An automated rotating lysimeter system for greenhouse evapotranspiration studies

Lysimeters are important tools in soil-plant-atmosphere research because they allow direct measurements of evapotranspiration and facilitate studies of water, nutrient, and solute balances. Heterogeneity in the atmospheric conditions in greenhouses causes spatial variations in evapotranspiration. Accurate design and management of water balance research in greenhouses is difficult due to restraints of replication and placement needed to statistically minimize the influence of heterogeneity. Precision and control are necessary to maintain precise boundary conditions, a prerequisite for accurate investigations of selected variables. We present a rotating structure that significantly enhances uniformity in environmental conditions between individual free-standing lysimeters placed on the structure. The system contains automatic irrigation (water and fertilizer) delivery and drainage collection devices. The system was tested in evaporation and plant growth experiments. A dual carousel setup was used to measure evaporation from containers placed on the soil surface of the lysimeters, as well as yield of lettuce (Lactuca sativa L.) plants growing in the lysimeters. Half of each carousel was covered with netting to reduce solar radiation by 50%. One carousel rotated throughout the experiment while the other one remained stationary. Variability in measured data was reduced as a result of rotation. The CV of measured evaporation from the rotating system (3.3%) was significantly lower than that of the stationary system (16.2%). Similarly, the CV of relative lettuce yields of the rotating system was 11.9% as compared with 20.9% for the stationary system. The proposed apparatus is very attractive as a research and teaching tool for studying plant physiological processes, flow and transport in soils, and plant response to management or environmental variables.