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For soybeans : Irrigation scheduler to be updated

In the Mid-South, soybeans are grown in many situations and many different ways. Arkansas Extension researchers want to know if their recommendations fit all.

“You may be familiar with the Arkansas soybean irrigation scheduler,” says Earl Vories. “It's a great tool for farmers managing a lot of acres. Many growers — even outside the Mid-South — are using it.”

Speaking to a tour group at the Northeast Research and Extension Center field day in Keiser, Ark., Vories, irrigation and water management Extension specialist, says soybean recommendations haven't changed in several years. Cultural practices, however, have. At the time the recommendations were developed, most soybeans were grown on 38-inch rows, many on beds.

“We rarely see that anymore. Now there are a lot of broadcast/drilled soybeans and narrow rows. We believe it is time to see if our recommendations are still appropriate.”

Setting up the irrigation scheduler, farmers answer only one question: What maturity group have you planted? Vories wonders if there should be more.

“It might be prudent to ask more questions. What row spacing is being used? What's your plant population? Many growers are interested in cutting population to reduce seed costs and technology fees.”

Striving to see if, indeed, the scheduler needs tweaking, Vories and colleagues have begun studies on 7.5-inch rows, 19-inch rows and 38-inch rows. In those spacings are populations of 50,000 plants, 100,000 plants and 150,000 plants.

“Soil moisture sensors are in the rows. We also have installed a subsurface drip irrigation system. Half the field is irrigated and half isn't. Because of the ample rain we've had this year, there's not a lot of difference. In a drier year, there will be.”

Newer technologies

Another facet of the study is digital photographs. “With a digital camera — some folks have them on their phones now — take a shot of the canopy,” says Vories. “From the photo, a computer counts the number of green dots (plants) and brown dots (soil). The computer program will relate that to bio-mass and how large the plants are. That tells the grower if the crop needs irrigation.”

Vories is also looking at a Normalized Difference Vegetative Index. “This has been used in cotton. A picture taken from an airplane will have seven colors. The colors correspond to different plant sizes. If Pix needs to be applied, the pictures help in adjusting rates. We're trying to bring that tool to soybeans.”

This effort employs a portable unit that can be held high above the canopy. At this time of the season, the middles are lapped and the tool's benefits aren't very obvious. Earlier, though, “we were picking up differences in the NDVI,” says Vories. “The lower populations didn't have as high an amount of biomass (which means there's less need for water). Also, we found the 38-inch rows didn't have nearly the biomass of the 7.5-inch rows.” The study will continue for another two years.

Editor's note: At the end of August, Vories, who has been at NREC since 1988, moved north to the agricultural research station in Portageville, Mo. There, he will serve as an engineer with USDA's Agricultural Research Service.

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