SURFACTANT AND SOIL FIXATIVE TREATMENT OF FIRE-IMACTED SOILS TO IMPROVE WETTABILITY AND REDUCE EROSION

Following the Cerro Grande Fire, we evaluated two commercial products designed to improve soil wettability and reduce erosion. An intensely burned soil area in the Santa Fe National Forest west of Los Alamos, New Mexico, was selected and divided into 6 plots (1 m by 7 m). The surfactant (Magic Wet^TM, Cognis Corp.), was applied to three plots at three different application rates (16, 33, and 82 ml/m²). A soil fixative (Terra-Control^TM, Cognis, 170 ml/m²) plus the surfactant (16 ml/m²) was applied to a fourth plot, a fifth plot was raked with no other treatment, and a sixth plot was an untreated control. For two months following the applications, soil hydrophobicity was measured using a water-drop test, and erosion was monitored visually. Both the surfactant and fixative are non-toxic, biodegradable over a multi-month time period, and used in agricultural (vegetable crop) and golf-course applications.

The shallow soil profile consisted of a black, burned soil from 0-2 cm, a light tan mineral soil from 2-3.5 cm, and a medium tan mineral soil below 3.5 cm across all plots. Results of the water drop tests showed that the uppermost, black soil layer tended to be very hydrophilic (instant drop adsorption) throughout the study. The light tan soil layer was consistently hydrophobic (drop adsorption greater than 30 minutes) in all plots before surfactant application.The lowest, medium tan layer, below 3.5 cm, tended to be hydrophilic in most cases. Surfactant application reduced hydrophobicity in the tan soil layer in some locations, and roughly correlated with amount of surfactant applied. The effect was uneven, even after rainfall. The soil fixative application was very effective in preventing erosion throughout subsequent heavy rain events. Reduction of hydrophobicity below the fixative layer was also uneven in the tan soil. Oak seedling germination was greatest in the fixative-treated plot. Additional hydrophobicity tests will be performed after this spring's snowmelt.