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Efficient
Fertilization Practices for Potted Chrysanthemums
Christopher
J. Catanzaro and Roger J. Sauve
Cooperative
Agricultural Research Program
Seminar Series
Tennessee State University, Nashville, TN
February 17,
1999
Introduction. In typical greenhouse and nursery
operations that do not recycle irrigation runoff, 30 to 50% of nutrients
applied to plants can be lost in runoff. High concentrations of nitrates
and other nutrients can eventually enter both surface water and
groundwater. Potted chrysanthemum [Dendranthema x grandiflorum
(Ramat.) Kitamura] is a major floricultural crop that requires a high
concentration of nitrogen during vegetative growth. In order to minimize
negative impacts of greenhouse fertilization practices on water quality,
studies were conducted on potted chrysanthemum with a range of
fertilizer release types, formulations and application timings.
Objectives. These studies were designed to
determine the effects of fertilizer treatments on: 1) shoot and root
growth and visual plant quality, 2) the amount of nitrogen taken up into
plant shoots and roots and the amount discharged or leached from
containers (leachate), and 3) soluble salt and pH profiles of leachate
over the course of crop production.
Methodology. Greenhouse studies were conducted
over four years which included the following mum cultivars: 'Charm',
'Delano', 'Spears' and 'Yellow Envy'. Rooted cuttings were potted in
15-cm azalea pots and grown using cultural practices for commercially
produced potted mums. Each test was laid out in a randomized complete
block experimental design with one to three plants per experimental unit
and four replications. Treatments included various rates, formulations
and application timings of two basic fertilizer types: liquid fertilizer
(LF) and slow release fertilizer (SRF). Pots were irrigated when they
lost 40% of their water-holding capacity with sufficient volume to
exceed container capacity by 20 to 30%. Watering and fertilization were
done by hand to maximize accuracy of delivery. Leachate was collected at
each irrigation and stored until lab analyses of pH and soluble salt
levels were conducted. Plants were harvested after 10 to 11 weeks, when
flowering peaked. Growth data were collected and then plants were dried
and ground for nutrient analysis.
Results. Shoot growth and plant quality met
commercial crop standards with most LF and SRF fertilizers. However,
root mass was higher with SRF than LF, suggesting a potential advantage
of SRF. Two-thirds of the nitrogen (N) applied with SRF was recovered in
plant tissues, whereas N uptake with LF was less than 50%. Leachate data
suggest another benefit of SRF. Leachate soluble salt levels were lower
with SRF than with LF. Nitrogen leaching losses over a ten-week period
with SRF were one-half to one-third of those with LF. However, stopping
LF when plants began forming flowers controlled leachate soluble salt
levels without affecting quality of finished plants. Single-application
SRFs with 3-4 month nutrient release produced mums that met commercial
growth standards with well developed roots, adequate tissue nutrient
levels and efficient nutrient uptake, without excessive leaching losses.
Impact. Results suggest that both fertilizers can
be used efficiently, even in non-recycling irrigation systems. Growers
must strive to maximize retention of nutrients applied to containerized
plants and the subsequent uptake of nutrients into plant tissues, rather
than allowing high concentrations of nutrients to be leached from
containers and discharged into the environment. In order to reach these
goals, growers should match nutrient supply with demand during each
stage of crop growth, water only when plants are sufficiently dry, and
limit irrigation volume.
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