LONG-TERM NITROGEN-FERTILIZATION IN SHORT-SEASON COTTON - INTERPRETATION OF AGRONOMIC CHARACTERISTICS USING STABILITY ANALYSIS

Lint yield and many other agronomic characteristics of cotton (Gossypi um hirsutum L.) are greatly influenced by environment, The objectives of this work were to evaluate the use of stability analysis on various agronomic characteristics of cotton and to assess some of the environ mental factors that influence their response. Lint yield, gin turnout, picked lint percentage, and micronaire data from a single-site, long- term, soil fertility experiment on cotton conducted in the field under irrigated, short-season conditions were analyzed using conventional s plit-plot in time analyses of variance. Stability analyses (linear reg ression of a response variable (e.g., lint yield) for a specific treat ment on the location/year environment mean for the same response varia ble) were also used to investigate the treatment by environment intera ctions. Stability analyses suggested that applied N had no effect on l int yield in low-yielding environments (defined as <500 lb/acre). Appl ied N resulted in significant increases in lint yield in high-yielding environments (>500 lb/acre). No significant yield advantage was detec ted for applying more than 40 lb N/acre in low or high yielding enviro nments. Applied N at 80 and 120 lb/acre reduced gin turnout in all env ironments, Higher N rates resulted in greater reductions in gin turnou t in high gin-turnout environments. Micronaire was reduced by applied N in low-micronaire environments, but was increased by applied N in hi gh-micronaire environments. Only in 2 of 11 yr did N fertilization inf luence micronaire of the cultivars tested. Stability analyses were use ful in detecting subtle treatment effects over multiple environments i n agronomic characteristics of cotton and for partitioning treatment b y year interactions. This information was enhanced by having a minimum of 10 yr of data for all characteristics evaluated.