Construction, installation, and performance of two repacked weighing lysimeters

Abstract

Weighing lysimeters are the standard method for directly measuring evapotranspiration (ET). This paper discusses the construction, installation, and performance of two (1.52 m × 1.52 m × 2.13-m deep) repacked weighing lysimeters for measuring ET of corn and soybean in West Central Nebraska. The cost of constructing and installing each lysimeter was approximately US $12,500, which could vary depending on the availability and cost of equipment and labor. The resolution of the lysimeters was 0.0001 mV V −1 , which was limited by the data processing and storage resolution of the datalogger. This resolution was equivalent to 0.064 and 0.078 mm of ET for the north and south lysimeters, respectively. Since the percent measurement error decreases with the magnitude of the ET measured, this resolution is adequate for measuring ET for daily and longer periods, but not for shorter time steps. This resolution would result in measurement errors of less than 5% for measuring ET values of ≥3 mm, but the percent error rapidly increases for lower ET values. The resolution of the lysimeters could potentially be improved by choosing a datalogger that could process and store data with a higher resolution than the one used in this study.

A calibration procedure for load cells to improve accuracy of mini-lysimeters in monitoring evapotranspiration

“…Since it is possible to make measurements at 10 min interval, the resolution of 0.027 mm of water corresponds with an ET of 0.162 mm h -1 . The overall resolution of a lysimeter system is dependent on the capability of the data logger in terms of voltage resolution and its significant digits (Payero and Irmak, 2008). However, these are not considered further as effective calibration and deviation minimisation schemes described here incorporated these features of the measurement system.…”

“…We used five sample load cells to investigate the hysteresis effects using six separate loads within 0-15.7 kg. Regression lines were fitted to these data in a way similar to that shown by Payero and Irmak (2008). Since there was no significant difference in signal during loading and unloading conditions for these five load cells, there was an overlap of regression lines fitted to signal vs. load data (graph not shown).…”

“…Performance of some lysimeters is influenced by hysteresis due to a shift of calibration line (Payero and Irmak, 2008) when load cells are exposed to an increase in load (for example during irrigation) or a decrease in load (as during evapotranspiration). We used five sample load cells to investigate the hysteresis effects using six separate loads within 0-15.7 kg.…”

“…Since data loggers and on some occasions, multiplexers are used for the collection of lysimetric data, these can affect the accuracy and resolutions of lysimeters (Evett et al, 2009). A recent review by Payero and Irmak (2008) of the performance of various types of lysimeters indicate that the sensitivity of lysimeters (in mm of water) can vary considerably depending on the area, weighing and data recording system used. The purpose of this work is to describe the design and performance aspects of a mini-lysimeter system using twelve load cells with specific focus on calibration to test the system's suitability for long-term monitoring of evapotranspiration in controlled environmental conditions (i.e.…”

Design and construction of a large weighing lysimeter in an almond orchard

“…The field is flat and is 5 ha in size. Most lysimeter facilities are located in fields that do not exceed this area (Allen & Fisher, 1990;Jia (e.g., van Bavel & Myers, 1962), they are still considered one of the most accurate methodologies to study the return of water to the atmosphere by the combined processes of evaporation and transpiration (Malone et al, 2000), and are the standard method to directly measure ET c (Reicosky et al, 1983;Payero & Irmak, 2008).…”