Document Type

Report

Publisher

Utah State University

Publication Date

2026

First Page

1

Last Page

13

Abstract

Efficient water management is essential for closed-loop food production in space applications. The Utah Reusable Root Module (URRM) is designed to support repeated cropping in the same peat-based growth media. Here, we report moisture sensor performance, nighttime-to-daytime evapotranspiration (ET) rate, yield, and water-use efficiency (WUE) in the Engineering Development Unit (EDU) using Outredgeous lettuce. Five previous crops had been planted in the same media, and this study reports growth and ET from the final crop cycle. Volumetric water content (θᵥ) was monitored using two electromagnetic moisture sensors (CS650 and TEROS ONE) across five root modules (RMs) with multiple types of top-cover containment approaches, including one RM containing newly replaced peat. Sensor-derived ET was compared with syringe pump-recorded water input. The CS650 generally overestimated ET, whereas the TEROS ONE underestimated ET. Nevertheless, both sensors accurately tracked temporal water-use dynamics and were highly correlated with pump-recorded water input (R² > 0.95). Total water use ranged from 3.9 to 8.2 L over the 28-day crop cycle. The RM containing fresh peat produced the greatest biomass; however, modules with reused peat and more permeable top-cover configurations achieved comparable biomass and WUE, suggesting that containment configuration had a greater influence on crop performance than substrate reuse alone. Nighttime-to-daytime ET ratios ranged from 0.44 to 0.49 across most RMs, consistent with previous findings in Outredgeous lettuce showing substantial nighttime ET under controlled-environment conditions, but increased to 0.72 ± 0.03 in the module with incomplete canopy development and an impermeable top cover. Although evaporation (E) varied by up to threefold among configurations, total ET was highly correlated with dry biomass (R² = 0.90). WUE ranged from 1.7 to 2.3 g L⁻¹, which is less than the typical WUE of approximately 3 g L⁻¹. This may have been caused by greater evaporation during early crop establishment. These results demonstrate that peat moss can be successfully reused for multiple crop cycles in the URRM, but containment design and early growth rate are important for maximizing crop productivity.

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