by David A. Widmar
Last year we wrote a post looking at harvested acres and found the share of planted acres taken to harvest can vary from year to year. This variability was not a surprise, and we noted this could be an overlooked source of changes in production. This week we take a deeper look unharvested crop acres, or abandoned acres, to evaluate the impact on production.
For any given year, total production is the product of harvested acres multiplied by reported yield. If one uses long-run averages for these factors – the average share of planted acres harvested and trend-yields – a baseline level of production can be calculated. Any gap between this baseline production (planted acres X avg share of planted acres harvested X trend yields) and actual production (harvested acres X reported yield) can be measured and evaluated. This gap, or departure from baseline production, can be broken down to its two components; the departure from baseline from changes in harvested acres, and the departure from changes in yield.
Yield versus Acres
For corn, soybeans, and winter wheat, Figures 1, 2, and 3 show the annual impact of harvested acres and yields on departures from baseline production. Each data point represents a year, and the axis corresponds with how production departed from baseline production. The impact of changes in the share of acres harvested is shown along the horizontal axis while the vertical axis reports the impact from above/below trend yields.
Across the three charts, a few broad observations stand out. First, the impact from harvested acres is often much smaller than yields. This doesn’t come as a surprise given how much attention yield estimates get. Base production is often impacted by 1-2% from changes in harvested acres, while yield impacts are frequently larger than 5%. With that said, the impacts of harvested acres are rarely zero. Even small changes in production are not insignificant given how sensitive prices can be to small changes in ending stocks.
While the impacts are often small, there have been years where changes from harvest acres have been quite large. Furthermore, these larger impacts typically arise from decreases in production.
Most recently, corn and soybeans have experienced an uptick in production, over the baseline expectations, from a larger share of harvested acres. We’ve written about recently large yields, and an uptick in harvested acres has accompanied these large yields.
Comparing Corn, Soybeans, and Wheat
Table 1 shows a few summary statistics of the impacts from harvested acres and yield across corn, soybeans, and winter wheat. For each crop, the maximum and minimum impacts from departures in harvested acres and trend yields are shown, along with the correlation between these two factors over time. Again, these data are from 1990 to 2017.
In all cases, the correlation between harvested acres and yield are moderately strong and positive. This means that year’s with above (below) trend yields often correspond with a larger (smaller) share of acres harvested. This partially contributes to the old adage of large crops get larger, and small crops get smaller.
When comparing across crops, soybeans have had the smallest impacts from harvested acres while winter wheat has had the most. Since 1990, baseline winter wheat production has been boosted by as much 8% from an increase in harvested acres and decrease by as much as -12% from an uptick in abandoned acres. While the impacts of yield are often much larger than any from acreage, this isn’t always the case. Since 1990, winter wheat has faced adverse impacts to production – relative to baseline production- of -12% from both acres and yield. (These events occurred in different years.) For corn and soybeans, the maximum and minimum impacts of harvested acres are much smaller than yield, but this difference is much smaller for wheat.
Wrapping it Up
When speculating on a given year’s production, changes from baseline expected production could come from a departure from the average share of acres harvested or a departure from trend yields. Rightfully, attention is often focused on yields. However, variation in the share of acres harvested – or changes in the share of acres abandoned- are also important to keep in mind. Harvested acres usually have a small impact, but the impacts are rarely zero and are occasionally large.
Across corn, soybeans, and wheat, the impact of harvested acres is often smallest for soybeans and most significant for wheat. In fact, a record share of abandoned acres reduced wheat production by as much as -12% from baseline in 2002.
Finally, the correlation between the impacts of yields and harvested acres is modestly strong, and positive. This makes intuitive sense but underscores the importance of not singularly focusing on yields. While recent corn and soybean yields been strong, those bumper crops have also been accompanied by an above-average share of harvested acres.