Are the differences among samples from agricultural trials analyzed by routine procedures experimental or only analytical?

Many experimental researches in the agricultural field involve chemical analyses. For a correct statistical data processing, it should be important to discriminate between the variability induced by the analytical method and by other sources of variation (experimental treatments and other causes of systematic variability). The object of the present communication is to present a simple and economical method for the evaluation of the analytical variability which does not require to replicate the analysis of each sample. The analytical method used in this study was the plant tissue determination of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), boron (B), copper (Cu), zinc (Zn), and sulfur (S) by plasma emission spectrometry (ICP). The repeatability and the reproducibility of the method for each element was obtained by analysing two times per day a reference sample. The use of these parameters in the statistical processing of the analytical data from experimental trials for a correct result interpretation are discussed.