Template:Chapter 4.3
4.3 - Shallow trenching to prevent erosion, conserve water
Shelby Straeche, University of Guelph,Canada
Suggested citation for this chapter.
Straeche,S. (2022) Shallow trenching to prevent erosion, conserve water. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org
Introduction to Soil: What is Erosion?
Soil is a multi property living organism full of rich organic matter, that if treated correctly and strategically, can be the much needed resource of many struggling farms to generate the highest and most successful crops possible (Pimentel and Kounang, 1998). By adopting simple strategies, farmers are able to sustain idealistic soil properties, such as adequate moisture and nutrients (Pimentel and Kounang, 1998). An important part of understanding how to keep soil in this ideal state is being aware of the processes that deteriorate, and degrade it; erosion is one of these processes. Caused by wind, rain and other natural agents, erosion is the wearing away of top soil, which consequently compacts, leaches, and dries farmland (IIRR and ACT, 2005). In Africa alone, there is approximately 630 million hectares of arable land available to practice agriculture (Munyaradzi et al., 2006). However, over the past half century productivity has seen a huge decline across this arable land due to the impact erosion has had on soil fertility. Africa’s diverse climates including deserts, savannas and rainforests, and diverse range of highlands and lowlands make it difficult to control the natural processes of erosion. Though all farmlands are susceptible to this phenomenon, it is most prominent, and devastating along hillsides. There are approximately 250 million people practicing agriculture along hillsides in Africa (Munyaradzi et al, 2006) and globally there are more than 2 million subsistence farmers who rely on successful yields to maintain food security. The more soil depreciates, companies and developed countries get incentives to push heavy reliance on expensive and sometimes dangerous fertilizers (Moldenhauer et al., 1988). However, by simply adopting strategic agricultural techniques, these impacts can be weakened.
Why is Erosion a Problem?
As the runoff of soil happens, the soil begins to lose moisture, to compact and cause nutrient leaching (Pimentel and Kounang, 1998). This has two major implications. First, once the crops are planted, they are deprived of the essential nutrients needed for growth due to the nutrient poor, depreciated soil. This results in significantly less successful yields; especially on sloping lands. Nigeria experienced a loss of 221 t/ha/yr on land with a 12% slope due to erosion, and a loss of 3 t/ha/yr on land with only a 1% slope (Pimentel and Kounang, 1998). Second, it becomes substantially more difficult to plant crops because the soil is much denser and drier, because the rich and moist topsoil layer (humus) is lost. In addition, labour and energy costs increase because it requires much more time, energy and attention to plant (Pimentel, et al., 1995).
The biggest devastation is that these impacts are not short term (Pimentel and Kounang, 1998). Unfortunately, once soil loses its moisture, nutrients, and organic matter (the essentials to successful crops) it is extremely difficult, if not impossible to get them back (Pimentel, et al., 1995). Corn yields alone have seen declines of up to 80% due to erosion (Pimentel, et al., 1995). Techniques that are simple and have potential for high adoption are needed to stop this devastating cycle.
To see the visual impacts of this phenomenon, please visit http://www.gettyimages.ca/photos/soil-erosion
Solution: Shallow Trenching
What is Shallow Trenching? Shallow trenching, otherwise known as contour ripping, shallow contour ripping or Keyline ripping, is a solution that can be adopted by farmers to prevent and control soil erosion caused by runoff (IIRR and ACT. 2005). Shallow trenches are ditches with little depth that are dug horizontally along farmland to catch rainwater to prevent soil runoff (Moldenhauer et al., 1988)
How will Shallow Trenches Solve the Erosion Problem and Conserve Water? -The ditches that are dug along the farmland act as a cup and catch water rather than letting the rainwater or wind move the soil. This prevention of soil runoff allows water to infiltrate into soil which means that soil will not depreciate in nutrients, moisture and organic matter (Moldenhauer, Hudson, & Editors, 1988). Not only does this solve the problem of erosion, but by planting the crops in between the trenches that the farmer has created, the seeds and roots get nourished by rainwater. This juristically reduces the amount of water that the farmers need to water their crops (Pimentel, et al., 1995).
Implementing The Solution: How To Create Shallow Trenches
Materials A major advantage to this method is the minimal requirement for materials. If available, a trenching hoe/grub hoe or shovel is ideal, however a stick is just as sufficient Anything that can be used to make groves in soil works. Seeds will also need to be chosen to plant after the trenches have been dug.
Steps Step 1: Establish the contour and slope of the farmland. The farmer will be digging the ditches perpendicular to the slope of the land because when rain falls, the holes, which are called ‘contour ditches’, will catch the water rather than letting it run down the slope (IIRR and ACT, 2005). This is critical because if the trenches are not dug in the correct direction, the dug trenches may act as a slide for rainwater and runoff will actually worsen.
Step 2: After the farmer has established the direction that the trenches will be dug, grab the chosen digging instrument, i.e. the trenching/grub hoe, shovel or stick, and start digging the contour ditches horizontally along the terrain. The steeper the slope, the deeper the holes should be due to an increased probability of experiencing erosion. TIP: If the terrain is on a steep incline, a contour ditch could be dug at the very top of the hillside to further protect the terrain (IIRR and ACT, 2005)
Step 3: Once all the contour trenches have been dug, take the selected seeds and plant them between the trenches as the farmer normally would. Maintenance: It is common that after extreme weather, the trenches may fill in. Constant checking of the depths and size of the trenches is critical to this methods success. Re-dig if necessary.
Having trouble deciding on depth, distance and length? Please refer to Table 1
Having trouble understanding the method to creating shallow trenches? Please refer to the SAK Picture book that corresponds to this chapter.
