Seasonal Root Biomass and Distribution of Switchgrass and Milk Vetch Intercropping under 2:1 Row Replacement in a Semiarid Region in Northwest China

Abstract

A root system has the plasticity to adapt to environmental change and species interaction. Root biomass and distribution were studied in three comparable stands in the fifth growth year (2005) in a semiarid region of northwest China: (1) pure switchgrass, (2) pure milk vetch, and (3) mixed switchgrass and milk vetch in 2:1 row replacement. The measurements were carried out three times (April, September, and November) in 2005 during the vegetation period using a soil core method (9 cm). For each species, the vertical distribution of root biomass (RB) was measured in six consecutive layers (0–20, 20–40, 40–60, 60–90, 90–120, and 120–150 cm deep) between rows, between plants, and at the center of the plant, respectively. Results indicated a flexible distribution strategy of switchgrass that tended to increase soil exploitation and space sequestration efficiency in soil layers. Milk vetch followed a more conservative strategy: its roots reached the same soil depth in the pure and mixed stands but showed greater root densities in shallower soil layers in the latter. Under intercropping, RB input and root/shoot ratio in switchgrass were reduced, while milk vetch put more photosynthate into root growth. The shift toward a more superficially distributed system of milk vetch in the mixture with switchgrass together with the high RB and wide vertical and horizontal distribution of switchgrass in the study indicates the greater belowground competitive ability of switchgrass in the mixture.