Potassium Uptake and Partitioning Relative to Dry Matter Accumulation in Cotton Cultivars Differing in Maturity

Dry matter may accumulate faster in fruit of earlier maturing cotton (Gossypium hirsutum L.) cultivars than in later cultivars, requiring more rapid K uptake and/or partitioning to developing bolls. Faster K uptake may require higher K fertility. We examined K uptake and partitioning relative to dry matter accumulation during boll filling of two cultivars contrasting in maturity, under two K fertility regimes at Jackson, TN. Plots fertilized with 56 kg K ha(-1) yr(-1) received the recommended rate of K, while plots receiving 112 kg K ha(-1) yr(-1) were overfertilized with K. 'PM 1218 BG/RW (PVP 200000213) matured earlier than 'DP 555 BG/RR'(PVP 200200047) in 2005, and 'FM 960BR' PVP 200400224 matured earlier than 'DP 555 BG/RR in 2006, but not 2007. Higher K fertility did not increase lint yields, but it delayed maturity in two of 3 yr. During boll filling, the earlier cultivar accumulated more dry matter and K in fruit than the later cultivar, and accumulated them faster in 2 of 3 yr. Higher K fertility shifted the partitioning of dry matter and K to vegetative organs relative to fruit. The proportion of plant K in fruit exceeded the proportion of dry matter in fruit, and the difference increased during boll filling. Evidently, K translocation to fruit exceeded dry matter accumulation in fruit, indicating that boll filling was not limited by K. Neither the K-uptake ratio (total aboveground K relative to residual soil K plus fertilizer K) nor the K-utilization ratio (lint produced per unit plant K) differed between cultivars with sufficient K fertility.