Impact of three irrigation scheduling tools on irrigation and alfalfa productivity under center pivots

Determining the amount and timing of irrigation events using scientific irrigation scheduling (SIS) may help optimize water use. Soil moisture sensors, commercial irrigation schedulers, and water balance programs are common SIS tools. These three methods were evaluated to test their impact on alfalfa (Medicago sativa) mass, nutritive value, and irrigation productivity, in comparison to experience-based irrigation depths chosen by cooperating growers. Trials were conducted at 10 farms across central Utah in 2019. Trials were repeated at nine of these farms in 2020 and six in 2021. Alfalfa mass was measured in a total of 47 cuttings from across all these fields over 3 years. The three SIS methods only impacted alfalfa mass in five cuttings, and it occurred inconsistently at various fields and years. Three cuttings had improved mass with SIS methods and two had reduced production. Forage nutritive value was more often impacted by SIS method than mass, but impacts were rarely large enough to change forage market value. Applied water was lower with most SIS methods than the grower control in 2019 and 2021 but not 2020. This was influenced heavily by the drought conditions and water restrictions during the latter 2 years of this study. As one of the first studies to directly compare how four irrigation scheduling methods for center pivots affect crop production and irrigation levels, results indicated that all three SIS approaches had comparable performance, and in some situations (especially wet years) could reduce applied water by 6%–25% without impacting alfalfa mass or nutritive value.