Estimating soil water contents from field water tables for potential rice irrigation criteria under contour-levee irrigation systems

Abstract

Contour-levee irrigation systems are commonly used in rice cultivation in Latin American and the Caribbean countries, but research-based criteria for irrigation timing have not yet been determined under field conditions. In this study, we determined the relationship between soil volumetric water content (SWC) and field water table (FWT) for potential use in developing practical irrigation criteria based on FWT. Field experiments were conducted at four farms in Ibagué, Colombia from 2017 to 2018. The SWC at different soil depths and the FWT were constantly measured over the crop cycle using soil moisture sensors and piezometers with water level sensors, respectively. The resulting relationships were fitted with linear-plateau models and validated with satisfactory prediction performances. The FWT at actual irrigation timings was observed and compared with the FWT at field capacity at 10 cm soil depth (reference FWT) using the validated relationship. The observed range of threshold FTWs (46.2 to 9.2 cm) was comparable to the reference FWTs except one field (21.4 to 12.9 cm). Although developing practical irrigation criteria as FWT still requires thresholds of SWC under a target contour-levee irrigation system, this study demonstrated the relationships between FWT and SWC in fields in Colombia.