Accuracy of Calculation of Parameters for Characterization of Emitters in Trickle Irrigation

Indoor laboratory tests were carried out to determine the accuracy with which the coefficient of manufacturing variation ($CV$), the discharge coefficient ($K$), and the emitter discharge exponent ($x$) may be measured and calculated, and the number of significant digits to be reported in the published data. An error analysis and the propagation of the error in the formulas beginning from the experimental uncertainties of the instruments were used. Two calculation methods were used and compared to obtain $K$ and $x$: the method of the two measurements and the data regression analysis. The results showed that, because of a calculation error of 15%, the maximum precision of the $CV$ obtained in this analysis allowed the use of only one decimal of significant digits. As regards $K$ and $x$, the method of the two measurements showed high levels of uncertainty (9% for $K$ and 3.6% for $x$, respectively) despite the accuracy of the measurements; therefore, only two significant decimal digits for $x$ and no decimals for $K$ were indicated. The regression analysis method was more precise, with a precision of 1.7% and one decimal significant digit for $K$ and a precision of 0.5% and three decimals for $x$. Therefore, the results showed that, when publishing the values of the parameters to characterize trickle emitters, the calculation method used should be reported along with the degree of accuracy of the measurements in order to improve the assessment of their actual characteristics, allowing a more objective comparison among similar products of different companies.