456 PLANT SOIL ENVIRON., 53, 2007 (10): 456–463 Kozak (2004) investigated nonsequential yield component analysis and proposed a parameter and its estimator of influence of yield components on yield; nonsequential components are such compo- nents that are co-related and develop at the same time during the plant ontogenesis. The parameter takes into account a specific multiplicative form of the relationship between yield and its compo- nents. It measures effects of components on yield, providing an estimated average yield in response to a change in a particular component, assuming the other components are fixed. The results by Kozak (2004) as well as those re- ported in this paper do not pertain to the situation in which yield components develop sequentially (e.g. Dofing and Knight 1992, García del Moral et al. 2003), but to what is called the non-sequantial development of yield components. Therein, yield components co-develop, making none of them a cause or an effect of another. This is why we call the methodology to analyze such a situation “nonsequential yield component analysis” (NYCA) to distinguish it from yield component analysis for the sequential case, which is sometimes called the sequential yield component analysis (SYCA) (e.g. McArthur and Eaton 1988). The paper by Kozak (2004) represented theoretical work on NYCA, focusing on deriving an appropriate expression for direct effects (parameter as well as its estimator), and comparing, theoretically and via simulation INFORMATION Applying statistics for nonsequential yield component analysis M. Kozak 1 , S. Samborski 2 , M.S. Kang 3 , J. Rozbicki 2 1 Department of Biometry, Warsaw Agricultural University, Warsaw, Poland 2 Department of Agronomy, Warsaw Agricultural University, Warsaw, Poland 3 Punjab Agricultural University, Ludhiana, India ABSTRACT In the paper, an application of the methodology for analyzing yield as affected by its components that develop at the same ontogenetic level is discussed; it may also be applied to any model in which several traits developing non-sequentially affect their product. he methodology is called “nonsequential yield component analysis”. Two applications are presented; the proposed approach is compared with path analysis, commonly applied for yield component analysis, and Piepho’s approach. In one example, grain yield of two cultivars of winter triticale (× Triti- cosecale Wittmack), Fidelio and Bogo, as affected by harvest index and biomass yield, was studied; the results of the three approaches compared were similar. However, in the study of nitrogen uptake as affected by nitrogen-uptake efficiency and crop nitrogen supply (the problem for which yield component analysis may be applied because of the underlying multiplicative model), the results of the methods were different. For both cultivars, path analysis and Piepho’s method showed a much stronger influence of crop nitrogen supply on nitrogen uptake than that of nitro- gen-uptake efficiency. In the proposed method, however, both these component traits influenced nitrogen uptake to a similar extent. he proposed method is shown to be methodologically better than the other approaches, and to provide different results in some situations. Hence, the new method should be used for nonsequential yield compo- nent analysis although it is suggested that path analysis may be applied if the determination coefficient of the linear model is close to 100%. Keywords: crop nitrogen supply; harvest index; nitrogen; nitrogen uptake efficiency; path analysis; yield components