Abstract

A field study was conducted to determine seasonal root biomass, root spatial distribution and water use efficiency (WUE) in milkvetch (Astragalus adsurgens Pall.), sainfoin (Onobrychis viciaefolia Scop.), alfalfa (Medicago sativa L.) and Lespedeza davurica (L. davurica) grown in semiarid region on the Loess Plateau, northwestern China. Soil core method (Ø9 cm) was used to determine root biomass in April, September and November in 2005. For each species, root biomass vertical distribution was measured down to 150 cm in increments of 0 - 20, 20 - 40, 40 - 60, 60 - 90, 90 - 120 and 120 – 150 cm for inter-rows, between plants and at the center of plants respectively. Roots were distributed throughout the profile with a high concentration at the top and decreasing with soil depth. Root biomass was mainly concentrated in 0 – 60 cm strata between rows and between plants of each species while at the center of plants it mainly distributed in 0 – 20 cm strata. Except L. davurica whose root biomass reached the maximum in September, root biomass of the other three legumes reached the maximum in November. Shoot biomass continued to increase from April to November for all the four legumes. In November, the root biomass for milkvetch and alfalfa accounted for about 2.93 and 2.30% of the total biomass (root plus shoot) respectively, while in sainfoin and L. davurica it accounted for 6.00 and 4.44% respectively. There were significant differences between the four legumes in WUE, and the order was same as shoot biomass, ranked as milkvetch>alfalfa>sainfoin>L. davurica. The seasonal and yearly high shoot biomass and low proportion of root biomass resulting to low root : shoot ratio may explain the significantly higher WUE of milkvetch and alfalfa in comparison to sainfoin and L. davurica.

Key words: Root biomass and distribution root: shoot ratio, water use efficiency (WUE), legume, Loess Plateau.