AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Spring 2001, No. 7
Cotton takes up about 60 pounds of nitrogen per acre for each 480-pound bale produced. Nitrogen is essential for the development of all plant organs including shoots, buds, leaves, roots, and bolls. Uptake of nitrogen by cotton peaks at about 2 to 3 pounds per acre per day during fruiting. Uptake is limited prior to squaring, and the majority of total nitrogen is taken up after first bloom. Therefore, split applications of nitrogen (e.g., preplant and at or before first bloom) improve the chances of meeting crop needs during peak demand periods. Texas Tech University researchers have shown that about 5 pounds of nitrogen are required per inch of water consumed. Since cotton is an indeterminate perennial, too much nitrogen late in the season may cause excessive vegetative growth and should be avoided. Soil and petiole tests can be helpful in determining preplant and midseason nitrogen management.
Approximately 30 pounds of phosphate per acre is taken up per bale of cotton produced. Phosphorus is important in early root development, photosynthesis, cell division, energy transfer, early boll development, and hastening of maturity. Banded application of phosphorus may be beneficial, especially where soil test levels are low or in reduced tillage systems. Insufficient phosphorus results in dwarfed plants, delayed fruiting and maturity, and reduced yield. Use soil tests to determine optimum phosphorus application rate.
Cotton takes up about 60 pounds of potash per acre per bale. Potassium is an extremely important nutrient in cotton production. It reduces the incidence and severity of wilt diseases, increases water use efficiency, and affects fiber properties such as micronaire, length and strength. It is important in maintaining sufficient water pressure within the boll for fiber elongation. Thus, the need for potassium increases dramatically during early boll set. About 70 percent of uptake occurs after first bloom, and uptake peaks at about 2 to 3 pounds per acre per day. Potassium deficiency may be expressed as a full season deficiency, or it may not appear until late season since this is the period of greatest demand. A shortage of potassium reduces fiber quality and results in plants that are more susceptible to drought stress and diseases. Preplant applications of potash, and in some cases mid-season foliar applications, are effective in correcting potassium deficiencies. Soil testing is the first step in predicting potassium needs.
Secondary elements and micronutrients are also critical to profitable cotton production. A high yielding cotton crop can take up as much as 30 pounds each of sulfur and magnesium. Cotton responds to trace elements such as boron, zinc and manganese where these nutrients are deficient. Soil tests, plant analysis, field history, and experience should be considered when establishing the need for secondary and micronutrients.
A complete fertility program is critical to achieving optimum cotton yields and maximum profit. Furthermore, balancing nutrient inputs with other critical management inputs including water, variety, tillage, and rotation, helps ensure that maximum efficiency of production and profit is realized.