Are crop coefficients for SDI different from those for sprinkler irrigation application?

Authors: Evett, Steven - Steve; Marek, Gary; Colaizzi, Paul; Brauer, David; HOWELL, SR., TERRY - Retired ARS Employee

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2020
Publication Date: 10/14/2020
Citation: Evett, S.R., Marek, G.W., Colaizzi, P.D., Brauer, D.K., Howell, Sr., T.A. 2020. Are crop coefficients for SDI different from those for sprinkler irrigation application? Transactions of the ASABE. 63(5):1233-1242. https://doi.org/10.13031/trans.13920.
DOI: https://doi.org/10.13031/trans.13920

Interpretive Summary: Fresh water supply for irrigation is decreasing due to decreases in supply and increases in competition from other uses. One solution is to increase the productivity of irrigation water use through newer irrigation delivery systems, including subsurface drip irrigation (SDI). There are more than 430,000 acres of SDI on the Texas Southern High Plains. However, best management practices for SDI are still under development. USDA ARS scientists at Bushland, TX, develop methods of accurately scheduling sprinkler irrigation of corn, cotton and other crops using crop coefficients but use of those methods for scheduling SDI was shown to result in over irrigation. Accurate crop coefficients for SDI were thus needed for efficient irrigation and water savings. The Bushland USDA ARS team measured corn water use for two years, comparing it between SDI and sprinkler irrigation, and showed that crop coefficients for SDI were 10% smaller than those previously developed using sprinkler irrigation. The use of new crop coefficients for SDI will decrease irrigation applications’ using SDI, thus saving water and reducing associated energy costs.

Technical Abstract: Subsurface drip irrigation (SDI) has become an important irrigation application method in the U.S. Southern High Plains where pan evaporation exceeds 2,400 mm per year. Early research comparing SDI with spray sprinklers showed that SDI was over irrigated when scheduling irrigations using crop coefficients developed using sprinkler irrigation. Thus, crop coefficients developed using SDI may be smaller than those developed using sprinkler irrigation. Grain corn was grown for two years on large, precision weighing lysimeters at Bushland, TX, with two lysimeters irrigated by SDI and two by mid elevation spray (MESA) irrigation. Crop coefficients developed for SDI (Kc_SDI) were compared with those developed for MESA (Kc_MESA) using ASCE standardized reference ET equations. The value of Kc_SDI ranged from 0.83 to 0.89 of Kc_MESA for the two years. Values of Kc_SDI remained consistently less than Kc_MESA even after maximum leaf area index was reached, indicating that considerable evaporative loss from the soil surface occurred with MESA irrigation even after full canopy cover. If we shortened the initial period after planting from 30 to 20 d, following FAO56 recommendations for surface drip irrigation under full-cover plastic mulch resulted in calculated basal Kc (Kcb) values that were reasonably close to our Kc values based on short crop reference ET (ETo) for the crop development and early mid-season periods but were greater than our data for the later mid-season and late season periods.