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Interpretive Summaries:
2005 - Potassium Uptake, Distribution, and Yield Response by Modern Cotton Cultivars
2004 - Potassium Uptake, Distribution, and Yield Response by Modern Cotton Cultivars
Potassium Uptake, Distribution, and Yield Response by Modern Cotton Cultivars, 2005
During the past several years, late-season potassium (K) deficiencies have been observed in many cotton fields across South Carolina. Current K fertilizer recommendations in South Carolina are based on pre-season K levels of the topsoil that is adjusted by depth and K content of the subsoil. Research was conducted to determine if current soil testing procedures and recommendations are valid to optimize yield of modern cotton varieties. A replicated field experiment was conducted in 2004 and 2005 at the Pee Dee Research and Education Center located in Florence, on a Norfolk-Bonneau soil complex identified as K-deficient in the previous growing season. Potassium fertilization rates were 0, 50, 85, 120, 155, 190, and 225 lb K2O/A applied as a broadcast prior to planting. Five modern cotton cultivars...DPL 555BR, ST 5599BR, FM 989BR, DPL 444BR, and PM 1218BR...were evaluated. Leaf and petiole samples were obtained during flowering to monitor K status of plants.
Soil test K levels in the surface horizon ranged from 15 to 135 lb/A Mehlich I extractable K, depending on prior year K application rates and differences in soil properties. Increasing soil test and fertilizer K dramatically decreased premature defoliation of cotton and increased leaf and petiole K levels, thereby substantially increasing seed cotton yield. Cultivars had somewhat different responses to K fertilization. Leaf K ranged from 0.4 to 1.59% during mid-bloom and was highly dependent on soil test K and fertilizer K rate. Petiole sap K ranged from 2,100 to 9,500 parts per million (ppm) and was also highly dependent on soil test K and fertilizer K rate. The response of the cultivars to soil test and fertilizer K differed to some extent and will be discussed in the completed annual report. SC-13F
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