Error analysis in estimating soil water balance of irrigated fields during the EFEDA experiment: 1. Local standpoint

Abstract

To associate a confidence interval with the results of a soil water balance, an estimate of the errors involved in the measurements and in the calculations is required. Volumetric water content, water storage and actual evapotranspiration were calculated from daily neutron scattering and tensiometer measurements, and the instrument, calibration and vertical integration components of their variance were compared from a local standpoint. In contrast to foregoing studies, water content values at different depths were not considered to be necessarily independent of one another, introducing supplementary covariance terms in the calculations. As an illustration, results are presented for two irrigated maize fields from the EFEDA experiment conducted in Spain in June 1991. The standard deviation of the total error was less than the standard deviation of either water storage or computed evapotranspiration between measurements.