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Timing, experience improve producer's cotton irrigation

A northeast Arkansas cotton producer is improving his irrigation efficiency and bumping yields with some new tools and technologies. But he stresses that when timing an irrigation, his own experience is often more valuable than science.

Manila, Ark., cotton producer David Wildy, speaking at the 2007 Beltwide Cotton Conferences in New Orleans in January, said that while his water resource is plentiful — his farm is surrounded by the St. Francis River on the west and the Big Lake Wildlife Refuge on the east — he is still “very sensitive to conserving water and being as efficient as I can when using it.”

Wildy farms about 7,500 acres of cotton, irrigating 1,035 acres by furrow and 6,100 acres with 42 center pivots. All but one of his center pivots use commercial power, rather than diesel, “simply due to economics.”

The farm has 16 wells that supply water for furrow irrigation, nine of which run on electric power, seven on diesel. Wildy says that while it would be more economical to go to commercial power on all the wells, “we may run the wells for furrow irrigating eight to 12 hours per week, whereas on the center pivots, we may be running four or five days out of the week.”

Wildy keeps good records on dryland (349 acres) versus irrigated yields, as well as costs and yield improvement over time. Fixed costs for his center pivots are around $21 an acre. “That's figuring a 20-year life span for the pivot, although I do have some that are 25 years old. Our average repair cost is about $7.50 per acre, per year. One reason our costs are so low is that we use a load control credit from our local co-op that allows them to shut our pivots off for five hours a day during peak demand periods, and we get a very sizable rebate for that.”

Wildy, who has gone to drop nozzles on many of his center pivots to minimize water loss, has found that center pivot irrigation helps most years. “Even in a good rainfall year and high dryland yields, we see a return of about $39 per acre.”

Wildy's furrow irrigation fixed costs are about $1.50, rollout pipe costs are about $10 an acre and repairs about $2.50. “We also get load control credit where we run commercial power. Returns are around $38 an acre. That's close to the cost of a center pivot, but I'm not including the cost of any land leveling, which can vary so much from field to field and producer to producer.”

Wildy notes that for the past 20 years, “there have only been two years when dryland cotton equaled our irrigated cotton and only two years when our furrow irrigation has equaled our center pivot irrigation.

“Over that 20-year period, we've increased yield 160 pounds on furrow-irrigated ground and 200 pounds on our center-pivot irrigated ground.” The pivot yield would be even greater, but Wildy could not get a true assessment of yield, “because we had to use the full field as our irrigated yield. About 18 percent, or 20 acres of that field, is dryland.”

With a yield monitor, however, Wildy was able to pull the dryland corners out of the average “and we've see that those center pivot yields are even higher. Yield monitors also help us recognize our drainage problems and that irrigation is not the only answer. We have other problems going on also.”

Other precision agriculture techniques have helped Wildy's irrigation program. “We did some grid sampling a few years ago to find out what was going on with pH in the dryland corners. We found out that we needed lime there and not over the rest of the field where we were watering. So we started a program where we were only liming the corners and checking them for low pH.”

Wildy has gone to surge valves on his furrow-irrigated cotton after yield monitor maps indicated he wasn't getting water all the way across the field, “and even when we were, we weren't getting the quantity on the lower end that we were on the upper end of the field. The surge valves have really helped out. They give us better distribution and less run time, less runoff and more uniform application from the low end to the high end of the field.

“We're also using well monitors, which is an inexpensive way to monitor our water. The systems will call our cell phone when we have a loss of water. We can also go to a computer screen which displays all the wells pumping and the ones that are off.”

On one center pivot-irrigated field, aerial imagery showed dry areas under a pivot close to the pivot point. “We went out there, and everything looked fine. We thought there might be some nozzles stopped up, but they looked fine, too. We lined buckets up (to catch water), and we found that the water distribution was not even and we weren't getting water up close to the pivot.”

Wildy found the problem — the smaller nozzles close to the pivot were more adversely affected by a buildup of iron than larger nozzles on the end of the pivot.

A test on Wildy's farm conducted by Tina Teague, professor of plant science, University of Arkansas, showed a 300-pound yield advantage to initiating irrigation at first square, rather than at bloom. “Irrigation timing was the only difference between those two plots,” Wildy said.

“There's no definitive answer to when we start irrigation,” says Wildy, “We have had several studies on irrigation initiation on the farm and have realized that we really start irrigating when the plant needs it. A lot of times, it's more experience than science.”

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