ISHS Acta Horticulturae 228: IV International Symposium on Water Supply and Irrigation in the Open and under Protected Cultivation
SOME ASPECTS ON THE USE OF THE NEUTRON PROBE IN IRRIGATION AND EVAPOTRANSPIRATION STUDIES. |
| Authors: | C. Ramos, J.R. Castel, D. Gómez de Barreda |
| Abstract:
In a experimental plot of irrigated table grapes twelve neutron tubes were installed in each of two irrigated basins. Calibration of the neutron probe was done by the regression of the count ratio (R) on the volumetric water content (  v). To check the accuracy of the slope of the calibration equation a comparison of the soil water changes expected after known additions of water to soil by rainfall or irrigation with those changes measured with the neutron probe was made.
This comparison showed that the neutron probe method on average overestimated the water change by about 22%. This overestimation is attributed to the type of regression used.
An alternative method is proposed consisting in taking the mean value between the slope calculated from the regression of R on v and then solving for v, and that calculated from the regression of v on R. It is suggested that measurement of the change in soil water content after a rainfall can be, under certain conditions, an easy way of testing the accuracy of the slope of the calibration equation.
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