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Audrey A. Trotman, P. David, D. Mortley, and J. Seminara

In a greenhouse experiment, the effect of the addition of higher levels of potassium (K) in the replenishment stock used to supply nutrients in a nutrient film technique system was examined. For this study, `TU-82-155' sweetpotato was grown hydroponically for 120 days under four nutrient application/replenishment treatments: 1) REG—solution was changed at 14-day intervals and volume allowed to fluctuate; 2) MHH—replenishment with 10× concentrate of a modified half Hoagland solution (MHH) or with water to regain set volume (30.4 liters) and maintain set point of electrical conductivity (EC, 1050–1500 μmho); 3) MHH + 2K—daily replenishment with 10× concentrate of a modified half Hoagland solution (MHH) or with water to regain the set volume and adjust EC to 1400 followed by application of 50 ml of a 2K stock solution to an EC of 1500; 4) MHH/2K—replenishment with 10× concentrate of a modified half Hoagland solution that incorporated the 2K component or with water to regain set volume (30.4 liters) and maintain set point of electrical conductivity (EC, 105–1500 μmho). The storage root yield (g fresh weight per plant) was significantly higher when the 2K treatment was incorporated with the 10× MHH stock. The storage root yield averaged 324.8 g/plant compared with a yield of 289.6 and 252.9 g/plant, respectively, for the REG and MHH nutrient application protocol. As in earlier experiments, the MHH treatment was comparable to the REG protocol, validating the use of a replenishment approach for nutrient supply in hydroponic sweetpotato culture.

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P.P. David, A.A. Trotman, D.G. Mortley, D. Douglas, and J. Seminara

A study was initiated in the greenhouse to examine the effects of five \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}:\mathrm{NO}_{3}^{-}\) \end{document} ratios on sweetpotato growth. Plants were grown from vine cuttings of 15-cm length, planted in 0.15 x 0.15 x 1.2-m growth channels using a closed nutrient film technique system. Nutrient was supplied in a modified half-strength Hoagland's solution with a 1:2:4 N:K ratio. \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}:\mathrm{NO}_{3}^{-}\) \end{document} ratios investigated were 100:0, 0:100, 40:60, 60:40, and a control that consisted of a modified half-Hoagland solution with an N:K ratio of 1:2:4 and an \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}:\mathrm{NO}_{3}^{-}\) \end{document} of 1:7. Treatments were initiated 30 days after planting (DAP). Sequential plant harvest began 30 DAP and continued at 30-day intervals until final harvest at 150 DAP. Results showed a linear increase in fresh storage root fresh weight until 90 DAP for all treatments. However, from 60 DAP until the end of the growing season, plants grown in a 100% \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} solution consistently produced significantly less storage roots than in all other treatments. While all other treatments showed a decrease in storage root fresh weight after 90 DAP, plants grown in 100% \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} and the control solution continued to increase linearly in storage root production. Storage root dry weight throughout the growing season followed similar trends to that of storage root fresh weight. Data suggest that a nutrient solution containing NO 3as its sole nitrogen source may be adequate for sweetpotato growth. This would make it possible for utilizing a one-way pH control method for nutrient solution.