Potted crop focus

November 21, 2012
Written by University of Guelph
This is the 10th edition summary of student research abstracts, this year prepared by the 2012 class taking the course “Greenhouse Crop Production” at the University of Guelph.

Most students are in their third or fourth year and working towards a bachelor of science degree in agriculture (B.Sc. Agr.) or are working on a BA degree.

The topics the students studied came mostly from suggestions by industry contacts or from personal interest. There were eight projects in total. These studies present the results of a single experiment, which had to be completed within a 10-week period (a semester). The goal is for the students to get some practical experience in growing plants and to determine whether research is up their alley. So, the reader has to be careful about making final conclusions from these projects.
   
Guelph-students
 

Students in the Greenhouse Production 2012 class (photo above), included, front row, from left to right: Selene Richens, Stephanie Campbell, Martha Lowry, Laura Wiser (audit), Kendal Vermeer, Scott Belton and Nicholas Gavin; back row, Jenna MacDougall, Juan Gutierrez, Eundong Kim, Kyle Phillipson, Kyle Mendritzki, Lisa Hanlon, Tyler Jean and Asena Goren. Absent during the photo session were Paul Kerrigan and Scott Koornneef.


THE EFFECT OF pH ON THE EFFECTIVENESS OF BONZI APPLICATIONS ON POTTED ROSES
By Stephanie Campbell and Selene Richens
 
■ To maintain the high quality of production in many potted perennial crops, plant growth retardants are often used to prevent or delay elongation. This study determined if solution-pH had an effect on the efficacy of common commercial growth retardants.

Figure_1  
Fig. 1: Pot rose ‘Kordana Patsy’ was treated with 10 ppm paclobutrazol at a solution pH 6.

 
Weekly Bonzi (10 ppm paclobutrazol) applications with solution pHs varying from pH 3 to 7 were applied to potted ‘Patsy Kordana’ roses (Figure 1 Above).
The pH of the Bonzi solution had no consistent or significant effects on plant width, fresh or dry weight, and leaf area.

In terms of height, the solution with pH 3 produced taller plants than at pH 4, with a slight increase in plant height when increasing pH above 4.

However, differences in effectiveness were well within 10 per cent of total height, and also were not much different from control plants that received the same pH but no Bonzi.


EXPLORATION OF COCO COIR AS A SUBSTRATE AMENDMENT FOR POTTED ROSES
By Asena Goren and Kendal Vermeer

■  Coconut coir is gaining popularity as a substrate amendment for greenhouse ornamentals. It has attractive physical and chemical properties (aeration, water holding capacity, drainage, cation exchange capacity), is ecologically friendly, and has seen positive reviews in studies on a wide range of ornamentals, including cut roses.

chart1  
Figure 2. The effects of different coco coir/Sunshine mixes on plant heights of potted rose measured on three dates. Plant height was the average of the lengths of the laterals. Error bars represent the standard error.

 
This study aimed to determine the performance of different concentrations (0 to 100 per cent in 10 per cent increments V/V) of coco coir combined with Sunshine Mix 4 on potted mini roses.

It was found that concentrations above 50 per cent coir were detrimental to plant health, causing decreased growth and visible leaf burning. Decreasing concentrations of coir increased overall plant performance, with 100 per cent Sunshine Mix 4 yielding the greatest plant height (Figure 2).

When deciding whether or not to use coco coir as a substrate amendment, consideration should be given to the species and its tolerance for salinity (sodium and chloride).

Figure 2. The effects of different coco coir/Sunshine mixes on plant heights of potted rose measured on three dates. Plant height was the average of the lengths of the laterals. Error bars represent the standard error.


THE EFFECT OF pH ON CALIBRACHOA GROWTH AND CHLOROPHYLL CONTENT
By Lisa Hanlon and Martha Lowry

■ Calibrachoa (Calibrachoa Cerv.) is an iron-inefficient species, which often suffers from micronutrient deficiencies at high pHs (above pH ~ 6). Micronutrient toxicities often develop below a pH 5. Four substrates were prepared by mixing peat with 1, 3, 4.5 and 6 kg of dolomitic limestone/m3, resulting in a substrate pH 3.70, 5.03, 5.42 and 5.65, respectively. Calibrachoa MiniFamous™ Vampire plugs were transplanted into 10 cm pots using the four substrates and grown for seven weeks in a glass greenhouse at about 21 C. Plants were watered with 20-8-20 fertilizer water (pH 6.90) at 250 ppm N.

Figure_3_-_representative_calib  
Figure 3. Representative sample of calibrachoa grown at average pH 3.70, 5.03, 5.42 and 5.65 (from left to right).
 
Weekly shoot height and substrate pH (the pour-through method) were measured. Absolute growth rate, fresh and dry shoot mass, flower count and relative chlorophyll content were analyzed.

The results showed that plants at pH 5.65 had significantly higher chlorophyll content than all other treatments and were visibly greener. The remaining results were found to be insignificant (Figure 3). A larger pH range may have given more significant results.


GREEN LIGHT DURING THE NIGHT MAY AFFECT BUDDING IN CHRYSANTHEMUMS
By Juan Gutierrez and Kyle Phillipson

■ Potted chrysanthemums (Chrysanthemum x morifolium) are short-day plants and require a long period of uninterrupted darkness to initiate flower buds. At night, growers are not able to work on the crop due to the strict darkness requirements.

It was theorized that green light could potentially be used during the night periods.

Figure_4  
Figure 4

 
Figure 4. The set-up of the night interruption experiment with the green LED on the left and the chrysanthemums spaced at given distances in order to obtain light intensities of 0.2, 0.8, 2.0 and 3.2 µmol/m2/s.

