Effects of deficit irrigation and plant density on the growth, yield and fiber quality of irrigated cotton

•Cotton growth and yield were impacted by irrigation and plant density interaction.•High plant density increased yield and irrigation water productivity under deficit irrigation.•Yield increase was due to the increased plant biomass and harvest index occasioned by high plant density or deficit irrigation.•Use of high plant density under deficit irrigation can be a promising alternative for water saving under arid conditions. Deficit irrigation is a new strategy to increase water use efficiency of cotton in arid areas, but it is not clear if it interacts with plant density. The objective of this study was to determine the effects of deficit irrigation and plant density as well as their interaction on the growth, yield and fiber quality of irrigated cotton. Two field experiments were conducted at three sites in 2013 and one site from 2014 to 2015 in an arid area of Xinjiang. A randomized complete block design with three replicates was used to determine the effects of 6 irrigation regimes on seedcotton yield in the first experiment, while a split-plot design was used in the second experiment with the main plots assigned to irrigation regime (saturation, regular and deficit) and the subplots to plant density (high, medium and low) to examine cotton yield, fiber quality and water productivity as affected by plant density under deficit irrigation. Averaged across the three sites, drip irrigation ranging from 3650 to 4700m3/ha did not significantly affect cotton yield, but seedcotton yield under 3650m3/ha in S1 was 6.3% lower than that under 4000m3/ha. Thus, it is quite appropriate to regularly drip-irrigate at 4000m3/ha in the experimental area. Deficit irrigation at high plant density also maintained a relatively higher leaf area index (LAI) and net assimilation rate (NAR), particularly at late stages of plant growth and development, than saturation or regular irrigation. Plant density ranging from 18 to 24 plants/m2 produced more seedcotton than 12 plants/m2 under regular irrigation. Increasing irrigation to saturation levels had little effects on cotton yield regardless of plant density; saturation irrigation at high plant density even reduced cotton yield compared with regular irrigation at medium plant density. Under deficit irrigation, the high plant density produced 9.1-17% greater yield and 9.3-16.8% higher irrigation water productivity (IWP) than low or medium plant density, and comparable yield to medium or high plant density under regular irrigation.