AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Spring 2003, No. 7
Approximately 30 pounds of P2O5 is taken up per bale of cotton produced. Of the total uptake, slightly less than 50% (14 pounds of P2O5) is removed per harvested bale. Phosphorus uptake by cotton follows closely the pattern of dry matter accumulation. By first flower the crop has accumulated about 20% of the total seasonal uptake. After this time, the rate of uptake increases dramatically. By peak bloom, about half of the crop’s phosphorus has been taken up, and by first open boll the crop has taken up over 70% of its needs. Peak daily uptake of phosphorus occurs 60 to 100 days after planting and can exceed one pound of P2O5 per acre. Failure to meet the uptake demand during the peak period will result in plant stress, yield loss, and a decline in lint quality. Phosphorus uptake is completed by the time the crop reaches the 50% open boll stage.
To ensure proper seed and lint development, adequate soil phosphorus levels must be built and maintained. A rule of thumb for raising soil test phosphorus is that it takes 6 to 14 lb P2O5 above crop removal to build soil test phosphorus by one pound per acre on sandy loam to silt loam soils. There are other important reasons to build soil test phosphorus levels into the high or medium to high range:
Adequate phosphorus nutrition is critical in optimizing yield, quality, and profit potential in cotton production. Insufficient phosphorus results in dwarfed plants, delayed fruiting and maturity, and reduced yield. While placement of phosphorus fertilizer is not as important as in the production of many other crops, banding phosphorus can increase yields in some situations (e.g., reduced or no-till, compacted soil conditions). Use soil tests to help determine optimum phosphorus application rate. Soil test levels should be maintained in the medium to high range to assure consistent production, and that phosphorus does not limit cotton yield and quality.
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