In this experiment, we set out to determine the effect of green light-emitting diodes (LEDs) with a peak wavelength of 522 nm on the flower bud formation and development.

Two different varieties (‘Juneau’ and ‘Bold New York’) were placed at different distances from a green LED to obtain intensities from 0.2, 0.8, 2.0 and 3.2 µmol/m2/s (Figure 4).

The lamp was turned on during the night for five hours (midnight to 5 a.m.) for the total short-day period. It was found that plants farther away from the light showed earlier initiation and more rapid development of generative buds, when compared to the plants closer to the light.

It was also found that plants receiving 3.2 µmol/m2/s of the green LED remained in the vegetative stage. These results were similar for both varieties. This experiment shows that using a green LED during the night may still delay flowering of chrysanthemums.


THE EFFECT OF DIFFERENT NITROGEN CONCENTRATIONS ON HEIGHT AND GROWTH OF EASTER LILIES
By Eundong Kim

■  Nitrogen concentration is one of the most important factors to consider when growing Easter lilies (Lilium longiflorum) since it can impact overall growth and possibly the height of the plants.

chart2  
Figure 5. Weekly height increase of 8/9 ‘Nellie White’ 

 
Two different sizes of ‘Nellie White’ (size 8/9 and 7/8) and ‘Grace’ (size 7/8 and 6/7) were used and placed on a bench and irrigated with three different nitrogen concentrations, namely, 375, 180, and 90 ppm NO3-N using 15-0-15. Plants were handwatered with 200 ml of solution for each plant once a week
initially after emergence, and twice a week after March 1.

Plant height and leaf unfolding were measured weekly and bud sizes as well as root lengths were measured at flowering.

There were no significant differences for leaf unfolding rate, overall height, root lengths and development of plants. However, plants with the highest nitrogen concentration, 375 ppm N, showed better flower bud development and flowered slightly earlier (Figure 5) than plants fertilized with either 180 or 90 ppm N (Figure 5).

Figure 5. Weekly height increase of 8/9 ‘Nellie White’ fertilized with different nitrogen concentrations.
 

GREENHOUSE PLANT PRODUCTON RESPONSE TO SUGARS
By Scott Belton

■ The use of supplemental sugars in nutrient solutions for plant production is not fully understood. The experimental objective was to determine whether supplementing sugars such as sucrose, fructose and glucose at concentrations of 0 (control), 0.01, 0.1, 1, 10 and 100 µM/L have a significant effect on plant growth and development.

Figure_6  
Figure 6. An overview of the hydroponic set-up. 

 
Sunflower seedlings were grown in a standard nutrient solution with sugar supplementation at the various concentrations for two months until harvest (Figure 6).

At harvest, final heights were taken, as well as stem diameters, root/shoot fresh weights, and pre-bud floral diameter. All plants died at 100 µM after two weeks in the solution independent of the sugar type.

Stem diameter appeared to decrease with increasing concentration for all sugar types, while there was no clear trend for the other plant parameters with increasing concentration for any of the sugar types.

Figure 6. An overview of the hydroponic set-up.
 

THE EFFECT OF PHOSPHORUS ON HEIGHT, GROWTH AND LEAF COLOUR OF LILIUM LONGIFLORUM
By Jenna MacDougall and Scott Koornneef

■ Easter lilies Lilium longiflorum need to be grown at a specific height and appearance for optimal success.

Figure_7  
Figure 7. ‘Grace’ lilies (size 6.5/7) that were fertilized with different phosphorus concentrations (from left to right): 1.0, 0.25, 0.5, 1.5, 2.0 and 0 (mmol P/L), respectively.

 
‘Nellie White’ (size 7/8) and ‘Grace’ (size 7/8 and 6/7) were grown under controlled irrigation and environment with different phosphorus concentrations to attempt to obtain an optimal concentration of phosphorus for plant height and leaf colour.

Six phosphorus concentrations (0, 0.25, 0.50, 1.0, 1.5 and 2.0 mmol P/L) were applied, while maintaining the same concentration of N and K.

Plants were treated through subirrigation starting five weeks after planting until flowering. Plants given no phosphorus (0 P) were considerably shorter and had smaller leaves than the plants that had received some phosphorus (Figure 7). This appeared to be the case for all lily types.


EFFECT OF LOW pH ON PHYTOTOXICITY IN THE SHOOTS AND ROOTS OF BEDDING PLANTS
By Tyler Jean

■ Plants are potentially exposed to extreme pHs due to acid rain and soil substrate, as well as fertilizer and pesticide applications.

The objective of this study was to determine how pH affects the growth rate and biomass of roots and shoots of rosa hybrida, chrysanthemum morifolium, tagetes erecta and viola hybrida.

Figure_8  
Figure 8. Harvested plants from the pH 2.0 spray treatment: A) roses, B) mums, C) marigolds and D) pansies showing minimal leaf and root damage. Drench applications at pH 2.0 killed all species (pictures not shown).

 
Drench and spray treatments were applied once a week for six weeks of pH 2.0, 2.5, 3.0, 4.0, 5.0, 6.0 and 7.0 by adding either citric acid or potassium bicarbonate to deionized water. For most species, the pH 2.0 drench killed the plants, while a drench of pH 2.5 showed minimal damage.

Drench treatment significantly reduced the growth rate and root/shoot biomass of the chrysanthemums, marigolds and pansies, while it minimally affected the roses. Spray damage was minimal at pH 2.0 or any other pH (Figure 8).

A general trend of increased growth with increasing pH was observed for most species, except roses. This reduction in growth at the lower pH can potentially be attributed to cell damage that inhibits transport, transpiration, metabolism and nutrient exchange.

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