Template:Chapter 4.5
4.5 - Living grass barriers to prevent erosion
Erica Carmount, University of Guelph, Canada
Suggested citation for this chapter.
Carmount,E. (2022) Living grass barriers to prevent erosion. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org
Background and History
Every year, a large quantity of soil is lost due to erosion caused by both wind and rain. Sheet erosion generates the greatest amount of destruction and occurs when “raindrops pound the ground dislodging soil particles which are then carried away by the surface runoff” (de la Garza, n.d.). It is a constant, yet slow form of erosion that covers large amounts of land. Unlike gully erosion, where soil is removed via drainage lines in the earth, sheet erosion is detected too late because it removes small quantities of soil over an extended period of time (de la Garza, n.d.). To combat erosion, living grass vegetative barriers can be implemented to slow water flow via their dense root system. An example of this is vetiver grass, a vegetative barrier system introduced by the World Bank in India as a low cost development project aimed at soil and water conservation (Grimshaw, 1993). Vetiver grass was already being used by South Indian farmers for approximately 200 years (Greenfield, 1990).
Description of Living Grass Barriers
Vetiver is a dense, wiry, tough perennial grass that promotes effective detention and infiltration of sediment runoff. Enhancing soil moisture and conserving soil itself is crucial for sustainable agriculture and key for societal survival (Grimshaw, 1993). Soil loses moisture from erosion which is caused mainly by the removal of vegetative ground cover by humans and livestock and our growing consumption of natural resources (Greenfield, 1990).
The grass is planted as a narrow hedge (less than 1 meter wide) to create a barrier across the slope of the land. If applied correctly it will slow rainfall runoff by spreading it out evenly and trapping runoff sediments to create natural terraces down the hillside. Vetiver grass is fairly inexpensive compared to more traditional practices that try to tackle the problem of soil erosion (Grimshaw 1993). Typically, there is a lack of funds, costs are too high, and the solutions put in place are ineffective and/or inappropriate for small farms. Vetiver grass can also grow over under a variety of conditions, is non-competitive with surrounding crops, is not a weed, is both pest and disease resistant, and can be used as fodder for livestock. Additionally, the grass is used to stabilize embankments and roads, is fire resistant and needs little maintenance (Grimshaw 1993).
Possible Benefits
Soil conservation and moisture retention- From Louisiana to India to Malaysia, farmers have witnessed both increased soil and moisture retention by implementing vegetative barriers, especially vetiver grass. As runoff races down a slope, it cause unnecessary erosion and very little moisture is stored. Once runoff reaches the grass hedges, it slows down, spreads out, drops its silt load, and oozes through the hedges as most of the water soaks into the soil (Greenfield 1990). No soil or excessive amount of water is lost. An effective vegetative barrier like vetiver grass slows and almost permanently reduces soil loss from almost 143 tons to 1.3 tons per hectare in one year. On protected land, with any sort of slope, there is a chance that valuable fertilizers and topsoil will be lost. Vetiver’s spongy root system binds the soil up to 3m below the plant, creating a “curtain” that prevents gullying and tunneling (Greenfield 1990). Gully erosion is created by the removal of soil via rain along drainage lines (Agriculture Victoria, 1999), wherein tunnel erosion is the removal of subsoil by rain, leaving a tunnel in its place (Queensland Government, 2013).
Durability and Versatility- Vetiver grass is both a xerophyte and a hydrophyte plant and can undergo long periods of drought, as it can withstand very little water, and flooding, whereby it acts as an aquatic plant. Therefore, it will have no problem growing in upland or wetland settings (Aalbersberg, n.d.). Vetiver grass will grow under a variety of conditions, in both the tropics and semi-tropics, on almost all types of soils, regardless of their pH level or salinity. “This includes sands, shales, gravels, even soil with high levels of aluminum toxicity” (Aalbersberg, n.d.). However, it does best on well-drained sandy loam. Vetiver will grow in climatic conditions of 200-6000mm of rainfall per year, with temperatures ranging from -9 to 45°C. It will also grow at most altitudes, taking the temperature into consideration (Grimshaw and Helfer, 1995).
