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The growth of New Guinea impatiens with controlled-release fertilizer in a recirculating subirrigation system
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With concerns increasing over the supply and quality of water, pressure on greenhouse growers to use water and fertilizers more efficiently is also increasing. Controlled-release fertilizers (CRF) and recirculating subordination systems are potential methods of reducing fertilizer runoff and conserving water. In a preliminary experiment (Experiment 1), petunias were grown with rates from 0 to 4 times the manufacturer's recommended rate of Osmocote 14N-6.1P-11.6K CRF in a recirculating subordination system. Plants exhibited increasing growth with increasing fertilizer rate. A typical trend in growth was exhibited by dry mass, with dry mass increasing up to the 3x rate and then decreasing slightly. Experiment 2 was conducted to determine the effects of CRF prill removal from growing media prior to extraction for EC and pH. CRF drills were either removed or not, prior to extraction of the media. No significant differences in EC or pH were found between pots which had drills removed and those that did not. Experiment 3 was a rate study of 0 to 8x CRF using New Guinea impatiens. By final harvest, all plants grown at rates above 2x were dead and it was concluded that elevated summer greenhouse temperatures contributed to this effect. Experiment 4 tested CRF rates from 0.5 to 2x. New Guinea Impatiens exhibited increasing growth with increasing CRF rate and optimum dry mass was achieved between the 1.25 and 1.75x rates. No symptoms of salt injury were visually apparent, even at the highest CRF rate. In Experiment 5, CRF rates from 0.25 to 1x and four CRF placements (incorporated, top-dressed, bottom, and dibble) were tested. Increasing growth was found with increasing fertilizer rate and plants with CRF incorporated throughout the growing medium exhibited greater dry masses than plants with other CRF placements. Experiment 6 was conducted to compare the release characteristics of the CRF in subordinated and top-watered systems. Over the 84-day experiment, subordinated and top-watered treatments released 54% and 55%, respectively, of the K in the 3 to 4 month CRF formulation. Of the K released from the drills, 77% and 83% were recovered in the plant for subordination and top-watering, respectively.
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Includes bibliographical references (leaves 93-101).
Issued also on microfiche from Lange Micrographics.
Richards, Daphne Ladean (1999). The growth of New Guinea impatiens with controlled-release fertilizer in a recirculating subirrigation system. Master's thesis, Texas A&M University. Available electronically from
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