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Water by design

Irrigation is a common staple in many crops. Are more tobacco growers considering using it?

By David Williams

A drought-stricken 2007 season left a lot of crops, including tobacco—wanting for water. The crop, stressed and damaged by an unforgiving sun and skies with no rain clouds, showed its strain at the warehouse and in the pockets of growers.
The situation, though uncommon in its severity, is not altogether uncommon in occurrence. Many seasons have gone by where a grower needed to get water to a field or add just a little to what the weather might have delivered a little too soon or a little too late.
Many growers have considered adding a form of irrigation to their plans, both as a way of augmenting what Mother Nature gives them, and as long-term assurance that their crop yield will not suffer from a situation over which they have no control.
As recently as last year, Dr. J. Michael Moore of the University of Georgia presented a paper on tobacco irrigation, which is available on our Web site, www.tobaccofarmquarterly.com. Back in 2001, Dr. John Buchanan, an associate professor for biosystems engineering and soil science at the University of Tennessee, presented a program on irrigation, calling it “Insurance Policy or Investment?”
Buchanan admits now that the change to contract buying has altered a grower’s outlook in considering an irrigation system. But the premise of irrigation’s practicality is still valid.
“If a farmer has contracted with a buyer to produce a certain poundage, then irrigation helps to ensure that the farmer can produce the pounds,” he said.
According to Buchanan’s study, a grower averaging 2,000 pounds an acre who uses irrigation as an insurance policy may not get additional yield through irrigation, but he will pay added costs to ensure he does not get below his 2,000-pound yield. As an investment, irrigation should increase a grower’s revenue to the point yield should go up to 2,500-3,000 pounds an acre of burley, for example, nearly every year.
“Growers traditionally think that ‘over the years, with our experience and with lower rainfall, we can expect 1,800 or 2,000 pounds,’ or whatever our poundage is,” Buchanan said. “But the question that is never asked is, ‘what if it was the perfect year?’ Then we would produce, say, 2,500 pounds. Now you have an opportunity to have a perfect year much more frequently with regard to water. You still have to do all the other management things right, but with regard to water, you can have a perfect year.”
A study of irrigation for tobacco at The University of Tennessee’s Highland Rim Station in 2001 helps to show the value of irrigation as a regular management tool.
In the study, burley tobacco given one inch of water every 10 days yielded 3,259 pounds per acre. By comparison, a non-irrigated crop in that test got 4.4 inches of water and yielded 2,271 pounds an acre. The price difference was significant as well—the irrigated plot got $6,198 an acre versus $4,311 an acre for the non-irrigated crop.
Irrigation can be done two ways—by sprinklers, commonly seen in fields where large water guns (or impact sprinklers) are on a wheeled stand, fed through aluminum pipe, or by drip tape, which is gaining popularity. In drip irrigation, water is fed through emitters similar to soaker hoses used in lawn maintenance. The hoses are placed between rows or in every other row.
Buchanan said that newer sub-surface drip systems embed the drip tape into the ground, creating a permanent system that does not have to be taken up before harvest.
“It is picking up popularity for large row crops such as cotton, corn and soybeans, and it has a good value for high cash crops, like tobacco, nurseries and such as that,” he said. “But it does bind the grower to that particular field.”
With drip irrigation, the irrigation system can be used to introduce nutrients—a process called fertigation—which releases dependence on rain to translocate those nutrients to the roots of the plants. The system does not require a pipe-fitter to set up, reducing labor costs and shortening time in setup.

Where to get water?
In these water-conscious times, the usage of water in agriculture is a touchy subject in a community setting. Neighbors who have to install low-flow shower heads and cannot water their lawns as they would like can be irked at the sight of a huge water cannon dousing plants in a field, seemingly for hours on end.
“If you are looking at putting an inch of water on every week or every couple of weeks, that is a significant amount of water,” Buchanan said. “For example, one inch of water over one acre is 27,156 gallons. So you have to have that volume of water available. If you start multiplying that over 10 or 20 or 50 acres to do irrigation, that is quite a large volume.”
Buchanan said locating a water source takes a lot of research, be it a groundwater source or a surface source.
“How far away is the surface water source? How far do you have to pump the water? How deep is the aquifer you are going to pump from?” he said. “You have got to have an understanding of what is available.”
When tobacco was sold at auction and many people had as few as three acres, using farm ponds for irrigation was viable. In today’s world of larger farms (at least in flue-cured production) with larger acreages, that is not a practical option.
Using rivers or other sources that are shared with public use is permitted under certain conditions. Buchanan said the Army Corps of Engineers requires growers who want to “withdraw from a river, creek or stream that is navigable or contributes to navigable waters” to seek permission to withdraw water with a permit. But that requirement can be waived if the withdrawal system is temporary.
“In other words, if you are using a flexible hose attached to a pump that is driven by a tractor or something portable, and you are irrigating your field,” Buchanan said. “If you go in there and put a big permanent pipe into the water and tear the bank down to get the pipe in the water, and you have a big electrical system to drive the pump or a 1,000-gallon diesel tank there that may be in the flood plain, then you may fall under scrutiny of how much water you were withdrawing.”
Irrigation for crops is considered an end use by the Corps of Engineers because it does not end up back in the river, unlike municipal water withdrawal, which releases the treated water back to the river.

