Does sample size of leaf osmotic potential significantly affect the evidence of its association with cotton yield?

Leaf osmotic potential at full turgor (π₀) has been used frequently to indicate turgor loss point of plant leaves. However, even a rapid measurement of π₀ using osmometry is time-consuming, if numerous leaf samples need to be measured. Because of this, researchers tend to use a small sample size to determine π₀ and relate it to indices of crop performance. Yet the statistical and agronomic significance of using a small sample size of π₀ to indicate crop performance is not known. We address this question using field measurements and statistical resampling. Six mature leaf samples were collected at the peak bloom stage from each of the 54 cotton plots in Texas, USA in 2024. The π₀ of the collected leaves were measured using an osmometer. Seed cotton yields from the field plots were measured near the end of cotton season. To test the effect of sample size on the evidence of the association between π₀ and cotton yield, 1–6 resamples of π₀ were randomly drawn with replacement from the original 6 measurements per plot for the 54 plots. The resampled data of π₀ were then used as independent variable to predict cotton yield. We found that, considering the labor and cost, sampling 3 leaves per plot would be adequate for the linear regression between π₀ and cotton yield.