Benefits
Water Conservation, Reduction in Soil Depreciation and Improved Crops There have been many studies administered by the FAO, NGOs etc. to examine the effectiveness of the shallow trenching method, especially in the dry lands of sub-Saharan Africa. A specific study, administered in 1999 though-out Eastern and Southern Africa evaluated the shallow trenching technique and found that this method was successful in reducing land degradation due to soil erosion (Rockström, 1999). The ditches were successful in retaining large amounts of water which aided fertilization of both the soil and the seeds (Rockström, 1999). This study is not unique in its conclusion. There are countless studies that demonstrate that this method is successful in conserving water. Why is this considered such a significant benefit? Retrieving water for plants is not only time consuming, but it takes a huge toll on the farmers themselves; carrying water on foot multiple times a day takes up a lot of energy. By making use of the rainwater being caught in the trenches to fertilize the seeds, it permits water infiltration and conserves the amount of water that is needed to be salvaged. This poses a major benefit as the saved time and labour can be used towards other pressing farming needs (Pimentel, et al., 1995).
To learn more about water conservation methods, principles, causes and advantages, please visit http://www.fao.org/docrep/T0321E/t0321e-11.htm
Critical Analysis: Issues
Labour, Time and Maintenance Before implementing any significant changes in farming practices, critical analysis of many factors needs to be considered to ensure that the farmer is adopting the technique best suited for their land. For instance, farmland soil needs to be managed differently depending on its texture, i.e. sandy, versus silty, versus clay soils. This method is best suited for silty soils because of its low clay content (Hillard and Reedyk, 2014). Rainfall causes clay soils to compact, dry and crust which in turn, causes more runoff. Trapping water in the contours to later be absorbed by the soil could actually increase speed up the erosion process. Silt soils do not have this clay content that would otherwise cause the soil to dry out from the rain water (Hillard and Reedyk, 2014). Implanting this solution on soils other than silty ones will further increase the labour, time and costs.
Maintenance is a heavy burden associated with shallow trenching. After intense rainfall there is a good possibility that the soil will move due to the water, and fill in the trenches. Unfortunately, it is a constant battle against soil accumulation and there are no actions that can be taken to prevent it. Depending on the size of the farm, and the amount of trenching that need to be dug will decide whether or not this is a good solution.
Though this method can be very effective, the energy costs, including labor, time and maintenance are heavy. If the ditches are dug by hand, this can be not only time consuming, but more importantly can cause significant physical hardship (Pimentel, et al., 1995) which would prevent the adoption of this practice. However, it is important to consider that by taking on extra labour and time costs now, greater labour and time may be saved in the future. It is up to the farmer to compare these costs with other techniques to determine what is the most effective and sensible option.
Picture Based Lesson to Train Farmers
For the South Asian version (pictures only, text for you to insert), click this link for lesson 5.3:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.3_south_asian.pdf
For the East/South Asian version (pictures only, text for you to insert), click this link for lesson 5.3:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.3e.s.a.pdf
For the Sub-Saharan Africa/Caribbean version (pictures only, text for you to insert), click this link for lesson 5.3:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.1subsaharan_africa_carribean.pdf
For the Latin-America version (pictures only, text for you to insert), click this link for lesson 5.3:http://www.sakbooks.com/uploads/8/1/5/7/81574912/5.3latin_america.pdf
Source: MN Raizada and LJ Smith (2016) A Picture Book of Best Practices for Subsistence Farmers. eBook, University of Guelph Sustainable Agriculture Kit (SAK) Project, June 2016, Guelph, Canada.
References
1.Agriculture and Agri-Food Canada. (2014). Soil Texture and Water Quality. Retrieved 12 1, 2016, from Agriculture and Agri-Food Canada: http:// www.agr.gc.ca/eng/science-and-innovation/agricultural-practices/soil-and-land/soil-and-water/soil-texture-and-water-quality/?id=1197483793077.
2.Hudson, N. W. (1987). Soil and Water Conservation in Semi-Arid Areas. Bedford, UK: Silsoe Associates, Ampthill. URL: http://www.fao.org/docrep/T0321E/t0321e-11.htm.
3.IIRR and ACT. (2005). Conservation agriculture: A manual for farmers and extension workers in Africa. International Institute of Rural Re- construction, Nairobi; African Conservation Tillage Network, Harare. URL: http://www.fao.org/ag/ca/AfricaTrainingManualCD/PDF%20Files/08WATER.PDF.
4.Moldenhauer, W. C., Hudson, N. W., & Editors. (1988). Conservation Farming on Steep Lands . Ankeny, Iowa, USA: Soil and Water Conservation Society. URL: http://pdf.usaid.gov/pdf_docs/PNABB290.pdf.
5.O'Riordan, T. (1999). Environmental Science for Environmental Management (2 ed.). Routledge. URL:https://books.google.ca/books?hl=en&lr=&id=3WeuBAAAQBAJ&oi=fnd&pg=PA287&dq=uneducated+about+erosion&ots=3wP7b5u3Aw&sig=1fPhDQTAW7MstxdyMPSBvHQ8vgw#v=onepage&q&f=false.
6.Pimentel, D., & Kounang, N. (1998). Ecology of Soil Erosion in Ecosystems. Ecosystems , 416-426. URL: http://www.jstor.org/stable/3658674?seq=1#page_scan_tab_contents.
7.Rockstorm, J. (1999). Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere. Nairobi, Kenya: Regional Land Management Unit. URL: http://www.sciencedirect.com/science/article/pii/S1464190900000150.