US corn yields have increased sevenfold since 1920 due to technology and engineering.

Judge against USDA NASS historical US corn yield data (bushels per acre) for about 1920 compared with the latest years before 2007-09-28 (about 2004–2007). The claim also says the rise was due to technology and engineering. True: the ratio of recent yields to yields around 1920 is about 7 (6.3–7.7), and agronomic sources attribute the gain mainly to technology (hybrids, fertilizer, mechanisation, breeding). Mostly true: the ratio is 5.5–6.3 or 7.7–8.5, with the attribution correct. Mixed: the ratio is 4.5–5.5 or 8.5–9.5. Mostly false: the ratio is noticeably off but still shows a large multiple (e.g. 3–4.5 or above 9.5), or the attribution to technology is contradicted. False: the ratio is under 3.

Set before the research began.

1. E1 Development of Hybrid Corn and the Seed Corn Industry Springer (chapter by A.F. Troyer, Handbook of Maize) · 2009

   “Corn hybrids were first commercially grown in the early 1930s when the annual U.S. corn yields averaged 1,518 kg per ha (24.2 bushels per acre)”

2. E2 Development of Hybrid Corn and the Seed Corn Industry Springer (chapter by A.F. Troyer, Handbook of Maize) · 2009

   “In 2007, the average U.S. corn yield was estimated at 9,474 kg per ha (151.1 bushels per acre)”

3. E3 Development of Hybrid Corn and the Seed Corn Industry Springer (chapter by A.F. Troyer, Handbook of Maize) · 2009

   “These increases were caused by better hybrids, improved cultural practices, and biotechnology.”

4. E4 Technological innovations have increased corn yields USDA Economic Research Service · 19 September 2017

   “Average national corn yield (a productivity measure) rose from around 30 bushels per acre in the 1930s (where it stood since USDA began measuring them in the 1860s) to nearly 180 bushels per acre in the present decade.”

E2 puts the 2007 average US corn yield at an estimated 151.1 bushels per acre. E4 says yields stood at about 30 bushels per acre from the 1860s through the 1930s, which implies about 30 around 1920 and a ratio of roughly 5. E1's early-1930s figure of 24.2 bushels per acre would give about 6.2, but that baseline is a decade after 1920. Both ratios fall below the 6.3–7.7 range the criteria set for "about sevenfold"; the more direct baseline of about 30 lands in the mixed band (4.5–5.5). E3 and E4 support crediting the gain to technology (hybrids, cultural practices, biotechnology), but the ratios the evidence supports, about 5 against E4's long-standing baseline of around 30 bushels per acre and about 6.2 against E1's early-1930s figure, fall below sevenfold.