Irrigation using overhead sprinkler systems (primarily center pivots) is commonly used for corn and cotton production in the southeast USA. Technology for variable rate water application is available; however, it is not widely used due to increased management requirements. Methods to develop prescriptions in-season in response to changing crop conditions are needed to move this technology forward. The objective of this research was to evaluate the potential of using normalized difference vegetative index (NDVI) to estimate crop coefficients for development of spatial irrigation prescriptions. Field studies were conducted near Florence, SC, USA under center pivot irrigation systems equipped with variable rate technology. Studies in maize were conducted over several years comparing NDVI-based irrigation management to management with soil water sensors. The two methods did not significantly differ for yield or water volume applied. A cotton irrigation study was initiated in 2016 that compared the checkbook method (applying irrigation amount based on age of the crop and weekly precipitation totals) to NDVI-based irrigation prescriptions. Soil water sensors were used to initiate irrigation events. Irrigation amounts during the season for the NDVI-basedmethod often differed from rates prescribed by the checkbook method up until about 70 days after planting when differences in NDVI among plant density treatments andfield areas no longer existed. The results, along with the emerging use of air- and land-based remote sensing techniques, suggest continued research into the use of NDVI-based irrigation prescription technology is warranted.
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