DESIGN, CONSTRUCTION, AND INSTALLATION OF LARGE DRAINAGE LYSIMETERS FOR WATER QUANTITY AND QUALITY STUDIES

Six large drainage lysimeters (4.85 × 3.65 × 1.35 m) were designed, constructed, and installed for quantifying crop coefficients and water quality impacts of drip and seepage irrigated watermelon in south Florida. Monitoring systems designed for the lysimeters included water quantity (irrigation, rainfall, runoff, drainage, soil moisture, and water table depth) and quality (nutrient concentrations in the root zone, saturated zone, drainage, and runoff). Lysimeters, made of mild steel plate, containing two plastic mulch plant beds and an irrigation ditch, were installed in a watermelon field. The soil profile (A and E horizons) was reconstructed using native soil from the field. Bi-weekly soil solution and saturated zone samples, and event-based drainage and runoff water quality samples were collected and analyzed for nitrogen (NH4-N, NO3-N, TKN) and total phosphorus. The watermelon crop was planted on plastic mulch beds. Four lysimeters received drip irrigation and two received seepage irrigation. Preliminary data for the first six weeks of watermelon crop for the drip and seepage irrigation systems indicated that lysimeters were working properly. Seepage lysimeter systems had higher ETc compared with drip irrigated lysimeters due to wetter soil and high evaporation losses during irrigation. Water quality data showed that total dissolved nitrogen discharges from the seepage lysimeters were higher than the drip lysimeters. Lower nitrogen loadings for the drip lysimeters were mainly attributed to higher soil water storage capacity and fertigation. The design and installation described in this study will be helpful for future studies with large lysimeters.