Potassium effects on canopy light interception and earliness of no-tillage cotton

Earliness of maturity is essential for adaptation of cotton (Gossypium hirsutum L.) to regions with short growing seasons, and it may be influenced by potassium nutrition. Our objectives were to determine effects of K fertilization on interception of photosynthetically active radiation and earliness, and to describe the relationship between earliness and light interception at different in-canopy heights. Research was conducted with no tillage on a Memphis silt loam (fine-silty, mixed, active, thermic Typic Hapludalf) with low extractable K. Using a split-plot randomized complete block design, 0 and 112 kg K ha-1 were soil-applied before planting each year as mainplot treatments, and 0 and 4.1 kg K ha-1 were foliar applied four times per season as subplot treatments. Canopy interception of photosynthetic photon flux density (PPFD) was measured at 23-cm vertical increments in 1993 and 1994. Plots were spindle-picked twice each year. Earliness was measured as the percent of total yield picked at first harvest. Relative to no fertilizer K, soil-applied K increased canopy PPFD interception at all heights measured. Neither soil-applied nor foliar K affected earliness in 1993, a drought year, but soil-applied K decreased percent first harvest from 78 to 65% in 1994. Foliar K did not affect canopy light interception in 1993, and it increased interception in 1994 only with no soil-applied K. At 111 d after planting, percent first harvest was negatively correlated with PPFD interception at all measured heights in the canopy, suggesting that higher K fertility delayed maturity as it increased upper-canopy light interception. In short-season environments, optimum K fertilization needs to be accompanied by cultivar selection and management that promote earliness of maturity