Potassium (K) and phosphorus (P) are essential to the growth and development of cotton. Phosphorus is necessary for plant metabolism and encourages early root formation and growth, vigorous plants, early fruiting, and plant maturity, while K is known to play an important part in photosynthesis, plant-water relations, enzyme activation, disease resistance, and fiber development. Not all P and K is positionally or chemically available during the growing season. With the fast-fruiting, early-maturing cotton cultivars the availability and uptake of both P and K is essential for optimum production. A long-term study was initiated in 1982 at the Delta Research and Extension Center on a Dundee vf sandy loam (Aeric Ochraqualfs) to evaluate the long-term effects of P and K fertilization on cotton lint production. A 3 x 3 factorial arrangement of P rates (0, 40, 80 lb P/A) and K rates (0, 60, 120 lb K/A) were included in a randomized complete block design with four replications. The fertilizer P (applied as concentrated superphosphate (CSP), 0-46-0) and K (applied as muriate of potash, 0-0-60) was applied in even years of the continuing study. The dry materials were broadcast-applied to partially flattened beds followed by incorporation with a spring-tooth harrow and re-hipping. All other cultural practices were maintained as appropriate for conventional cotton production. Composite soil samples were taken each year after harvest, then processed and analyzed through the Soil Testing and Plant Analysis Laboratory at Mississippi State University operated by the Mississippi Cooperative Extension Service. These samples were used to monitor changes in soil test P and K with respect to fertilizer applications. Those plots receiving no fertilizer P and K were allowed to continue a gradual decline in available nutrients throughout the duration of the experiment.