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Osamu Kawabata and Joseph DeFrank

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Osamu Kawabata and Joseph DeFrank

A modified power function, y = (A + B·x)–C, was developed for determining the relationship between plant growth and growth retardant treatment. This function accounts for the plant response characteristics by incorporating three coefficients: A, growth level of the nontreated plants; B, the degree of growth reduction; and C, the smallest effective dose of the growth inhibitor. The function accounted for 97% of the variation in purple nutsedge (Cyperus rotundus L.) leaf length as a function of the amount of a growth retardant applied. The procedure resulted in a smaller error sum of squares than several common nonlinear functions because of its greater shape flexibility.

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Osamu Kawabata and Richard A. Criley

MacroMixer, a microcomputer spreadsheet program, offers 15 commonly used nutrient sources for quick formulation of a macronutrient mix in solution culture. The program displays the total concentration of each macro-element and the contribution of each source when the user specifies the desired volume of the mix and the amount of source considered. This program, used with trial and error, eases computational complexity, as sources may contain more than one controlled macro-element.

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Osamu Kawabata and Richard A. Criley

An aqueous solution of dikegulac-sodium at 0, 2000, 4000, 6000, or 8000 mg a.i./liter was sprayed on a mature Murraya paniculata hedge as the first leaves expanded on newly developing lateral shoots after trimming. The lateral shoots from each 0.09-m2 hedge surface elongated less and the coefficient of variation (cv) decreased as the growth regulator concentration increased. Application of dikegulac-sodium at 4000 mg a.i./liter to the most distal leaf on topped, single-leader seedlings inhibited the elongation of distal shoots while it enhanced proximal shoot growth. Dikegulac-sodium spray between 4000 and 6000 mg a.i./liter to the hedge decreased apical dominance among lateral shoots and enhanced uniform regrowth without causing visible damages. The cv reduction was attributed to the growth regulator-induced weakening of apical dominance. Chemical name used: sodium salt of 2,3:4,6-bis-O-(1-methylethylidene)-α-l-xylo-2-hexulofuranosonic acid (dikegulac-sodium).

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Osamu Kawabata and Richard A. Criley

In solution culture experiments, determining the quantity of nutrient sources to dispense in a solution mix is time consuming. When a source contains more than one controlled element (e.g., calcium nitrate [Ca(NO3)2]), a change made to control one element (Ca) requires an adjustment to the other element (N). To ease the computational chore, MacroMixer, an application program for mixing macro-nutrients, was developed using a spreadsheet for microcomputers.

MacroMixer consists of two parts. The first part computes the weight (volume for a liquid) of source necessary to give the target element concentration from each source. The second part computes the total concentration for each macro-element from a set of sources in the final mix. The total volume of the mix is specified at the beginning of program, but it can be changed later. Users can obtain a required weight for each source using the first part to use as a starting value in the second part. Adjustments are made among sources to achieve target element concentrations in the final mix.

The spreadsheet format hides computational formulae and constants for a clear view of solution composition; thus users are encouraged to exercise trial and error to achieve the most balanced mix. Using this program, we quickly formulated 13 mixes used in a 5 K-levels × 5 Ca-levels partial factorial experiment.

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Hector R. Valenzuela, Osamu Kawabata, and Harry Yamamoto

Methanol sprays reportedly increased yields of several crops in Arizona by 50 to 100 percent (Nonomura and Benson PNAS 89:9794(1992). Reports from other parts of the country have shown conflicting results with regards to the effect of methanol sprays on yields of horticultural crops. Several greenhouse and growth chamber (controlled temperature. day length, and photosynthetic photon flux) experiments were conducted to evaluate the effect of methanol sprays on the growth and productivity of several vegetable crops in Hawaii. Treatment spray solutions consisted of 20-25% methanol, 0.5% low biuret urea. 0.001% chelated iron, and 0.02% surfactant. Control sprays only contained urea, chelated iron, and surfactant. Each experiment consisted of at least 5 weekly methanol sprays. Flowering cabbage, Brassica campestris var. parachinensis, had greater biomass production when sprayed with methanol in the late summer months. Similar results were obtained with choi sum in a 2 by 2 factorial experiment with methanol and water stress treatments. However, choi sum did not respond to methanol treatments in follow-up greenhouse trials. perhaps attributable to the shorter and Overcast days experienced in the fall and winter. Okra, chili pepper, and eggplant showed no response to methanol sprays. Okra showed a trend toward increase yields in response to methanol sprays, but differences were not significant. Follow-up studies in the greenhouse and in the field, which include evaluation of photosynthetic efficiency through chlorophyll fluorescence determinations will be presented.