Cotton represents the major crop grown on the southern high plains of Texas where over one million hectares are planted annually. About 40% of the planted area is irrigated with the remainder dependent upon rainfall. Over the past 10-15 years, yields of irrigated cotton have declined rapidly at a rate of 10 kg/ha per year. Although the total amount of water applied as irrigation has also declined, it is probably not the major cause of the continuous decline in yield. A recent soil fertility survey of four major cotton producing counties revealed that the concentrations of nitrogen and phosphorus in the root zone (top 1.0 m) were very deficient and a likely cause of the yield declines. For various reasons, producers have not been replacing the amounts of nutrients removed by production and have allowed severe deficiencies to exist.