steadyGROWpro and Rockwool as a Growth Media for Greenhouse Production of Vegetables. by: Purdue University
This study was conducted at the Department of Horticulture greenhouses of Purdue University in West Lafayette, Indiana to determine the effectiveness of steadyGROWpro as a greenhouse growth media. Experiments were conducted in a greenhouse zone of 1200 square feet. Supplemental light was provided by high pressure sodium lamps. Computer driven environmental system controlled the drip irrigation, air flow, evaporative cooling, sunshade and lighting. This facility supports year round production of plants under controlled environment.
Objectives:
- Analyze the physical – chemical properties of steadyGROWpro and Rockwool growth medium
- Evaluate growth and yield parameters of tomato and cucumber on two types of steadyGROWpro media and rockwool.
Project Procedure and Scope:
Seeds were sown on steadyGROWpro (low water retention - yellow), steadyGROWpro H+ (high water retention - brown) and rockwool plugs and placed in a mist chamber for germination. Plugs with germinated seedlings were then transferred into 4" x 4" x 2 5/8" blocks of the three respective media. Blocks were then placed on 3" x 6" x 36" slabs. Nutrient solutions were not recycled in this study. The plants were maintained in the same growth media throughout the study. Twenty seven plants of each variety were grown in replicated trials. This included nine plants in each type of media. The following seed varieties were used:
Tomato: Growdena (primed) from Rogers / Syngenta
Cucumber: Camaro FL from De Ruiter Seeds
The plant growth observations and analysis included germination rate, fruit weight, plant longevity, general plant health and fruit quality.
When testing the physical-chemical characteristics of the three growth mediums, a minimum of three replications of each test was conducted. Each medium was tested for:
pH (of the media slurry)
CEC (cation exchange capacity)
EC (electric conductivity)
Air to media ratio
Capillary Rise
Water Retention over time
Time of Year
August 2008– seed germination
March 2009 – termination of plants
Greenhouse Temperature
Greenhouse Temperatures ranged from 65 degrees F to 85 degrees F.
Watering/nutrient supply Regiment
Cucumbers – 6am to 6pm = 400ml per plant per hour / 6pm – 6 am = NONE
Tomatoes – 7am to 7pm = 1.6 litres per plant per hour / 7pm – 7 am = NONE
Lighting
Natural and artificial lighting was combined to provide 16 hours of light daily.
pH Test Results
The initial pH of the nutrient solution was 5.85, pH value of the leachate were as follows:
steadyGROWpro (low retention yellow) = 6.07
steadyGROWpro H+ (high retention brown) = 6.20
Rockwool = 5.85
CEC (Cation Exchange Capacity) Results
The CEC'c were determined by saturating samples of foam or rock wool with Ammonium bicarbonate, washing out unbound ammonium, displacing bound ammonium with KCl, adding a known quantity of NaOH to the eluate, boiling off the ammonia formed during the reaction and titrating the remaining OH with standardized HCl. Results were as follows:
steadyGROWpro (low retention yellow and H+ high retention brown) = 4.03 meq/100 gm
Rockwool = 3.41 meq/100gm
EC Results (Electric Conductivity)
steadyGROWpro (low retention yellow and H+ high retention brown) = 2.2 mmhos/cm
Rockwool = 2.1 mmhos/cm
Air to media ratio
| Media type | Volume of air immediately after soaking |
Volume of air after 48 hours of soaking |
|---|---|---|
| Rockwool | 5.2% | 20.6% |
| steadyGROWpro H+(brown) | 11.1% | 27% |
| steadyGROWpro (yellow) | 41.5% | 55.8% |
Capillary Action Results (water column height in the media)
4" x 4" x 2 5/8" blocks were sub irrigated with a 3" flash flood of water. Blocks did not rest in water for an extended period of time, and the blocks were not irrigated again for the duration of the test.
Water columns results were as follows:
| Time Frame | steadyGROWpro (low retention yellow) |
steadyGROWpro H+ (high retention brown) |
Rockwool |
|---|---|---|---|
| Immediate | 1.5 " | FULL | FULL |
| 1 hour | 1" | 2" | FULL |
| 8 hour | .75" | 1.5" | 2" |
| 24 hour | 0 | .75" | .75" |
| 48 hour | 0 | .1" | .5" |
Water Retention Over Time – Overhead Irrigation
4" x 4" x 2 5/8" blocks were completely saturated with overhead irrigation and weighed immediately and at different times indicated below. Blocks were not irrigated again for the duration of the test.
Water retained in grams was as indicated in the chart below. Dry weight of the media was subtracted to calculate water retention.
| Time Frame | steadyGROWpro (low retention yellow) |
steadyGROWpro H+ (high retention brown) |
Rockwool |
|---|---|---|---|
| 5 hours | 159.6 grams | 479.9 grams | 492.6 grams |
| 24 hours | 130.8 grams | 442.2 grams | 460.7 grams |
| 48 hours | 107.6 grams | 415.2 grams | 429.1 grams |
| 96 hours | 59.5 grams | 331.6 grams | 326.8 grams |
| 144 hours | 18.3 grams | 233.4 grams | 217.3 grams |
Germination Results
20 seeds each of tomato and cucumber were sowed in each of the three media. Results of germination rate were as follows (plants with cotyledons after 7 days):
| steadyGROWpro (yellow) |
steadyGROWpro H+ (brown) |
Rockwool | |
|---|---|---|---|
| Cucumber | 20/20 | 20/20 | 5/20 |
| Tomato | 13/20 | 15/20 | 5/20 |
Yield Results
Overall, the steadyGROWpro H+ (high retention brown) was the best performing growth medium in terms of average grams of fruit harvested per plant in tomatoes and cucumbers. In total, steadyGROWpro H+ produced 19% more cucumber in terms of weight per plant than steadyGROWpro (low retention yellow) and 47% more in fruit weight per plant than Rockwool. Both steadyGROWpro media out performed rockwool in promoting growth of tomatoes as reflected by 23% in harvested weight.
Final Observations
steadyGROWpro performed well against rockwool. In addition to the positive yield results found in growing cucumbers and tomatoes in the greenhouse, it does offer additional advantages as well. Cucumber fruit set and matured a week earlier in steadyGROWpro (low retention yellow). Also, particularly with steadyGROWpro (low retention yellow), throughout the duration of the study, the media was relatively free of algal growth. In general the surface of steadyGROWpro remained dry and thus suppressed the growth of algae along the top surface of the blocks.
Disclaimer:
This study was conducted at the Department of Horticulture, Purdue University under the direction of Dr. Raghothama. The researchers do not directly or indirectly endorse any product used in this study.
