Nutrient uptake in vegetative poinsettias grown with two fertilizer concentrations and two pinching dates1

Abstract

The effects of varying fertilizer application rates [100–15–100 or 300–46–300 mg L‐1 of nitrogen (N)‐phosphorus (P)‐potassium (K)] and pinching dates on nutrient uptake patterns of poinsettias were studied. During the first seven weeks after potting, varying the N‐P‐K fertilization rate from 100–15–100 to 300–46–300 mg L‐1 N‐P‐K had no effect on plant height, dry weight, nutrient concentration, or nutrient content of poinsettias. The uptake ratios for NO3‐N, K, calcium (Ca), and magnesium (Mg) all were <40% of the amount that was available at the 100 mg L"1 N and K fertilization rate, indicating that poinsettias require lower levels of NO3‐N, K, Ca, and Mg than what was available from the 100–15–100 mg L"1 N‐P‐K fertilization rate. The higher uptake ratios of >60% and >70%, respectively, for NH4‐N and P at the 100 mg L"1 N and K fertilization rate indicated the plants utilized a higher percentage of the available NH4‐N and P, indicating that an application rate >18 mg L‐1 NH4‐N and >15 mg L‐1 P would be required by poinsettias from the week before the plants were pinched through three weeks after pinching. The 300–46–300 mg L‐1 N‐P‐K fertilization rate provided excessive nutrients that were not utilized by the plants during the early stages of plant growth.