Quantifying Crop Coefficients for Corn Irrigation Scheduling in the Lower MS Delta Using an Eddy Covariance Method

Author(s): Anapalli, S.; Reddy, K.; Fisher, D.; Sui, R.

The water levels in the Mississippi river valley alluvial aquifer is falling fast due to water withdrawals for crop irrigations that are not replenished with rainfall recharge. Irrigation applications based on the exact crop evapotranspiration demands—consumptive water requirements—can be the way forward for preserving this aquifer-water resources for its sustainable use for irrigations in the region. In this direction, in a pioneering study, we quantified ETc from corn using an eddy covariance (EC) approach (ETe). In the EC system, vertical velocity of eddy transport and sonic temperature were measured using a Gill New Wind Master sonic anemometer (Gill Instruments), and water vapor density in the eddies was measured using the LI-7500-RS open-path infrared gas analyzer (LI-COR Inc.). All instruments were calibrated once in a year before moving to the field for measurements. The sensors were mounted on a telescopic, height adjustable tower, and the sensor height was maintained at twice the canopy height. Recognizing the unresolved problems in balancing energy fluxes in the EC approach, we also monitored ETc by computing latent heat energy flux (LE) from the system following a residual energy balance (EB) approach (ETb) using added instrumentation and compared the fluxes. The unclosed energy fluxes in the EC was post-analysis corrected using the Bowen ratio (BR) and LE methods. The measurements were conducted in a 31 ha clay soil field planted to irrigated corn in the lower Mississippi Delta, USA, in 2017. Further, for scheduling irrigations in corn, based on grass and alfalfa reference crop ET calculated from weather data, averages of the ETb, ETebr, and ETele daily estimates were used in deriving corn crop coefficients (Kc).

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