The 2009 ASHS Annual Conference

Field grown garden mums (Chrysanthemum x morifolium) are often produced using drip irrigation with water soluble fertilizer (WSF).  This practice can yield high quality plants but may result in nutrient leaching to the soil.  Controlled release fertilizers (CRF) have the potential to greatly reduce nutrient leaching.  The objective of this experiment was to quantify nutrient leaching and plant growth in response to WSF, or CRF amended with 0, 2, 4, or  6 weeks of WSF (denoted as CRF+0, CRF+2, CRF+4, CRF+6).  Rooted cuttings of Chrysanthemum ‘Helen’ were transplanted outdoors into 9.5 inch pan pots containing a commercial peat-based substrate.  Plants were irrigated daily (or as needed) using drip irrigation with a 20% leaching fraction.  WSF plants were fertigated using a commercially available fertilizer at a rate of 200 to 400 ppm N depending on growth stage.  CRF plants were fertilized using substrate incorporated Osmocote Plus 15-9-12 with an 8-9 month release.  There were 4 replicates per treatment.  During the 10 week production period leachate samples were collected twice weekly and pooled into one weekly sample per plant.  Leachate was analzed for phosphorus, ammonium-nitrogen, and total-nitrogen concentration.  Leachate nutrient concentration was significantly affected by fertility treatment and production week.  When averaged across the entire sampling interval, WSF plants had more than five times the P and N leachate concentration compared to CRF+0 plants.  For example, average P leachate concentration was 22, 55, 75, 91, and 112 ppm, respectively, for CRF+0, CRF+2, CRF+4, CRF+6, and WSF.  For CRF treatments that contained added liquid fertilizer (CRF+2, CRF+4, and CRF+6) leachate concentrations were similar to WSF for the weeks that they had added liquid fertilizer.  For these treatments, once liquid feed was ended, leachate concentration declined to CRF+0 levels within 1-2 weeks.  Plant dry weight was significantly reduced for plants not receiving any liquid feed; and plant diameter was reduced for treatments receiving less than 6 weeks of liquid feed.  We conclude that when CRF is used as the primary fertilizer source nutrient leaching can be substantially reduced in garden mum production.  However, more work is required to determine a CRF rate that provides optimal plant growth while still reducing nutrient leaching.