Irrigated cotton (Gossypium hirsutum) is a major crop of the San Joaquin Valley (SJV) of California with an acreage exceeding 1.1 million acres in 1995. Over the past 20 years new cultural production techniques and cultivars have improved seed and lint yields. With these new cultural practices and cultivars attention has been focused on updating fertility management of Acala cotton varieties. A primary focus of this research has been to address late-season K deficiencies which limits lint yield on approximately one-fifth of the annual acreage (Gulick et. al 1989).