Abstract
Addressing within-field and within-season variability of crop water stress is critical for spatially variable irrigation. This study measures interactions between spatially variable soil properties and temporally variable crop water dynamics; and whether modelling soil water depletion is an effective approach to guide variable-rate irrigation (VRI). Energy and water balance equations were used to model crop water stress at 85 locations within a 22 ha field of winter wheat (Triticum aestivum L.) under uniform and spatially variable irrigation. Significant within-field variability of soil water holding capacity (SWHC; 145–360 mm 1.2 m−1), soil electrical conductivity (0.22–49 mS m−1), spring soil water (314–471 mm 1.2 m−1), and the onset of crop water stress were observed. Topographic features and modelled onset of crop water stress were significant predictors of crop yield while soil moisture at spring green-up, elevation, and soil electrical conductivity were significant predictors of the onset of crop water stress. These results show that modelling soil water depletion can be an effective scheduling tool in VRI. Irrigation zones and scheduling efforts should consider expanding to include temporally dynamic factors, including spring soil water content and the onset of crop water stress.
Highlights
Accepted: 5 July 2021Worldwide demand for freshwater is increasing to accommodate growing populations, declining groundwater levels, deteriorating water quality, environmental regulation and other factors [1]
Climate conditions often do not allow for increasing freshwater demand, such as the Western United States which is in the midst of a “mega drought” [3]
Electrical conductivity ranged from 0.22 mS m−1 to 49 mS m−1 (Figure 2c)
Summary
Accepted: 5 July 2021Worldwide demand for freshwater is increasing to accommodate growing populations, declining groundwater levels, deteriorating water quality, environmental regulation and other factors [1]. Variable-rate irrigation (VRI) is a promoted tool to improve water use efficiency by spatially matching irrigation rates to crop water demand. Field scale spatial variability of soil and crop water status is well documented, and utilizing VRI to match spatial crop water demand during a growing season could decrease irrigation inputs while maintaining crop yield [4,5,6]. This was observed in potato (Solanum tuberosum L.) production where the total irrigation consumption was not significantly greater, but water productivity improved under VRI management [7]. Delineating irrigation zones from apparent electrical conductivity and utilizing a water balance approach to inform irrigation rates, VRI reduced
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