Does sample size of leaf osmotic potential affect its relationship with cotton yield?

Leaf osmotic potential at full turgor ({pi}0) has been used frequently to indicate turgor loss point of plant leaves. However, even a rapid measurement of {pi}0 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 {pi}0 and relate it to indices of crop performance. Yet the statistical and agronomic significance of using a small sample size of {pi}0 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 {pi}0 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 strength of the linear relation between {pi}0 and cotton yield, 1-6 resamples of {pi}0 were randomly drawn with replacement from the original 6 measurements per plot for the 54 plots. The resampled data of {pi}0 were then used as independent variable to predict cotton yield. We found that, considering the labor and cost, sampling 3 or 6 leaves per plot may not make a significant difference for the linear regression between {pi}0 and cotton yield.