Field Crops Research 161 (2014) 128–136 Contents lists available at ScienceDirect Field Crops Research journal homepage: www.elsevier.com/locate/fcr Any chance to evaluate in vivo field methods using standard protocols? R. Confalonieri a , C. Francone a,∗ , M.E. Chiodini a , E. Cantaluppi b , L. Caravati b , V. Colombi b , D. Fantini b , I. Ghiglieno b , C. Gilardelli a , E. Guffanti b , M. Inversini b , L. Paleari a , G.G. Pochettino b , S. Bocchi a , S. Bregaglio a , G. Cappelli a , P. Dominoni a , N. Frasso a , T. Stella a , M. Acutis a a Università degli Studi di Milano, Department of Agricultural and Environmental Sciences—Production, Landscape, Agroenergy, Cassandra lab, Via Celoria 2, I-20133 Milan, Italy b Università degli Studi di Milano, Students of the Cropping Systems Ms Course, Via Celoria 2, I-20133 Milan, Italy article info Article history: Received 24 April 2013 Received in revised form 28 February 2014 Accepted 2 March 2014 Available online 27 March 2014 Keywords: Accuracy ISO 5725 Leaf color chart Precision Rice Chlorophyll meter abstract The lack of standardized information on the evaluation of in vivo field methods is an important source of uncertainty in the interpretation of field data. The same words precision and accuracy can be frequently found in the agronomic and ecological literature, although often used without a real attempt to give these terms rigorous and shared meanings. On the contrary, standard protocols for determining accuracy and precision of analytical methods were successfully proposed in the last two decades and are now routinely used, especially within the chemical community. A first attempt to compile a standard guideline for in vivo field methods, derived by adapting the ISO 5725 protocol for the validation of analytical methods, is here presented. The concepts of levels, reference material, and inter-laboratory test derived from the protocol are redefined, and the underlying assumptions behind the adaptation of the ISO norm are introduced and discussed. Applicability and effectiveness of the proposed procedure are shown by means of a case study where the accuracy – i.e., trueness and precision, the latter composed by repeatability and reproducibility – of two diagnostic methods for indirect estimates of plant nitrogen nutritional status (chlorophyll meter and leaf color chart) was determined. The chlorophyll meter was more precise than leaf color chart, with precision value – expressed as relative standard deviations – lower than 6%. On the other hand, trueness indices showed better performances for leaf color chart, thus demonstrating the suitability of this method for supporting low-income farmers in managing topdressing fertilization, although at the price of performing a large number of reading replicates. However, these results are not aimed at drawing conclusions on techniques for supporting fertilization: the one presented is indeed just a case study used to assess the possibility of adopting the proposed procedure, as well as to highlight potential limits for its application. In this regard, the identification of reference values – needed for trueness quantification – is surely the most delicate issue, since the absence of conventional true values leads to the need of finding the most suitable solution according to the specific variable investigated and to the specific contexts in which the method under evaluation is applied. Hence, in light of both the encouraging results and the underlined limits, we just aim here at opening a discussion on the need for standardizing approaches and terminology for the evaluation of indirect field methods. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Methods for in vivo data collection in field campaigns are often evaluated without providing readers with crucial information ∗ Corresponding author. Tel.: +39 02 50316578; fax: +39 02 50316575. E-mail address: caterina.francone@unimi.it (C. Francone). related to the methods themselves, such as accuracy, precision, trueness, etc. (Balasubramanian et al., 1999; Hyer and Goetz Scott, 2004). In other cases, the lack of clarity in the exposition of results may lead to a mis-conception or mis-use of these terms, that are associated to qualitative or quantitative concepts without any standardization, leading to uncertainties in the interpretation of the information coming from these evaluations and to difficulties in the comparison of results achieved by different authors with the http://dx.doi.org/10.1016/j.fcr.2014.03.002 0378-4290/© 2014 Elsevier B.V. All rights reserved.