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The problem of statistics in horticultural research as reported in HortScience and the Journal is not unique to ASHS. Other societies are fighting the same battle. And certainly no one can disagree with Padaki’s comments. However, the question of inconsistencies in the use of statistics is a great deal more complex than he has stated. If all experiments could be easily analyzed as regression, multiple comparison and contrasts, and factorial experiments, the statistical issue would be greatly simplified. However, add to that list sampling, time (years), nonhomogeneity of variance, outliers, percent, transformation, subsamples, split-plots, interactions, unequal observations, dead plants, poorly designed experiments, lack of statistical consultants, poor access to statistical packages, etc. There is “no cookbook” to follow for every experiment nor do statisticians always agree on a single “correct” procedure. The problem is not easily solved.

Open Access
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Statistics is a very important tool for the horticultural scientist. But, like any tool, statistics can be, and often is, misused and abused. In nearly all cases the misuse is not intentional but rather a misunderstanding of how to correctly use the tool.

Open Access
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Controlling variability is central to the principles o f scientific experimentation. The researcher starts with a written statement of the question or questions and the hypotheses. The researcher uses “planned or controlled variability” (treatments) in an experiment to test these hypotheses. However, for valid conclusions, the researcher must also consider “non-planned or unwanted variability” when designing the experiment (Fig. 1). The following quote from the 1920s about field experiments graphically makes this point:

“As Fisher put it in correspondence, the experimenter games with the devil; he must he prepared by his layout to accommodate whatever pattern of soil fertilities the devil may have chosen in advance.” (1)

The main statistical tools for measuring and/or controlling variability are replication, randomization, and blocking.

Open Access
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Abstract

Daylengths ≤ 12 hours greatly reduced the time required to form visible stolons in Chlorophytum. Three weeks of 8 hour daylengths were the minimum number of short days required to reduce the days to visible stolon formation. The all-green plant (Chlorophytum capense (L.) Voss) was less responsive to photoperiod than the variegated plant (Chlorophytum comosum (Thunb.) Jacques cv. Vittatum).

Open Access

`Supjibi' poinsettias (Euphorbia pulcherrima Willd.) were grown hydroponically for 15 weeks in nutrient solutions with 100-15-100, 200-30-200, or 300-46-300 (in mg·L-1 of N-P-K) to determine nutrient uptake patterns and accumulation rates. Results indicate that increasing fertilization rates from 100 to 300 mg·L-1 of N and K did not significantly influence the plant dry mass or the nutrient concentration of P, K, Ca, Mg, Na, B, Cu, Fe, Mn, Mo, and Zn in poinsettias. NH4-N concentration in the leaves, stems, and roots were lowest with the 100-mg·L-1 N fertilization rate and increased as the N application rate increased to 200 and 300 mg·L-1. Leaf P concentration levels from 1 week after potting through anthesis were above 1.3%, which exceeds the recommended level of 0.9%. When the plant tissue dry mass for each fertilizer rate was transformed by the natural log and multiplied by the mean tissue nutrient concentration of each fertilizer rate, there were no significant differences among the three fertilization rates when the total plant nutrient content was modeled for N, P, or K. Increasing the fertilizer application rate above 100 mg·L-1 N and K and 15 mg·L-1 P decreased total plant content of Ca, Mg, Mn, and Zn and increased the total plant Fe content. The results of the weekly nutrient uptake based on the total plant nutrient content in this study suggests that weekly fertilization rates should increase over time from potting until anthesis. Rates (in mg) that increase from 23 to 57 for N (with 33% of the total N supplied in the NH4-N form), 9 to 18.5 for P, 19 to 57 for K, 6 to 15 for Ca, and 3 to 8 for Mg can be applied without leaching to poinsettias and produce adequate growth in the northern United States.

