Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2009
Publication Date: 2/18/2009
Citation: Evett, S.R., Mazahrih, N., Jitan, M.A., Sawalha, M.H., Colaizzi, P.D., Ayars, J.E. 2009. A weighing lysimeter for crop water use determination in the Jordan Valley, Jordan. Transactions of the American Society of Agricultural and Biological Engineers. 52(1):155-169.
Interpretive Summary: A weighing lysimeter is a container of soil enclosed in an underground vault except for the top surface at which the soil in the box is at the same level as the soil in the surrounding field. The soil box rests on a scale in the underground vault that is used for direct measurement of crop water use. A crop is planted and grown in the box and in the surrounding field so that the crop growth is the same in both. Weighing lysimeters are essential tools for accurate determination of crop water use and water use efficiency in irrigated agriculture. In furtherance of the President’s management agenda, the USDA-ARS Soil and Water Management Research Unit, Bushland, Texas cooperated with the National Centre for Agricultural Research and Extension, Hashemite Kingdom of Jordan, to design and construct a weighing lysimeter in the Jordan River Valley, which is an important irrigated area in the water-short Middle East for which crop water use is poorly understood. The lysimeter will be used as the primary ground truth for determination of crop water use and implementation of accurate irrigation scheduling for farmers of the region. It is a key tool in the multi-lateral U.S. sponsored project, the Middle Eastern Regional Irrigation Management Information Systems project (http://www.merimis.org/), which has partners and 15 weather stations in Israel, Jordan and the Palestinian Authority. The lysimeter has resolution of 0.064 mm of water and is capable of half-hourly, daily and seasonal determination of crop water use. It is easily maintained and is located at 224 m below sea level on a research farm of the government of Jordan, adjacent to a research location of the University of Jordan, which fact will allow training of university students while experiments on crop water use and water use efficiency are underway.
Technical Abstract: Efficiency of water use in irrigated agriculture can be improved by providing irrigation scheduling information to farmers that will help them to obtain acceptable yields and crop qualities while reducing losses of fertilizer to deep percolation and runoff, thus improving profitability and sustainability. Since 2003, a regional project has focused on improving irrigation scheduling in Jordan, Palestine and Israel. The Middle Eastern Regional Irrigation Management Information Systems (MERMIS) project involves cooperators from Palestine, Jordan, Israel and the United States and has established a network of 15 weather stations to support an irrigation scheduling service using the paradigm that crop water use is equal to a reference evapotranspiration (ET) value (calculated from weather data) multiplied by a crop coefficient. However, crop coefficients developed in one region often do not transfer exactly to another region – thus, crop coefficient values should be developed for those crops commonly grown in the Middle Eastern region and for the agronomic practices, including row spacings, prevalent in the region. Row spacings in this region are often wider than in other regions so that full canopy cover is often not attained, leading to an important crop cover factor influence on ET rates throughout the growing season. This paper describes the site selection, design, construction, calibration and preliminary results for a weighing lysimeter built by the MERIMIS team for determination of crop coefficients in the Jordan Valley. Distinct features of the design include the low roof that guarantees at least 1.5 m of soil depth all around the lysimeter, the tall scale-support piers that allow for suspension of the vacuum drainage tanks from the scale so that drainage does not change lysimeter mass, the elevated load cell and data logger that provide insurance against the unlikely event of flooding, and the rectangular surface that accommodates the wide variety of row spacings used in the Jordan Valley. The lysimeter is sited in the center of a 100-m by 200-m drip irrigated field, is 2.4 m by 3 m in surface area and 2.5-m deep, and has a calibrated accuracy of 0.11 mm and resolution of 0.064 mm. Preliminary data show that the lysimeter and associated weather instrumentation are working as expected and are able to detect half-hourly changes in weather (needed for reference ET calculations) and associated ET rate responses.