If you look around farms, especially between planting seasons, you will see uncovered soil stretching across hillsides and plains. Farmers call it a "resting time” for the land, while scientists see it as a disaster slowly unfolding.

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The problems associated with uncovered soil are often visible, though some go unnoticed. Firstly, when it rains, water flows down slopes, carrying soil particles with it and reducing the topsoil layer – according to a recent report, Rwanda loses 27 million tons of topsoil annually due to erosion – that took centuries to form.

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Secondly, the runoff also carries away essential soil nutrients such as nitrogen and organic matter. These elements directly limit crop yields for most smallholder farmers in the country, and once lost, they cannot be cheaply replaced.

Thirdly, without ground cover, weed seeds germinate and compete with crops for light, water, and nutrients. Furthermore, in regions that experience frequent and prolonged dry periods such as Bugesera, uncovered soil loses moisture rapidly.

Rwanda has invested heavily in strategies such as terracing and anti-erosion campaigns. However, these problems are not independent; they form a cycle. For example, eroded soils with poor fertility support weaker plant growth, which in turn leaves the ground more exposed to further erosion and nutrient loss.

The case for cover crops

Cover crops are plants grown specifically to protect and restore the soil. They prevent erosion, reduce weed pressure, fix nitrogen from the air, and build up organic matter that keeps the soil alive.

They can be grown simultaneously with the main crop at planting time as intercrops. They can also be introduced into standing main crops at a later growth stage, a practice called "relay cropping.” This strategy minimizes competition with the main crop while extending soil cover beyond harvest. Lastly, cover crops can be planted during the period between main cropping seasons and terminated before the next planting.

What cover crop options do farmers have?

Several crop species adapted to Rwanda’s diverse agro-ecological zones have been identified. Leguminous types such as Canavalia, Greenleaf desmodium, Mucuna, Lablab, Sunnhemp, and Calliandra are among the most promising options for farmers.

They are available from institutions like Rwanda Institute for Conservation Agriculture (RICA), Rwanda Agricultural and Animal Resources Development Board (RAB) stations, One Acre Fund Rwanda, and elsewhere. These institutions also provide information to help farmers to choose between species based on their specific goals or local growing conditions. Maintaining soil cover is one of RICA’s eight principles of conservation agriculture.

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Knowledge is not always enough; action is needed.

The case for cover crops in Rwanda’s farming system is no longer a matter of scientific uncertainty.

Science clearly shows how to deploy them and the benefits they offer. Furthermore, the national agriculture strategy – specifically PSTA 5 – places sustainable land management and soil health among its top priorities.

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Now it is a matter of implementation. This is a call for extension systems to translate knowledge into practice. Time and land, however, in the context of Rwandan smallholder farming, are precious, and the idea of growing something that cannot be sold can feel like a luxury. Therefore, extension programmes must prioritise multipurpose species that enable farmers to receive an immediate, tangible return alongside long-term soil benefits.

The writer is a lecturer and row and forage cropping systems lead at Rwanda Institute for Conservation Agriculture (RICA).