The objective of this research was to develop and validate a ruler that measures the leaf area of the cotton plant, in a quick and non-destructive manner and directly in the field. Ninety days after the emergence of the crop, leaf samples of tencotton plants of cultivar BRS 187 8H were collected, of which all leaves were removed to prepare the samples and, after that, they were photocopied and length measurements were done with the help of a planimeter to define the range of the ruler. In the second stage of the experiment, the cultivars BRS Safira, BRS 201 and BRS Verde were used to test the ruler. The analysis of regression between the leaf area measured in samples of leaves and the estimated areas showed a good adjustment with coefficient of determination equal to 0.95. Comparing the means of both the methods, it was verified that the mean leaf area of the four cultivars of cotton, measured with the proposed ruler, did not differ statistically from the mean area measured with the planimeter. The ruler can be recommended to determine, directly in the field, the leaf area of cotton cultivars with cordiform and planofile leaf structure, in relation to the horizontal.
regression equation; okra leaf; growth analysis
