In the coffee shops of agricultural communities all across the country, producers like to talk about the weather. And weather is important because it is, arguably, the single largest driver of their favorite part of production agriculture, yields. Whether it’s grass in pastures or corn in Iowa, yields are important to farmers for many reasons.
Humans have made great advancements in crop yields over time. Yield improvements have been critical in avoiding the tragedy of population limits Thomas Malthus predicted in 1798. Some of those most recent and successful advance has been the yield growth of corn. So how does sorghum stacked up?
The first graph, below, shows yields for corn and sorghum since 1929. Corn yields have always been higher than sorghum, but the gap hasn’t always been as great. In 2013, the average sorghum yield in the U.S. was 37.5% of the U.S. average corn yield. In 1929, the average sorghum yield was 55.3% of the average corn yield. A quick glance at the graph shows that the departure in yields appears to have begun in the late 1950’s.
After digging into the data, sorghum and corn yields began to depart around 1957. This is also when sorghum production peaked in acres planted and total bushels harvested. The second graph shows the U.S. average yields for corn and sorghum since that date. This graph shows the same general story that was observed in the first, a divergence in national average yields, but this graph also includes a trend-line for each crop. From the trend-line analysis (included on the graph) we can begin to measure the rate at which yields for corn and sorghum increased. Corn experienced a yield growth of about 1.8 bushels per acre per year. Sorghum on the other hand, only increased a growth rate of 0.4 bushels per acre per year. Over the 56 year period, this difference in growth rates created a 78.5 bushel advantage for corn.
One of sorghum’s biggest bragging points is its tolerance for drought. A lot of research has gone into understanding how sorghum genetics can be used, and enhanced, to increase grain production across the globe. The research concludes that sorghum “drinks” less water per bushel and would be less susceptible to the damaging effects of droughts. If sorghum can’t beat corn on yields, perhaps it can beat corn on yield risks.
The de-trended yield graph shows the annual yields since 1957 with the influence of increasing yields over time removed. Like adjusting dollars from 1957 for inflation, these yields numbers have been adjusted for yield increases due to technology improvements. The purpose of this procedure is to allow us to look at the variations in yields that aren’t directly attributed to improvements in time, such as weather.
The first observation is that the average corn yield over time, de-trended, is slightly more than 158 bushels per acre. Sorghum’s average de-trended yield is much lower at 68.8 bushels per acre. Secondly, if you were to look at the graphs only, you might also conclude that corn yields are more erratic and more variable. The peaks and dips away from the dotted lines (representing the mean yield) seem to be less severe with sorghum.
Looking at the detailed data, however, paints a different picture. For the de-trended yields since 1957, the standard deviation (a measure of yield variation) for the corn is 10.2 bushels while only 7.6 bushels for sorghum. But keep in mind, these two crop have different means to compare their standard deviation to. When we take these standard deviations and make them relative to their respective mean, we find that the Relative Standard Deviation for sorghum is 11.0% of the mean yield and is 6.5% of corn. The implications for these results are that, across the U.S., you can expect sorghum yields to have more variation relative to their mean, and are more risky, than corn yields. And while this doesn’t discount the research suggesting that sorghum might be more drought-tolerant, it highlights an important point that a crop with more drought tolerance does not necessarily have less yields risk.
Sorghum, which has struggled to maintain acres, has also struggled competing with corn on yield improvements over the last several decades. Given the difference in growth rates, the gap between corn and sorghum yields will only grow over time. And if that wasn’t enough, further analysis shows that U.S. sorghum yields have shown more variation – more volatile and risk – than corn. It is possible that some of this result is due to sorghum being grown in less hospitable climates than corn. Nevertheless, the results indicate that sorghum will likely struggle to gain acres on corn.
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