Supplemental information for "Comparing Passive Wick Lysimeter Against Soil Water Balance and Simulation Models in High and Perched Water Tables and Coarse Sandy Soils"

Understanding soil water and nutrient dynamics is pivotal for agricultural and environmental research, particularly the accurate measurement of components like deep drainage. This study critically compares the efficacy of passive-wick drainage lysimeters to the soil water balance approach in field conditions marked by high and perched water tables and coarse sandy soils. The study was conducted at the North Florida Research and Education Center, Live Oak, FL, over four years (2019-2022). Forty passive-wick drainage lysimeters, with 25 in-row and 15 out-row placements, were installed 61 cm below the soil surface to record deep drainage measurements. The results showed lysimeters exhibited poor correlation (R² = 0.04) with soil water balance estimates during the crop growing season, alongside a Root Mean Square Error (RMSE) of 7.9 liters, indicating substantial measurement discrepancies. The average deep percolation from the lysimeter was 2221 mm (SD = 1490 mm), which was 841% higher than the soil water balance method, 741% higher than the DSSAT (Decision Support System for Agrotechnology Transfer) simulated deep drainage, and 774% higher than the HYDRUS-1D simulation. Furthermore, lysimeters placed out-row exhibited a higher mean drainage volume compared to those placed in-row, with a percent bias (%bias) of 8.3. These findings highlight the challenges and potential limitations in utilizing passive-wick drainage lysimeters for deep drainage measurement under perched, high-water table and coarse sandy soil conditions. The substantial overestimation of drainage volumes by lysimeters, particularly evident across various crops, calls for a cautious interpretation of lysimeter data in soil water and nutrient flux studies, especially in environments with similar soil and hydrological properties.