Different tree age affects light competition and yield in wheat grown as a companion crop in jujube-wheat agroforestry

Abstract

Effects of tree shading on crops within an agroforestry system in Hetian oasis regions in northwestern China are poorly understood. Measurements of light intensity, light use efficiency (LUE), light extinction coefficient, leaf area index (LAI), crop yield and biomass were studied in determining the effects of tree shading on crop yield in a jujube (Zizyphus jujuba Mill.)/wheat (Triticum aestivum L.) intercropping system. The treatments comprised (1) sole-cropped wheat, (2) 6-year-old sole jujube trees, (3) 8-year-old sole jujube trees, (4) 10-year-old sole jujube trees, (5) intercropping of wheat/6-year-old jujube trees, (6) intercropping of wheat/8-year-old jujube trees and (7) intercropping of wheat/10-year-old jujube trees. We found that the land equivalent ratios (LERs) of all three jujube tree/wheat treatments were larger than one and this indicated that plant growth factors were used more efficiently by the intercrop than by sole crops and the land use advantages of the intercropping systems were significantly greater than monoculture crops. Because of shading by trees, there was a decrease in intercropped wheat LAI, growth and yield, and the fruit yield of the intercropped jujube trees also decreased to a certain degree. The light interception of intercropped wheat was significantly decreased by different tree ages up to a certain point. The LUE results ranged from 1.68 to 1.31 and 1.13 g DM MJ [photosynthetically active radiation (PAR)]−1, indicating that LUE can be significantly affected by increasing tree age. Compared to intercropping 8-year-old jujube trees, a higher light extinction coefficient was found in intercropping 6- and 10-year-old jujube trees.