Effects of Controlled-Release Fertilizer Placement on Nutrient Leaching and Growth of Bedding Impatiens

Abstract

Bedding impatiens plants were grown with a 16N-3.9P-10K controlled-release-fertilizer (CRF) of 5–6 or 8–9 month longevities placed at four positions in the container: top-dressed, incorporated, top-one-third, and bottom. These were compared to plants grown with a 20N-4.4P-16.6 water-soluble fertilizer (WSF) at a rate of 150 mg·L−1 nitrogen (N) (150 ppm N). All treatments received the same volume of tap water (CRF treatments) or fertilizer solution (WSF treatment), which was enough to achieve a 20 to 30% leaching fraction. Leachates were collected and measured at each irrigation and the concentrations of N, phosphorous (P), and potassium (K) were measured. Shoot dry weight (SDW) and canopy cover (CC) were also determined. Fertilizing with WSF produced plants of similar size as CRF treatments. CRF applied at the bottom of the substrate leached the highest amount of N among all treatments. Higher concentrations for most nutrients were measured in the leachates from containers treated with 5–6 month CRF during the first 20 d after planting than the next 23 to 34 days. The higher levels of nutrients in the leachates observed within two weeks after planting does not support the use of 5–6 month CRF at the application rates used in this experiment with short-cycle plants such as bedding plants in compared to use of WSF. Except for the bottom placement treatment, the use of 8–9 month CRF resulted in generally less nutrients leached than WSF.