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ARS Home » Plains Area » Bushland, Texas » Conservation and Production Research Laboratory » Soil and Water Management Research » Research » Publications at this Location » Publication #257710
Title: Determination of growth-stage specific crop coefficients (Kc) of cotton and wheat

Author
item Ko, Jonghan
item PICCINNI, GIOVANNI - Monsato Seed Company
item MAREK, THOMAS - Texas Agrilife Research
item Howell, Terry

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2009
Publication Date: 8/8/2009
Citation: Ko, J., Piccinni, G., Marek, T., Howell, T.A. 2009. Determination of growth-stage specific crop coefficients (Kc) of cotton and wheat. Agricultural Water Management. 96(12):1691-1697.

Interpretive Summary: Cotton and wheat are important crops in the Southwestern Texas region known as the Winter Garden. This region uses groundwater from the Edwards Aquifer that is nearly the sole water source for the city of San Antonio. Consequently, improved irrigation water conservation in this region is imperative. In order to achieve greater water conservation, accurate crop water use for irrigated crops, like cotton and wheat are needed to improve irrigation scheduling. Water use from cotton and wheat was measured at Uvalde, Texas, using accurate weighing, monolithic lysimeters that were 1.5 x by 2m in area and 2.2 m deep. Crop water use ranged from 689 to 830 mm for cotton and from 483 to 505 mm for wheat. The crop coefficient values (ratio of the crop water use to that of a short, cool-season grass) varied from 0.2 to 1.5 for cotton and 0.1 to 1.7 for wheat. Some of the crop coefficient values corresponded and some did not correspond to those from published sources from Texas and world-wide. The development of regionally based and growth-stage specific crop coefficient values for this region will aid irrigation management and provide precise water application information to conserve water.

Technical Abstract: Development of crop coefficient (Kc), the ratio of crop evapotranspiration (ETc) to reference evapotranspiration (ETo), can enhance ETc estimates in relation to specific crop phenological development. This research was conducted to determine growth-stage-specific Kc and crop water use for cotton (Gossypium hirsutum) and wheat (Triticum aestivum) at the Texas AgriLife Research field at Uvalde, Texas, United States, from 2005 to 2008. Weighing lysimeters were used to measure crop water use and local weather data were used to determine the reference evapotranspiration (ETo). Seven lysimeters, weighing about 14 Mg, consisted of undisturbed 1.5 m x 2.0 m x 2.2 m deep soil monoliths. Six lysimeters were located in the center of a 1-ha field beneath a linear-move sprinkler system equipped with low energy precision application (LEPA) and a seventh lysimeter was established to measure reference grass ETo. Crop water requirements, Kc determination, and comparison to existing FAO Kc values were determined over a 2-year period on cotton and a 3-year period on wheat. Seasonal total amounts of crop water use ranged from 689 to 830 mm for cotton and from 483 to 505 mm for wheat. The Kc values determined over the growing seasons varied from 0.2 to 1.5 for cotton and 0.1 to 1.7 for wheat. Some of the values corresponded and some did not correspond to those from FAO-56 and from the Texas High Plains and elsewhere in other states. We assume that the development of regionally based and growth-stage-specific Kc helps in irrigation management and provides precise water applications for this region.