FAO56 crop and water stress coefficients for cotton using subsurface drip irrigation in an arid US climate

Authors: Hunsaker, Douglas - Doug; Bronson, Kevin

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2021
Publication Date: 4/1/2021
Citation: Hunsaker, D.J., Bronson, K.F. 2021. FAO56 crop and water stress coefficients for cotton using subsurface drip irrigation in an arid US climate. Agricultural Water Management. 252. Article 106881. https://doi.org/10.1016/j.agwat.2021.106881.
DOI: https://doi.org/10.1016/j.agwat.2021.106881

Interpretive Summary: Reducing irrigation water use is a priority in water-limited agricultural regions, such as the arid US desert southwest, where flood irrigation systems are still widely used. To adapt to increasing water shortages,cotton growers in the region are adopting subsurface drip irrigation (SDI) and deficit irrigation practices to save water. However, information on appropriate irrigation management with SDI is limited, particularly for deficit irrigation. ARS scientists in Maricopa, Arizona, conducted a 3-year cotton SDI study to determine seasonal crop water use and to develop crop and water stress coefficients for desert regions that can be applied in the widely used FAO56 crop water requirement procedures. Results showed crop water use for cotton increased in SDI compared to flood irrigation. However, the study also developed information that will improve deficit irrigation scheduling and reduce water use. Using the SDI coefficients derived in the study with FAO56 procedures can potentially save water and increase yields compared to flood irrigation. This information will be of particular interest to cotton irrigation farmers, cotton industry, irrigation consultants, government agencies, and industry.

Technical Abstract: Water shortages are a continuing reality for today’s irrigated agriculture including in the arid US southwest where cotton (Gossypium hirsutum L.) is a primary crop. Decreasing water availability in the region coupled with high cotton water requirements are inducing water conservation practices including adoption of subsurface drip irrigation (SDI) and deficit irrigation management. A 3-year cotton study was conducted on a sandy loam soil using SDI at Maricopa, Arizona, USA. Objectives were to determine the actual single (Kcact) and basal (Kcb act) crop coefficients, corresponding growth stage lengths, and water stress adjustment criterion for estimating crop evapotranspiration (ETc) by the widely used FAO56 procedures. Treatments evaluated were full irrigation (100%) and deficit irrigation (70%), both replicated three times and managed at an optimum N rate. Irrigation scheduling was based on a FAO56 Kcb curve locally developed in earlier studies at the Maricopa location using furrow irrigation. Actual ETc was determined by a soil water balance using water content measurements made every 6-14-days. Actual ETc rates were high for the 100% treatment, often exceeding 12.0 mm d-1 during the mid-season stage in all years. Cumulative actual ETc for the 70% treatment was 21-23% less than that for the 100%, consistent with the average reduction in cumulative irrigation for the 70% of 24%. Lint yields for the deficit irrigation treatment were reduced only 15-16% in two of the years, however, by 36% in one year when soil water stress occurred early in the growing season. An important result was that the Kc act and Kcb act values at mid-season using SDI were higher by 0.05-0.06 than those obtained using furrow irrigation at the same location. For SDI in this arid climate, the recommended Kc and Kcb values for cotton at mid-season are 1.31 and 1.26, respectively. These values are consistent with the FAO56 mid-season standard cotton value after adjustment to the climate.