Effects of N application levels and post-decapitation smearing of NAA on fruit abscission and yield of cotton (Gossypium barbadense L.) in saline soil

A field experiment was conducted to investigate the effects of decapitation (a conventional cotton cultivation technique in Xinjiang) and smearing NAA after decapitation on the yield and fruit abscission of cotton under low (226.5 mg·kg^-1) and high (346.5 mg·kg^-1) nitrogen doses in a saline soil. The results showed that fruit abscission rates of decapitation and smearing with NAA after decapitation were lower than those of non-decapitation treatment under both low and high nitrogen levels. Compared with the conventional decapitation treatment, smearing with 0.3 mmol·L^-1 NAA after decapitation increased boll retention rate and cotton yield by 1.3% and 23.7%, respectively. It, however, decreased fruit abscission rate by 0.8%, under low nitrogen application. In terms of boll retention rate, fruit abscission rate and cotton yield under high nitrogen application, no significant difference was noted between smearing with 3 mmol·L^-1 NAA after decapitation and conventional decapitation practices. Boll retention rate, weight per boll and number of opened boll were lower under high nitrogen level than under low nitrogen level. Furthermore, ginning yield was not different between different nitrogen levels in the same decapitation treatment. Lint weight under low nitrogen level was higher than that under high nitrogen level. It was concluded that smearing cotton with proper concentrations of NAA after decapitation increased boll retention rate and decreased fruit abscission rate, which eventually enhanced cotton yield. Cotton yield decreased with excessive nitrogen application level.