[en] In previous studies soil water contents were measured in different plots and different depths using a neutron probe. Since a large number of measurements has been made, the data collected could be useful to establish criteria for the rational use of this method of measuring soil water content. One question that immediately arises to the investigator using the neutron moderation method is that of how many access tubes are necessary to have a measurement which is representative for the particular field. This number depends on the variability of the instrument (neutron probe) and on the variability of the field. In this paper a study of these variabilities suggesting criteria for the use of the neutron probe in a particular field site is presented