Growth and nutrient content of poinsettia (Euphorbia pulcherrima Willd. ex Klotz) in a soilless growth medium containing sewage sludge pellet fertilizer

Abstract

The effectiveness sewage sludge pellet fertilizer (SPF) as a nutrient source for containerized poinsettia (Euphorbia pulcherrima Willd. ex Klotz) was determined by comparing the growth and nutrient element content of ‘Eckespoint Celebrate 2’ plants grown with SPF in the growth medium versus plants fertilized with conventional water‐soluble fertilizer (WSF). Plants were grown in 1.6‐L pots of soilless growth medium with SPF incorporated at planting at the rates of 1.0, 1.5, 2.0, 2.5, or 3.0 gm nitrogen (N) pot^‐1. Sludge pellet fertilizer plants received either no WSF or a dilute solution of 2ON‐4.3P‐16.6 potassium (K) (50 mg N L^‐1) twice a week. Control plants had no SPF and were fertilized with WSF at 250 mg N L^‐1 twice a week. At the end of the experiment plant growth measurements were made, leaves were analyzed for their nutrient element content, and growth medium was analyzed for pH and electrical conductivity (EC). Plants grown with SPF, with or without dilute WSF, were of commercially acceptable quality, but were somewhat smaller than the control plants. Plants growing with SPF alone and no WSF developed a chlorosis suggestive of N deficiency which was largely prevented by the application of WSF. Foliar analysis revealed that N in the leaves of plants receiving SPF alone was at the critical level for deficiency established for poinsettia. In treatments where dilute WSF was applied, the N content of the leaves was within the normal range. The foliar levels of all other nutrients fell within the normal ranges established for poinsettia in all SPF treatments. In addition to N deficiency, high growth medium EC at planting and low EC by the end of the experiment might also explain the inhibition of growth with SPF versus the WSF control. Results of this study suggest that poinsettia can be successfully grown using SPF as the sole source of nutrition, however the best growth is possible only when a dilute solution of N‐containing WSF is applied on a regular basis.