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Transplant efficiency

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Follow the road to the most usable number of transplants by establishing uniform germination

by Rocky Womack

The road to transplant efficiency begins with the typical quality peat moss and tobacco seed for good germination.
However, a well-known agronomist says the efficiency is better measured from the end result.
“You want to use [the] highest percentage (of usable transplants) as you can possibly use, because all of your expenses in the greenhouse are on a square-foot basis or on a per-greenhouse-space basis,” says David Smith, an Extension tobacco specialist and head of the crop science department at North Carolina State University in Raleigh, N.C. “The more plants you get into the field, the lower the cost per plant.”

Following the path to efficiency
To grow the most usable transplants and reach that end result, Smith says a grower must strive for the highest percentage of plant germination as possible, and shoot for at least 90 to 95 percent germination. The germination must be uniform with no more than a five-day range from when the first seedling emerges to the last seedling. The latest germinating plants are the most susceptible to salt or disease injury, or to shading out by taller plants.
Once growers reach 90 to 95 percent germination and see plants covering the tray sides, Smith says they can come pretty close to predicting their percent of usable transplants.
Once the seedlings have germinated, Smith advises to keep them growing at the same rate. The next biggest threat is potential salt injury, but he says a grower can minimize injury by delaying when he adds fertilizer to the water.
Extension tobacco specialist David Reed at Virginia Tech’s Southern Piedmont Agricultural Research and Extension Center in Blackstone, Va., has done considerable research on applying fertilizer in the transplant water. He has found that a grower can achieve a higher percentage of surviving seedlings and receive more uniform growth if he waits a few days after seeding to add fertilizer. In fact, fertilizing at seeding results in an average seedling mortality rate of 15 percent, compared with 6 percent when fertilizer is added three days after seeding, according to the center’s 2007 Flue-Cured Tobacco Production Guide.
Stephen Barts, the Extension tobacco agent for the Virginia counties of Pittsylvania and Franklin, says Virginia Cooperative Extension recommends applying 150 parts per million (ppm) of nitrogen in one to three days after seeding and applying the fertilizer evenly throughout the water bay. Growers should follow that with 100 ppm nitrogen at four weeks after seeding.
Barts tells growers to know the nutrient content in the float water and measure the nutrient content of the water bay in several spots versus in one location. The fertilizer is more effective if spread evenly throughout the bay, so all the seedlings can absorb the nutrients.
He also advises paying attention to the volume of water in the bay. A drop in water-bay level can throw off any calibration of chemical and fertilizer injections, he says.
“If you’re floating your trays in three inches or four inches of water and you lose an inch of water over a period of time, spread that over the area in a bay, and that’s a lot of water loss,” Barts says. “That will definitely affect how many gallons you’ve got floating in that bay at that time. When you lose that water and you go to put fertilizer in it and you are trying to get it 50 ppm, well 50 ppm in 1,000 gallons of water is a whole different kind of concentration than it is in 2,000 or 3,000 gallons.”
Smith advises to monitor the conductivity or fertilizer salts in the potting soil and monitor it in the right place. He says many growers measure the salt level with a conductivity meter by dipping it constantly into the water.
“Conductivity of the water is important, because it affects the potential conductivity of the growing medium,” Smith says, “but what is most important to the young plant is the conductivity near the surface of the growing medium where the roots are.
“High temperatures and strong air flow in the greenhouse increase evaporation from the surface of the medium and concentrate the fertilizer salts near the surface, potentially injuring plants,” Smith adds. Next, he advises to be aggressive in adding water from overtop of the seedlings, if needed.

Temperature control
More fans in the greenhouse can improve air circulation inside, Barts says, and even out the temperature from front to back. He recommends briefly opening the greenhouse side curtains early in the morning and late in the afternoon to reduce the naturally occurring condensation (moisture) and temperature during the day. Maintain temperatures inside between 70 and 72 degrees Fahrenheit. If the temperature drops too low, it delays germination, he says. Too high, and the heat can damage the plants.

Clipping
How much is too much clipping?
“For the farmers who mow 10 and 15 times, that means they seeded too early,” Smith says. “This year with fuel prices like they are, they need to wait until later. Valentine’s Day for the bulk of eastern North Carolina is early enough.”
Virginia Cooperative Extension’s clipping program calls for mowing plants 2 to 2.5 inches above the bud the first time, then 1 to 1.5 inches the next, Barts says. The program calls for clipping on a three-day schedule for the first three clippings. Further clippings should be five days apart. Before and after mowing, Barts advises cleaning the mower blade and collecting all the clippings to prevent future disease pressure.

Sowing too early
Smith believes some farmers seed too early. This results in higher fuel prices during the last days of winter, increased salt and disease injury, and wild temperature fluctuations.
“Roughly, 21 days after you seed, your usability is pretty much set no matter what you do,” he says, “unless something happens to kill plants, such as a disease or high temperatures. You can do little to improve potential usability after 21 days, but you can do a lot to decrease usability after this point.”

Transplanting
Dan Timmer, marketing manager with Mechanical Transplanter Co. LLC in Holland, Mich., believes that the most efficient transplanter for flue-cured and burley tobacco growers to use is the carousel model with front-wheel drive.
“These machines, first of all, allow the farmer to use existing toolbars or pull-type trailers,” he says. “Models of this nature can be treated as just replacement units.”
He adds when using the carrousel model, ground conditions do not have to be ideal, because the front-wheel drive helps prepare the soil ahead of the transplanter.
Before hooking the transplanter to the three-point hitch, Timmer says growers should learn how to use carousel transplanters properly so they won’t encounter any unknown problems while in operation.
Timmer suggests when using a transplanter that the transplants are well mowed. This toughens them up and reduces bruising at transplanting time.