Rongai — Small farmers across sub-Saharan Africa are turning to simple, affordable techniques to increase harvests and help them cope with climate extremes - from growing trees on their land, to keeping their soils healthy and making their own fertiliser.
Nelson Mwangi has managed to boost the maize yield from his 0.3 hectare (0.8 acre) plot in Rongai, 170km from Kenya's capital Nairobi, to 18 bags from around seven bags since adopting a method known as conservation agriculture three years ago.
"I have reached a position where I don't need to use (chemical) fertiliser on my farm anymore because I have enough manure and compost," says the 54-year-old father of four. The former agriculture teacher is now saving around KSH 3,900 ($46) in fertiliser and KSH 2,500 ($29) in labour costs each planting season.
Conservation agriculture involves minimum or zero tillage of the soil, keeping the earth permanently covered with organic matter, and rotating crops. Limiting disturbance of the soil ensures that it releases very little carbon dioxide and nitrous oxide - key greenhouse gases - into the atmosphere.
The use of harvested crop residue as soil cover helps retain moisture, meaning farmers are less reliant on rainfall. And when the residue decomposes, it enriches the soil further. Crop rotation helps control soil-borne diseases, reducing losses.
Increasingly, farmers are combining this approach with agroforestry, which involves planting leguminous tree species on the land.
As well as sequestering carbon, these "fertiliser trees" capture nitrogen from the atmosphere and fix it in the soil, boosting its nutrient content. As a result, farmers are less dependent on commercial fertilisers.
The Mutui Museu Chumani Self Help Group in Kibwezi district, some 220km east of Nairobi, has latched on to the benefits and is promoting agroforestry locally.
"We have four nurseries of the trees, which we hope to start distributing to members in a few weeks' time," says group leader William Ngumo Munya. The hope is that higher soil fertility will boost yields of cow pea and green gram (mung bean), he adds.
August Temu, who manages partnerships for the World Agroforestry Centre (ICRAF), believes expanding the adoption of natural fertilising methods is "critical", as there is likely to be a global shortage of phosphate in the near future, which is used to manufacture fertilisers.
Fertiliser is produced in only four countries in Africa: Senegal, Nigeria, Mauritius and Zimbabwe. Dwindling deposits of phosphate will make fertiliser scarcer and therefore more expensive for farmers on the continent, who already apply an annual average of only 10kg/hectare, compared with 150kg/hectare in Asia and well over 300kg/hectare in Europe and North America.
"Supplementing natural systems with (natural) fertilisers will enable us to achieve much higher productivity than if we relied entirely on a component that may not be available in large amounts in the future. Agroforestry provides this opportunity," explains Temu.
The fertiliser tree species used in agroforestry include acacia, sesbania, gliricidia, tephrosia and pigeon pea.
Until recently, conservation agriculture and agroforestry were often promoted independently in Africa. But that is starting to change.
A scoping study released in March - supported by the Swedish International Development Agency, ICRAF and the African Conservation Tillage Network (ACT) - suggests that by combining the two approaches, small farmers can both improve their crop yields and significantly enhance their resilience to climate change.
"By promoting the two practices together, you reap the synergies of both conservation agriculture and trees, and gain more benefits than when they are applied separately," says Saidi Mukomwa, chief executive of the ACT.
Task forces made up of researchers and agricultural policy makers have already been formed in Kenya, Tanzania, Ghana and Zambia to see how it could be done on a large scale.
Elijah Phiri, a task force member and lecturer at the University of Zambia, says the methods have shown great potential in his country.
"Small-scale farmers in Zambia have had problems accessing inputs such as fertiliser, and whenever drought occurs, they had even lower yields," he says.
According to Phiri, where Zambian farmers practice conservation agriculture, they raise maize yields from the usual 1 tonne/hectare to no less than 3 tonnes. Most maize varieties grown in Zambia even have the potential to produce up to 5 tonnes/hectare if the method is strictly applied, he adds.
But not everyone is convinced that conservation agriculture with trees is the best way to improve African farm yields.
Saa Dittoh, head of the food and nutrition security unit at the University for Development Studies in Tamale, Ghana, argues that the two practices are not enough by themselves.
"We have a population that is growing very fast and we need food urgently. We need fertiliser to get the (production) jump we need, and it has been shown throughout the world that we cannot stop using not just some, but a lot of fertiliser," the professor told a workshop in Nairobi last month on how research can inform agricultural policy in sub-Saharan Africa and South Asia.
What's more, some African small farmers have come across barriers to adopting conservation agriculture with trees, mainly because of what is referred to as "livestock-crop conflict", according to Leah Mong'ara, a government agriculture extension officer in Kenya's Rongai District.
Farmers are finding it difficult to leave harvested crop residue on their fields when they could just as easily feed it to their livestock.
One solution, according to Mukomwa of the ACT, is to start growing grasses and cover crops such as vevet beans and desmodium.
"We can improve the organic content of the soil not only by using crop residue, but by introducing grasses which have more below-ground root biomass," he explains.
Geoffrey Kamadi is a freelance journalist based in Nairobi. He has written widely on science and health issues for local newspapers as well as online publications.