The objective of this study was to evaluate the efficiency of the leaf disc method for estimating the leaf area index (LAI) of soybean plants in comparison with the digital photo method. A split-plot experimental design was used with three replications. The LAIs calculated by the leaf disc and digital photo methods were compared at four growth stages in four soybean cultivars (subplot). These soybean cultivars were sowed in Guarapuava, Paraná State, Brazil, at three different sowing dates (main plot) in the 2010/2011 growing season. Regression analysis was used for each group of samples, and the efficiency of the leaf disc method was evaluated on the basis of the coefficient of determination (R²), the calculated F and the intersection and abscissa errors. The regression analysis that compared the two methods resulted in highly significant F values and low errors for all sample groups, which showed the effectiveness of the leaf disc method. Although the R² value was high for all of the analyses, the values were minor for the separate growth stage analysis, especially for the samples collected at the V9 and R2 stages. The results indicated that the specific leaf area calculated by the leaf disc method was lesser to the specific leaf area calculated by the digital photo method. The leaf disc method is an efficient and robust method for estimating the LAI of soybean plants.
Glycine max; cultivars; digital photos; growth stages; sowing dates
