Production and Postproduction Performance of Two New Guinea Impatiens Cultivars Grown with Controlled-release Fertilizer and No Leaching

The objectives of this study were to determine 1) the minimum controlled-release fertilizer (CRF) rate and the lowest constant medium moisture required to produce the highest quality plants and 2) if this production system affected quality of these plants under two postproduction light levels. Two New Guinea impatiens ( Impatiens sp. hybrids) 'Illusion' and 'Blazon' (Lasting Impressions Series) differing in salt tolerance were grown for 42 days with a CRF at three rates (3.3, 6.6, or 9.9 g/pot) and two medium moisture levels (low or high) without leaching. The high moisture level (tension setpoints of 1 to 3 kPa) and 6.6 g of CRF/pot produced optimum biomass. Low medium moisture (tension setpoints of 4 to 6 kPa) reduced leaf area, leaf number, leaf N content, root, stem, and leaf dry masses as CRF rate increased from low to high for 'Illusion'. Similar results in 'Blazon' were observed as CRF rates increased from 3.3 to 6.6 g. Biomass decreased no further at the high rate of 9.9 g/pot. Biomass increased in both cultivars under high medium moisture when CRF rates increased from 3.3 to 6.6 g. Biomass of 'Illusion' decreased at 9.9 g/pot, although no symptoms of salt sensitivity were observed (i.e., leaf tip burn). 'Blazon' maintained a similar biomass when amended with 9.9 or 6.6 g CRF/pot, although electrical conductivity (EC) in the medium was 5.9 dS·m -1 in the upper half and 4.1 dS·m -1 in the lower half of the medium at the end of production. Growth of 'Illusion' responded more favorably to postproduction light levels that were similar to those of production regardless of treatment imposed during production. Similar biomass responses occurred for 'Blazon' regardless of the postproduction light level. The establishment of minimum fertilizer and water require- ments for the production of a greenhouse crop has become increasingly important to growers as they are faced with higher water and fertilizer costs, mandatory reduction of runoff water, and governmental fines for contaminating surface water and groundwater. One method of reducing water and fertilizer use is to reduce leaching. Recent studies have shown that high-quality greenhouse crops can be grown with little or no runoff by maintaining the soil moisture at a constant level (Kiehl et al., 1992; Lieth and Burger, 1989). Constant soil moisture levels can be maintained with the use of a tensiometer-based computer irrigation system. However, crops sensitive to soluble salts may exhibit reduced biomass production or higher mortality rates during production or postproduction when grown under this system, due to the lack of leaching and subsequent soluble salt accumulation. Using controlled-release fertilizer (CRF) instead of water- soluble fertilizer (WSF) for container-grown plant production can effectively limit the loss of nutrients that are leached from grow- ing media (Rathier and Frink, 1989; Sharma, 1979). However, several studies have shown that nutrient loss through leachate is not uniform during the entire growth period (Cox, 1993; Hershey and Paul, 1982; Rathier and Frink, 1989). These studies demon- strated that the largest loss of N in leachate occurred during the early part of the production cycle. The nutrient loss in runoff can be prevented by growing plants without leaching. Lieth and