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2002 Annual Report

Response of Irrigated Sunflowers to Water Timing

Joel P. Schneekloth, CSU Regional Water Resource Specialist

INTRODUCTION: With declining water supplies in the central Great Plains Region, water conservation is an important issue for producers. Many areas have reported declining groundwater levels for 20 or more years within Colorado, Kansas and Nebraska. As groundwater levels decline, well output has declined in some regions to the point that systems are limited in their capability to fully irrigate a single crop under the entire system. Sunflower is a crop that has been proven to be beneficial to dryland producers because of its drought tolerance. However, little is known about the responsiveness of sunflowers to limited water and the timing of water needs for that crop.

METHODS AND MATERIALS: An experimental site was developed at the U.S. Central Great Plains Research Station at Akron, CO. Soil was a Weld silt loam (fine, smectitic, mesic, Aridic Argiustolls) with a plant available water holding capacity of 2 inches per foot. The previous crop was rainfed corn in 2001. Sunflowers were planted May 23, 2002 no-till into corn stubble. Varieties planted were Triumph 658 Nu-Sun for oil and Triumph 765C for confectionary. Planting rates were 24,000 seeds per acre for oil and 21,000 for confectionary in 30-inch rows. Fertilizer application was 100 lbs/acre of nitrogen and 30 lbs/acre of phosphorous. Furadan was applied at 1 quart per acre in-furrow at planting for stem weevil control. Herbicide application was Spartan at 2.3 oz/acre and Round-up at 20 oz/acre applied on May 15, 2002 and hand weeding for weed escapes.

A split-plot design was used for this experiment with timing of water application being the main plot with sunflower type (oil vs confection) as the sub-plot. Main plots were 15 ft (6 rows) by 130 feet with 4 replications with sub-plots 65 feet long. Water was applied with a surface drip system on 60-inch centers. The application rate of the system was 0.08 inches per hour and operated to apply 0.8 to 1.0 inches per application. Soil moisture was monitored weekly with the neutron attenuation method to a depth of 5 feet in 1 foot increments for each treatment. Plots were hand harvested on October 8, 2002. The middle two rows of plots were harvested for a total row length of 20 feet.

RESULTS: Weather: Precipitation for the cropping year of 2002 was characterized as below normal for a majority of the growing season (Table 1). Precipitation for the year (October 2001 – September 2002) was 57% of normal. Approximately 50% of the yearly precipitation occurred in August and September of 2002. Precipitation from May to July, during the vegetative growth stage, was less than 35% of normal. Dry weather and soil conditions hampered germination of seeds after planting. On August 24, three separate hailstorms caused severe damage to the sunflower crop. Reduction in leaf area was estimated to be greater than 90%.

Grain Yield: Grain yields and test weights for confection and oil sunflowers are reported in Table 2. Irrigation amounts are reported in Table 3. Grain yields were found to increase with the increased amount of water applied to both confection and oil sunflowers. Fully irrigated oil sunflowers yields were greater than limited irrigation oil sunflower. Yields of confection sunflowers were similar when irrigation began during the R1 growth stage or earlier. If irrigation was delayed to R4 growth stage or later, grain yields were reduced. Yields for both confection and oil sunflowers were greater when irrigation was initiated at R1 growth stage or before, rather than during later growth stages. Grain yields for oil sunflowers, when irrigation was initiated prior to the reproductive growth stage, were greater than yields when irrigation was initiated at R1. This was due to the lack of stored soil moisture and precipitation during the vegetative growth stages.

Test Weight: Test weights (Table 2) for irrigated confection sunflowers were not statistically different. Rainfed confection sunflowers generally had a lower test weight than irrigated. There was a tendency for test weight to increase when water was withheld during the early reproductive growth stages for confection sunflowers. When irrigation was initiated on or after R4 growth stage, test weights were generally more than when irrigation was initiated at R1 regardless of the length of time irrigation was continued.

Test weights for oil confections generally increased the later irrigation was initiated during the reproductive growth stage. However, the lowest test weights occurred when irrigation was initiated during the R1 growth stage. Test weights for both confection and oil sunflowers were more when irrigation was initiated during the R6 growth stage followed by the R4 growth stage.

Irrigation Water Use Efficiency: The efficiency of each irrigation strategy is important in limited water management. Irrigation water use efficiency (IWUE) is defined as the following:

IWUE = Irrigated Yield – Rainfed Yield

Irrigation Amount

The IWUE shows how efficient irrigation water applied during each growth stage was converted to grain yield. A higher IWUE value indicated each inch of irrigation applied was converted to more grain production.

Maximum IWUE for both confection and oil sunflowers occurred when the crop was irrigated during the R1-R3 growth stages. Each inch of water applied at this growth stage was converted to approximately 190 lbs/acre of seed. With confection sunflowers, the longer and more irrigation water was applied, the IWUE decreased, indicating that maximum yield was being approached while oil sunflowers IWUE response decreased slightly.

CONCLUSIONS: 2002 was historical in terms of drought and was the driest year on record. Sunflowers yields responded positively to additional water applied through irrigation. Oil type sunflowers tended to have greater yields than confectionary under rainfed and full water management. Yields under limited water for both confection and oil sunflowers were similar.

A hailstorm on August 24, 2002 and dry weather during emergence limited the yield potential for the irrigated sunflowers. Changes that are planned include watering the sunflowers after planting with a hand-move sprinkler system to ensure adequate germination.

Table 1. Yearly precipitation for Oct 1, 2001 to Sept. 30, 2002 by month and long-term average precipitation.

Table 2. Grain yield and test weight for oil and confection sunflowers irrigated at different growth stages.

Treatments within a column followed by the same letter are not significantly different (PR>.05).

Table 3. Irrigation amounts and irrigation water use efficiency for irrigated oil and confectionary sunflowers.

The author may be reached via e-mail at: Joel P. Schneekloth
or phone: 970-345-2259.