Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Plant, Soil and Environmental Sciences

Major Professor

Forbes Walker, Amy Fulcher

Committee Members

Neal Eash, James Altland


Developing management practices that make more efficient use of irrigation is important for improving the sustainability of agriculture. Biochar, a byproduct of pyrolysis, can potentially increase the amount of available water and improve irrigation efficiency and plant growth. The goal of this study was to evaluate the impact of irrigation schedules and biochar on water use and biomass gain of container crops. Containers were filled with pine bark and amended with 10% or 25% by volume of biochar. Boxwood and hydrangea plants were irrigated when the volumetric water content reached the water buffering capacity set point of 0.25 cm3·cm-3 in the first experiment. Biochar amendment increased water-holding capacity and reduced water consumption of a high water use crop, hydrangea. However, reduction of plant biomass in 25% biochar treatment suggests that sufficient water might not be available to plants in this substrate. Another study was initiated to address this problem by using physiological parameters to monitor hydrangea plant water status under different irrigation schedules that were designed to maximize plant available water. Plant physiology or substrate physical properties basis irrigation scheduling, in combination with biochar substrate amendment, reduced the water requirement for hydrangea without any negative effect on plant dry weight by maintaining sufficient plant water status and gas exchange rate. In order to validate the irrigation schedules in an outdoor environment, independently controlled irrigation zones were designed to test irrigation schedules. Total water use was unaffected or lower in the on-demand irrigation systems. However, plant dry weight and water use efficiency was greater in on-demand irrigation scheduling systems compared to the conventional irrigation. This research demonstrated that automated irrigation systems coupled with plant physiology or substrate-based irrigation scheduling and a water retentive substrate amendment have the potential to reduce nursery water use without negatively affecting plant growth.

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