Potassium Effects on Partitioning, Yield, and Earliness of Contrasting Cotton Cultivars

Received for publication October 19, 2006. Potassium nutrition requirements may differ in cotton (Gossypium hirsutum L.) cultivars that contrast in maturity and growth habit. Our objectives were to determine the effects of K fertility on carbohydrate and biomass partitioning, earliness, and lint yields of two contrasting cultivars. Fertilizer rates of 56 and 112 kg K ha^–1 yr^–1, representing 1x and 2x recommended K rates, were applied to long-term K fertility plots on a no-tilled Loring silt loam (thermic Oxyaquic Fragiudalf) in Jackson, TN. Plant samples were harvested at early bloom and cutout, to evaluate carbohydrate and dry matter partitioning during boll filling. Earliness was determined as the percentage of total yield at the first of two harvests. The more determinate cultivar, ‘Paymaster PM1218 BG/RR’, had higher aboveground dry weight, main stem starch concentrations and percentage first harvest, representing earlier maturity than the more indeterminate ‘Deltapine DP555 BG/RR’. The 2x K rate delayed maturity relative to the 1x rate, reflected in biomass partitioning and lint yield distribution. Lint yields were lower at the 1x than at the 2x K in the more determinate cultivar, but K did not affect the indeterminate yields. The two cultivars had equivalent lint yields at the 2x K rate, but the indeterminate cultivar produced more vegetative biomass, further delaying its maturity. Results suggest that an earlier, more determinate cultivar may require more K fertilization for optimal yield response with no tillage.