Sir, Your editorial "Time for a second green revolution' (June 3) calls for a range of strategies to boost crop yields obtained under diverse conditions. Crucial are the implications for sub-Saharan Africa. The continent's highly varied eco-agricultural zones imply that Africa cannot just replicate Asia's transformation of the 1960s and 70s. The Asian experience was based on the use of reliable irrigation, fertilisers and improved seeds, beginning in fertile regions and eventually moving to arid areas. Much of Africa is akin to the drier regions of Asia. Only 5 per cent of the cultivated area is irrigated compared with south Asia's 40 per cent. So, a green revolution in Africa will need to begin at the opposite end from Asia's, by improving the productivity of rain-fed crops such as millet, sorghum and cassava. The good news is that superior varieties have been developed for several. And technologies are available to conserve moisture and to enrich soils. But these technologies need to be adapted and disseminated widely, and supported by better agricultural services. Strengthening the use of irrigation, fertiliser and infrastructure will help an Asian-style green revolution to take roots eventually in Africa. Meanwhile, the continent's distinct conditions call for the greatest initial push to be made in transforming rain-fed agriculture. Vinod Thomas, Director-General, Independent Evaluation Group, World Bank Group, Washington, DC 20433, US Copyright The Financial Times Limited 2008