Soybeans
© United Soybean Board
Overview
Soybeans are widely grown throughout the eastern half of the country, with the greatest production in Iowa, Illinois, Indiana, Missouri and Minnesota. Over time, a larger share of acreage has shifted farther west into the Dakotas and Nebraska. The summary chart for soybeans shows clear improvement from 1980 to 2000 across the indicators, with progress slowing in the past two decades (Figure 1.9.1). Land use and irrigation water use efficiency saw the greatest improvements over the last two decades, while little or no improvements were observed for soil erosion, energy use and GHG emissions. A summary of all indicators for soybeans for reference years is shown in Table 1.9.1.
Figure 1.9.1. Summary chart of indicators for soybeans during 1980-2020 Data are presented in index form, where all indicators have been scaled by indicators averages for the period 1998-2002. A 0.1 point change is equal to a 10 percent difference. Index values allow for comparison of change across indicators with different units of measure. A smaller area represents improvement over time.
Additional illustrations of soybean sustainability on a per acre basis and for total resource use are available in Appendix B, accessible from the Download Report link.
Land Use
The area planted to soybeans in the U.S. declined in the 1980s before increasing steadily to the present day (Figure 1.9.2). Overall production has increased much more than can be explained by the area increase (Figure 1.9.3). Land use efficiency has consistently improved throughout the study period, indicating improvement in crop yield (Figure 1.9.4).
Energy Use Efficiency
Energy use efficiency per bushel of soybeans showed improvement from 1980 to 2000, with a largely flat trend over the past two decades (Figure 1.9.5). The per acre energy use for soybeans has increased since around 2005 (Figure B.33), driven by increased use of fertilizers, herbicides and fungicides since 2000. Energy used for management has declined due to increasing rates of no till prior to and through around 2005, when no-till systems reached 40% of soybean acreage, since which time the management energy has declined slightly (Figure B.34).
Greenhouse Gas Emissions
Greenhouse gas emissions per bushel of soybeans improved substantially between 1980 and 2000 and have since followed a flat trend similar to energy use (Figure 1.9.6). Due to the slightly higher use of nitrogen fertilizer compared to previous years, there has been an increase in nitrous oxide emissions since around 2005, and this is reflected in the increase in per acre GHG emissions for soybeans, which were higher in 2020 than at any other time in the period of analysis (Figure B.35). Table 1.9.2 lists the top four contributors for energy use and GHG emissions for soybeans during 2010 to 2020.
Irrigation Water Use
Irrigation water use efficiency for soybeans has overall improved from 1980 to 2020 (Figure 1.9.7), although substantial variability from the trend line is observed. A consistent trend of water use improvement up to the year 2000 was reversed until the early 2010s, likely a result of large-scale rainfall deficit across large regions. Since 2013, the irrigation water use efficiency has improved. The average irrigated harvested acreage was approximately 9.5% across the 2008, 2013 and 2018 Irrigation and Water Management Survey for soybeans, when compared to the total harvested acres.
Soil Erosion
Soil erosion for soybeans also saw substantial improvement from 1980 to 2000, with additional slight reduction in the early 2000s (Figure 1.9.8). Since 2010, soil erosion has held largely steady for soybean-producing fields at just over 4 tons per acre per year.
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