Optimizing Forest Garden Productivity with Soil and Water Conservation Techniques
By Olivier Allongue - Training Manager Contributeurs : Mgonzo Dunia Ally - Tanzania Country Trainer Peter Kingori - East Africa Trainer and Babou Ndao - Senegal Country Trainer
Working in agriculture is a challenging profession. With climate change and the long-term effects of conventional agriculture techniques on already degraded soils, it is only getting harder. Farmers all over the world are dealing with increased frequencies of failed harvests as a result of drought or unsubstantial yield from soils depleted of the nutrients needed to grow crops. Forest Gardeners are learning to mitigate these challenges through the use of a wide range of soil and water conversation techniques that better utilize these limited resources.
From the start, farmers in the program focus on protecting their field – not only from unwanted intruders like grazing livestock – but also from harmful winds that can sweep away their nutrient-rich topsoil. By planting multiple protective rows of living fences in combination with a windbreak, farmers begin to stabilize their soil and reduce the damage caused by strong winds.
To ensure that the wind doesn’t simply hurdle the windbreak and drop back into the field, causing interior damage, farmers plant alleys of trees to segment and further protect their cropping areas. These alleys, placed every 10 meters or so, serve as smaller windbreaks. Leguminous, nitrogen-fixing trees are often selected for alley cropping. The roots of these trees fix atmospheric nitrogen into the soil for uptake by surrounding crops. The roots also absorb nutrients from deep in the soil where they are transported and stored in the plants’ leaves and branches as they grow. Farmers can prune these leaves and small branches and spread them around their crops using a technique often called “chop and drop”. These leaves and stems cover and protect the soil as they decompose, slowly releasing their nutrients back into the root zone of the soil where more shallow-rooted crops can use it. As the chop and drop technique protects soils from sun and wind exposure, soils are able to retain a higher moisture content, which is extremely important at times of limited rainfall.
If a farmer’s Forest Garden is on sloped land, as we see in Eastern Uganda, runoff from heavy rains makes water and soil conservation a challenge. Instead of straight alleys planted on flat fields, hillside farmers use an alternative technique known as contour planting. This involves planting vegetative barriers that follow level lines across their fields, to slow down runoff and trap soils that would otherwise be carried away. To create a more effective barrier, farmers dig trenches across the contour lines and use the excavated soil to create a parallel berm alongside the trenches. They then plant trees or grasses along the berms to create dense barriers that can eventually turn a sloped site into a series of terraces.
After living fences and alleys or contours are established, Forest Gardeners can divert more attention to soil fertility. Farmers are often working on degraded soils, with limited nutrients needed to grow healthy crops. Instead of purchasing expensive synthetic fertilizers that create a short- term nutrient boost at the expense of long-term sustainability, farmers following the Forest Garden Approach establish compost piles or pits. Compost is an essential building block of regenerative agricultural systems as it turns crop residues, food waste, and animal manure into a nutrient-rich humus that builds sustainably healthy soils. Compost is a critical element for farmers looking to make better use of their available water while also greatly improving the fertility of their soil. Compost hosts, and feeds, a multitude of beneficial insects that burrow networks of tunnels around plant root systems, allowing for better aeration and water infiltration. It contains an abundance of nutrients that help crops grow. The organic matter in the compost retains water and nutrients for long periods, minimizing leaching and helping crops tolerate dry conditions for longer. You can learn all about composting in Chapter 14 of the Technical Manual.
Once a farmer’s compost is ready, it is time to plant vegetable nurseries and develop and establish the permagarden. To ensure these elements of the Forest Garden have the resources they need to flourish, farmers will practice techniques like mulching, cover cropping, crop rotation, and earthworks.
Mulching is one of the most common techniques Forest Gardeners use to conserve water and protect their soils. By spreading a layer of organic matter on the soil surface, farmers are able to mitigate resource competition by suppressing weed growth, reduce evaporation, and allow for greater moisture retention. In Uganda, mulching material usually includes bean residues or maize straws. In Senegal, farmers often use peanut shells or millet bran as well as dried grasses.
When farmers are dealing with extremely degraded lands, and applying composting across the entire plot is simply not possible, they can ease their soils into production by planting a cover crop. Cover crops are usually planted as a soil revitalizer instead of a harvestable product but farmers in the Forest Garden program are always keen to harness multi-purpose attributes of plant species. In Senegal, farmers plant potatoes, squash, watermelon, and beans, allowing them to protect their soils from sun and wind exposure, while also having an eventual pay day and something to eat at home. After harvest, cover crop foliage is left in place to serve as green manure and eventually decompose and release valuable nutrients back into the soil.
Even if farmers are using all the techniques mentioned above, they would still face problems if they planted the same crops season after season. As different plant families require specific nutrients to grow, repeated planting of the same family will quickly deplete the nutrients they need for a healthy harvest. To avoid this monoculture-like trajectory, Forest Gardeners practice crop rotation. By rotating crops from a different plant family from what was previously cultivated, farmers can better utilize the different nutrients in their field. The Forest Garden Approach recommends a cycle of planting a leafy crop (which needs more nitrogen), followed by a fruit crop like tomato (which needs less nitrogen and more phosphorous), followed by a root (which needs little nitrogen, more potassium, and some phosphorous), followed by a legume (which returns nitrogen to the soil).
Earthworks are another major technique Forest Gardeners apply across their Forest Garden. This technique refers to a group of soil and water conservation structures, generally constructed with soil, stones, or other locally available materials, to slow or stop runoff and soil erosion. Forest Gardeners must be very intentional when establishing these structures – making sure water is getting to where it is needed most and staying there. One of the most common earthwork structures used across Senegal, Uganda, and Kenya is a cuvette. These are small circular mounds of dirt, also referred to as berms, that farmers form around the root zone of their fruit trees. When watering the trees, or applying mulching and compost, these protective walls ensure the water and nutrients are maintained and absorbed around the root zone, where it is needed most, rather than spreading out to other areas.
Farmers with sloped Forest Gardens can also harness the same benefits as cuvettes through the use of “half-moon” or “boomerang” berms. Rather than completing the full circle as a berm, farmers will form a semi -circular berm on the downside of the tree so that rainfall runoff will be caught and forced to sink around the root zone of the trees. To maximize efficiency with these berms on sloped lands, Forest Gardeners will carefully stagger their trees with their paired half-moons so that when one berm gets filled with water and begins to overflow, that runoff will be slowed down and caught by the next half-moon berm further down slope.
Farmers around the world are battling the effects of climate change on already limited resources. The Forest Garden Approach helps farmers think about the long-term productivity and health of their land while taking critical steps to make their agricultural systems as resilient and productive as possible. One of the important ways they do this is by taking advantage of a wide variety of soil and water conservation techniques. With that in mind, our training team is always looking to experiment with and add new techniques to the Forest Garden Approach repertoire. Do you have any techniques to contribute? Reach out to us at firstname.lastname@example.org with the subject line: “SWC contribution”.