AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Spring 1998, No. 4
At least 60 pounds of nitrogen is needed to produce a bale of cotton. Nitrogen is necessary for photosynthesis, is a part of proteins and chlorophyll, and adequate supplies increase water use efficiency. Uptake of nitrogen by cotton peaks at about 2 to 3 pounds 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, for example, preplant and at or before first bloom improve the chances of meeting crop needs during peak demand periods. 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 25 to 30 pounds of P2O5 is required to produce a bale of cotton. Phosphorus is important in early root development, photosynthesis, cell division, energy transfer, early boll development, and hastening of maturity. Banded application 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.
About 60 pounds of K2O is needed to produce a bale of cotton. Potassium functions in enzyme systems, is important in reducing the incidence and severity of wilt diseases, increases water use efficiency, and affects fiber properties like micronaire, length and strength. Potassium uptake increases during early boll set and peaks at about 2 to 3 pounds per acre per day. About 70 percent of uptake occurs after first bloom. 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 deficiencies. Soil tests should be used to determine 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 micronutrients like boron, zinc and manganese where they are deficient. Soil tests, plant analyses, and field history should be used to establish need for these nutrients.
A complete fertility program is critical to attaining maximum profit and cotton yield. Furthermore, balancing nutrient inputs with other management inputs like water, variety, tillage, and rotation helps insure that maximum efficiency of production and profit are achieved.