Water supply, growing season length, and nutrient supply limit cotton (Gossypium hirsutum) production on the Southern High Plains of Texas. The precipitation:evaporation ratio is less than 0.25 in most years during the growing season. Approximately one-half of the total cotton acreage in the area is capable of supplemental irrigation however the supply is usually considerably less than the demand and deficit water management is common. Irrigation management is often limited by water sources that cannot be controlled by the producer. Growing season length is limited by heat unit accumulation rather than frost-free days with both cool springs and falls common. The major factor left to the producer's control is fertility. Fertility management can affect maturity of cotton which can affect water use efficiency. The development of more efficient nutrient management strategies is needed to maximize use of all available resources in cotton production. The main concern of phosphorous fertilization is that the soil system has a high pH and free calcium that forms insoluble calcium phosphates that limit phosphorous availability to cotton. Applying multiple applications of nutrients in small amounts through the irrigation water during the time of peak crop need will increase phosphorous availability and maximize use efficiency of water and other nutrients. This study will compare different methods of phosphorous application (no phosphorous, pre-plant, sidedress, and fertigation) to determine if there is a real difference in the application methods. The ratio of nitrogen:phosphorous will be compared to determine which level is most effective through fertigation. The ratios are 5:0, 5:1, 5:2, and 5:3 (lb. N:lb P₂O₅) per inch of total water. In two years of research we have found that fertigation is an acceptable method of applying phosphorous to the cotton crop and that higher phosphorous ratios give a yield response through more lint per boll. Using fertigation as an application method will give producers the opportunity to manage their fertilizer inputs based on in season yield potential saving them both time and money.