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Using
Nutrients Efficiently to Produce Herbaceous Perennials
Chris
Catanzaro and Sarabjit Bhatti
Cooperative
Agricultural Research Program
Seminar Series
Tennessee State University, Nashville, TN
October 23, 2002
Sorption by the substrate is desirable when plants are
experiencing luxury consumption of nutrients. As the concentration of
nutrients in the soil solution decreases during crop production, release
of nutrients (desorption) back into the soil solution is desirable,
making them available for plant uptake. This cycle of sorption and
desorption over the course of crop production buffers nutrient
concentrations. Many recent studies have shown that floriculture crops
grown at relatively low, yet constant nutrient levels meet commercial
standards. Additionally, nutrient buffering prevents loss of excessive
concentrations of macronutrients (especially nitrogen, phosphorous) into
groundwater, which can occur with relatively high irrigation volumes in
a conventional greenhouse production system.
Three greenhouse experiments were initiated in September
2002 to determine the ability of clay amendments to reversibly sorb
fertilizer macronutrients. Three cultivars of poinsettia, Euphorbia
pulcherrima Willd. ex Klotzsch, are being grown according to
standard commercial practices in a glass greenhouse on the CARP/TSU
Farm. The cultivars are ‘Christmas Cookie’, ‘Christmas Dream’ and
‘Christmas Season’ (Selecta/HMA). The clay amendments are: attapulgite
(mesh size) 16/30, attapulgite 8/16, Fuller’s earth 5/20, and
montmorillinite at 16/30, 8/16 and 5/30 (OILDRI Corp. of America,
Chicago, IL). The clays were incorporated into a peat-based substrate
(10% v/v), after which plants were potted and topdressed with 9.0 g of
19-6-12 Osmocote controlled release fertilizer (3-4 mo. formulation).
Plants of each cultivar are laid out in a randomized complete block
design (7 treatments x 4 replications with single-pot replicates).
Irrigation is applied by hand weekly with sufficient volume to collect a
leaching fraction of 0.2. Leachate is collected and analyzed for
electrical conductivity and pH. Plant height is recorded weekly as an
indicator of vegetative plant growth.
Preliminary results suggest that attapulgite, Fuller’s
earth, and montmorillinite (fine particle size) are sorbing a
significant concentration of applied nutrients. In ‘Christmas Dream’,
Fuller’s earth has reduced nutrient discharge by 36% without reducing
plant height. Data suggest that both clay type and particle size are
significant factors determining sorption of nutrients and the efficiency
of nutrient uptake by model crops such as poinsettia.
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