The primary factors which may be involved in potassium deficiency appear to be: 1) Higher peak demands caused by a condensed fruit set period combined with higher yields, 2) Reduced vegetative storage capacity for K due to lower harvest index of some modern cultivars, 3) An apparent decline in root activity during the boll fill period, 4) Reduced uptake and translocation of soil K resulting from soil-borne pathogens, 5) Soils which cannot supply the daily K rates demanded during the boll fill period, resulting either from low soil K levels or slow rates of K release from soil minerals. Other factors, such as irrigation, fertilization, subsoil fertility, tillage, compaction, crop protection and growth regulators can interact with these basic factors to alter fruiting, root distribution and K availability. Long term drawdown of K by soybeans, alfalfa and silage corn have also contributed. Potassium deficiency appears most likely to occur in soils of California, the Mid-South, and to a lesser extent, the Southeast. In California and the Mid-South, deficiency symptoms in the upper plant have been reported in soils testing high in K, and in some cases, it appears that current petiole monitoring programs may not prevent yield losses. In the Mid-South, drought induced deficiencies may account for these unpredictable deficiencies. In California, monitoring programs are based on lower yielding, antique cultivars. Soil and petiole monitoring programs are currently being reevaluated (calibrated) for modern cultivars. In the Southeast, deficiencies are for the most part, traditional in nature, and primarily result from low soil K supplies.