If biomass yields double, the land needed for US biofuel falls to 25 million acres.

This is conditional arithmetic resting on the 50-million-acre base. True: for a fixed fuel output, land required scales inversely with yield, so doubling yields halves the land, and credible analyses support about 50 million acres at baseline yields (35–65 million), making about 25 million acres (17–33 million) the doubled-yield figure. Mostly true: the halving logic holds and the implied doubled-yield land is within about 1.5× of 25 million acres. Mostly false: the halving arithmetic is right, but the base is unsupported, so the doubled-yield land requirement is about 2–3 times 25 million acres (50–75 million). False: the doubled-yield requirement is more than 3 times 25 million acres, or the proportional logic itself fails materially, for example because doubled yields would not halve land owing to processing or conversion limits.

Set before the research began.

1. E1 Where will biofuels and biomass feedstocks come from? Grist · 22 January 2008 Own record

   “6. If winter over crops do not provide any biomass, I project energy crop usage of 57M acres in 2030 — furthermore, if yields are 18 tons/ac instead of 24, I project total land use at 76M acres.”

2. E2 Where will biofuels and biomass feedstocks come from? Grist · 22 January 2008 Own record

   “I believe, as estimated in my papers elsewhere, that 2,500 gallons of ethanol equivalent per acre annually is a reasonable assumption.”

3. E3 Where will biofuels and biomass feedstocks come from? Grist · 22 January 2008 Own record

   “(Assuming corn grain yields of 140 to 170 bushels/acre, typical of the mid-Western corn belt, and 2.8 gallons of ethanol from a bushel of corn — the range in ethanol production from corn is only 392 to 476 gallons/acre.)”

4. E4 Where will biofuels and biomass feedstocks come from? Grist · 22 January 2008 Own record

   “For the U.S., the world's most oil intensive economy, my calculations show that a small dose of vision, two decades of agricultural development, and process technology that is in pilots today, with less than 5% of our annual crop and timberlands, could more than supply our biofuel needs to replace all of our light-vehicle gasoline usage by 2030.”

5. E5 Where will biofuels and biomass feedstocks come from? Grist · 22 January 2008 Own record

   “If winter over crops do not provide any biomass, I project energy crop usage of 57M acres in 2030 — furthermore, if yields are 18 tons/ac instead of 24, I project total land use at 76M acres.”

6. E6 Where will biofuels and biomass feedstocks come from? Grist · 22 January 2008 Own record

   “In the short and medium term, at biomass yields of 10 tons/acre (by 2030 we expect about 20-25 tons/acre), 100,000 acres of land would be needed per cellulosic ethanol plant, or 40,000 acres by 2030.”

7. E7 Where will biofuels and biomass feedstocks come from? Grist · 22 January 2008 Own record

   “Yield projections (tons per acre) are based on fertile land. The usage of degraded land will result in lower yields.”

8. E8 Sun Grant/DOE Regional Feedstock Partnership: Final Technical Report South Dakota State Univ. (DOE-sponsored final technical report, OSTI)

   “Publication of The Technical Feasibility of a Billion-Ton Annual Supply (Perlack et al., 2005) in 2005, with its associated yield assumptions, led to the realization that the yield goals and assumptions utilized in that analysis required careful validation.”

9. E9 [PDF] II. Producing Cellulosic Biomass for Biofuels - USDA ARS Council for Agricultural Science and Technology (CAST) · November 2007

   “Bold and optimistic assumptions in some reports indicate future production systems have the capacity to meet the projected feedstock demand (Perlack et al. 2005; Smith et al. 2004).”

10. E10 Renewable Fuel Standard: Potential Economic and Environmental Effects of U.S. Biofuel Policy National Academies of Sciences (National Research Council) · 2011

    “Unless there are major increases in agricultural yields or improvements in the efficiency of converting biomass to fuel, an additional 30 to 60 million acres of cropland would be required to produce enough biomass to meet the Renewable Fuel Standard by 2022.”

11. E11 Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply Oak Ridge National Laboratory / US Department of Energy · 2005

    “The purpose of this report is to determine whether the land resources of the United States are capable of producing a sustainable supply of biomass sufficient to displace 30% or more of the country's present petroleum consumption.”

The halving is simple arithmetic, so the claim depends on whether about 50 million acres is a credible baseline for the fuel target Khosla had in mind. The only acreage figures that tie land to yield come from Khosla's own Grist piece (E1, E5, E6). His footnote projects 57M acres of energy crop use in 2030 if winter cover crops provide no biomass, and 76M acres of total land use if yields are 18 rather than 24 tons per acre; these are his own projections, not independent support. The independent sources do not settle the baseline. E10 estimates 30–60 million additional acres of cropland to meet the Renewable Fuel Standard by 2022, a different fuel target from his, and E8 and E9 only say the yield assumptions were optimistic or needed checking, without giving a land figure that can be compared.