STABILIZING STEEP SLOPES WITH SOIL CONDITIONERS AND PLANTS

The approach in this study of runoff and erosion control on steep slopes was to combine soil stabilizers with the planting of drought-resistant, perennial plants. The effect of 10 t ha-1 phosphogypsum (PG) + 70 kg ha-1 polysaccharide (PS), 10 t ha-1 PG and 20 kg ha-1 polyacrylamide (PAM), and 200 kg ha-1 PS on the erosion of steep slopes (30-60%) was studied in plots 2 m in width and of different lengths (12-20 m), at three different sites in Israel (semiarid conditions), and under natural rainfall conditions. Likewise, observations on the establishment and development of nonirrigated, drought-resistant, perennial plants on steep slopes (40-60%), combined with 10 t ha-1 PG + 70 kg ha-1 PS, were conducted at two sites in Israel. PS + PG and PAM + PG treatments were very efficient in erosion control in a wide range of soil types, ESP, CaCO3 levels, and weather conditions. These treatments reduced erosion six- to eleven-fold in comparison with the control. No significant difference was found between PS + PG and PAM + PG treatments. However, the application of PAM was problematic due to its very low dissolution rate and its high viscosity in water. Two-hundred kg PS without PG was found efficient only at one experimental site with calcic haploxeralf soil and 300 mm average annual rainfall. The combination of PS + PG, and drought-resistant, perennial plants was very sucessful. The plants developed very well without irrigation throughout the long, dry summer. Only one year later, the creeper plant canopy covered an area of 0.75-1.5 m, and the bushes were 0.8-1.2 m in height.