Vijay Rapaka, Ph.D. Manager, Corporate Research and Technical Support Manager, Smithers-Oasis Company, Kent, OH
SH Park, Corporate Polymer Research Scientist, Smithers-Oasis Korea, ChoongNam-Do, South Korea
Brenton Williams, Greenhouse Research Technician, Smithers-Oasis Company, Kent, OH
A new OASIS® Horticubes® hydroponic propagation medium with enhanced biodegradability but with the same improved performance as Horticubes® XL growing medium.
A case study with various lettuce types
The key for successful hydroponic production is to start with a strong young plant. Propagating in engineered media ensures uniform germination and growth without any concerns for plant diseases and food safety. OASIS® Grower Solutions has brought the most successful and reliable hydroponic propagation media to the hydroponic industry viz., Horticubes® and later Horticubes® XL, which are exclusively engineered for commercial hydroponic production. Over the last few years, hydroponic local food production has been significantly increasing because of the change in food habits, desire for consuming fresh produce, and to mitigate food safety related issues. Furthermore, hydroponic local food production has the solution to improve environmental sustainability and reduce the carbon foot. OASIS® Grower Solutions, which is committed to grower success as well as environmental sustainability, has developed an engineered hydroponic media, Horticubes® eS, which has enhanced biodegradable properties without affecting the plant growth performance. Horticubes® eS foam has been shown by ASTM D5511 to biodegrade 75% within 335 days in a biologically active landfill condition.
The objective of this following experiment is to determine the plant growth performance in Horticubes® eS medium and to compare against the growth performance in Horticubes® and Horticubes® XL Medium.
Materials and Methods
The trials were conducted during July/August of 2016 with Horticubes®, Horticubes® XL and Horticubes® eS foam with three different types of lettuce. The various lettuce types include: Butterhead ‘Rex’, Oakleaf ‘Rouxai’, and Romaine or Cos ‘Coastal Star’.
Seeding and initial watering:
With all the three types of foam media, 276 count sheets with single-seed dibble hole were used. The foam sheets were seeded with one seed per hole using an automated vacuum seeder, then placed in a carrying tray with drain holes. The foam sheets were lightly watered on the top to set the seed in the dibble holes. After that, the foam sheets were float saturated, followed by complete overhead leaching with 1 mS/cm (125 ppm N) of OHF 16-4-17 using a hose and a breaker.
Note: Initial watering with fertilizer is extremely important for uniform growth. Using complete nutrient solution at 1 mS/cm (125 ppm N) instead of clear water with initial watering (that includes both float saturation and overhead leaching) will double the lettuce seedling growth. For detailed information on initial watering, please refer to the protocol sheet.
Following initial watering, the seeds were covered with vermiculite.
Note: Generally, top dressing with vermiculite is not required with Butterhead ‘Rex’. However, with certain varieties of Oakleaf, Romaine, and lolla, top dressing with vermiculite is required, to promote uniform seedling growth without any issues of seedlings pushing out of growing medium. In this trial for consistency purposes, all the varieties were top dressed with vermiculite.
Propagation and production: The sheets were placed in a greenhouse and were not watered during the first two days. On day 3 and day 4, the sheets were misted and after that watered once a day or as required with a hose and a breaker using 1 mS/cm (125 ppm N) of OHF 16-4-17. For further information, refer to the protocol sheet. At 14 days after seeding, lettuce seedlings were transplanted into an NFT system. An EC of 1.17 mS/cm (150 ppm N) was supplied, using OHF 16-4-17, and the pH was maintained between 5.8 and 6.
Greenhouse conditions: The daytime heating and venting set points are from 65° F and 75° F (18° C to 26° C), respectively. The night- time heating and venting set points are from 55° F to 65° F (12.5° C to 18° C), respectively. A 16h day length was provided using HPS lighting, and the DLI was targeted at around 17 to 18 moles / day. When light levels exceed 500-600 μ. moles/m2/s the greenhouse was covered with shade curtains. The greenhouse relative humidity was maintained between 50% and 60%.
Observations: The germination study was conducted with at least 3 replications (one sheet per replication). At day 7 after seeding, percent germination was recorded. At day 14 after seeding, seedling fresh weight was recorded and photos were taken. The grow out study in the NFT system was conducted with at least 3 replications (3 plants / replication). After 21 days after transplant, lettuce weights were recorded and photos were taken. The data was subjected to statistical analysis to determine significant differences.
No seedling pushouts were observed with any of the three lettuce types when propagated in Horticubes®, Horticubes® XL and Horticubes® eS growing medium. The seedling growth at 14 days after seeding was significantly better in the case of Horticubes® XL and Horticubes® eS compared to Horticubes® Foam. On an average, the seedlings grown in Horticubes® XL and Horticubes® eS were 2 days ahead compared to the seedling grown in Horticubes® foam (Fig. 2 and Fig. 5). Therefore, generally speaking, the seedlings propagated in Horticubes® XL and Horticubes® eS can be transplanted 2 days earlier. Both in the case of Horticubes® XL and Horticubes® eS foam, roots penetrated through the bottom of the foam by 7 days after seeding (Fig. 4). The root growth was much more vigorous with profuse secondary roots in the case of Horticubes® XL compared to Horticubes® foam. The root growth in Horticubes® eS foam is comparable to Horticubes® eS Foam (Fig 5).
At 21 days after transplant into the NFT system, the lettuce that was started in Horticubes® XL and Horticubes® eS foam weighed more compared to the lettuce that was started in Horticubes® foam. However, the degree of differences varied among cultivars, with smaller weight differences in the case of Butterhead and Oakleaf, whereas major weight differences in the case of Romaine (Fig. 3). It should be noted that all the seedlings grown in different types of media were all transplanted at the same time, day 14. As a result, the larger seedlings in Horticubes® XL and Horticubes® eS were at a disadvantage, as they were overgrown and competing for light.
In general, the plant growth performance in the brand new foam technology with enhanced biodegradability, Horticubes® eS, is comparable to the growth performance in Horticubes® XL and significantly better than the performance in Horticubes® foam.