Effects of regulated deficit irrigation on accumulation and distribution of biomass and nitrogen, and yield of island cotton

Water is one of the main limiting factors of crop yield in southern Xinjiang. Water not only affects the accumulation of biomass, but also farm operations and crop nitrogen uptake. There have been several studies on the interactions among water, nitrogen and other farm/crop attributes. However, few studies have investigated the accumulation and distribution characteristics of biomass and nitrogen in island cotton under regulated deficit irrigation. Thus a field experiment was conducted to study the effects of regulated deficit irrigation at budding stage on the accumulation and distribution characteristics of biomass and nitrogen, and yield of island cotton. The aim of the study was to show the regularity of nutrient migration in island cotton under regulated deficit irrigation and to provide theoretical basis for efficient utilization of water and nitrogen in order to promote the cultivation of high-yield island cotton. The experiment was set up as a split plot design with two varieties (‘Xinhai24’ and ‘Xinhai35’, sub-area) of cotton and three drip irrigation quotas severe deficit irrigation (with 0 m³·hm^-2 irrigation at budding stage and 2 850 m³·hm^-2 irrigation during growth period), mild deficit irrigation (with 900 m³·hm^-2 irrigation at budding stage and 3 750 m³·hm^-2 irrigation during growth period), and abundant irrigation (with 1 800 m³·hm^-2 irrigation at budding stage and 4 650 m³·hm^-2 irrigation during growth period). The results showed that maximum aboveground biomass accumulation rate under severe deficit irrigation occurred 3 d and 7 d earlier than under mild deficit irrigation and abundant irrigation, with the maximum accumulation rates lower by 45.1% and 51.0%, respectively. Duration of rapid increase of biomass under different treatments ranked as severe deficit irrigation < mild deficit irrigation < abundant irrigation. Maximum nitrogen accumulation rate under severe deficit irrigation respectively occurred 8 d and 15 d earlier than that under mild deficit irrigation and abundant irrigation. Maximum accumulation rate of nitrogen was highest under mild deficit irrigation, followed by abundant irrigation and then severe deficit irrigation. There were significant difference in proportion of nitrogen distribution in stems and leaves among severe deficit irrigation, mild deficit irrigation and abundant irrigation. However, nitrogen distributions in stems and leaves were similar under mild deficit irrigation and abundant irrigation. Mean bud, flower and boll nitrogen accumulation under mild deficit irrigation was highest after full budding stage. Lint yield under mild deficit irrigation was highest (average of 2 372.9 kg·hm^-2), 11.0% higher than that under abundant irrigation and 41.8% higher than that under severe deficit irrigation. Maximum aboveground biomass and maximum nitrogen accumulation rate occurred earlier for ‘Xinhai24’ than for ‘Xinhai35’. As aboveground biomass and nitrogen accumulation rates were larger, lint yield was higher for ‘Xinhai24’ than for ‘Xinhai35’. The results showed a good correlation between the eigenvalues of biomass and nitrogen accumulation of island cotton under mild regulated deficit irrigation (drip irrigation quota of 900 m³·hm^-2 at budding stage). Under this irrigation quota, the distribution proportions in various organs of cotton were reasonable and lint yield high. Lint yield of ‘Xinhai24’ was 2 488.2 kg·hm^-2 and that of ‘Xinhai24’ was 2 257.6 kg·hm^-2. Thus drip irrigation quota of 900 m³·hm^-2 at budding stage was recommended as appropriate irrigation scheme for potential high increase of yield of island cotton.