State Yield and Acreage Trends

  • Irrigated soybean yields are rising at a rate of 0.648 bu/ac year, which is about 2/3 of a bu/ac per year.
  • Rainfed soybean yields are also rising but at a slower rate of 0.378 bu/ac year.
  • USA yields (mostly rainfed) are rising at a rate of 0.424 bu/ac year, which is not much more than the foregoing NE rate.
  • Large season-to-season fluctuations occur in rainfed soybean yields, due to unexpected annual variance in rainfall amounts and distribution.
  • Irrigated soybean yields are predictably high each year, so investing in yield-improving technological inputs are less risky and potentially more profitable.
  • Such investments are likely why the yield difference between irrigated and rainfed production is widening, on average, by about 1/4 bu/ac per year.
USA and NE Irrigated and Rainfed Yields

Excel Chart 1: NE Soy Yield Trends
Data Source: National Agricultural Statistics Service

Yield Improvement in Soybean

Many producers (and even some scientists) think that soybean yield improvement is not keeping pace with corn yield improvement. This perception arises because the yield trends of both crops are typically compared in absolute terms, as shown in the below chart:

Corn Yield vs. Soybean Yield Trends Over time

Excel Chart 3: NE Irrigated Corn & Soy Yield Trends (absolute terms)
Data Source: National Agricultural Statistics Service

However, any argument about the pace of yield improvement requires that the yield trends of the two crops be compared in relative terms, because of these substantive physiological differences between corn and soybean:

  • The photosynthetic CO2 acquisition system in corn (C-4) is much more efficient (though it requires more light than the one in soybean (C-3), which makes corn intrinsically more productive than soybean in terms of “using a crop to harvest the solar energy to produce seed”.
  • Corn seed is comprised primarily of carbohydrate (75%), with minimal protein (10%) and oil (5%), whereas,
  • Soybean seed is high in protein (40%) and oil (20%) relative to carbohydrate (35%).
  • Seed protein and oil require more photosynthetic energy to produce than carbohydrate, and thus plants producing such seed typically yield less.
  • To generate the amino nitrogen needed for plant & seed proteins, both corn and soybean assimilate the nitrate absorbed from the soil by roots.
  • However, soybean also uses nitrogen (N2) fixation (occurs in soybean root nodules) to generate about half of its amino nitrogen needs,
  • But, the energetic cost (to the plant) for N2 fixation is slightly greater than the energetic cost of nitrate absorption and reduction.
  • These physiological attribute differences between corn & soybean give rise to an intrinsic 3-fold productivity advantage for corn over soybean.
  • In Nebraska's irrigated production systems (no crop water stress), this intrinsic productivity advantage translates into a corn/soybean yield ratio of 3.25 / 1.00 (in bu/ac). Thus, if your irrigated corn yield is 234 bu/ac, your irrigated soybean yield should at least be 324/3.25=72 bu/ac.

In the below chart, the corn yield units on the left axis (60 to 210 bu/ac) and soybean yield units on the right axis (19 to 65 bu/ac) have been coordinately adjusted to reflect the typical 3.25 : 1.00 corn/soybean yield ratio that has prevailed since 1971 in Nebraska’s irrigated corn & soybean production fields. The negligible difference between the irrigated corn & soybean trend lines indicates that in relativeterms, soybean yields have improved at a pace nearly equivalent to the pace of improvement in corn yields.

Corn Soy bu-ac-yr 

Excel Chart 4: NE Irrigated Corn & Soy Yield Trends (relative terms)
Data Source: National Agricultural Statistics Service

Actually, as the below chart shows, the corn/soybean yield ratio in Nebraska's irrigated production systems has not changed much over the past 37 years, and was a projected 3.24 / 1.00 in 2008. In Nebraska's rainfed production systems, the ratio was a projected 2.83 / 1.00.

NE Corn / Soybean Yield Ratio - Irrigated and Rainfed Production Trends

Excel Chart 5: NE Corn / Soy Yield Ratio Statisics
Data Source: National Agricultural Statistics Service

NE Irrigated & Rainfed Acreage Trends

  • In 2012, 2.31 million irrigated acres (46%) and 2.68 million rainfed acres (54%) of soybeans were grown in Nebraska.
  • Irrigated acreage, which in 1976 was less than 7%, rose to 30% in the next 15 years, and in the late 1990s spurted to a 2006 high of 48%.
  • Rainfed acreage followed a similar trend, but the late 1990s, the spurt in rainfed acres was not as large as the spurt in irrigated acres.
  • The 2007 dip in irrigated and rainfed soybean acreage was due to producer anticipation in the spring of ethanol-driven higher corn prices.

NE Irrigated and Rainfed Acreage Trends

Excel Chart 2: NE Soy Acreage Trends
Data Source: National Agricultural Statistics Service