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CASE STUDY:

RTO PROJECT

WITH CHAP

Test Crops

Lettuce                      Kale

Lettuce
Kale

AIM = To explore and evaluate GyroCup's efficiency in plant growth and germination in hydroponic systems, with gel-based and paper-based substrates compared to single-use substrate rockwool.

SUBSTRATES  - Rockwall, Agar, Guar gum, AEH Hydrogel, Seed Tape, Hydrates Water Crystals

Green plant growing out of a GyroCup

SUMMARY

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CHAP conducted research on the effectiveness of water-based gels combined with GyroPlant technology for germination and plant growth in hydroponic systems. They tested five substrates, including agar, guar gum, AEH Hydrogel, seed tape, and hydrated water crystals, along with rockwool plugs as a control. Kale and lettuce were chosen as test crops. Results showed that rockwool, agar, and AEH Hydrogel had the highest and fastest germination rates, resulting in uniform crops with the most established plants. Seed tape performed best in the growth chamber due to consistent saturation. Guar gum and water crystals performed poorly. The study emphasises the importance of early germination stages and recommends focusing on substrates that retain water well for successful crop output. The GyroCup combined with agar, AEH Hydrogel, and seed tape showed promising results and warrants further investigation.

MATERIALS AND METHODS

Experimental design

The experiment was conducted at CHAP's Vertical Farm Development Centre using one level with 14 hydroponic benches totaling 28 m². Lettuce and kale were grown in plastic plug trays holding GyroCups. Two treatments were evaluated: germination conditions (dedicated room or in-situ) and substrate type (four gel-based substrates, seed tape, and rockwool plugs). Each treatment had 3 to 4 replicates, randomised within benches. GyroCups and rockwool plugs were evenly spaced, with 15 per substrate, representing independent replicates.
 

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Methods

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Substrate Preparation : 
 

Substrates were prepared as follows:

  • Agar: 2.6 g of agar powder mixed with 520 ml nutrient solution, heated, poured into a tray, refrigerated, and cut into 1 cm³ cubes.

  • Guar gum: 26 g of guar gum powder dissolved in 520 ml nutrient solution, spread in a tray, refrigerated, and cut into 1 cm³ cubes.

  • AEH Hydrogel cubes were cut from fresh cubes stored for 2 weeks.

  • Seed tape: 3 seeds enclosed between 1 cm x 1 cm squares of seed tape paper, sealed with water, and refrigerated overnight.

  • Water crystals: 50 g of dried crystals mixed with 500 ml nutrient solution until absorbed at a 1:10 ratio.

Germination: 

Crops were germinated in either a germination room or a growth chamber in darkness. The germination room had active humidification, with benches on the floor and daily misting to prevent surface drying. In the growth chamber, benches were irrigated and covered with black plastic to maintain high humidity. Temperature and humidity were monitored in both locations during germination.

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Trials:

After germination, benches from the germination room were moved to the growth chamber, where lighting and irrigation schedules began. A shallow water irrigation system mimicked NFT hydroponics, maintaining 2.4 cm of solution on benches continuously, with hourly 3-minute irrigations to refresh it. Growing parameters were outlined in Table 3. After 25 days, aboveground biomass was harvested and weighed.

Benches moved to shallow water irrigation system in growth chamber.


Crops assessed for germination rate and plant uniformity.

Trial set up:

GyroCups were cleaned and filled: agar, guar gum, and AEH Hydrogel had cubes placed inside, seed tape had squares inserted, and water crystals were scooped in. Rockwool plugs were saturated and placed in trays, with halved plugs used to match GyroCup levels. Selected GyroCups and rockwool plugs were weighed for consistency. They were arranged on benches following a layout, and seeds were placed on each substrate. Benches were misted lightly overhead.
 

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Measurements

GyroCup plant growth progress images
GyroCup plant growth progress images

After 29 days of growth plants harvested, weighed and counted. 

Six germination assessments were conducted at various intervals, counting emerged cotyledons. Uniformity during growth was estimated by observing evenness in plant height and biomass. At harvest, the number of plants and biomass were recorded. 

RESULTS

ROCKWOOL

Rockwool substrate
Rockwool substrate

AGAR

Agar gel
Agar gel

HYDRATED WATER CRYSTALS

Hydrated water crystals
Hydrated water crystals

Rockwool, agar and AEH Hydrogel = fastest and highest germination, excellent water retention, uniform crops.
 

SEED TAPE

Seed tape
Seed tape

Seed tape = performed best in growth chamber.

