|Evett, Steven - Steve|
|MAREK, THOMAS - Texas Agrilife Research|
Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: 7/28/2012
Publication Date: 7/29/2012
Citation: Howell, T.A., Evett, S.R., Tolk, J.A., Copeland, K.S., Marek, T.H. 2012. Evapotranspiration and crop coefficients for irrigated sunflower in the southern high plains. Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE). Paper No. 12-1338306.
Interpretive Summary: The water use of irrigated sunflower was measured with weighing lysimeters in 2009 and 2011 at Bushland, Texas. The mean crop water use was 638 mm (25 in.). The average yield was 3,080 kg/ha or 2,750 lb/ac. The water use efficiency averaged 0.49 kg/m**3 or 110 lb/ac per in. The "basal" crop coefficients for irrigation scheduling using the daily ASCE reference equation was 0.15 from planting to the eight leaves, and then increased to 1.22 when the flower bud developed, remained constant until the back of the heads turned yellow with green bracts remaining, then declined at maturity to near the "initial" values. There was not a difference if the crop coefficients were based on a time scale or on a crop growing degree day scale. Sunflower may be a desired alternative crop for the Texas High Plains, but its economics are not as strong as corn or cotton.
Technical Abstract: Sunflower (Helianthus annuus L.) is diverse crop grown for oil or confectionary uses in the Southern High Plains often under irrigation. Crop water use (evapotranspiration or ET) was measured in 2009 and 2011 in two 4-ha fields using two precision 9 m**2 weighing lysimeters containing 2.3-m deep monoliths of Pullman clay loam soil. The fields were irrigated with a lateral move sprinkler system with nozzles ~1.7-1.8 m above the ground and ~1.5-m apart. The sunflower ET averaged 638 mm; seed yields averaged 308 g m**-2; and the lysimeter water productivity averaged 0.49 kg m**-3. The crop coefficients based on the FAO-56 curve method were 0.15 for Kcbini and 1.22 for Kcbmid based on the daily ASCE Reference ET (ETos). The Kcbmid based on the ASCE taller, rougher Reference ET (ETrs) was 0.80. Using a thermal-time base (growing degree day) for the crop coefficient did not improve the crop coefficient for the diverse planting dates in these seasons.