http://gisgeography.com/agriculture-maps-global-farming/
Food and Agriculture Organization of the United Nations- AQUASAT- global water information system: http://www.fao.org/nr/water/aquastat/main/index.stm
Nat. Geo. Global Water Footprint of Key Crops (+ other resources): http://environment.nationalgeographic.com/environment/freshwater/global-water-footprint/
Interesting point: “Soil water is the limiting factor for photosynthesis” http://drought.unl.edu/ranchplan/DroughtBasics/GrassesDrought/SoilMoisturePlantGrowth.aspx