6. Vegetative hedges or strips

Runoff velocity can be reduced drastically by planting vegetative hedges, bunch grass, or shrubs on the contour at regular intervals (Plate 32). These hedges can increase the time for water to infiltrate into the soil, and facilitate sedimentation and deposition of eroded material by reducing the carrying capacity of the overland flow. Vegetative hedges or narrow grass strips serve as porous filters. These hedges may not reduce runoff amount but can drastically decrease soil loss. The data in Table 21 from Puerto Rico show that narrow grass strips reduced total soil loss compared with a conventional tillage system. Similarly, the data in Table 22 from Java show that 0.5- to 1-m-wide grass strips were extremely effective in controlling runoff and soil erosion. By the fourth year of establishment, grass strips reduced erosion to zero.

Table 21 Effect of grass strips on runoff and soil erosion for three soils in Puerto Rico

Barnetl et al. 1972)

Table 22 Effect of grass strips on runoff and soil erosion from an Inceptisol on 15% to 20% slope in Java

(Ahujamin et al. 1984)

A wide range of grasses is commonly used as hedges (Table 23). A widely adopted grass for growing vegetative hedges to control erosion is vetiver or khus grass (NRC, 1993b). Vetiver is a densely tufted, aweless, wiry, and glabrous perennial grass. It has a deep, strong, and fibrous root system. It grows in large clumps from the root stock and is propagated vegetatively. The grass can be planted on the contour to establish protective contour hedges (Plate 33). Vetiver can also be established on earth banks or buns and on terraces to reinforce and stabilize these structures. Its thick root system prevents slope failure due to rifling, gullying, or tunneling. The establishment of continuous hedges of vetiver with no gaps provides maximum protection. While controlling soil erosion, vegetative contour hedges of vetiver also conserve soil water by enhancing infiltration and decreasing losses due to runoff.

(Lal, 1984)

Growing perennial shrubs as contour hedgerows is another commonly used form of vegetative hedge. This topic is discussed under the subsection on agroforestry under nutrient management systems.