Keeping Soil in its Place

In Malawi, studies estimate that nutrient loss from soil erosion has resulted in a 4 to 25% loss in agricultural yields. Using a conservative estimate, this translates to a loss of approximately MK7.5 billion per year, or 1.6% of Malawi’s GDP. These models further indicate that “lost agricultural productivity from soil degradation over the period 2004 – 2015 will leave more than 1.88 million people in poverty who would otherwise have escaped it.”[1]

Numerous factors contribute to the high rates of erosion, however agricultural expansion, deforestation, overgrazing, and increased cultivation on marginal lands have all played a major role.

Looking close to home, this past rainy season we have seen massive gullies forming along the roads and fields around the centre, with heavy afternoon downpours nearly washing away the main road. In Southern Malawi, which experienced heavy flooding early in the season, entire fields were washed away due to lack of permanent, well-established vegetation. It is easy to see that, even on a mild slope, the heavy rains typical in Malawi severely erode unprotected topsoil.

Agroforestry species, such as acacia, faidherbia, pigeon pea, and tephrosia, improve soil structure and add nitrogen to the soil

This nutrient-rich soil is incredibly important in agricultural production and at Kusamala’s demonstration centre much of our work focuses on building soil structure and health. This is particularly evident at our staple field, which is in full-production as we near the end of the rainy season.

Over the past year, we have adopted a number of practices specifically designed to reduce this erosion of soil nutrients:

• Contour: By building plant beds perpendicular to the slope of the hill, the beds catch water runoff, slowing the flow of water and soil down the hill, and allowing it to sink into the ground.
• Swales: We’ve built large, vegetated swale along the contour of the hill, spaced one swale for every meter of elevation change. These swales stop and sink water to recharge the water table.
• Agroforestry: Intercropping agroforestry trees improves soil structure and reduces wind erosion by providing a windbreak.
• Mulch: Using living mulch and leaving crop residue on the field reduces impact from wind and rainfall.
• Permanent Beds: Building permanent beds, rather than the typical ridges, reduces harmful tillage that can break up soil structure, making it more susceptible to wind and soil erosion.

In addition to the erosion control techniques we’re implementing at the centre, through our partnership with the Red Soil Project we have also been able to expand these methods to surrounding communities.

During the rains, Sam, one of our market gardeners, had a river rushing through his front yards, sweeping away topsoil and creating gullies. When Kusamala staff visited his house to help him create a permaculture design around his home, they built a large, vegetated swale uphill to catch and divert the water. Sam’s father, initially skeptical, is now impressed that hardly any water comes through their compound.

A swale planted with moringa slows water runoff and provides vitamin-rich vegetables

While a good step in the right direction, erosion techniques alone are not enough to reclaim the lost agricultural potential from topsoil loss. They must also be combined with practices that build soil structure and health, putting lost nutrients back into the ground. Permaculture provides a compelling solution, combining these factors and more, taking a holistic view of the health of the agricultural system.