Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 14, 2006
Publication Date: November 1, 2006
Citation: Evett, S.R., Ruthardt, B.B., Copeland, K.S. 2006. External full-time vacuum lysimeter drainage system. Applied Engineering in Agriculture. 22(6):875-880. Interpretive Summary: A weighing lysimeter is a box of soil installed in a field on a scale such that the lysimeter surface is at the same level as the field soil and the lysimeter becomes essentially invisible once a crop is planted on it and the surrounding field. These lysimeters are considered to be the most accurate means of determining crop water use and are frequently used to develop the knowledge base required for irrigation scheduling to reduce waste of water and nutrients. Thus, lysimeters are key tools in irrigation water conservation affecting the 50% of national fresh water withdrawals that are devoted to irrigation. However, weighing lysimeters are often not deployed due to their high cost. Alternative, low-cost designs have been developed, but these lack systems to drain excess water from the lysimeters, reducing their accuracy by possibly supplying more water to the crop planted on the lysimeter than is available to the crop in the surrounding field. We describe the design, installation and successful testing of a low-cost lysimeter drainage system that can be added externally to a low-cost weighing lysimeter, improving lysimeter management for accurate crop water use determinations.
Technical Abstract: Low cost weighing lysimeters have been demonstrated with accuracies better than 0.1 mm. However, these low cost lysimeters lack full-time vacuum drainage systems; and they lack access to the lysimeter tank for installation and maintenance of a vacuum system. Without frequent manual drainage, such lysimeters can become waterlogged. We designed, implemented and characterized the performance of an automatic vacuum drainage system that can be added to a low-cost lysimeter externally (provided that drainage filters were installed in the lysimeter and plumbed to the outside). The system consists of a buried vertical cylindrical vacuum chamber, inside of which a drainage collection tank is suspended from a load cell. A small enclosure, containing a vacuum pump, vacuum sensor and ports for accessing the drainage chamber, is situated above the vacuum chamber and level with the field surface. Disturbance of wind patterns and energy and water balances in the field is minimized by the buried system. At 0.0013 mm, accuracy of drainage measurement was nearly two orders of magnitude better than that of the lysimeter mass measurement, ensuring that the continuous drainage measurement may be included in the mass balance determination of evapotranspiration (ET) without diminishing the accuracy of ET values. The system design, installation, and testing are described.