Plant density affects light interception and yield in cotton grown as companion crop in young jujube plantations

• Productivity and light use of cotton in jujube-cotton intercrop can be increased by optimizing plant density.
• Increasing plant density modified the distribution pattern of the light within the canopy.
• The highest yield and light use efficiency of intercropped cotton were achieved at 18.0 plants m−2.

Tree-crop mixtures may increase yield and revenue especially during the early years of tree plantations. Jujube is grown widely in China for their fruits, and cotton is gaining popularity as an understory crop in young jujube plantations. There is a need for information on productivity and optimal planting densities of cotton in these mixed systems. Field experiments were carried out in 2012 and 2013 in Hetian, Xinjiang, China. Three cotton plant densities (13.5, 18.0 and 22.5 plants m−2) were tested in 6–7 years old jujube plantations, in which the cotton was grown in a 6 m-wide space between the tree rows. Cotton leaf area index increased but plant height decreased with plant density. Cotton light interception increased with density, but at early and mid-season, the difference in light interception between 18.0 and 22.5 plants m−2 was only marginal. Increasing plant density modified the distribution pattern of the light within the canopy, thus affected overall cotton light interception and use efficiency. The highest yield and light use efficiency of cotton were achieved at 18.0 plants m−2. Spatial distributions of light intensities and extinction coefficients were affected by the shading of jujube trees within the cotton canopy in the intercrop. Jujube growth, yield and light utilization were not significantly affected by cotton plant density. We conclude that the productivity and light utilization of cotton in jujube-cotton intercropping can be increased by optimizing cotton plant density.