Doctor of Philosophy, The Ohio State University, 2008, Horticulture and Crop Science

Increased environmental awareness combined with a decrease in available water for irrigation has required the nursery industry to evaluate water and nutrient efficiencies. The production of plants in containers reduces the rooting volume available to the plant by about 95% resulting in a limited reservoir of moisture and nutrients. The substrates most commonly used in container production are soilless and porous, with pine bark comprising all or at least a majority of the substrate. This production environment requires nursery producers to irrigate daily to maximize plant performance. As irrigation volume increases both water and nutrient efficiencies decrease. This work investigates the interactions of irrigation, fertilizer rate, and water and nutrient efficiencies.A plant-integrated, gravimetric, substrate moisture monitoring system was used to control irrigation volume and limit leachate volumes to near-zero levels. Effective container capacity (ECC) was used to determine irrigation volumes and frequency. ECC was defined as the maximum mass of the container, substrate and plant unit after gravitational water loss. The system used the ECC target to deliver irrigation within a narrow range of substrate moisture contents to study the effects of irrigation volume on growth, water use, and nutrient uptake of baldcypress (Taxodium distichium L.). In the summer of 2006, the gravimetric substrate monitoring system was proven as an effective, plant-integrated method of reducing leachate volume that required minimal maintenance under the four month experimental period. Under a near-zero leachate irrigation system, irrigation volume and leachate volume (by definition) are decreased; substrate nutrient concentration was increased resulting in increased plant tissue nutrient concentration, and an increase in water-use efficiency. Nitrogen use efficiency was not affected by irrigation regime in this study, as fertilizer rate impacted uptake of nitrogen.

Committee: Daniel Struve PhD (Advisor); James Metzger PhD (Committee Member); Hannah Mathers PhD (Committee Member); Robert Hansen PhD (Committee Member) Subjects: Horticulture