Nearly three decades have now passed since this warning of unsustainability, and the “shortcut” continues to deliver production gains. Others say scaling up agroecology is difficult because it is management-intensive and knowledge-intensive at the beginning. One 2014 paper from a UK environmental organisation put it this way: “Poorer and more marginal farmers, in particular, may decide not to adopt these practices if they do not have enough time and resources to invest in learning and experimentation.” Learning agroecology practices may indeed be laborious, but the bigger problem is that the practices themselves are laborious.

One example was the system of mixing trees with crops known as “alley farming”, designed in the 1970s by researchers at the International Institute for Tropical Agriculture (IITA) in Nigeria. The goal was to plant rows of crops in the “alley” between strips of leguminous trees, hoping that the roots of the trees would fix nitrogen in the soil to fertilise the crops. Alley farming worked fine on research stations, but actual farmers in Africa either refused to adopt the practice or abandoned it soon after adopting. A 1995 review by the UK’s Overseas Development Institute revealed that farmers resisted the system because the trees required too much time-consuming pruning, and because crop growth suffered due to shading and root competition from the trees.

Yet another excuse for the weak scale-up of agroecology is that choices are constrained because “policies and market signals are stacked against agroecology”. Many developing countries have indeed made fertilisers and pesticides artificially cheap for farmers to speed the transition to Green Revolution farming. But sub-Saharan Africa has not done this, and agroecology has still failed to take off.

In sub-Saharan Africa, average fertiliser use remains at only 16 kg per hectare, or just one eighth as much as in Latin America and only one tenth as much as in South Asia.