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What Is Up with Soybean Yields

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by Scott Irwin, Agricultural Economist - University of Illinois

Soybean yields in the U.S. have been very high the last four years. The U.S. average yield set new records in a stair-step fashion each year between 2014 and 2016. The 2016 yield reached the remarkable level of 52.1 bushels. While not a record, the 2017 yield (based on the November 1 USDA estimate) was 49.5 bushels, the second largest ever. On top of the high U.S. average yields are the numerous reports of field-level yields in the 70s, 80s, and even a few in the 90s.





The high soybean yields of recent years have sparked a debate about what is driving the exceptional yields. In thinking about this debate it is important to understand that there are only three possible sources of soybean yield gain. The first is weather during the growing season. The second is genetic improvement in soybean varieties. The third is a management, which encompasses all aspects of the soybean production process. Genetic improvement and management sometimes go hand-in-hand so that one requires the other.

It is a not an easy task to disentangle the complex and sometimes interacting impacts of weather, genetics, and management on soybean yields. One approach is to use a crop weather regression model to estimate the separate impacts of weather and technology on soybean yield, where technology is the combined impact of genetic improvement and management. I estimated this type of model for U.S. average soybean yields over 1970–2017. A linear time trend was used to represent technological change and summer precipitation and temperature variables were used to represent growing season weather. The modeling results showed that U.S. average soybean yields in 2014, 2015, and 2017 could be explained by a continuation of the linear improvement in technology and good growing season weather. The exception was 2016, when yield was substantially higher than what could be predicted based on a linear technology trend and good weather. It is not clear from this exercise whether we should view the 2016 yield like a 100-year flood or a permanent jump in soybean yield potential.

Agronomic data can be helpful in further disentangling genetic improvement from other sources of soybean yield gain. One recent study collected seed for over 150 soybean varieties released from the 1920s through the 2000s. Using randomized trials from across the country in 2010 and 2011, the study estimated “pure” genetic improvement in soybean yields. The results indicated a linear progression of soybean genetic yield gain from 1970 through 2008. This indicates that the historical pattern of soybean genetic gains in yield have been steady and marked jumps in the rate of improvement are rare. Soybean variety test results from the Department of Crop Sciences at the
University of Illinois provide relevant data through 2017. The yield of conventional soybean varieties relative to the older Williams variety shows no change of trend in recent years. Overall, there is little evidence to date that soybean genetics have been improving at a faster rate in recent years.

If we dig into the soybean yield data for the U.S. state-by-state an interesting pattern emerges that points to important changes in management practices. In general, soybean trend yields in the Southeastern U.S. have been growing at a much faster rate than in other growing regions. This non-linear trend appears to be related to a number of management practices, which can be roughly described as having the purpose of replicating Midwestern growing conditions. This includes planting much earlier in the past, planting earlier maturing indeterminate varieties, including corn in the crop rotation to increase organic matter in the soil, and using raised bed production systems. These management practices have allowed soybean yields in the Southeast to largely catch up with those in the rest of the country.

In sum, the data indicate that the biggest factor explaining high soybean yields in recent years is simply exceptionally good growing season weather. Improved management practices, particular in the Southeastern U.S., have also certainly contributed. A jump in the rate of genetic improvement in soybeans was not likely a big contributor to the surge in soybean yields.

Areas of Above & Below Trend Yields in the Corn-Belt

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Farmers in Illinois and other parts of the eastern corn belt have had above average yields over the last several years. Gary Schnitkey wondered if this was due to the weather or some other reason. He explored the topic and came to three conclusions.



First, yield expectations in the current year likely are more heavily influenced by more recent experience. In those areas where yields have been high, it may be tempting to building financial budgets and expectations on relatively high yields. Doing so could result in higher projections of incomes than are warranted. Farmers in Illinois and other recent high yielding areas should be cautious about building in high yield expectations.

Second, the comparison of above average yields in Illinois and near average yields in Iowa is instructive in understanding whether high yields are caused by technological change. The high yields in Illinois in recent years likely are not a result of technological changes. If technological change was causing the yield differences, Iowa would have had above trend yields as well as Illinois. Rather, high Illinois’ yields likely are the result of good growing conditions. Over time, areas with good growing conditions will move around the greater Corn Belt, as has happened in the past.



Third, the above yield maps likely are indicative of relative financial performance since 2012. Overall, incomes have been lower since 2012. However, farmers in Illinois and other higher yielding areas likely have fared better than farmers in Iowa and other regions with near average yields. Again, weather variations can change from year-to-year, so areas with higher and lower yields will change over time.

