|Hunsaker, Douglas - Doug|
|Waller, Peter - University Of Arizona|
|Andrade-sanchez, Pedro - University Of Arizona|
Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2015
Publication Date: 9/20/2015
Citation: Hunsaker, D.J., French, A.N., Waller, P., Bautista, E., Thorp, K.R., Bronson, K.F., Andrade-Sanchez, P. 2015. Comparison of traditional and ET-based irrigation scheduling of surface-irrigated cotton in the arid southwestern USA. Agricultural Water Management. 159:209-224.
Interpretive Summary: Improving water conservation and crop yields are a priority in water-limited, semi-arid and arid regions where surface irrigation systems are still predominantly used. Conserving water in surface-irrigated fields requires improved crop irrigation scheduling. This means that the irrigation timing and amount of irrigation applied to the field must closely match the actual crop water use. However, the actual crop water use is difficult to measure and it can vary widely throughout these large fields. To help growers improve irrigation decisions, we developed a method that uses remote sensing and field data to estimate the actual crop water use at many small areas (32 m2) within the field. We tested this method in experiments with cotton grown in a large field (4.9-ha). Results showed that our estimates of crop water use at these smaller areas in the field matched the crop water use determined by field measurements. Using this method to guide irrigation schedules can potentially save water and increase yields compared to traditional irrigation scheduling. This information will be of particular interest to surface irrigation farmers, irrigation consultants, government agencies, and industry.
Technical Abstract: The use of irrigation scheduling tools to produce cotton under-surface irrigation in the arid southwesternUSA is minimal. In the State of Arizona, where traditional irrigation scheduling is the norm, producersuse an average of 1460 mm annually to grow a cotton crop. The purpose of this paper was to determinewhether or not the use of ET-based irrigation scheduling methods could improve lint yield and irrigationwater use productivity over traditional cotton border irrigation scheduling practices in the region. A fieldstudy with four irrigation scheduling treatments replicated in 4 blocks was conducted for two cottonseasons (2009 and 2011) in 16, 12-m × 168-m cotton borders at the Maricopa Agricultural Center (MAC),in Arizona, USA. Remotely-sensed vegetation indices (VI) were used to estimate basal crop coefficients(Kcb) at 40, 4-m × 8-m zones within borders for two treatments, denoted as VI A and VI B, whereas asingle Kcb curve was applied to all zones in borders for a third treatment (FAO). Daily ETc for these threetreatments was estimated using FAO-56 dual crop coefficient procedures with local weather data andirrigation scheduling for the three treatments were based on soil water balance predictions of soil waterdepletion (SWD). For the VI A and FAO treatments, irrigations were given when predicted SWD of all 160zones in the treatment averaged 45% of total available water (TAW). For the VI B treatment, irrigationswere given when 5% of the 160 zones in the treatment were predicted to be at 65% SWD. A fourthtreatment (MAC) represented the traditional irrigation scheduling treatment and was scheduled solelyby the MAC farm irrigation manager using only experience as a guide. The study showed that the lintyields attained under the MAC farm manager’s irrigation scheduling equaled or exceeded the yields forthe three ET-based irrigation scheduling treatments. Although the MAC irrigation scheduling resultedin somewhat higher irrigation input than for the other treatments, the MAC treatment maintained orexceeded the irrigation water productivity attained for other treatments that had lower irrigation inputs.A major conclusion of the study was that present-day irrigation water use for cotton in surface-irrigatedfields could be substantially reduced. When compared to Arizona state cotton averages, any of the fourtreatments presented in the study could potentially offer methods to significantly reduce cotton irrigationwater use while maintaining or increasing current lint yields levels.