Class(ic) projects

August 31, 2010
Written by Dr. Theo Blom, University of Guelph
Introduction: This is the eighth edition of our annual summary of abstracts prepared by students in the 2010 Greenhouse Crop Production class at the University of Guelph. There were four projects in total.

This year, we had the privilege of an exchange student from Mexico, who did the project on his own. He studied the effects of light intensity in combination with calcium nutrition on Easter lilies.

There were two projects studying light quality and organic production, respectively. The third group (referred to as the Leamington connection) tackled the effect of phosphorus on cucumber growth.

All students were third- or fourth-year students, and were working towards a bachelor of science in agriculture (B.Sc. Agr.) degree. The research topics came mostly from suggestions by industry contacts. These studies present the results of a one-shot experiment, which had to be completed within a 10-week period, so there were no replications.



THE EFFECT OF LIGHT QUALITY ON GROWTH AND DEVELOPMENT OF POTTED GERBERA
By Diane Relyea and Patricia Slaght

Abstract: Potted gerbera daisies (Gerbera jamesonii) were used to identify the effect of light quality on growth and development. Plants were exposed to three light qualities – blue, red or white light (control) by using different fluorescent light bulbs (Penatron, TS bulbs). The total amount of light (8 mol/m2/day) was the same in each growth chamber.

project1  
Figure 1. Gerbera plants that were grown for five weeks under three different light spectra in a growth chamber. Total light sums were maintained the same (8 mol/m2/day). The plant groupings are, from left to right: red, white and blue light from fluorescent lamps.

 
Plant growth was determined weekly by determining both fresh and dry weights, as well as the number of fully expanded leaves. The number of flower buds and the week of their appearance were used to measure the development of the plants.

Plants exposed to red light had consistently higher plant mass and a larger number of leaves than plants under blue light (Figure 1). The plants exposed to blue light showed a slightly increased rate of development in the flower buds compared to plants under red light. Plants exposed to white light were intermediate in terms of plant mass.



GROWTH COMPARISONS OF THREE INORGANIC AND ORGANIC FERTILIZERS ON GREENHOUSE-GROWN SALAD MIX
By Rebecca Hodges

Abstract: The objective of this study was to compare three organic fertilizers with inorganic fertilizers and the growth of four leafy vegetables. All the plants were given 100 ppm of total nitrogen while the three organic fertilizers contained different amounts of phosphorus and potassium (4-2-3; 3-3-3; and 16-0-0).

The inorganic fertilizers contained the same amounts of nitrogen, and relatively equal amounts of (P2O5) and (K2O) as the organic. The source of nutrients in the organic fertilizers was blood meal, bone meal, seaweed extracts and fish meal.

project2  
Figure 2. Lettuce plants grown with organic fertilizer compared to inorganic fertilizer. From left to right, pots alternate organic and inorganic starting with 4-2-3 fertilizer (left), 16-0-0 fertilizer (middle), and 3-3-3 organic fertilizer (right).

 
The plants were grown in a soilless substrate for 21 days in a greenhouse at 20℃ after transplanting. The type of fertilizer made no difference on the number of leaves. However, the plants given inorganic fertilizer had larger leaves, as well as higher fresh and dry weights. This is likely due to the slower mineralization of nutrients in the organic fertilizer. Plants grown with phosphorus and potassium in the fertilizer (4-2-3 and 3-3-3) grew significantly bigger than those without P and K (Figure 2).



EFFECTS OF LIGHT INTENSITIES AND CALCIUM NUTRITION ON THE HEIGHT OF EASTER LILIES (LILIUM LONGIFLORUM)
By Oscar Atilano Ruvalcaba

Abstract: Easter lilies (Lilium longiflorum ‘Nellie White’) were grown under three different levels of shade inside a greenhouse (0, 25 and 50 per cent shade) using neutral shade materials. Within each shade regime, plants were irrigated at every watering with three concentrations of calcium (0, 2.5, and 5 mM [millimole/L]) using otherwise complete nutrient solutions.

project3  
Figure 3. Easter lily grown at the Bovey Greenhouses, University of Guelph.

 
For each shade with calcium combination, 10 plants were used and a mixture of peat and perlite (SunGro #4) was used as substrate. At flowering, plant height increased with shade: 52.9 cm (no shade), 59.7 cm (25 per cent shade) and 64.0 cm (50 per cent shade). Flowering dates as well as the number of healthy and aborted buds were not affected by shading. Calcium nutrition did not show any significant visible effect on the plants.



EFFECT OF DIFFERENT PHOSPHORUS CONCENTRATIONS ON OVERALL PLANT GROWTH OF GREENHOUSE CUCUMBERS
By Steve Stasko and Tyler Sabelli

Abstract: A cucumber crop was studied to investigate the effect of different phosphorus concentrations on overall plant growth. The cucumber plants were irrigated with three different phosphorus concentrations: 0.25 mmol P/L, 1.0 mmol P/L and 4.0 mmol P/L (Figure 4).

project4  
Figure 4. Set-up of cucumber experiment using three rates of phosphorus in the nutrient solution.
 
Results indicated that leaf surface area, percentage of phosphorus in the leaf, and fresh and dry weights were all greater as the treatments with higher phosphorus content in the solution increased. The removal of additional side shoots and fruits were also measured comparing each treatment as well as recording any visual differences in the roots. A plant tissue analysis of the leaves, showed a deficiency in terms of phosphorus content based on recommended levels in the 0.25 mmol P/L solution, which helped to explain its reduction in growth (leaf surface area, maturation and delayed timing of fruit set) compared with the other two solutions. A level of 1.0 mmol of phosphorus in the nutrient solution seems to be a minimum for seedless cucumbers. ■

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