2016 Corn and Soybean Yields in Perspective


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The National Agricultural Statistical Service (NASS) recently released 2016 county yields for both corn and soybeans. In this article, maps are produced showing actual 2016 yields minus 2016 trend yields. Examination of these maps shows areas of above trend and below trend yields for 2016. Areas of above trend yields will have higher 2016 incomes relative to those areas with below trend yields.


Individual county trend yields are calculated using data from 1972 through 2016. A linear line is fit through these yields using ordinary least squares. The 2016 trend yields were based on these linearly fit relationships.

The following maps report actual minus trend yields. By calculating trend yields, the inherent productivity of the farmland is taken into consideration, and actual yields are stated relative to that productivity.






Schnitkey reports those areas with above trend yields will have relatively higher incomes than those areas with below trend yields. In 2016, lower grain farm incomes will be more pronounced in the eastern corn belt and particularly in Indiana and Ohio.

Soybean Yields in Illinois

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by Gary Schnitkey, Agricultural Economist - University of Illinois

In recent years, soybean yields in Illinois have been exceptional, leading to questions on whether technologies have caused a "jump" in soybean yields. While the 2016 state yield will be an outlier, it is too early to say that a new regime of soybean yields exists. Relative to corn yields, soybean yields must increase more to have the same relative yields as in the early 1970s.

Comparing Soybean Yields to Trend

State soybean yields for Illinois have been exceptional from 2014 through 2016. In 2014, Illinois' soybean yield was 56 bushels per acre. The 2014 yield was a record high, 4.5 bushels per acre higher than the next highest yield of 51.5 set in 2010. The 2015 state yield again was 56 bushel per acre. In 2016, a new record will be set, with state yield estimated at 62 bushels per acre in the October Crop Production report produced by the National Agricultural Statistical Service. A 2016 yield of 62 bushels per acre would be 6 bushels per acre higher than the previous highest yield set in 2014 and 2015.

Comparisons to trend further illustrate how high recent yields have been in Illinois (see Figure 1). Fitting a linear trend through soybean yields results in an increase of .48 bushels per year. The 2014 through 2016 yields are significantly above the trend: 5.1 bushels in 2013, 4.6 bushels per acre in 2015, and 10.1 bushels per acre in 2016. The 2016 yield is a statistical outlier. Only one other yield has been 10 bushels away from the 1972-2016 trend, that being in the 1988 drought year when the actual yield was 11.5 bushels below trend



Why are Soybean Yields High?

Recent high soybean yields then lead to the question of what is causing the high yields. Have growing conditions been abnormally good in the past three years, leading to the high yields? Or has technology changed such that a higher yield should be expected in the future? Perhaps genetics have improved, or farmers' use of fungicides and other inputs have been leading to higher yields.

This question - is it good weather or technology changes - is difficult to answer from just observing time series of data. Two contradictory thoughts. Recent yields have been high, and the 2016 yield is a statistical outlier, suggesting technology changes. On the other hand, historical jumps in yields or trends have rarely occurred in the last 50 years. For example, corn yields appeared to be increasing at a faster after 1995 than before 1995. Belief in an increasing yield trend decreased after the poorer yields of 2010, 2011, and 2012. The recent high soybean yields in recent years may simply be a signal of exceptional growing conditions.

Soybeans Compared to Corn Trends

While soybeans have had exceptional yielding years recently, soybeans relatively to corn yields have not been at historically high levels. Figure 2 shows soybean yields divided by corn yields. Higher levels indicate that soybean yields are higher relative to corn. In 2016, soybeans divided by corn yield is .31, which is not above average.



Over time, soybeans-to-corn yields have been trending downwards. An expected level of soybean-to-corn yields in 1972 was .32. The .31 value in 2016 is below the expectation in 1972. The Illinois state yield for 2016 is projected at 202 bushels per acre. For a .32 soybean-to-corn yield ratio to result in 2016, soybean yield would have to be 64.6 bushels, 2.6 bushels higher than currently projected.

Soybean yields have been declining relative to corn yields because of higher trends for corn. In Illinois, corn yields have been increasing by 1.8 bushels per year compared to .48 bushels per year for soybeans. Over time, the higher increase in corn yields causes lower soybean-to-corn yields

Summary

Soybean yields in Illinois have been exceptional in recent years, with yields being much higher than trend yields. It is too early to say that a permanent change has occurred, and history suggests permanent changes occur rarely.