Root Distribution in 1- to 48-Year-Old Stripmine Spoils in Southeastern Montana

Abstract

A study was initiated in June 1976 at Colstrip, Montana, to determine root distribution to 1- to 48-year-old stripmine spoils and in undisturbed soils of the area. Root distribution was determined using three methods: (1) soil profile description, (2) root biomass, and (3) radioactive tracer (32 P). Results from all three methods showed that old spoils had substantially more roots below 100 cm than new spoils or undisturbed soils. Differences in root abundance were attributed to species composition. Old spoils were dominated by half-shrubs, while new spoils and undisturbed soils were dominated by grasses and forbs. Root biomass in the upper 100 cm of new spoils was 44% less than in undisturbed soils and 43% less than in old spoils. Maximum rooting depths of 15 important plant species were determined using the radioactive tracer method.