Competitive interaction in jujube tree/cotton agroforestry system in Xinjiang province, northwestern China

Abstract

A field study was conducted at Hetian oasis, southern Xinjiang, northwestern China, to investigate root distribution and morphology affected by interspecific interactions between jujube trees (Ziziphus jujuba Mill.) and cotton plants (Gossypium hirsutum L.). The treatments comprised (1) sole cotton, (2) 5-year-old sole jujube trees, (3) 7-year-old sole jujube trees, (4) 9-year-old sole jujube trees, (5) intercropping of cotton/5- year-old jujube trees, (6) intercropping of cotton/7-year-old jujube trees, and (7) intercropping of cotton/9-year-old jujube trees. Roots in each plot were sampled vertically by auger to a depth of 100 cm at 20-cm intervals and horizontally up to 150 cm away from the base of the trees at 30-cm intervals. The results showed that all jujube/cotton intercropping systems exhibited advantages of intercropping, with a land equivalent ratio > 1. The roots of both intercropped cotton and jujube had lower root length density (RLD) and root diameter (RD) at all soil depths compared with those of sole-cropped cotton and jujube trees. Interspecific competition with jujube trees altered the root development and morphology of the cotton plants. The roots of the trees spread underneath the crop and the roots of intercropped cotton tended to have a shallower distribution in the soil profile. A greater distance from the trees resulted in less influence on the RLD and RD of intercropped cotton. Older jujube trees had more developed roots and consequently higher RLD and RD. These findings may partly explain the interspecific competition effects in jujube tree/cotton agroforestry systems. However, the mechanisms underlying the root interactions between cotton and jujube require further investigation.