Competitive interaction in a jujube tree/wheat agroforestry system in northwest China’s Xinjiang Province

The jujube tree (Zizyphus jujuba Mill.)/wheat (Triticum aestivum L.) agroforestry system is frequently used in China’s Xinjiang Province. The system improves land-use efficiency and increases economic returns. A field experiment was conducted at the Hetian oasis in southern Xinjiang Province to investigate the relationship between root distribution and interspecific interaction between the two intercropped species. The study included seven treatments: sole-cropped 5, 7, or 9-year-old jujube trees (treatments 1–3); 5, 7, or 9-year-old jujube trees intercropped with wheat (treatments 4–6); and sole-cropped wheat (treatment 7). To determine vertical root distribution, soil cores were collected in 20-cm increments from the 0 to 100-cm soil depth. The cores were collected at horizontal distances of 30, 60, 90, 120, and 150 cm from the jujube rows. The results showed that the land equivalent ratios were >1 for the three jujube/wheat intercropping systems. This indicated that these systems were advantageous compared with sole cropping. Tree height, breast height diameter, and mean crown radius were less in the intercropped treatments than in the corresponding sole-cropped treatments. Intercropping reduced the root length densities (RLDs) and root diameters (RDs) of both jujube and wheat at all soil depths. The RLD and RD of 9-year-old jujube trees were greater than those of the 5- and 7-year-old trees, which indicated that the root systems of the 9-year-old trees were more developed. Wheat root growth was inhibited more by older jujube trees than by younger ones. In conclusion, jujube tree/wheat intercropping can be practical and beneficial in the region. However, the mechanisms involved in the belowground interspecific interactions are still unknown. Additional research is needed to provide optimal management strategies and technologies for jujube/wheat intercropping.