Institute for Applied Systems Analysis (Fischer _et al._ 2002) to assess potential rainfed yields that can be achieved on a given plot in light of prevailing agro-ecological conditions. This predicts potential yield for rainfed cultivation of five key crops (maize, wheat, soybean, sugarcane, oil palm) based on simulated plant growth at each stage of the vegetative cycle based on factors including soil, temperature, precipitation, elevation, and slope, allowing for different climate change scenarios as well.<sup>5</sup> Applying a price vector then allows the determination of the crop that produces the highest revenue. As market access will affect transport cost and profitability, we classify potential crop areas based on whether they are within 6 hours of an urban center with a population of at least 50,000. Full details of the model and data sources are provided in Deininger _et al._ (2011).

Depending on current land use, this technique provides two parameters of interest. For cultivated areas, the difference between possible output and what is currently attained taking crop choice as given provides an estimate of the ‘yield gap’ which can indicate the extent to which gaps in technology, institutions, or other public goods (e.g. infrastructure) prevent existing cultivators from realizing there potential. Uncultivated areas with high potential could be possible candidates for area expansion if they are not designated as a protected area, not forested, located reasonably close to markets and have low population density so that whatever existing interests are displaced can be compensated.

Two key results stand out. First, yield gaps vary widely across regions and can be large (table 5).

Oceania is close to realizing its potential, followed by North America (0.89), Europe (0.81), and South America (0.65). Sub-Saharan Africa realizes only 20 percent of potential production, offering large potential for increasing yields. If it were to attain 80 percent of potential yield, a level usually considered economic, it could quadruple maize output, equivalent to expanding area by of 90 million ha – more than the area suitable for maize expansion close to infrastructure globally – at current yields.

Second, the non-forested non-cultivated area suitable for rainfed cultivation of at least one of the crops considered here amounts to 446, 306, or 198 million ha for population density cut-offs of 25, 10, and 5 persons per km<sup>2</sup> (table 6).

In all scenarios, non-cultivated area suitable for rainfed cultivation is highest in Africa (202, 128, and 68 million ha corresponding to 45, 42, and 34 percent of the total, respectively), followed by Latin America. Within Africa and Latin America, available land is concentrated in a few countries and not always close

> 5 To keep things tractable, we use a 5’ x 5’ resolution that divides the world into 2.2 million grid cells. Computation of output in each cell is based on more disaggregated data. Yields are for 2008. Suitable area is not currently used for crop production, could attain at least 60 percent of the potential yield for this crop, is located in an area with population density less than 10 persons/km<sup>2</sup> , and at 2005 prices will not yield higher gross revenues with any other of the five crops considered here (maize, soybean, sugarcane, oil palm, wheat). Close to infrastructure means a travel distance of less than six hours to the next market based on available transportation.

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