Case Study 3: A meta-analysis of conservation agriculture in sub-Saharan Africa

No-till conservation agriculture. Credit A4I

No-till conservation agriculture. Credit A4I

Conservation agriculture (CA) is widely promoted as a key solution to climate change adaptation for farmers in sub-Saharan Africa. Slow adoption of the method across the continent, however, has raised questions to its effectiveness and the value of such practices for smallholder farmers. A meta-analysis by the Climate Change Agriculture and Food Security (CCAFS) research programme analysed 41 studies comparing CA with conventional tillage practices across a variety of agroecologies and climate conditions. Although sustainable farming practices like CA are critical to overcome the challenges of changing climates and growing populations, CA may not be the solution for all.

By combining no tillage and mulching, yields will increase on average 300kg more per hectare in the first 3 years of adopting CA and even more in subsequent years compared to conventional farming. Though, yields may be lower over the long run if without combining no tillage with soil cover and crop rotation. Further, fertiliser use with CA is an important condition for success. Farmers can yield 400kg more per hectare when applying nitrogen fertiliser in excess of 100kg per hectare. As nitrogen fertiliser use is low across sub-Saharan Africa, microdosing can help farmers to fully benefit from CA. Rainfall levels matter too. Overall, rainfall above 1,000mm results in greater yields on average across the studies. However, in some cases the opposite was also true as heavy rains on mulched soils can induce waterlogging.

Despite successes in some reasons, the major reasons for limited adoption is the competition for crop residues. Mixed crop-livestock farmers use crop residues as animal fodder and poor families also use stalks from maize, sorghum or millet as cooking fuel. The returns to various uses for the crop residue must therefore be considered. Further, CA may not suit all soils. CA works better on loamy soils compared to sandy and clay soils. Lastly, crop rotation with nitrogen-fixing legumes has many benefits, but may not always be attractive to farmers if there isn’t a ready market.[1]

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