In Australia, premature senescence (PS) is occurring with increasing frequency in cotton crops on soils with high levels of available K. However, by the time PS is noticed, it is generally too late to take corrective measures and the use of plant tissue testing as a diagnostic tool has not been widely successful in predicting K deficiency (Kirby and Atoms, 1985). Therefore, it is important to detect beforehand susceptible crops, so that timely action can be taken