Soil barriers

Soil barriers slow down runoff and retain the soil lost by sheet erosion. They may be made of wood or rocks; over time, they may develop into live fences of trees and shrubs. In Papua New Guinea and the Philippines, barriers are constructed with logs and branches across the slope. These are placed against wooden stakes driven into the ground. The upper side of the barrier is filled with grass and other materials to act as a sediment trap. The width of the cropland between barriers depends on the slope gradient, but is usually 4 m to 8 m. Crops such as maize, sweet potato and tobacco are planted in the alley.

Advantages

· Slows down surface runoff.
· Retains sediment behind the fences.
· If properly maintained, natural terraces develop over time.
· Allows cultivation even on steep slopes that may not otherwise be feasible to crop.

Limitations

· Wooden barriers do not usually last for more than 2-5 years.
· Barrier construction requires significant labor.

Factors affecting adoption

Biophysical

· More likely to be adopted if land with more moderate slopes is not available to grow crops.

Socioeconomic

· Labor to build barriers may not be available.

· Allows farmers to grow relatively high-value crops on slopes otherwise impossible to cultivate (e.g., tobacco in the Philippines).