Drip irrigated cotton lint yields were correlated to various Heat Unit indices. Twenty-eight data sets were used comprising yield and climatological data (all daily maximum and minimum temperatures throughout the growing season). The data sets included yields ranging from virtually nothing to five bales per acre.

A matrix of Heat Unit indices was formed by varying base temperatures (50 F to 80 F) against various levels of ceilings on the daily maximum temperature (no maximum ceiling to an 85 F-ceiling). The elements of this matrix were correlated to yield to see what would be the best predictor of potential yield. Season length and accumulative daily maximum and daily minimum temperatures were also correlated to yields. The best fit (on a linear basis) was with accumulative daily maximum temperatures (R²I = 0.738). Within the matrix itself, best fit was with the 50 F-base with no maximum daily temperature ceiling (R² = 0.703). Correlation decreased with use of higher bases, as well as, with more imposition on the daily maximum temperature.

The results indicate to the author that high daily temperatures --at least for drip Irrigated cotton-- are not non-productive, as is sometimes felt. Using the summation of maximum temperatures as the yield predictor, approximately 10,000 F must be accumulated before any lint will be produced, at which point, every accumulated 6 F thereafter, will produce a pound of lint.