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Irrigating ‘Flowers: When Less Can Mean More

Saturday, April 15, 2006
filed under: Irrigation/Water Use

When it comes to irrigating sunflower in the High Plains, it’s all in the timing. And it’s a prime example of when less can mean more.

Research by Joel Schneekloth, Colorado State University extension water resource specialist, Akron, demonstrates that timely irrigation of both oil and confection sunflower using less water than full irrigation can actually have better yield, better oil, and larger seed size.

It’s good news for growers in the High Plains who are becoming increasingly challenged by low water volumes and skyrocketing costs of irrigation. “In some areas, we just don’t have enough water anymore to grow corn with low capacity wells,” says Schneekloth. “We get to July-August and if it’s hot and dry, we don’t have the water supply to meet the ET (Evapotranspiration, or crop water use) demand of an irrigated crop under pivot.”

Thus, growers in the High Plains are increasingly adopting strategies to irrigate more effectively. This includes growing crops with varied growth and maturity under pivot that compliment each other – strategic irrigation when each crop needs water most.

“If we have low capacity systems, and we’re trying to plant the full pivot to one or two crops that both require water at the same time, it just doesn’t work,” says Schneekloth. “The answer is simple: plant two crops with completely different water needs, and irrigate at the critical time period of each crop under pivot.”

He advises adjusting crop rotations under irrigation by growing crops that have varying peak water needs. Good crop combinations to consider that would complement each other under pivot, Schneekloth suggests, would include corn/canola, corn/winter wheat, winter wheat/sunflower, corn/sunflower.

Another example might be winter wheat, corn, and sunflower on three pivots or one pivot split into thirds, irrigating for stand establishment and during the reproductive stages of all three crops. Irrigation will no longer be needed on the winter wheat after about June 1, when irrigation efforts can be focused on corn, which should be tasseling around July 20. The corn crop’s critical peak water period will conclude around August 10, and irrigation efforts can then be focused on sunflower, which will begin blooming around August 10.

Some growers still put the water to sunflower like they would to corn, Schneekloth says. Not only is this unnecessary (and costly) water management, too much water during sunflower’s vegetative stage can actually be detrimental, resulting in taller plants that may lodge easier and that are more susceptible to disease.

It’s important to realize that some stress during the life of a sunflower plant is OK. In fact, the crop is relatively resistant to the effects of short water stress periods, holding up well in dry conditions due to its deep, aggressive root system.

The seasonal water need of sunflower is typically around 20 to 22 inches under good moisture conditions. In general, yield is directly related to water availability. A conservative estimate is that each inch of available water will produce about 100 pounds of seed. Others have estimated sunflower yield response to available water at 150 lbs of seed per acre produced for every inch of water use after the first seven inches.

Past research has indicated that water is most critical to sunflower at stand establishment and growth stages R-4 to R-8, or just prior to flowering through seed filling. Schneekloth’s research substantiates that, with additional data that demonstrates differences between oils and confection, as well as limited irrigation versus full irrigation.

Evaluating irrigation timing

Schneekloth conducted his sunflower irrigation research at the U.S. Central Great Plains Research Station at Akron, Colo., from 2002-05 on oil type, and 2002-04 on confections.

Dryland corn was used as the previous crop. Hybrids evaluated were Triumph 658 Nu-Sun for oil and Triumph 765C for confectionary. Seed drop was 26,000 seeds/ac for oil and 24,000 for confection, 30” rows no-till. Fertilizer application was 100 lbs/ac of nitrogen and 30 lbs/ac phosphorous. Furadan was applied at 1 quart per acre in-furrow at planting for stem weevil control. Herbicide application was Spartan at 2 oz/ac, Prowl at 2 pt/ac and glyphosate burndown at 20 oz/acre. Water was applied with a surface drip system on 60 inch centers. The application rate of the system was 0.08” per hour and operated to apply 0.8” to 1.0” per application, for total irrigation of about 2” per week, with soil moisture monitored weekly.

Pre-watering was conducted just once during the course of the study, in 2004. Otherwise, six watering treatments were compared: 1) dryland/no irrigation; 2) full season irrigation; 3) irrigation only at sunflower growth stage R1-R3; 4) irrigation only at R1-R5; 5) irrigation at R4-R5; 6) irrigation at R6-R7.

See the evaluation results – note that in some years, the dryland sunflower with no irrigation yielded nearly as well as sunflower that was fully irrigated. But when the crop is severely stressed by drought, clearly irrigation is beneficial. In the very dry year of 2004, for example, irrigation of oil sunflower at R4-R5 returned almost 350 lbs/ac for every inch of irrigation water compared to dryland. Schneekloth notes that the 2002 trial did see some hail, which helps explain why yield results were so low that year.

Conditions were also extremely dry in 2002 as well as 2004, and with the severe drought, full irrigation tended to result in the best yield and oil. That’s before you consider the cost of irrigation, however. When water use efficiency is considered – getting the best bang for the irrigation buck when water is limited – irrigation only at R4-R5 was the best strategy for oil sunflower over the course of this evaluation. For confections, water use efficiency was best R1-R5.

“You’re getting nearly as good or better yield and oil when irrigating at R4-R5 for oil sunflower compared to full irrigation, and nearly as good or better yield and seed size for confections compared to full irrigation,” Schneekloth says, “with a significant savings in irrigation cost. If you’re irrigating only at R4-R5, you’re saving about 6” to 7” of water compared to full irrigation. Assuming a high irrigation cost of about $10 per inch per acre, that’s about $60 to $70 per acre in savings. If you’re irrigating confections at R1-R5, you’re saving about 3” to 4” of water over full irrigation, or about $30 to $40/ac.”

Schneekloth’s sunflower irrigation recommendations based on these results: If soil conditions are extremely dry, consider pre-watering, filling the soil profile before planting. Then irrigate oil sunflower from R4 (inflorescence begins to open and when viewed from directly above, immature yellow ray flowers are visible) to about R5 (beginning of flowering) or R6 (flowering is complete, ray flowers are wilting) if conditions are dry, to ensure optimal oil content. On sandier soils, or in extremely dry conditions, consider supplemental or full irrigation, especially if crop stress is becoming apparent.

For confections, pre-water if needed, and start watering a bit sooner than you would oils, at R1 (terminal bud forms a miniature green head rather than a cluster of leaves; when viewed from directly above, the immature bracts form a many-pointed star-like appearance) to about R5, again considering supplemental or full irrigation if needed.

See a chart that illustrates the growth stages of sunflower online at Go to ‘Growers’ then ‘growth stages.’ This illustration of sunflower growth stages can also be found in the print publication NDSU EB-25 and the High Plains Sunflower Production Handbook, available through county extension offices. – Tracy Sayler

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