A COMPARISON OF SEDIMENT PRODUCTION ON CHEMICALLY TREATED AND UNTREATED SAGEBRUSH RANGELAND IN THE RIO PUERCO HEADWATERS NEAR CUBA, NEW MEXICO

Chemical treatment of sagebrush rangeland has been utilized in the southwest United States for two decades and has improved overall land conditions. Sagebrush eradication allows grasses and other plants to increase their vegetative cover, thereby reducing runoff, erosion, and sediment transport.

Rainfall simulations on 1 m² grass, shrub, and bare plots were used to evaluate treated and untreated sagebrush rangeland in a small tributary of the Rio Puerco in northern New Mexico. Total sediment yields (kg/ha/mm) for three grass and three shrub plots are significantly higher in untreated than in chemically treated areas. Bare plots acted as controls and show no significant differences. The suspended solids yield collected after each rainfall simulation produced comparable results.

Comparison of the runoff to rainfall ratios between treated and untreated areas shows significant differences for grass and shrub plots. Averages of untreated grass plots are almost three times higher than those of their treated counterparts. Untreated shrub plot ratios are twice that of treated ones.

Twenty vegetation transects were taken with all percentages for grass, shrub, and bare cover categories showing significant differences between both treatment types. Comparison of averages reveals that untreated areas contain 16% grass cover versus 54% for treated. Treated areas also improved in terms of bare soil patches, which cover 33% compared to 56% in the untreated area. Grass bunches increased in area size between 2 to 5 times after treatment. However, averaged bare soil patches, although decreasing in overall percentage, are only slightly smaller in the treated area. Therefore, it is not their size that changed, just the abundance of bare soil.

Estimated Green-Ampt conductivities were used to evaluate infiltration variations and prove to be significantly higher for treated grass plots. The differences are due to percent vegetative cover and not any underlying changes in soil properties. We therefore confirm that the chemical treatment of sagebrush increases vegetation cover, thus increasing infiltration and reducing runoff and sediment yield.