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Calculation of ET rates using soil moisture measurements (water balance method) depend on the assumption that there is essentially 2-dimensional, vertical, flow. With point sources and sinks (drippers or vines, for example), crop water use calculations need to be corrected for sensor position relative to the source/sink. A sensor near a source (dripper), or mid-way between sources, may show almost no change. Do Eddy correlation methods also have to take into account non-uniform flow ? On the question of calibration of soil moisture sensors (Terry A. Howell) it is of interest that the purpose of the exercise is to quantify crop ET. This is essential a *rate*, and the important calibration of the soil moisture sensor is of course the *slope*, the intercept (assuming it is linear) is not important. Of great importance for a sensor, however, is repeatability from site-to-site, stability and hysteresis. In order to calculate actual daily ET rates (which is presumably what is wanted), do the Eddy correlation methods have to integrate over a 24 hour period ? ---- Trevor Finch Research Services New England 8/16 Nicholson St, Balmain NSW 2041 Australia email: rsne@mpx.com.au tel: +61 (2) 9810 3563 fax: +61 (2) 9810 3323 ----