Nothing like a little H2O - Second Quarter 2009
An efficient irrigation plan can cut expenses and increase yield
TFQ Editorial Staff
The fact that tobacco is considered a drought-tolerant crop was of particular importance to growers the last two years, as weather conditions in the Southeast were less than ideal to say the least. With an increased demand for fresh water from industrial and municipal sources, and the costs of physically getting the water out to the fields increasing, it is more important than ever to monitor soil moisture and properly manage your irrigation. Conserving water will directly help offset rising municipal water costs, as well as reduce expenses for energy, chemicals and labor.
According to the U.S. Department of Agriculture, agriculture accounts for more than 80 percent of water consumed in the nation, and while only 16 percent of harvested cropland is irrigated, this acreage generates nearly half the value of all crops sold. A series of tests in North Carolina determined that properly irrigated tobacco crops produced 15 percent more yield and 10 percent higher purchase prices than nonirrigated tobacco. So obviously irrigation is critical to a high-yielding farm, but the days of haphazardly watering the fields are clearly behind us.
“Efficient irrigation systems and water management practices can help maintain farm profitability in an era of increasingly limited and more costly water supplies,” wrote Glenn Schaible and Marcel Aillery for the USDA’s Economic Research Service. “Improved water management practices may also reduce the impact of irrigated production on offsite water quantity and quality, and conserve water for growing nonagricultural demands.”
The good news for tobacco farmers is that because of its efficient root system, tobacco can not only survive through drought conditions, but with a little properly managed irrigation, it can actually thrive. In fact, tobacco is more susceptible to damage by having too much water in the soil than having too little, and thus irrigation should be used to supplement pronounced rainfall shortages, as opposed to being used excessively on a regularly set schedule.
Out in the fields
In a 2007 article for tobaccofarmquarterly.com, Dr. J. Michael Moore, a professor and tobacco extension agronomist with the University of Georgia, said withholding irrigation prior to pulling transplants in drought-prone areas will harden the plants and promote root regeneration. He then suggested using 100 to 200 gallons of water per acre at transplanting to create a hospitable environment for root development, to later be followed by 0.5 inches of irrigation before severe wilting occurs to get water beneath the roots. “Irrigation after transplanting may be the most beneficial water applied during the season,” he said, as the water helps settle the soil around the roots and encourages faster development. Proper moisture at this point will promote fast growth and early maturity, which will make the plants less suseptible to damage from weather, disease and insects.
For the next four to six weeks, until the plants are knee high, withholding water will create a moderate stress that is beneficial to tobacco as it promotes deeper root development, and thus irrigation is only recommended during extreme drought conditions during this early-growth phase. After that, though, when the plants enter the rapid growth stage, moisture again becomes extremely important to ensure maximum yield and quality.
Soil moisture sensing devices such as tensiometers and resistance blocks should be moitored regularly (about three times per week), with the results logged in a water balance sheet in order to create an efficient irrigation schedule, helping growers maintain adequate soil moisture in the top two feet of soil. According to Moore, tobacco plants at their peak—usually around week eight—use about .25 inch of water a day, therefore irrigation should generally never top 2 inches per week, as excessive irrigation during this critical period may cause damage to the root system.
Irrigation at harvest is not generally required as slight moisture stress is beneficial, but in extreme drought conditions it will help increase the maturity rate and improve the curability of the leaf.
A penny saved
Aside from using the proper amounts of irrigation at the proper times, growers can also take several other steps to develop an efficient water management program. Applying water at night (or early in the morning if diseases such as rhizoctonia, blue mold or brown spot are of concern) as opposed to the heat of the day will drastically reduce water lost to evaporation. Also, be sure the water you are using is safe and not contaminated by disease from runoff (proper irrigation practices will likewise help this problem), and be sure you know its chlorine content if it is a municipal supply and nitrogen content if it comes from a manure lagoon.
Switching from an overhead irrigation method to a drip system is another possible option. While the drip system does require a substantial upfront investment, reports suggest it can reduce water use by 30 to 50 percent. A drip system also introduces the posibility to inject fertilizers into the water, likely increases the quality of the plant’s lowest leaves (by not splashing soil up) and reduces soil erosion and potential runoff problems.
On the other hand, though, beyond the expense of installing wells and system components, drip irrigation systems will require the disposal of mulch and tubing and often cause a tendency to over-irrigate, leading to the leaching of nutrients. In fact, the USDA says that 40 to 60 percent of these low-pressure-irrigated acres could still benefit from improved water management, proving again it’s not just the tools that make the difference, it’s the grower.
In the end, recent research shows that an increase of as little as 73 pounds per acre in yield will justify the use of irrigation, and gains from a well-managed irrigation system can increase yield 500 to 1,000 pound per acre.
For a more complete account of irrigation practices for tobacco growers, please read Dr. J. Michael Moore’s entire article HERE.