Gun or drip line?
Using the sprinkler method requires water flow rates from 50 gallons a minute to 500 gallons a minute, 60-80 pounds per square inch of pressure at the gun, and up to 150 psi at the pump. Drip irrigation uses considerably less water and needs much less pressure, but it has its drawbacks as well.
Sprinkler systems cannot be run at night as it increases the environment for possible disease. And while these systems can irrigate 10 acres in a 16-hour day, some systems require repositioning of the power source and the pump for a pull longer than the pipes can reach. In addition, some plants will be damaged by the movement of the big-wheeled sprinklers.
A drip system requires very clean water to prevent blockage in the drip pipes, which means growers must use good filters or very clean water sources.
“The drip irrigation really does look like a big benefit, because it is going to put the water on at such a slow rate that 90 percent of it is going to soak in,” Buchanan said.
Sprinkler irrigation wets everything in the field and requires high pressure. Drip irrigation places water at the roots and does not waste it in application but has additional costs in filters and labor. Growers should consider which method provides the biggest benefit and the smallest costs.
A grower considering irrigation should also be able to determine the moisture content of his soil, either through estimation of the water used by the plants, or measurement of the water contained in the soil, which eliminates the guesswork. Using a “checkbook method” of soil moisture content determination requires keeping a minimum balance of moisture in the soil. The use of watermark sensors, or tensiometers, helps in this process.
A popular misconception about irrigation is that the irrigation “waters the plants.” Buchanan said the truth is that irrigation recharges the reservoir of moisture in the soil from which the plants draw water.
“If you wet the crop, that means nothing,” he said. “The crop goes to the soil for the water. We have got to put moisture back in the ground. So if you have a big gun system out there, you could be putting several thousand gallons down on soil that cannot soak it up as rapidly as it is being applied. It becomes runoff, and that is a waste of diesel fuel. If it runs out of your field, it didn’t go into the soil and the crop won’t be able to get to it.”

Costs of irrigation
Gary Bullen, an agricultural Extension associate at North Carolina State University, prepared a recent presentation on costs of installing an irrigation system for the Piedmont and Coastal Plain regions of North Carolina. Bullen noted in his conclusions that a very small yield increase—as little as 73 pounds per acre—can justify the use of irrigation.
Chief among the reasons not to consider irrigation is the lack of a water source. While dams and suitably sized ponds can be constructed on a farm, the costs of these structures will skew the profitability of irrigating crops for several years.
While many growers struggled with water sources after last year, a wet winter has replenished many of the surface water sources. While the drought is not completely erased, it has been significantly quenched in many areas. Kentucky and Tennessee growers are enjoying particularly good restoration of ground moisture.
The cost assessment used a hard-line traveling sprinkler system with a diesel engine and pump. Such a system can supply an inch of water an acre per hour, which is necessary once a week in peak growth periods. In times of moderate drought, the system would require 2 to 3 irrigation events, while in times of severe drought, up to six events per year would be needed.
A single-reel system would cost $62,000, or $861 per acre, in a 72-acre field. With fixed and variable costs, the total goes up another $10,700, or $148 an acre. A double-reel system, which reduces pumping costs and doubles the amount of acreage covered, is an investment of $110,000 ($763 an acre) with fixed and variable costs for a three-cycle irrigation event going to $18,827 ($130 an acre).
But the benefits can be significant. The study indicated that a grower getting $1.50 a pound on his tobacco would need to increase his yield only 87 pounds an acre to pay for a double-reel system.
The million-dollar question is whether the increase in yield provided with an irrigation system offsets the cost increase.
A grower also should consider the effects of using irrigation long term if he is to invest in a system. Can he see a need for irrigation for the next several years? And can he afford to operate the system efficiently, considering time, resources and management?
“The true educational aspect of irrigation is to know when to turn it on and when to turn it off,” said Buchanan. “It’s fairly common for folks to have a significant investment in irrigation, and they will wait until it is too late before they turn it on—until it is really dry and the crop has already been set back. They need to have an understanding of the soil-water-plant relationship as to when they are starting to lose productivity.”