INFLUENCE OF SOURCE, RATE, AND METHOD OF APPLICATION CONTROLLED RELEASE FERTILIZER ON NUTRIENT RELEASE AND GROWTH OF SAVANNAH HOLLY

An experiment was conducted to determine the effect of rate of fertilizer application and method of application on the rate of nutrient release and growth of 'Savannah' holly (Ilex x attenuata Ashe) using three controlled release fertilizers. The controlled release fertilizers used were Osmocote 17N-3P-9. 9K, Sierrablen 17N-3P-8.3K, and High-N 24N-1.7P-5.8K, all 12 to 14 month formulations. The three fertilizers had different release rates as determined by leachate nitrate-N and electrical conductivity (EC) measurements. Topdressing of fertilizer had the greatest release rate at seven days after treatment compared to fertilizer incorporation which had the lowest EC readings at 120 days after treatment. Fertilizer source had no effect on the shoot growth of 'Savannah' holly. Growth index and shoot dry weight of 'Savannah' holly increased linearly as N rate increased from 0.9 to 2.1 kg N m-3. A significant linear relationship (R2 = 0.97, Nitrate-N = 409 (EC)) between nitrate-N and EC indicates that nitrate-N concentration can be estimated from EC readings when the pour-through method is used with multicoated controlled release fertilizers. The controlled release fertilizers used in this study provided adequate nutrient release rates for up to four months under outdoor nursery conditions during the months of June through October.