For the second year, Nutwood Farm has submitted an educational display to the Cummington Fair Agricultural Hall during the 151st Annual Fair! This year’s display focuses on swale and berm earthworks: how to lay out, build, and plant a swale system to maximize water retention, manage flash flooding events, and mitigate drought on the farm.
Come and see our exhibit! August 22-25, Cummington Fairgrounds
Swale-and-Berm Earthworks: Regenerative Agriculture Techniques
What is Regenerative Agriculture?
Regenerative agriculture, also called “carbon farming,” is a set of practices intended to restore degraded lands and improve the health of soils and ecosystems while producing a yield. It has been shown to increase the complexity and diversity of the life in the soil leading to higher fertility, better drought resistance, reduced need for pesticides, fertilizers and other fossil fuel inputs, and improved soil structure.
What are Earthworks?
A technique often used in Regenerative Agriculture, “earthworks” are practices that alter the slope or contour of the land to better harvest, store, and distribute water. Installing earthworks on sloped land is an ecological method that has been used by small-scale farmers around the world for thousands of years. When used in conjunction with low- or no-till operations and perennial crops, it is very effective in reducing soil erosion and improving water retention, enhancing the overall agro-ecosystem.
How it Works: Swale-and-Berm
This style of earthworks involves excavating a shallow band of soil on contour and moving the earth down slope to create a small earthen dam just below. The concave ditch or “swale” creates a place to collect water during heavy rainfall events, allowing it to slowly seep into the water table below instead of running off and eroding precious topsoil. The convex dam or “berm” provides a large raised bed for planting multiple species, including perennial shrubs and trees, keeping their roots high and dry while giving them access to ample moisture from the swale above.
Most earthworks projects are a one-time intervention that will vastly improve the health of the agroecosystem for tens or hundreds of years. Many farms use a side-throwing plow or an excavator to dig and shape their earthworks system. To be effective, new swales and berms should be planted and mulched as soon as possible to prevent soil erosion and rebuild the soil structure. The alleys in between the swales and berms can also be planted with annual crops, grazed by animals, or used for hay production. Integrating perennial crops and livestock has been demonstrated to sequester carbon very effectively and support extremely healthy and diverse soil microbiology.
How to Build a Swale 1-2-3
- Find and mark the contours of your land. This is the line of equal elevation across a landscape that is perfectly horizontal. It is often used in topographic maps to show valleys and hills, and the steepness or gentleness of slopes. You can do this by hand with a simple A-frame or a water level, also known as a bunyip. Or you can use a laser level if you are working on a larger scale. Mark points of equal elevation perpendicular to your slope and “connect the dots” to create a contour line.
NOTE: The number of contour lines you mark will vary by the size of the land and steepness of the slope, and your intended use. Consider if you will be planting annual crops in between your swales, or grazing livestock, or simply harvesting from the perennial crops on the berm. For more information on sizing and spacing earthworks appropriately, see Brad Lancaster’s Rainwater Harvesting for Drylands and Beyond, Vol. 2, Water Harvesting Earthworks
- Dig a shallow ditch along the contour line and move the excavated soil down slope creating a band of earth to act as a dam, preventing water from spilling out of the ditch. You can use a shovel and garden rake for small projects, or you can dig with an excavator for large scale projects. If your soil is sandy, you can also bury branches and other woody debris in the berm to slowly break down and increase the organic matter in the soil. If your soil has heavy clay, be careful not to make your berms too large or it may cause a landslide in heavy rain events.
- Plant the swale and berm right away to minimize erosion after disturbing the soil. Clover is a good choice for the swale as it can tolerate more moisture. Larger trees and shrubs can be planted on the top of the berm, and any mixture of quick-growing annuals and deep-rooted perennials can be planted into the sides of the berm. If you cannot seed cover crops or plant perennials right away, you can mulch the soil heavily with grass clippings, straw, or woodchips. This will also increase the soil organic matter while preventing erosion and building fertility.
Where Has All The Soil Gone?
The FAO led Global Soil Partnership reports that 75 billion tons of soil are eroded every year from arable lands worldwide—a rate that is about 13–40 times as fast as the natural rate of erosion. This equates to an estimated financial loss of US$400 billion per year. Approximately 24% of the world’s agricultural land is seriously degraded. According to the United Nations, an area of fertile soil the size of Ukraine is lost every year because of drought, deforestation and climate change.
Soil loss is exacerbated by poor agricultural practices such as excessive tillage and bare soil cultivation. Wind and water are both natural forces of erosion that can be managed with simple techniques such as continuous cover cropping, reducing tillage, planting wind breaks, intensive rotational grazing, and leaving crop residues in the field to biodegrade.
Not only is soil erosion bad for agriculture, it also causes global climate change by releasing more carbon into the atmosphere. Conventional agriculture is currently responsible for 10% of global carbon emissions, yet we could sequester more than 100% of current annual CO2 emissions by switching to regenerative organic agriculture (Rodale). Healthy soil has the power to prevent soil loss and reverse global climate change.
In the US, overall trends of soil loss have improved over the last 25 years. Water and wind erosion has dropped from about 7.3 tons per acre in 1982 to 4.8 tons per acre in 2007 (NRCS). Many farmers are learning to adopt new techniques to prevent soil erosion, improve soil fertility, and increase their bottom line.