Research looks at irrigation, tillage interaction

The relationship between irrigation and tillage has always been a complex one, and current research being done by the National Peanut Research Laboratory in Dawson, Ga., aims to further examine the interaction between the two inputs that probably affect farm profitability more than any other factor.

A long-term crop rotation study compares the water usage of three tillage systems under four water management levels, according to Wilson Faircloth, NPRL researcher.

“We did a study in 1997 that showed there was a 500 to 800-pounds yield increase in irrigated versus non-irrigated peanuts,” says Faircloth. “We think that if you have irrigation, you’ll have a greater crop yield. We also had an improvement in the grade of irrigated peanuts, meaning that irrigation put more money in your pocket, in five of the seven years of the study.”

There are some years when irrigation doesn’t pay, he says, but 2006 obviously wasn’t one of those years. And 10 years after the NPRL’s peanut irrigation study, questions still remain about how irrigation and tillage interact in various cropping systems.

“There are still no two inputs that affect your profitability quite as much,” says Faircloth. “There’s the fixed costs of irrigation plus pumping costs ranging up around $10 per acre per inch that is applied. And there’s the fuel costs involved in running your tractor and implements or to pull a disk or other piece of equipment across the field. Ten years later, we still have questions about the utility of irrigation in our systems — whether it pays and how it affects our bottom line.”

Everyone knows conservation-tillage works, he says, in terms of reducing runoff, preventing erosion, and increasing organic matter. But the adoption of conservation-tillage systems has lagged in peanuts compared to crops like cotton and corn, he adds.

Conservation-tillage adoption runs anywhere from 50 to 65 percent in corn and cotton production while peanut producers are adopting minimum-tillage systems at the rate of 30 to 40 percent.

“Mississippi, which is a relatively new player in peanut production, is at about 60 percent, and this is primarily strip-tillage peanuts. But a significant portion of the Georgia and Alabama peanut crops are still at less than 30-percent conservation-tillage,” says Faircloth.

Several issues probably have slowed the adoption of conservation-tillage in peanuts, he says, including digging and pegging concerns with residue in place and the contamination of the harvested crop with residue. “A lot of our research has proven these concerns to be false. But we haven’t yet had a GMO or Roundup Ready peanut — it goes hand in hand with the adoption of conservation-tillage techniques.”

Turning to the relationship between irrigation and tillage, Faircloth says water use has become a very political issue. “What if we ever come under water reduction policies? We need to be able to address that with current research. The interaction between reduced irrigation capacity and tillage — including the possible conservation of water with reduced-tillage — is of vital interest to growers,” he says.

In the NPRL’s research, three tillage systems were replicated three times each in one of four irrigation levels — 100 percent of a recommended amount, 66 percent, 33 percent, and zero percent or dryland. Irrigation was based on the Irrigator Pro software model for each crop.

Tillage systems, explains Faircloth, were conventional-tillage, wide-strip-tillage, and narrow-strip-tillage. Beginning in 2005, the narrow-strip-tillage treatments were converted to a strict no-till system. The test area was planted in triplicate, in a peanut-cotton-corn rotation, with each crop being present each year.

Yield of all three crops was highly dependent on seasonal rainfall and degree-day accumulation, he says. However, peanut yield was equivalent to the 100-percent treatment with one-third less irrigation applied in three of four years, regardless of tillage treatment. Corn yield was equal to the 100-percent level with one-third less water in one season and two-thirds less in 2004. Cotton yields were equivalent regardless of irrigation treatment or year.

All crops responded positively to conservation-tillage, says Faircloth, with corn yielding a 36 bushel per-acre average increase for either type of conservation-tillage system versus conventional. Peanut and cotton yielded greater under conservation systems, though not always significant for that year.

All crops yielded significantly greater under conservation-tillage systems in the dryland system, suggesting that non-irrigated farms may see the most benefit from conservation-tillage practices. Net returns, an indicator of farm profitability, were positive each year only in the conservation-tillage treatments, regardless of irrigation.

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