GUAR GUM

Guar gum
Guar gum

AEH HYDROGEL

AEH Hydrogel
AEH Hydrogel

Guar gum and water crystals = worst performing substrates.

Germination

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Lettuce :

For lettuce, rockwool, AEH Hydrogel, and agar substrates, germination was rapid (>98%) by 2 DAS in both the germination room and growth chamber. Seed tape initially matched guar gum until 4 DAS in the germination room, then surpassed it. In the growth chamber, seed tape's germination exceeded 90% by 5 DAS, while guar gum lagged behind. Water crystals performed poorly (<10%) in both treatments.


 

Kale:

Germination of kale was slower than lettuce. Agar showed the fastest germination (>90% by 4 DAS), followed by AEH Hydrogel and rockwool (>90% by 5 DAS). In the growth chamber, seed tape's germination matched agar, AEH Hydrogel, and rockwool (>90% by 5 DAS). However, in the germination room, seed tape's germination slowed after transfer to the growth chamber, reaching 84% by 18 DAS. Guar gum outperformed water crystals in the germination room but not in the growth chamber, where both were the poorest substrates.

 

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Notes on the data:
The germination data for seed tape substrates may underestimate actual germination rates because germination was only recorded when the tape broke apart and seedlings were visible. Additionally, germination in the growth chamber may have been faster than indicated since it was not possible to directly observe the central plug trays.

Uniformity

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Lettuce : 

For lettuce, agar and AEH Hydrogel showed the highest uniformity (>90%) in both germination locations. Rockwool had slightly lower uniformity (76-79%). Seed tape resulted in much higher uniformity when germinated in the growth chamber compared to the germination room (86% vs 51%). Uniformity of plants grown on guar gum was generally low, but slightly higher in the germination room than the growth chamber.



Kale:

For kale, uniformity was similar among rockwool, agar, and AEH Hydrogel, with greater uniformity observed for plants germinated in the germination room compared to the growth chamber (83-88% vs 77-80%). Seed tape also showed good uniformity, similar to rockwool, agar, and AEH Hydrogel. Guar gum had comparable uniformity when germinated in the germination room, but poor uniformity in the growth chamber (22%). Water crystals resulted in poor uniformity overall (<20%) due to the low number of plants available for assessment, not accounting for failed germination.

Plant number and fresh weight

Lettuce :
For lettuce, agar and AEH Hydrogel led to the highest plant fresh weights, surpassing rockwool. Fresh weights were greater for plants germinated in the growth chamber for agar and AEH Hydrogel. The number of established plants was similar for agar, AEH Hydrogel, and rockwool, with AEH Hydrogel in the growth chamber having the most (99%). Seed tape plants in the growth chamber also had higher fresh weights than the rockwool control, but less than those in the germination room. There was high variation between seed tape plants, with slightly fewer established compared to agar, AEH Hydrogel, and rockwool.


Kale:
For kale, agar, AEH Hydrogel, and seed tape resulted in similar plant fresh weights, all exceeding the rockwool control. However, fewer plants were established for seed tape. Unlike lettuce, fresh weights for agar and AEH Hydrogel were higher for plants germinated in the germination room compared to the growth chamber. There was high variation between plants for seed tape, affecting its fresh weights.

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Observations

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At 2-3 days after sowing, guar gum settled to the base of GyroCups, hindering germination. Submerged seeds due to irrigation led to unsuccessful germination for 56-91% of seeds. Water crystals expanded after irrigation, causing overflow and likely seed losses. They later rapidly decreased in volume. Despite high humidity in the germination room, substrates like seed tape and guar gum dried quickly, needing daily misting. In the growth chamber, covered benches and retained irrigation solution slowed substrate drying due to evaporation and condensation.

CONCLUSIONS

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The GyroCup in combination with agar, AEH Hydrogel and seed tape performed better than rockwool.

Further investigation into these substrates will continue.

 
Rockwool, agar, and AEH Hydrogel showed the fastest and highest germination rates for both crops, resulting in uniform crops and the highest number of established plants. Seed tape performed best in the growth chamber due to retained irrigation, while it dried quickly in the germination room. Guar gum and water crystals had poor performance. Mixed results were observed for different substrates and germination locations. The importance of water availability during germination, especially for substrates with poor water retention like seed tape, was highlighted. Guar gum and water crystals showed low germination rates despite the irrigation regime, possibly due to seeds being submerged or washed away. The reasons behind some mixed results remain unclear.

 

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