Characterizing evaporative losses from sprinkler irrigation using large weighing lysimeters

Authors: Marek, Gary; Evett, Steven - Steve; Thorp, Kelly; DeJonge, Kendall; MAREK, THOMAS - Texas A&M Agrilife; Brauer, David

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2023
Publication Date: 3/13/2023
Citation: Marek, G.W., Evett, S.R., Thorp, K.R., DeJonge, K.C., Marek, T.H., Brauer, D.K. 2023. Characterizing evaporative losses from sprinkler irrigation using large weighing lysimeters. Journal of the ASABE. 66(2):353-365. https://doi.org/10.13031/ja.15300.
DOI: https://doi.org/10.13031/ja.15300

Interpretive Summary: Effective irrigation systems that increase crop water productivity by minimizing evaporative losses are paramount for extending the longevity of finite groundwater resources in the semi-arid U.S. Southern High Plains (SHP). Although subsurface drip irrigation (SDI) is becoming more prevalent, sprinkler systems remain the dominant method of irrigation in the SHP. While application drift and evaporative losses are easily measured under fallow conditions, quantifying evaporative losses under cropped conditions is difficult. Researchers from USDA-ARS and Texas A&M AgriLife Research compared lysimeter-derived crop water use values for SDI-irrigated and sprinkler-irrigated corn fields near Bushland, TX to characterize sprinkler application losses. Findings suggested that sprinkler drop height had little effect on losses as they were largely mitigated under full canopy conditions. However, cumulative losses were considerable during early season conditions when coupled with hot and dry conditions. Knowledge of these findings may prove useful for both producers and water mangers when considering irrigation management strategies.

Technical Abstract: Effective irrigation systems that increase crop water productivity by minimizing evaporative losses are paramount for extending the longevity of finite groundwater resources in the semi-arid U.S. Southern High Plains (SHP). Although subsurface drip irrigation (SDI) acreage has increased in recent years, center-pivot sprinkler systems still account for greater than 85 percent of irrigated area in the SHP. Modern sprinkler configurations are typically classified according to application height as either mid-elevation spray application (MESA) or low-elevation spray application (LESA). While application drift and evaporative losses are easily measured under fallow conditions, quantifying evaporative losses under cropped conditions is difficult. Lysimeter-derived daily evapotranspiration (ET) values for SDI-irrigated and sprinkler-irrigated fields planted to corn in 2016 (MESA) and 2018 (LESA) near Bushland, TX were compared for days when sprinkler irrigation events occurred and for subsequent days, when possible. Differences (extra ET) were attributed to evaporative losses associated with MESA and LESA irrigation. Average daily extra ET values for both sprinkler irrigation methods were similar on the day of irrigation, although MESA was slightly larger than LESA at 1.4 and 1.2 mm, respectively. Average daily extra ET values for incomplete canopy conditions were 2.2 mm for MESA and 1.9 mm for LESA, while values were identical for both methods at 0.6 mm for full canopy conditions. Average daily extra ET values were also expressed as percentage of daily standardized grass reference ET (ETos) values. Average values for MESA and LESA were 20.1 and 13.5 percent, respectively for the season with similar findings of 29.3 and 19.4 percent for incomplete canopy conditions. Average extra ET/ETos values for incomplete canopy conditions were similar at 7.5 and 7.7 percent for MESA and LESA, respectively. Evaporative irrigation losses, calculated as the percentage of extra ET to irrigation depth, were slightly larger overall for the day of irrigation for MESA (5.4 percent) than LESA (5.2 percent). Losses of 7.9 and 7.0 percent were observed for incomplete canopy conditions for MESA and LESA, respectively. Average losses for LESA (3.5 percent) under full canopy conditions were greater than those for MESA (1.9 percent). Comparison of extra ET values for days following irrigation revealed that evaporative losses from irrigation events extended beyond the day of irrigation. MESA extra ET values for the day following irrigations increased by 57.1 percent (2.2 mm) overall, 13.6 percent (2.5 mm) for incomplete canopy conditions, and 150.0 percent (1.5 mm) for full canopy conditions. The same was true for LESA with increases of 125.0% (2.7 mm) overall, 78.9% (3.4 mm) for incomplete, and 216.7 percent (1.9 mm) for full canopy conditions. Summing of extra ET values for the day of irrigation and the subsequent day yielded average values more than double that of those for the day of irrigation only, at 3.9 and 4.3 mm for MESA and LESA respectively. Similarly, values for extra ET as a percentage of irrigation depth were also more than double those for the day of irrigation only, with the greatest loss values of 39.5 percent for MESA and 28.0 percent for LESA. These findings suggest that although LESA appears to mitigate evaporative losses marginally more in corn than MESA on the day of irrigation, considerably more evaporative losses occurred for both methods during the subsequent day, with slightly increased losses for LESA, resulting in not much difference between overall losses over the two days. This may in part be explained by a temporary cooling effect by the irrigation inside the canopy on the day of irrigation which is diminished by the second day. Greater discrepancy between evaporative losses for MESA and LESA are likely to be observed for crops hav