Bungoma — In the west Kenyan village of Siilila, 27-year-old Geoffrey Wanjala and other members of his farmers' group are trying out a way of working the land that avoids ploughing and releasing the carbon dioxide stored in the soil. So far it is also cutting their costs and boosting yields.
Traditionally, farmers across Kenya till their land at least twice before planting, then weed it after their seeds have germinated. But the new method, known as conservation agriculture, aims to leave the land in its natural state as far as possible.
"It involves minimal or no soil disturbance in terms of tilling," said Wanjala, chairman of the Tumaini (Hope) Farmers Field School, a group of 25 young men and women in Bungoma County.
The farmers keep the soil covered, so it retains moisture and nutrients, by laying mulch on the field. They also practise intercropping (growing two or more crops together) and crop rotation, Wanjala added.
"Farming without ploughing sounds like a contradiction of what we have always understood about crop husbandry. But new evidence suggests the practice reaps the greatest rewards, when land is protected from the sun and the plough," explained Alfred Micheni, a research scientist with the state-owned Kenya Agricultural Research Institute (KARI), which is implementing the project with technical assistance from the International Maize and Wheat Improvement Centre (CIMMYT).
"There is limited soil erosion, nutrients are kept intact, and there is no harm to the soil's natural structure," Micheni added.
The pilot project is mainly targeted at improving food security in Kenya. But there is another purpose too - enabling the soil to store carbon, which is otherwise released when it is tilled.
According to scientists, rising concentrations of carbon dioxide in the Earth's atmosphere are largely responsible for temperature increases on its surface, which are altering the planet's climate, bringing more extreme weather and rising seas.
Plants take in carbon dioxide, the main greenhouse gas, from the atmosphere through the process of photosynthesis. When they die and their organic matter is buried in the soil undisturbed, the absorbed carbon remains there - a process known as carbon sequestration. This helps limit carbon levels in the atmosphere, thereby mitigating the climate change.
The Food and Agriculture Organization of the United Nations (FAO) says that sequestration of carbon in the soil during the first decade after adopting best practice in conservation agriculture can offset up to 1.8 tonnes of carbon emissions per hectare per year. However, the rate at which soils store carbon differs around the world depending on environmental factors including the climate, landscape and plants.
The trial project in Kenya started in 2010, and involves six groups of 250 small-scale farmers in western and eastern areas.
It is part of a wider initiative working to sustainably intensify maize-legume cropping systems for better food security in Eastern and Southern Africa (SIMLESA), with funding from the Australian Centre for International Agricultural Research (ACIAR). Other participating countries are Ethiopia, Malawi, Mozambique and Tanzania, where conservation agriculture is being trialled on a small scale.
"This is the second season we are harvesting under the project. We mainly intercrop maize and legumes such as beans, cowpeas and desmodium (tick-trefoil). After harvesting, we retain the crop residue on the farm to form mulch," Wanjala explained.
Instead of weeding, the farmers apply chemical herbicides, which dry up the weeds, turning them into mulch.
According to the FAO, there is growing proof that conservation agriculture can make a significant contribution to reducing greenhouse gas emissions by storing carbon in organic matter in the soil. And it improves the state of the soil too.
"There is evidence that soil organic carbon is fundamental to the development of soil quality and sustainable food production systems," said John Achieng', a KARI agronomist and head of the SIMLESA trial project in western Kenya.
Conservation agriculture has been deployed successfully in a number of countries, including Australia, Argentina, the United States and Brazil.
BARRIERS IN AFRICA
But the practice has yet to be widely adopted in sub-Saharan Africa, according to Achieng'. "Farm holdings in this region are small, making it difficult to practice crop rotation, which is the primary principle for conservation agriculture," he explained.
It also requires a relatively high level of investment at the outset and specific farming equipment, which is a deterrent for poor African farmers. "But with the kind of research and trials going on at the moment, we will most likely find the most suitable methods for (these) farmers to use," Achieng' added.
In Siilila, participating farmers have plots where they practice conservation agriculture and separate plots for conventional agricultural methods. This helps them compare the labour and expenditure required for each approach, as well as the results in terms of yields.
So far, the farmers are more concerned about boosting crop production than how much carbon is being sequestered in the soil through the accumulation of organic biomass.
"There has been a clear difference considering the past two seasons. With conservation agriculture, there were less farm inputs compared to the control plots. Yet the harvest on the conservation trial plots almost doubled yields from the same (land) in previous years," Wanjala said.
According to Achieng', KARI is also encouraging farmers involved in the project to use more climate-resilient maize varieties it has developed, which can also increase yields.
"As much as zero tillage reduces labour and the amount of farm inputs to ensure the farmer gets maximum profits, improved varieties will help ensure the crops do not get ruined by bad climatic conditions," he said.
Isaiah Esipisu is a freelance science writer based in Nairobi.