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Open AccessArticle

Impact of Deficit Irrigation on Shallow Saline Groundwater Contribution and Sunflower Productivity in the Imperial Valley, California

1
Civil Engineering Department, Faculty of Engineering, Port Said University, Port Said 42523, Egypt
2
UC Kearney Agricultural Research and Extension Center, University of California, Parlier, CA 93648, USA
3
Department of Plant Biology, University of Georgia, Miller Plant Sciences, Athens, GA 30602, USA
*
Author to whom correspondence should be addressed.
Water 2020, 12(2), 571; https://doi.org/10.3390/w12020571
Received: 29 December 2019 / Revised: 2 February 2020 / Accepted: 14 February 2020 / Published: 19 February 2020
(This article belongs to the Section Water Use and Scarcity)
Yield and production functions of sunflower (Helianthus annuus) were evaluated under full and deficit irrigation practices with the presence of shallow saline groundwater in a semi-arid region in the Imperial Valley of southern California, USA. A growing degree day (GDD) model was utilized to estimate the various growth stages and schedule irrigation events throughout the growing season. The crop was germinated and established using overhead irrigation prior to the use of a subsurface drip irrigation (SDI) system for the remainder of the growing season. Four irrigation treatments were implemented: full irrigation (100% full sunflower crop evapotranspiration, ETC), two reduced irrigation scenarios (95% ETC and 80% ETC), and a deficit irrigation scenario (65% ETC). The salinity of the irrigation water (EC) (Colorado River water) was nearly constant at 1.13 dS·m−1 during the growing season. The depth to groundwater and groundwater salinity (ECGW) were continuously monitored in five 3 m deep observation wells. Depth to groundwater fluctuated slightly under the full and reduced irrigation treatments, but drastically increased under deficit irrigation, particularly toward the end of the growing season. Estimates of ECGW ranged from 7.34 to 12.62 dS·m−1. The distribution of soil electrical conductivity (ECS) and soil matric potential were monitored within the active root zone (120 cm) at selected locations in each of the four treatments. By the end of the experiment, soil salinity (ECS) across soil depths ranged from 1.80 to 6.18 dS·m−1. The estimated groundwater contribution to crop evapotranspiration was 9.03 cm or approximately 16.3% of the ETC of the fully irrigated crop. The relative yields were 91.8%, 82.4%, and 83.5% for the reduced (95% and 80% ETC) and deficit (65% ETC) treatments, respectively, while the production function using applied irrigation water (IW) was: yield = 0.0188 × (IW)2 − 15.504 × IW + 4856.8. Yield reduction in response to water stress was attributed to a significant reduction in both seed weight and the number of seed produced resulting in overall average yields of 2048.9, 1879.9, 1688.1, and 1710.3 kg·ha−1 for the full, both reduced, and deficit treatments, respectively. The yield response factor, ky, was 0.63 with R2 = 0.745 and the irrigation water use efficiencies (IWUE) were 3.70, 3.57, 3.81, and 4.75 kg·ha−1·mm−1 for the full, reduced, and deficit treatments, respectively. Our results indicate that sunflowers can sustain the implemented 35% deficit irrigation with root water uptake from shallow groundwater in arid regions with a less than 20% reduction in yield. View Full-Text
Keywords: Helianthus annuus; groundwater contribution; soil salinity; water use efficiency; yield components; Imperial Valley Helianthus annuus; groundwater contribution; soil salinity; water use efficiency; yield components; Imperial Valley
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Eltarabily, M.G.; Burke, J.M.; Bali, K.M. Impact of Deficit Irrigation on Shallow Saline Groundwater Contribution and Sunflower Productivity in the Imperial Valley, California. Water 2020, 12, 571.

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