Terrace formation in cropping strips protected by tall wheatgrass barriers

Tall wheatgrass barriers have been successfully tested in the northern Great Plains for wind erosion control and plant protection. Our objective was to document the passive formation of hillside terraces occasioned by grass barriers on a variable 2 to 4% west to east slope. Eleven double-row tall wheatgrass [Elytrigia elongata (Host) Nevski] barriers with 10 15-m-wide cropping intervals 530 m long were established in 1967 on a Williams loam (fine-loamy mixed, Typic Argiboroll) 11 km north of Culbertson, Montana. The barriers were oriented north and south in traditional field orientation. In 1991 we established four transects 15 m apart across the barrier system and designated five sampling points along the transects in each cropping interval for a total of 200 sampling points. To avoid confounding by slopes parallel to the barriers, we selected a segment of the barrier system on a near 0% north to south slope for the measurements. Elevation was determined at each point, and soil cores were taken to a depth of about 90 cm to determine depth to CaCO3 layer, and to determine total and organic carbon by 5 cm increments. A stair-step pattern, with a maximum drop of 30 cm from one grass barrier to an adjacent cropping interval, was documented. Depth to CaCO3 and organic carbon concentration increased downslope between barriers, showing soil movement. Grass barriers may serve as a substitute for mechanically built terraces.