High young plant density doesn’t have to be efficient, and here’s why

“It isn’t just about your substrate or production methods; it’s about how it travels through your system,” says Bill Riffey, the general manager of grower operations at OASIS® Grower Solutions for the Americas, Europe and Africa. Joined by OASIS’ global research manager, Dr. Vijay Rapaka, Bill spoke about the importance of choosing the right substrate and substrate configuration to make the best use of production space.

Speaking namely about the production of leafy greens, Bill and Dr. Rapaka describe how a 30-day crop cycle is split between time in the propagation area and in the production area. By appropriately sizing the propagation area and managing the time spent in each zone, growers can increase the number of cycles per year.

Young plant trays of Lettuce ‘Rex’ grown in Horticubes® AeroMax. Growth 7 days after seeding
276 cell ct.              162 cell ct.             104 cell ct.            50 cell ct.

“If you reduce the time in the propagation area, you see the proportionate increase of time in the production area, which is an inefficient use of space and more expensive to maintain. A lot of this comes back to the substrate configuration, as high-density sheets cannot remain in the propagation area for long,” explains Bill.

OASIS Grower Solutions offers multiple substrate configurations ranging from 50-to-276-cell sheets (10x20x1.5”), with the higher cell numbers having a smaller substrate volume per seedling. As such, the seedlings outgrow the substrate much faster than in a less dense sheet.

“At lower seeding densities, depending on growing conditions, plants can remain in the propagation area for 18 days whereas at the highest density, only 12 days and then transplanted into the production area for 18 days,” explains Bill.

Young plant trays of Lettuce ‘Rex’ grown in Horticubes AeroMax. Growth 12-18 days after seeding  

276 cell ct./12 days, 162 cell ct./14 days, 104 cell ct./16 days, 50 cell ct./18 days

Appropriate substrate configuration helps optimize labor, improve plant health
As Dr. Rapaka explains, choosing the appropriate substrate configuration and opting for larger cells allows growers to optimize labor costs by reducing the need to re-space seedlings. This also translates into fewer touches and less risk of crop damage. Further, seedlings in larger substrates can be kept in the propagation area longer, meaning that stronger and more mature plants are transplanted into the production area. This reduces transplant shock, keeping the plants more vigorous and ensuring a smooth transition into the production area.

“With growing media, the tendency is to go with the highest density possible to reduce costs per square meter,” says Dr. Rapaka. “But what is missed in the equation is if you reduce the grow time during the propagation period, you have the proportionate increase of time in the production area.”

Finished plants of Lettuce ‘Rex’ started in Horticubes® AeroMax and transplanted into an NFT system. Growth 30 days after seeding

276 cell ct.          162 cell ct.              104 cell ct.            50 cell ct.

While larger (i.e., lower density) substrate sheets are somewhat more expensive than the high-density sheets, Dr. Rapaka and Bill explain that being able to keep plants in the propagation area longer can reduce the time needed in the production area by two days, eventually adding up to an additional rotation in the greenhouse.

“Let’s say a grower earns 100,000 euros per crop rotation. If you could get one additional turn, it would add another 100,000 euros to their bottom line. And if they sell their lettuce for 1 euro and the larger substrate costs 1 Eurocent more, it is worthwhile,” says Bill.

For more information:
Bill Riffey, General Manager, Grower Operations
Dr. Vijay Rapaka, Global Research Manager
OASIS Grower Solutions

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