Animal Fodder- If managed correctly, the young leaves of vetiver grass are edible and can be used as fodder for livestock. However, in most cases vetiver is generally not eaten by livestock. For example, a case study in Malaysia shows that sheep will not eat vetiver when there are other vegetative options but “cut tops” were consumed when given to penned sheep (Grimshaw 1993).
Low Competition- Vetiver grass is non-competitive, meaning it will not significantly hinder the crop it is meant to protect and will therefore not have a negative impact on crop yield. Vetivers’ roots contain beneficial mycorrhiza, so the grass may actually improve crop yields (Aalbersberg n.d.). For example, when grown with cassava, elephant grass hedges were shown to reduce yield by almost 33%, wherein there was no yield loss when grown with vetiver hedges (Grimshaw 1993). Similarly, vetiver is not considered a weed because it is effectively sterile as its roots are not stoloniferous and it does not produce rhizomes. A rhizome is “a horizontal underground plant stem capable of producing the shoot and root systems of new plants” (Encyclopaedia Britannica, 2014). There is a possibility that natural spreading will occur under swamp conditions but not under upland conditions. It is recommended that only the non-seeding “accessions” be used (Grimshaw 1993).
Low Cost- Vetiver grass is a more economically sound option than conventional engineered systems that can cost up to $500 per hectare, compared to $30 per hectare for vetiver grass. The economic return is more than 90% compared to only 20% with conventional systems. Costs can also vary between site conditions: on slight inclines, vetiver grass can be implemented in 50 m intervals, in which case only 100 m of hedge is needed per hectare. Likewise, on steeper clines of approximately 60%, the distance between hedges is much less, wherein 2500 m of hedge is required per hectare. Hedges may stand 4m part or less. The cost also depends on how planting materials are acquired. For example, plants grown in nurseries are more expensive than those produced through mechanical methods. The most economically viable solution is to divide pre-existing vegetative hedges for replanting as new hedges (Grimshaw 1993). This method might be the best option in situations where access to seeds is limited.
How living grass barriers are conducted
Vegetative barriers, especially vetiver grass hedges, are versatile and can be applied on multiple eroding sites, not just cropland. In a parallel formation, barriers are planted on or near the contour of the land and across the highest concentration flow of runoff at angles that are convenient for the farmer. Eventually, “sediment and tillage will fill in the swale areas and contours will adjust to be closer to the barriers” (de la Garza, n.d.). Farmers will plow their fields according to the formation of the vegetative barriers which will contribute to the creation of terraces between each row. Note that proper vegetative barriers must be 3 feet wide and have a stem density of 50 per square foot.
Grass Selection When selecting a grass for vegetative barriers, consider a stiff stemmed perennial species that is resistant to water flow and good at retaining sediment. Spear Grass (Heteropogon contortus) is a grass used in India to prevent erosion on a slope on and up to 20 degrees. It is native to Africa and South Asia and is versatile in use (Heuze et al, 2015). Another grass used to prevent erosion is foxtail millet (Setaria italica), a grass found in southern Asia that is commonly used in India and China (FAO 2011). When selecting grass species, it is ideal to select locally adapted grasses that do not spread as they will encroach onto the cropland.
Obtaining Plant Material Vetiver plants are commonly regenerated in nurseries, where slips are cut from the main clump of plant and used in the fields. The slips, a handful of grass and roots, are harvested from the preceding crops so that the nursery remains viable (Grimshaw and Helfer 1995). Before slips are planted, the tops are cut 15-20cm above the base and the roots are cut 10cm below the base. “This will improve slips chances of survival after planting by reducing transpiration level and thereby preventing them from drying out” (Grimshaw 1993). Slips are planted at the beginning of the wet season and are planted directly into the furrow that marks the contour of the land. When planting them, it is important to ensure that roots remain turned down and are spaced 10-15 cm apart.
Correct Usage and Common Problems
Vetiver grass can grow in areas of low rainfall (300-400mm) but will require more maintenance. In these conditions, and in conditions of extreme weather, vetiver grass suffers. It will not grow in cold climate or permafrost sites (Grimshaw 1993).
