Comparison of ET measured with neutron moisture meters and weighing lysimeters

The neutron moisture meter (N.M.) method of determining crop water use is\nfrequently used in research and irrigated agriculture. This study was conducted to\ncompare crop evapotranspiration (ET) estimated by the N.M. method with ET measured\nwith a weighing lysimeter. Neutron meter data were obtained in a furrow-irrigated field\nof alfalfa (Medicago sativa L) equipped with a weighing lysimeter and in alfalfa plots\nirrigated with a line-source sprinkler system. Seasonal ET estimated from the N.M. data\nfor the furrow irrigation treatment was 15% less than lysimeter ET when only a 2-m soil\nprofile was considered, and was 10% less than lysimeter ET for a 3-m profile. The\nseasonal ET estimated from N.M. data for the sprinkler treatment with a dry subsoil layer\nwas within 2.5% of lysimeter ET. The N.M. method lacked capability of measuring root\nextraction of water from the relatively wet, lower soil layers which existed with furrow\nirrigation.