Time-normalized evapotranspiration reveals substantial nighttime water loss in a controlled-environment system

Abstract

Efficient water management in closed-loop plant production systems requires accurate characterization of evapotranspiration (ET), because crop water loss influences atmospheric moisture conditions within the controlled environment. Day–night ET dynamics were quantified in the Engineering Development Unit of the Utah Reusable Root Module, a zero-discharge system for controlled-environment crop production. Volumetric water content was monitored at high temporal resolution using two electromagnetic sensors installed at different depths within five independent root modules with different surface-containment configurations. Hourly ET was derived from water-content depletion and cross-checked against irrigation inputs. Following seedling emergence, system ET increased from <1 L d⁻¹ to approximately 3 L d⁻¹ by day 12. During rapid growth, defined as the four consecutive days when system ET exceeded this threshold, hourly ET differed significantly among four light-period categories, with daytime ET highest, followed by night-transition, day-transition, and nighttime ET. Although the cumulative daily nighttime-to-daytime ET ratio from the upper CS650 sensor was 0.29 ± 0.01, time-normalized analysis from the same sensor yielded a mean hourly ETₙ/ET d ratio of 0.47 ± 0.03 during rapid growth, approximately 1.6 times greater. These results show that daily totals can underrepresent nighttime water-loss intensity. The time-normalized ratio therefore provides complementary information for characterizing the intensity of nighttime water loss independently of photoperiod duration. This metric may inform future water-budgeting and humidity-control assessments in closed-loop and other resource-constrained production systems.

The authors' abstract, as published at the source. Smart Agricultural Technology, 2026 · DOI ↗