Interpretative Summary

• If people keep on eating and multiplying and farmers keep on tilling and harvesting as today, the imperative of food will take another tenth of the land, much from Nature. So farmers work at the hub of sparing land for Nature.
• Calories and protein from present cropland would give a vegetarian diet  to ten billion. A diet requiring food and feed totaling 10,000 calories for ten billion, however, obviously would exceed the capability of present agriculture on present cropland.
• global totals of sun   on land, CO   in the air, fertilizer,   and even water   could produce far more food than ten billion need.
• By eating different species of crop and more or less vegetarian diets people can change the number who can be fed from a plot. And large numbers of people do change diets.
• Encouraged by incentives,   farmers  use new technologies  to raise more crop per plot and more meat and milk per crop, keeping food prices down despite rising population.  Differences in yields among nations and between average and master farmers continue showing that yields can be raised more.
• Foreseeing the future demands seeing through fluctuations  in crop production.
• For each ton of production, growing more food per plot lessens the fallout,   for instance, of silt and pesticides, into the surroundings. If several limiting factors are improved together, even adding water and fertilizer can diminish fallout.
• Although the uneven distribution of water among regions and its capricious variation among seasons plague farming, opportunities to raise more crop with the same volume of water kindle hope.
• In Europe and the United States, rising income, improving technology,  and leveling populations--which all nations aspire to--elicit forecasts of shrinking cropland.
• So by harvesting more per plot, farmers can help ten billion spare some land  that unchanging yields would require to feed them. Glimmers can be seen even of changing diets,   never-ending research, encouraging incentives, and smart farmers feeding ten billion at affordable prices while sparing some of today's cropland for Nature.

Figure S-1. The land that Indian farmers spared by raising wheat yields. The upper curve shows the area that they would have harvested at 1961-1966 yields to grow what they produced. The lower curve shows the area that they actually harvested. They spared the difference. The figure extends a table compiled by Borlaug (1987).[Bor87]

Figure S-2. Annually since 1960, the farmers of the world lifted average corn yields 0.06 t/ha. In the Tall corn State, Iowa farmers lifted their average 0.10. And winners of the Iowa Master corn Growers' contest stayed ahead, pushing up winning yields 0.14. So far, rising averages continue sparing land, and the persisting gap between averages and winners sustains hope for future sparing.

Figure S-3. Sparing part of 2.8 billion ha as farmers raise yields and ten billion people each account for 3,000 or 6,000 calories daily. The 2.8 is twice the present cropland as ten billion is roughly twice the present population. On the left of the graph at a yield of 1 t/ha, people accounting for 3,000 would spare none, and for 6,000 would take more than 2.8, a negative sparing. Near the middle, a yield of 4 t/ha would spare much of the 2.8 billion ha. If farmers lifted yields to 6 t/ha on the right, they would spare a bit of today's cropland, even if each of the ten billion accounted for 6,000 calories daily.