Declining Yield Variability and 2025 US Corn and Soybean Yield Distribution

By Carl Zulauf and Gary Schnitkey et.al

US corn and soybean yields have deviated notably less from trend yields during the first quarter of the 21^st Century than during the last quarter of the 20^th Century.  The decline is especially large for US corn if the 2012 drought is treated as an outlier event.  Percent deviations from trend yield that have occurred so far in the 21^st Century imply a 2025 US harvested yield distribution that varies from 142 to 205 for corn and from 43 to 57 for soybeans.  Using the percent deviations during the last quarter of the 20^th Century, the ranges are 138-210 and 42-59.

Data and Procedures

US corn and soybean yields for the 1974 through 2024 crop years were obtained from the Quickstats database maintained by USDA, NASS (US Department of Agriculture, National Agricultural Statistical Service).  Over these 51 years, the linear time trends are:

Corn yield = 85.73 bushel (bu.) / acre+ 1.91 bu. / acre ● (time), where ● = multiply

Soybean yield = 26.80 bu. / acre + 0.51 bu. / acre ● (time)

Time is measured as a count variable starting with 0 for 1974 and ending with 50 for 2024.  Explanatory power of the linear time trend is 88% for corn and 90% for soybeans.  The linear yield trend is 3.76 times larger for US corn than soybeans (1.91 / 0.51).  Figure 1 contains the graph of US harvested yield for corn and soybeans over 1974-2024, plus the linear trend yield estimated using the above equations.