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- Author or Editor: P. Allen Hammer x
Abstract
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.
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).
Abstract
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.
Abstract
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.
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).
Three cultivars each of zonal geranium (Pelargonium ×hortorum `Candy Lavender', `Fireball', and `Patriot Red') and ivy geraniums (Pelargonium pelatum `Global Deep Lilac', `Global Salmon Rose', and `Global Soft Pink') were grown in root media with pHs varying from 4.3 to 7.8. In Expt. 1, a mixture of sphagnum peat, fine perlite, and fine pine bark was modified with limestone and hydrated lime at the following rates: 0, 1.2, 3.0, 4.7, and 11.9 kg·m–3 limestone; 11.9 limestone plus 5.9 hydrated lime; 11.9 limestone plus 8.3 hydrated lime; and 11.9 kg·m–3 limestone plus 10.7 kg·m–3 hydrated lime to give the various root medium pH treatments. Plants were grown for 11 weeks in glass greenhouses. In Expt. 2, plants were grown in two commercial soilless mixes with one being modified with the addition of 0 kg·m–3 limestone, 6.0 kg·m–3 limestone plus 0.6 kg·m–3 hydrated lime, and 6.0 kg·m–3 limestone plus 2.4 kg·m–3 hydrated lime. In both experiments, greatest dry weight was recorded in zonal and ivy geraniums plants grown at root medium pHs above 6.4. This study showed a root medium pH of 6.4 to 6.5 should be recommended for the greenhouse production of both zonal and ivy geraniums.
Limestone requirement tests are routine in agronomic laboratories; however, no tests exist for soilless root medium although there is still a need to predict the limestone additions. This research was to develop a rapid, accurate test to determine the limestone requirement of soilless root media for a specific pH. Thirty-four media formulations were amended with increasing rates of limestone. Media were incubated in the greenhouse. Pots were irrigated to container capacity every 2 days with RO-water; pH was recorded after 5 weeks; and limestone requirement for pH 5.5 was determined for each media. A modified SMP buffer procedure for mineral soils was used. A 40-mL aliquot of the SMP buffer was added to 6 g of media, equilibrated for 48 hours and pH determined. Media-buffer pH was plotted against the incubation limestone requirement for pH 5.5. A separate regression was required for media containing coir since the modified SMP buffer test overestimated the limestone requirement of coir media. The correlation for non-coir media was –0.97 (Y = -1.19x + 7.52) and -0.94 (Y = –1.12x + 6.14) for coir media. The procedure was verified using 15 media. Media-buffer pH was determined and the limestone requirement was calculated using the corresponding regression equation. Two sets of media treatments were potted and incubated in the greenhouse. Rooted cuttings of geranium `Candy Lavender' were transplanted into one set of pots. Pots were irrigated every 2 days with RO-water and geraniums were irrigated with nonacidified fertilizer water. Media pH was determined at week 5. Media was nonsignificant for pots or geraniums (P ≤ 0.01). The mean pH of non-coir media was pH 5.66 and 5.67 for pots and geraniums and pH 5.39 and 5.39, respectively, for coir media.
Field studies were conducted on the potential of annual statice as an outdoor cut-flower crop for the Midwestern United States. Data was collected on seven cultivars in 1989 and 42 in 1990. In 1989, total fresh stem weight, stem count, and average stem weight differed significantly among cultivars. Yellow cultivars had more stems harvested than the rose, apricot, and blue cultivars, but stems of the yellow cultivars weighed less. The number of stems harvested over time tended to be concentrated in the first 8 weeks after flowering begins. In 1990, the average stem fresh weight was significantly different among the apricot, blue, and rose cultivars, but the number of stems harvested was significantly different only between the blue and rose cultivars.
Chemical plant growth retardant (PGR) treatments (mg·liter–1) were applied as foliar sprays to three zonal geranium cultivars: chlormequat at 1500, applied two, three, and four times, a combination of chlormequat at 750 and daminozide at 1250, applied one and two times, and paclobutrazol applied once at 5, 10, 20, and 30; twice at 5, 10, and 15; and three times at 5, plus an untreated control. Two paclobutrazol drench treatments at 0.1 and 0.25 mg a.i. per pot were also applied. The results of the PGR applications were significant at the cultivar × treatment interaction for leaf canopy height and plant diameter. Paclobutrazol rates of 10 to 15 mg·liter–1 resulted in acceptable height control for `Medallion Dark Red' and `Aurora'. `Pink Satisfaction' is a less vigorous cultivar and lower paclobutrazol rates of 5 to 10 mg·liter–1 were more suitable. When the total concentration of the single and multiple applications were compared, no additional height control was realized with the multiple applications of paclobutrazol.