Comparison of ET Measured with Neutron Moisture Meters and Weighing Lysimetersby James L. Wright, USDA-Agricultural Research Service, United States,
Abstract: The neutron moisture meter (N.M.) method of determining crop water use is frequently used in research and irrigated agriculture. This study was conducted to compare crop evapotranspiration (ET) estimated by the N.M. method with ET measured with a weighing lysimeter. Neutron meter data were obtained in a furrow-irrigated field of alfalfa (Medicago sativa L.) equipped with a weighing lysimeter and in alfalfa plots irrigated with a line-source sprinkler system. Seasonal ET estimated from the N.M. data for the furrow irrigation treatment was 15% less than lysimeter ET when only a 2-m soil profile was considered, and was 10% less than lysimeter ET for a 3-m profile. The seasonal ET estimated from N.M. data for the sprinkler treatment with a dry subsoil layer was within 2.5% of lysimeter ET. The N.M. method lacked capability of measuring root extraction of water from the relatively wet, lower soil layers which existed with furrow irrigation.
Subject Headings: Measuring instruments | Vegetation | Soil treatment | Crops | Water meters | Irrigation | Water resources | Water use
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