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Tips For Improved Sunflower Irrigation Management

Wednesday, February 1, 2012
filed under: Irrigation/Water Use

By Freddie Lamm, Danny Rogers, Joel Schneekloth & Rob Aiken*

Irrigation management of sunflower starts with the same premise as any other crop — namely, to mitigate the effects of yield-limiting water stress with the ultimate goal of increasing net farm income. To accomplish this goal, producers must carefully manage many factors. Some of these factors are related and some interact with each other in different manners, requiring delicately balanced irrigation management decisions. As the new cropping season approaches, here are some tips for improved irrigation management.

1. Management with Respect to Previous Crop — Although it may seem odd to begin a discussion of irrigation management of sunflower by considering the previous crop, this is an important topic when the ultimate goal is to maximize net farm income. Previous crops leave behind residual soil assets, such as soil water and nutrients, which can be used to offset input costs in the coming year, thus requiring the producer to consider net farm income in a multi-year horizon.

For example, irrigated corn requires ample supplies of water and nutrients late in the cropping season to ensure optimum yields. So producers often choose sunflower as a rotational crop after corn in order to utilize the residual soil water and nutrients.

In addition to the economic benefit, producers obtain environmental benefits from reduced usage of scarce water resources and reduced potential of nutrient leaching. Producers should evaluate the available soil water in the profile prior to planting so that they can wisely manage their irrigation inputs.

2. Management with Respect to Post-Sunflower Cropping — The crop following sunflower should also be considered in irrigation management in a multi-year cropping system. Sunflower is a deep tap-rooted crop that can deplete the soil water profile to a greater extent and depth than most crops. The soil water profile may not be recharged to a great extent over winter because of the relatively low winter precipitation in the semi-arid Great Plains. Sunflower production has been found to reduce the yield of subsequent crops when soil water reserves are deficit; but it may actually increase the yield of the subsequent crop when soil water is adequate.

Sunflower seed and oil yield sensitivity to water stress is greatest during the period immediately prior to flowering through seed formation (R3 to R7). Concentrating irrigation applications during this period not only benefits the sunflower, but also partially replenishes depleted soil water reserves that may be needed by the following crop.

However, any concentration of irrigation to a specific growth period requires adequate irrigation capacity [i.e., flow rate/area (e.g., gpm/acre, inches/day)] and a reliable irrigation system that is not subject to frequent breakdowns.

3. Management with Respect to Split-Cropping Scenarios — Sunflower is often grown in split-cropping scenarios with a second crop, such as corn, under center pivot irrigation systems. This allows better management when the system has an insufficient irrigation capacity or when restrictions are placed on total irrigation amount. Although sunflower and corn have very similar peak crop water use (evapotranspiration or ET) rates, sunflower has a shorter growing season and a total seasonal crop water use that is approximately 20% less than corn.

Additionally, the sunflower peak ET rate period is approximately 15% shorter in duration and is typically shifted later in the growing season, away from the critical silking period in corn. Irrigation needs are greatest for sunflower in August (when planted in early to mid-June), while corn requires more irrigation in July. Producers with lower-capacity irrigation systems or a limited seasonal water supply may plant an earlier-maturing corn hybrid and attempt to fully irrigate the corn through the critical reproductive period — and then concentrate irrigation on the sunflower later in the season.

4. Management with Respect to Agronomic Practices — Because the overall goal is to increase net farm income, the optimization of agronomic practices for higher-input production systems (i.e., pumping costs and irrigation system depreciation costs) is necessary.

For example, greater yields that are expected under irrigation can be limited by disease, weeds and insects. Producers might be tempted to accept a few percentage points yield reduction under nonirrigated cropping; but this might be a costly mistake for irrigated cropping. Also, producers should select optimal planting dates and seeding rates (plant population) for high production and oil content in their region.

Nitrogen fertilization should be closely matched with irrigated yield goals because excess nitrogen can reduce both seed yield and oil content. Sunflower typically requires 65 lbs of nitrogen (N) for each 1,000 lbs of seed yield; but this requirement should account for all sources of N (e.g., previous cropping, manure, residual soil levels, mineralization, nitrate N in irrigation water, etc.).

Germination and obtaining sufficient and uniform stands can be a problem with sunflower production, so good seeding equipment and seeding practices should be used. Producers should be prepared to provide light irrigation applications to enhance germination and crop establishment if needed and should regularly evaluate the germination status. Heavy irrigation applications at planting should be avoided to prevent crusting and excessive cooling of the soil, but light applications may still be beneficial if heavy rainfall has caused crusting.

5. Management with Respect to Irrigation Capacity — Sunflower is thought to be better able to withstand short periods of crop water stress than are corn or soybean — and the duration of peak water needs is shorter. So sunflower can be a good choice for marginal-capacity irrigation systems. Because relative yield reductions are less for sunflower than corn and soybean, many producers choose to deficit irrigate sunflower, resulting in an annual irrigation amount that is often four to five inches less than with fully irrigated corn or soybean.

Since the ultimate severity of drought conditions cannot be known prior to the growing season, producers may want to plant a portion of their production area to sunflower in order to reduce their overall crop production risk. Decision support software programs are available to evaluate cropping options and land/water allocations (e.g., Crop Water Allocator).

6. Management with Respect to Weather Conditions — Irrigation scheduling is typically defined as “determining when to irrigate and how much to apply.” Looking to the future, a more conservation-oriented and economically profitable definition can be stated as “delaying any unnecessary irrigation with the hope that the cropping season ends before the next irrigation is needed.”

The crucial meaning of these two alternatives is not fundamentally different, but the complexity of “perfect” irrigation scheduling is best illustrated by the second definition. Fortunately, producers can easily make great strides at improving irrigation management while on the difficult journey toward that “perfect” management.

The easiest way to accomplish this task is through day-to-day irrigation scheduling for the entire season. In the Great Plains, weather-based irrigation scheduling water budgets have been shown to be a highly effective and easy-to-implement scheduling method. These water budgets (also known as checkbook irrigation scheduling) are based upon calculations or measurements of crop water use (ET), a withdrawal and deposits of precipitation and irrigation. When the budget (checkbook) reaches a predetermined level, irrigation is applied.

Many states in the Great Plains have automated weather stations that provide the necessary weather information required in water budget irrigation scheduling, and some states also have software for easy management of the irrigation scheduling process (e.g., KanSched2 from K-State Research and Extension).

In addition, total season, day-to-day irrigation scheduling aids the producer’s decision process in the majority of previously mentioned topic areas and helps in determining initiation and termination of the irrigation season.

7. In Conclusion — Irrigated sunflower production need not be a daunting task. The goal of increasing net farm income is the same for all crops. Some of the topics above overlap, but careful attention to these tips should help producers improve their overall irrigation management of sunflower.

For additional information, High Plains Sunflower Production Handbook online.

* Freddie Lamm is irrigation engineer with Kansas State University at Colby; Danny Rogers is extension agricultural engineer with KSU, Manhattan; Joel Schneekloth is water resource specialist for Colorado State University, based at Akron; and Rob Aiken is crop research scientist with KSU, Colby.
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