Better tobacco yields: Reduced nitrogen rates improve crop

Tobacco farmers David and Ken Hinnant are using about 14 pounds of nitrogen less per acre than what's recommended for this part of the country. Yet, they're actually producing a better crop, in terms of yields and quality on 100 acres of flue-cured tobacco.

At the same time, the Wilson County, N.C., brothers are helping to lay the groundwork for precision tobacco production.

The Neuse Crop Management Project is promoting nutrient management as a Best Management Practice (BMPs). The project is educating growers on selecting BMPs to help agriculture reduce nitrogen losses into the Neuse River by 30 percent.

Major fish kills on the Neuse River in 1995 promoted officials and scientists to find a solution to source- and non-source runoff into the 200-mile river basin.

Good business sense

For David Hinnant, it's just good business sense to do his part. He and his brother were among the first farmers involved with the Neuse project. “A whole lot of blame was being put on agriculture and I felt like agriculture needed to be part of the solution.

“In agriculture, we want to do our part (in reducing non-point source runoff), but we also want to put enough plant food there so that we can maintain a profitable operation,” he says. To help achieve these goals, David Hinnant serves on the Wilson County local advisory committee that is determining how agriculture will meet the goals of the Neuse rules.

Over the past several years, the Hinnant brothers have fine-tuned their nitrogen rates on a field-by-field basis and have discovered they can use less nitrogen per acre and increase yields and quality at the same time.

Unique project

The uniqueness of this project is underlined once you realize that N rates for tobacco are based on depth of clay. Using nutrient management in crops such as cotton, corn and wheat, N rates are based on the productivity of the soil. For a soil, there is a certain yield called realistic yield expectations (RYE), says David Hardy, coordinator of the NCMP in soil science Extension at North Carolina State University. RYEs may be established by growers through yield monitoring, averaging the best yields three out of five years or acquired through soil survey information for the predominant soil type.

For example, research has shown that about one pound of nitrogen is needed to produce a bushel of corn. Farmers can calculate the amount of N needed by multiplying the RYE by the nitrogen factor for a particular soil type. By using GPS-generated yield maps, cotton, corn and wheat farmers can apply nitrogen at variable rates throughout the field.

Depth of clay gives an indication of how efficiently nitrogen is expected to be used by tobacco. More nitrogen is needed on deeper sands due to a higher potential for leaching. The nitrogen factor is used somewhat similarly for other crops. But this isn't available to tobacco farmers.

Tobacco farmers normally use 75 pounds of N per acre on more productive soils, says Norman Harrell, Wilson County Extension field crops agent. Productive soils are those not prone to excessive leaching with depths of clay within 10 to 12 inches of the soil surface.

To find out the depth of clay at the Hinnant's farm, they used a soil probe to find the variability in the field. This work at the Hinnants foreshadows precision agriculture in tobacco.

“This is a much simplified version,” Harrell says. “It requires having specific places marked in the field which is not practical from a grower's perspective. Research is being conducted on how to measure depth of clay with sensing equipment in the field. If this is achieved, rates could be adjusted in the field automatically through coordinating yield maps with GPS and variable-rate technology.” In the on-farm test at the Hinnant farm, N.C. State tobacco specialists are looking at uniformly high rates, low rates and variable rates of nitrogen.

Actual application

As for the actual application in the test plots, the folks at NCMP called on technician Jeremy Barnes to outfit North Carolina State's 1968 Farmall 140 with a hydraulically-driven John Blue squeeze pump. The squeeze pump meters 30 percent N solution at the appropriate rate to two openers that knife the N into the ground, one row at a time. Although this is one-row equipment, the squeeze pump is equipped with eight plastic hoses so multiple rows are possible.

Eight plastic hoses draw the liquid nitrogen out of a tank mounted on the side of the Farmall. Two pipes lead to slits in the middle of disks that knife the N in the ground, one row at a time. The tractor operator varies the rates of nitrogen (the speed of the squeeze pump) by using a lever, similar to the accelerator lever on old-type tractors.

Through his own experimentation, David Hinnant has already seen enough to convince him to cut back on nitrogen rates.

“The quality of the tobacco will improve because it's uniform,” Hinnant says. “If you can sell tobacco that is uniform, you're going to get a better price for it. The more uniform the crop, the easier suckering, harvesting and curing are to do.

“Last year we used about 61 pounds of nitrogen per acre and had better yields and better quality,” Hinnant says. “We're cutting back on nitrogen rates trying to find the point to make the most profit from the crop and still not hurt it by adjusting back. It's on a trial and error basis.”

Actual benefit

To gauge how much real-world benefit he's getting from variable rate N applications, Hinnant, as part of this project, put load cell sensors on the back of one of his tobacco combines.

“We haven't been able to do that before in tobacco,” Bill Lord, North Carolina State Extension area specialized agent in Franklin County.

“We did that to measure green weight coming out of the field,” Hinnant says. “We took a sample of that in the curing barn and got the conversion rate from green to dry weight.” The bottom line was a more uniform crop that leads to better yield and quality — therefore, a desired end result.

Lord says the search for correct N rates based on depth of clay, as well as “playing with yield monitoring,” is part of trying to put together a system of precision agriculture for tobacco.

Hinnant sees the benefit in such a system, but knows the cost of the equipment would prohibit it being adopted on his farm. “The benefit of this project is that it gives us information so we can make the best use of our nitrogen rates.”

Just one target

“Nutrient management is just one BMP that we are promoting,” Hardy says. At four sites throughout the basin in the Piedmont and Coastal Plain, the project is helping farmers understand and comply with the Neuse rules and make informed decisions that are good both for water quality and profitability.

Researchers are also looking at buffers and filter strips along drainage ways in the Piedmont and central Coastal Plain, as well as controlled drainage in the lower Coastal Plain. “Coupling nutrient management with these BMPs is an extremely effective way to reduce nitrate-N concentrations in shallow groundwater as it flows to surface waters.”

The project is also working from an IPM perspective, with a computer program that aids farmers in determining when to spray for weeds.

Additional information about the project is located on the Internet at

The project gives the Hinnants a tangible way of finding out just how much N their tobacco really needs. They found they could produce better quality tobacco at variable nitrogen rates of 61 pounds per acre. “Before this project, variable rate technology meant dipping your hand in a bucket and dropping nitrogen on the ground,” he laughs.

“As variable-rate technology evolves in tobacco, farmers will be able to take advantage of it,” David says. “The equipment will be the main thing.”

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