Accuracy of measurements of soil-water content made with a neutron-moisture meter calibrated gravimetrically in the field

Soil-water storage changes were measured over 2 yr in weighable loess soil monoliths. Parallel measurements were made with a neutron-moisture probe. To evaluate the accuracy of neutron-probe measurements, the relative deviation of measured changes in water content was defined as Delta X = ( Delta W sub(N) - Delta W sub(L) )/ Delta W sub(L) , where W sub(N) is the water content determined by neutron-probe measurements and W sub(L) is that determined by direct weighing. The mean value of Delta X showed a -25% systematic deviation of neutron-meter measurements from those of the lysimeters.