Testing of a Modified Methodology for Determination of Mean Stage of Development in Alfalfa

Abstract

For all crop species, an accurate, quick, and simple method for determination of mean development stage of plants has a key role for scientific and practical use. The investigation was performed to validate a modified methodology for determination of mean stage of development in alfalfa (Medicago sativa L.). The modified methodology, mean stage by fresh weight (MSFW), assumes that mean stage by weight (MSW) could be determined by fresh, and not only by dry weight, as was required by the original methodology. A total of 198 alfalfa samples were collected in 2010 and 2011. Sampling completely covered three growth cycles: spring growth and first and second regrowths. The correlation (r) between MSW and MSFW was >0.99. In 92% of samples, absolute deviation between MSW and MSFW was lt 0.15 on a scale between 0 and 9. The equation for prediction of MSFW based on measured MSW, MSFW-predicted = 0.9808. MSW, was developed with the data from the first year (n = 141) and tested with second-year samples (n = 57). Prediction error, expressed by root mean squared deviation (RMSD), was 0.045, while components of mean squared deviation (MSD), such as squared bias (SB), nonunity slope (NU), and lack of correlation (LC), were 8.12 x 10(-4), 5.45 x 10(-4), and 6.67 x 10(-4), respectively. Values close to zero in all three MSD components show that validation line had a approximate to 0, b approximate to 1, and r(2) approximate to 1. As a simpler methodology, MSFW gives an opportunity to be more applicable in practice with all of the benefits of the MSW methodology.