Going From 1 to 3 Tons/Ha in Africa with More Variable Rainfall.

The goal of the African Green Revolution can now be quantified as going from 1 to 3 tons ha^-1 of cereal grain yields by 2020, primarily by the use of fertilizers and hybrid maize. Maize yields surpassed the 3-ton ha^-1 mark (or equivalent in other crops) in 78% of the Millennium Village households, meeting or exceeding the annual caloric requirements. The nationwide input support program of Malawi, where maize yields almost tripled at the national scale transformed a country depending on food aid for 43% of its population into a food-exporting nation that also became a food aid donor to its neighbors. Now it is the time to include organic inputs grown in the same field as the cereal crops, but after initial adoption most farmers abandon them. The main reason is the lack of financial incentives. Rockström and colleagues showed that at cereal yields of 1-ton ha^-1, two thirds of the water vapor flow is soil evaporation and one-third transpiration. When the crop canopy closes at about 3 tons ha^-1, two thirds of the vapor flow goes through plant transpiration and one third through soil evaporation. Increasing yields in tropical Africa from 1 to 3 tons ha^-1 can be done without increases in water.