Evaporative loss differences between SDI and sprinkler irrigation - Southern High Plains experience

Authors: Evett, Steven - Steve; Marek, Gary; Colaizzi, Paul; Brauer, David; O`Shaughnessy, Susan

Submitted to: Irrigation Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/16/2018
Publication Date: 12/4/2018
Citation: Evett, S.R., Marek, G.W., Colaizzi, P.D., Brauer, D.K., O'Shaughnessy, S.A. 2018. Evaporative loss differences between SDI and sprinkler irrigation - Southern High Plains experience. In: Proceedings of the 2018 Irrigation Association Conference, December 3-7, 2018, Long Beach, California. p. 1-21. https://www.irrigation.org/IA/Resources/Technical-Paper-Library.aspx.

Interpretive Summary: In the face of declining water supplies, it is important for economic sustainability to maximize the yield per unit of water used in crop production, the so-called crop water productivity or CWP. It is not well understood how irrigation application method affects the CWP. Increasing CWP in the face of limited water supplies is a key objective in irrigation and agronomic research because it directly affects profitability, water sustainability and intensification of agricultural production. The irrigation application method can have an effect on CWP that is as large as or even larger than the effects of irrigation scheduling. Scientists at the USDA-ARS Conservation & Production Research Laboratory, Bushland, Texas, compared the water use and yield of grain corn and sorghum grown using sprinkler and subsurface drip irrigation (SDI) methods. Using the SDI application method, loss of water to evaporation from plant and soil surfaces was reduced by two to more than five inches compared to the loss suffered with sprinkler irrigation. The increased evaporative loss from sprinkler irrigation was due to wetting of the crop leaves and soil surface. Using SDI reduced overall corn water use by six inches while increasing yields by 20% and CWP by 61% compared with sprinkler irrigation. Although the SDI system is more expensive to install than sprinkler irrigation systems, the benefits of SDI are convincing in the dry climate of the Southern High Plains. Using SDI can result in long term gains in profitability and sustainability of irrigated grain production.

Technical Abstract: Subsurface drip irrigation (SDI) has steadily gained ground despite being considerably more expensive to install than center pivot irrigation. SDI now serves greater than 8% of land irrigated by pressurized irrigation systems (sprinkler, surface and subsurface drip and other microirrigation methods) in the US. In the Texas High Plains, the most southern extension of the High Plains, irrigation water is completely derived from “fossil” aquifers, the most important of which is the declining Ogallala Aquifer, a fossil aquifer that is recharged at most about one inch per year. Well yields are steadily declining, making it difficult in some cases to find adequate capacity to serve a center pivot irrigation system. An SDI system can be zoned to accommodate the smaller well yields. Although center pivot variable rate irrigation (VRI) systems can also accommodate declining well yields, the acceptance of VRI systems is relatively small – although growing. However, other factors influence acceptance of SDI, including larger yields, particularly with cotton, after conversion to SDI. Research has shown warmer soil temperatures obtained with SDI due to the reduced evaporative cooling early in the season, and crop rooting and early growth are improved in the warmer soil, particularly for cotton, which is one reason for larger yields. Not as well established is the degree to which the reduced soil water evaporation in SDI systems affects the soil water balance, water available to the crop, and overall water savings. Grain corn (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) were grown on four large weighing lysimeters at Bushland, Texas in 2013 (corn), 2014 and 2015 (sorghum) and 2016 (corn). Two of the lysimeters and surrounding fields were irrigated by subsurface drip irrigation (SDI) and the other two were irrigated by mid elevation spray application (MESA). Evaporative losses from SDI fields were two to five inches less than those from sprinkler irrigated fields. Differences were strongly affected by plant height, essentially disappearing when plant height reached the elevation of spray nozzles, indicating that use of LEPA or LESA nozzles could decrease the evaporative losses from sprinkler irrigated fields in this region with its high evaporative demand. Annual weather patterns also influenced the differences in evaporative loss, with differences being exacerbated in dry years.