Competition with Crops The major problem with vegetative barriers is that they take up space and thus might try to encroach on the main plots as a weed. It may compete with crops for water, light and nutrients leading to decreased yields (Guto et al. 2011). A method for deciding what to plant is a “split plot” agriculture design, where blocks are used as experimental units for a variety of factors. Fields are divided into whole and split plots and then individual plots to monitor different treatments (Jones and Nachtsheim, 2009). In the case of vegetative barriers, farmers should plant only half of their field with barriers in order to see if crop yield decreases.
Slow Economic Return A vegetative system’s full potential is only met when a hedge has formed. A thick hedge can be grown in the first season but it usually takes two or three for the grass to be dense enough to stop sediment and withstand torrential rains. Hence, gaps must be filled until plants are strong (Greenfield 1990).
Helpful Hint
This website sells a variety of grasses from all around the world https://www.seedman.com/ornamentalgrass.htm
Picture Based Lesson to Train Farmers
For the South Asian version (pictures only, text for you to insert), click this link for lesson 5.5:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.5_south_asian.pdf.
For the East/South Asian version (pictures only, text for you to insert), click this link for lesson 5.5:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.5e.s.a.pdf
For the Sub-Saharan Africa/Caribbean version (pictures only, text for you to insert), click this link for lesson 5.5:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.5subsaharan_africa_carribean.pdf
For the Latin-America version (pictures only, text for you to insert), click this link for lesson 5.5:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.5latin_america.pdf
For North Africa And Middle East version (pictures only, text for you to insert), click this link for lesson Chapter 5. 4.4:http://www.sakbooks.com/uploads/8/1/5/7/81574912/4.4n._africa_middleeast.pdf
Source: MN Raizada and L Smith (2016) A Picture Book of Best Practices for Subsistence Farmers. eBook, University of Guelph Sustainable Agriculture Kit (SAK) Project, June 2016, Guelph, Canada.
Helpful Images
This picture demonstrates how vegetative barriers prevent excessive runoff. As you can see in the picture, the barrier has stopped soil from flowing down in the hill and has developed terraces in the process. http://www.nzdl.org/gsdl/collect/hdl/index/assoc/HASHf4f4.dir/p062.png
This picture gives a better understanding of the different types of erosion that plague farmers who do not protect their fields. http://images.slideplayer.com/17/5334503/slides/slide_19.jpg.
References
1.Aalbersberg, Bill (Ed.). (N.d.). Vetiver: The Proven Soil Conservation Technique. Suva: University of South Pacific.
2..Agriculture Victoria. (1999, November). Retrieved from http://agriculture.vic.gov.au/agriculture/farm-management/soil-and-water/erosion/gully-erosion
3.FAO (2011). Grassland species. Retrieved November 17, 2016, from http://www.fao.org/ag/AGP/AGPC/doc/GBASE/Default.htm .
4.Greenfield, J. C. (1990). Vetiver grass: the hedge against erosion (Vol. 64). World Bank Publications.
5. R. G. (1993). The role of vetiver grass in sustaining agricultural productivity. Asia Technical Department. The World Bank, Washington DC USA.
6.Guto, S., Pypers, P., Vanlauwe, B., Ridder, N. D., & Giller, K. (2011). Tillage and vegetative barrier effects on soil conservation and short-term economic benefits in the Central Kenya highlands. Field Crops Research, 122(2), 85-94. doi:10.1016/j.fcr.2011.03.002.
7.Heuzé V., Tran G., Giger-Reverdin S., Lebas F., 2015. Spear grass (Heteropogon contortus). Feedipedia, a programme by INRA, CIRAD, AFZ and FAO.
8.Jones B., Christopher J. Nachtsheim. (2009). Split-plot designs: what, why, and how. Journal of Quality Technology, vol. 41, pp. 340-341
9.Kika de la Garza Plant Materials Center. (n.d.). Vegetative Barriers for Erosion Control.
10.Queensland Government. (2013, December). Retrieved from https://www.qld.gov.au/environment/land/soil/erosion/types/
11.Rhizome. (2014, December). In Encyclopaedia Britannica. Retrieved from https://www.britannica.com/science/rhizome
12.Richard G. Grimshaw and Larisa Helfer. (1995). Vetiver Grass for Soil and Water Conservation, Land Rehabilitation, and Embankment Stabilization (Vol. 1). Washington DC: The World Bank.