Root distribution and productivity in a poplar tree + alfalfa silvopastoral system in northwest China’s Xinjiang Province

Abstract

Silvopastoral systems have been a way to address issues related to land use and desertification on the fringe of cities, particularly in northwest China where fast-growing urban population and threat of desertification have become serious problems. A field experiment conducted in northwest China evaluated the root distribution and interspecific interaction between the poplar (Populus L.) and alfalfa (Medicago sativa L.) in a silvopastoral system. Roots were sampled once every 15 d using an auger sampling method in a seven-year-old poplar tree + three-year-old alfalfa silvopastoral system, a three-year-old sole alfalfa, and a seven-year-old sole poplar. The results showed that intercropping had a negative effect on the root length density (RLD) of alfalfa and reduced the average root diameter (ARD) of alfalfa at 20–60 cm soil depth. The specific root length (SRL) of alfalfa in silvopastoral system was higher compared to sole cropping. In contrast, intercropping with alfalfa had a positive effect on the RLD and ARD of poplar at the alfalfa grown areas at 0–20 cm soil depth, but less effect on the SRL of poplar. Intercropping caused the reduction of alfalfa yield, but had not significant effect on the yield of stem wood volume of poplar. Calculating the land equivalent ratio in a poplar tree + alfalfa silvopastoral system, it showed that this system was advantageous in the utilization of resources and had a higher productivity compared with sole cropping. In conclusion, root competition and interactions between two intercropped species affects yield of alfalfa and the root distribution of intercropped species in a poplar + alfalfa silvopastoral system.