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United States Department of Agriculture

Agricultural Research Service

Title: Mobile Research Gas Exchange Machine - Mrgem: Instrumentation Update

Authors
item Wagner, Steve
item Reicosky, Donald

Submitted to: International Evapotranspiration Irrigation Scheduling Conference
Publication Type: Proceedings
Publication Acceptance Date: April 12, 1996
Publication Date: N/A

Interpretive Summary: Accurate tools for measuring crop water use or evapotranspiration (ET) are needed to develop accurate methods for determining when to irrigate farm crops. Closed chamber measurements provide one tool for measuring crop water use and plant growth. The chamber is placed over plants or bare soil for 60 s while water vapor increase and carbon dioxide change are recorded once per second. A Mobile Research Gas Exchange Machine (MRGEM) has provided closed-chamber measurements of ET and growth rates or Carbon Dioxide Exchange Rate (CER) through the past 15 growing seasons. As new technology and resources became available, the on-board instrumentation was updated. We describe the current state of the art for the MRGEM measurement system, including the tractor, the closed- chamber with mixing fans, pumps and plumbing, gas analysis instrumentation, data collection system, computer, software, and flux calculation methods. It takes only one minute to measure crop water use with MRGEM. These measurements can be made in remote field locations on a research plot or a farmer's field. These measurements can be used to verify models that estimate crop water use. We can compare the amount of water used for various crop management systems, and compare measured ET with non-direct or remotely-sensed irrigation scheduling criteria such as crop leaf temperatures.

Technical Abstract: Developing and verifying irrigation scheduling methods requires accurate tools for quantifying evapotranspiration (ET) in the field. Closed chamber measurements provide one tool for measuring crop gas exchange and water use. A Mobile Research Gas Exchange Machine (MRGEM) has provided closed- chamber measurements of canopy ET and Carbon Dioxide Exchange Rate (CER) through the past 15 growing seasons. As new technology and resources became available, the on-board instrumentation was updated. We describe the current state of the art for the MRGEM measurement system, providing a detailed description of the tractor, closed-chamber with mixing fans, pumps and plumbing, gas analysis instrumentation, data acquisition system, computer, software, and flux calculation methods. This portable tool provides ET measurements at the crop canopy level in remote locations within one minute. These measurements can be used to verify predictive ET models, compare water use efficiencies of various production techniques, and compare measured ET with non-direct or remotely-sensed irrigation scheduling criteria such as leaf water potential and canopy temperatures.

Last Modified: 9/21/2014
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