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<br />Water Supply Reserve Account - Grant Application Form <br /> <br />Form Revised October 2006 <br /> <br />Item 4: Additional information on previous work. <br /> <br />Weighing lysimeters characteristically are composed of two tanks, an inner soil tank (control <br />volume) which can move freely within an outer containment tank. Weighing lysimeters work on the <br />principle of weight change as a direct measurement of water added by irrigation and/or rainfall and <br />water lost by drainage and/or ET from the control volume. With irrigation, rainfall, and drainage <br />water all measured independently, crop ET can be computed from weight cl1ange rn~asured on the <br />lysimeter. With precision weighing instrumentation, crop ET over very short intervals (15-60 <br />minutes) can be accurately measured. Weighing lysimeters can be classified by the type of <br />weighing mechanism used: hydraulic, floating, mechanical, electronic, combination electronic- <br />mechanical (Howell et aI., 1991; Grebet, 1991; Aboukhaled et aI., 1982). <br /> <br />The soil mass in a lysimeter is either generally an undisturbed soil block (monolith) or is disturbed <br />soil backfilled into the lysimeter using the soil excavated from the pit where the lysimeter is <br />installed. Soil monoliths should be used whenever excavation and backfilling will cause major <br />changes in soil physical or chemical properties (Schneider and Howell, 1991). Rocky, layered or <br />stratified soils are examples. Procedures for collecting large soillTIonoliths are described by <br />Schneider and Howell (1991), Schneider, et aL (1993), Schneider, et ale (1996). Schneider, et aL <br />(1998) describe a combination monolith and reconstructed soil profile for lysimeters from high <br />water table sites. Monolith lysimeters have higher initial costs because of the complexities of <br />collecting and handling the soil monolith. Quality data can usually be collected the first year of <br />operation, however (Schneider and Howell, 1991). <br /> <br />Design of lysimeter area and depth is based on the expected crops to be studied, their rooting depths <br />and research objectives relative to irrigation regimes that range from well-watered conditions to <br />water stress conditions (Howell, et al., 1991; Howell, et aI., 1985). Grebet (1991) states the size of <br />the lysimeter soil tank is a compromise between minimizing tank costs or total weight and the need <br />to provide for an adequate root zone and sufficient reservoirs of moisture, air, and heat to be <br />sufficiently representative of surrounding field conditions. He suggests a minimum area of 2 m2 <br />with optimum area of 4 m2. Minimum depth under irrigated conditions is 0.8 to 1.0 m and 2 m for <br />non-irrigated conditions. Aboukhaled, et a1. (1982) recommend a 4-m2 area for lysimeters to be <br />used for ET research on grass and most field crops. <br /> <br />References: <br />Ab oukhal ed, A., A. Alfaro, and M. Smith. 1982. Lysimeters. Irrigation and Drainage Paper 39. <br />Food and Agriculture Organization of the United Nations. Rome, Italy. <br />Allen, R.G. and D.K. Fisher. 1990. Low-Cost Electronic Weighing Lysimeters. Transactions of the <br />ASAE, Vol 33(6):1823-1833. Amer. Soc. of Agricultural Engineers, St. Joseph, MI. <br /> <br />11 <br />