Free access

A central composite rotatable design was used to estimate quadratic equations describing the relationship of irradiance, as measured by photosynthetic photon flux (PPF), and day (DT) and night (NT) temperatures to the growth and development of Rosa hybrida L. in controlled environments. Plants were subjected to 15 treatment combinations of the PPF, DT, and NT according to the coding of the design matrix. Day and night length were each 12 hours. Environmental factor ranges were chosen to include conditions representative of winter and spring commercial greenhouse production environments in the Midwestern United States. After an initial hard pinch, 11 plant growth characteristics were measured every 10 days and at flowering. Four plant characteristics were recorded to describe flower bud development. Response surface equations were displayed as three-dimensional plots, with DT and NT as the base axes and the plant character on the z-axis while PPF was held constant. Response surfaces illustrated the plant response to interactions of DT and NT, while comparisons between plots at different PPF showed the overall effect of PPF. Canonical analysis of all regression models revealed the stationary point and general shape of the response surface. All stationary points of the significant models were located outside the original design space, and all but one surface was a saddle shape. Both the plots and analysis showed greater stem diameter, as well as higher fresh and dry weights of stems, leaves, and flower buds to occur at flowering under combinations of low DT (≤ 17C) and low NT (≤ 14C). However, low DT and NT delayed both visible bud formation and development to flowering. Increased PPF increased overall flower stem quality by increasing stem diameter and the fresh and dry weights of all plant parts at flowering, as well as decreased time until visible bud formation and flowering. These results summarize measured development at flowering when the environment was kept constant throughout the entire plant growth cycle.

Free access

Abstract

In the article “Evaluation of Nutrient Deficiency and Micronutrient Toxicity Symptoms in Florists’ Hydrangea”, by Douglas A. Bailey and P. Allen Hammer (J. Amer. Soc. Hort. Sci. 113(3):363–367, May 1988), the following corrections should be noted: 1) In Table 3, percent dry weight of N for the –N treatment should read “1.40”, not “4.40”; 2) the significance levels in footnote z of Table 3 should read “0.05 ≥ α ≥ 0.01 (*), at 0.01 ≥ α > 0.001 (**), or at α ≤ 0.001 (***)”; 3) Tables 4 and 5 are numbered incorrectly—they should be switched; and 4) the significance levels in footnote z of the renumbered Table 5 should read “0.01 ≥ α > 0.001 (**) or at α ≤ 0.001 (***)”.

Open Access

Plant growth retardant (PGR) substrate drench treatments (mg a.i./1.5-L pot) of ancymidol at doses of 0.5 to 8, paclobutrazol from 1 to 16, and uniconazole from 0.125 to 2 were applied to tuberous-rooted dahlias (Dahlia variabilis Willd.) to compare their effectiveness for controlling height. When the first inflorescence opened, the number of days from potting until flowering, leaf canopy height, inflorescence height above the foliage, and plant diameter were recorded. Total height control achieved using PGRs was primarily due to reduced inflorescence height, rather than leaf canopy height. Paclobutrazol, ancymidol, and uniconazole at all doses reduced total plant height of the less-vigorous `Red Pigmy' by >21% compared to the untreated control, with a height of 43.5 cm for the untreated control plants. Marketable potted plants were produced with doses of 2 to 4 mg of paclobutrazol, 0.25 to 0.5 mg of uniconazole, or 0.5 mg of ancymidol. All paclobutrazol, ancymidol, and uniconazole doses reduced total plant height of the more-vigorous `Golden Emblem' by >11% compared to the untreated control, with a height of 82.1 cm for the untreated control. Marketable potted plants were produced with 4 to 8 mg of paclobutrazol, 0.5 to 1 mg of uniconazole, or 2 mg of ancymidol.

Full access

Abstract

Although foliar applied glyphosate to Easter lily (Lilium longiflorum Thunb.) caused little damage at concentrations up to 540 x 10-4m (2.2 kg/ha), direct exposure of roots to glyphosate at concentrations as low as 2.7 x 10-4m (0.1 kg/ha) resulted in death. Glyphosate application after simulated flooding of the greenhouse floor indicated that plant injury would not occur if glyphosate is applied as recommended.

Open Access

Salpiglossis sinuata R. et P., a floriferous member of the Solanaceae, was studied for potential as a flowering potted plant when modified by growth retardants. Seedlings of an inbred line P-5 were covered with black cloth for an 8-hour photoperiod to permit vegetative growth to ≈16 -cm-diameter rosettes. Plants were then exposed to an 18-hour photoperiod for the duration of study. Flowering occurred 40 days after the plants were transferred to long days. Neither spray applications of uniconazole at 10, 20, 40, or 100 ppm, nor chlormequat chloride at 750, 1500, or 3000 ppm significantly retarded plant height. Applications of daminozide, ranging in concentration from 1000 to 5000 ppm, alone and in combination with chlormequat chloride, were effective at retarding plant height; however, concomitant restriction of corolla diameter was frequently observed. Chemical names used: 2-chloro- N,N,N -trimethylethanaminium chloride (chlormequat chloride); butanedioic acid mono(2,2-dimethylhydrazide) (daminozide); and (E) -1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl) -1-penten-3-01 (uniconazole).

Free access