An Evaluation of the Effect of Fertilizer Rate on Tree Growth and the Detection of Nutrient Stress in Different Irrigation Systems

Early season monitoring of nutrient stress is important in red maple (<i>Acer rubrum</i> L.) and flowering dogwood (<i>Cornus florida</i> L.) to optimize management practices and ensure healthy crop production in containers. Two different irrigation systems (drip and overhead irrigation) were used in this study. Two rates (low and high) of controlled-release fertilizer were used with no fertilizer as a control treatment. Data were recorded for plant height, stem diameter, substrate pH and electrical conductivity (EC), chlorophyll content, normalized difference vegetation index (NDVI), visual observation of plant quality, and leaf nutrient content. The results of this study showed that the increase in plant height and stem diameter was greater among the fertilized maple tree, whereas no differences were observed in the flowering dogwoods for an increase in plant height. NDVI was greater for drip irrigation for both fertilizer rates in both red maples and flowering dogwoods. A positive correlation of 73% to 83% was observed for red maples and 79% to 83% was observed for flowering dogwoods between handheld NDVI and unmanned aerial vehicle-mounted NDVI sensors. In red maple, a high fertilizer rate resulted in greater substrate pH, whereas in flowering dogwood, no differences were observed. Varied responses were observed among the treatments for nutrient content; however, both rates of fertilizer application were sufficient for both tree species. Drip-irrigated red maples had higher nitrogen and phosphorous content, whereas nitrogen content was higher in both irrigation systems in flowering dogwoods. This study provides useful insights into understanding the effect of nutrient stress on tree growth and the application of sensing technology for the monitoring and early detection of nutrient stress in container-grown nursery crops.