management of orchards in hot and humid subtropical climates can reduce soil organic matter (OM). This research explored how the addition of OM amendments impact soil and tree parameters in two field studies and how proximity to OM may elicit unique genomic response of peach roots in a split-root pot study. The first field study applied two rates of compost (1x and 2x) and subsequently reduced fertilizer applications annually to a virgin and replant orchard location. While both compost rates successfully replaced fertilizers, only the 2x rate in the replant location increased soil OM, phosphorus, and tree size compared to the control without compost over time. Larger tree size was most likely due to improved soil moisture within the compost-treated soil in comparison to the control during each growing season, but trees had similar water status and carbon assimilation when measured. In the second field study, municipal mulch (M) and poultry litter with mulch (PLM) were topically applied to cover the herbicide strip under mature trees to maintain a depth of 15 cm annually. The M and PLM treatments had similar foliar nutrient concentrations during the summer, but more nitrogen was available in the PLM treatment over time and led to excessive vegetative growth, a delay of fruit maturation, and reduced yield after three years. Both M and PLM treatments covering the soil appeared to limit soil moisture evaporation during the spring but prevented rewetting later in the growing season. Regardless, trees often had similar water status by treatment. A split-root pot study designed to understand gene expression of peach roots growing in heterogeneous OM soil environments revealed higher numbers of differentially expressed genes (DEGs) when roots were split between two different soil treatments, suggesting OM can elicit a systemic response like other abiotic or biotic stimulants. Additions of the OM amendments allowed for a reduction of synthetic fertilizer in the field, but additional studies will be required to understand the influence of OM amendments on orchard pests and pathogens, the orchard economy, and long-term changes to soil quality and soil health.

Author ORCID Identifier


Available for download on Sunday, December 31, 2023