Issue No. 20, Article 6/August 24, 2012
Drought and the Illinois Corn Crop: Comparing 2012 with 1988
First published as an Alert on August 13, 2012
One of the questions frequently heard since drought began to take shape earlier in the 2012 season was how yields might be affected in comparison with yields in 1988, when the last widespread drought hit Illinois. Interest centers on whether the development of genetically modified hybrids and the general improvement in hybrid yield potential and stress tolerance have made the corn crop more "drought-proof" now than it was in 1988.
The projected 2012 Illinois corn yield, released by NASS on August 10, is 116 bushels per acre. That may not hold up as the final yield, but for now it's the estimate we'll use. Projected yields range from 143 bushels in the Northwest crop reporting district to 80 bushels in the East Southeast district.
In 1988, the average Illinois corn yield was 73 bushels per acre, with a range from 87 bushels in the Southeast (actually higher than the estimate of 86 for this year in that district) to only 63 bushels in the Northwest. So the patterns of dryness were very different in the two years, with southern Illinois relatively better than northern Illinois in 1988. In 2012, dryness has been more evenly distributed, creating closer correlation between soil water-holding capacity and yield.
To look at how much yield was lost to drought in 1988 and 2012, I projected trend-line yields for each drought year based on yields over the 30 previous years. The expected (trend-line) yield for 1988 was 129 bushels per acre; the actual yield was 73, so the loss was 56 bushels per acre. In 2012, the expected yield was 173 bushels per acre and the estimated yield is 116, so the projected loss is 57. Measured in terms of bushels per acre less than expected, the two years are almost identical.
The 1988 yield represents a loss of 44% of expected yield, while in 2012, with higher yield expected, the percentage loss was only 33%. So in relative terms, the 2012 crop lost less yield than the 1988 crop, but in absolute terms, losses were almost identical between the two years.
It's not clear whether percentage loss or bushel loss is the better measure of drought effects, but what is clear is that serious drought continues to cause serious yield loss, even with today's faster-growing, higher-yielding hybrids. We don't yet know if hybrids improved specifically for drought tolerance will be less affected by drought this year, but it's unlikely that any hybrid will produce high yields in areas and soils where most well-managed fields yield little or nothing.
As we look at plot and field yields this year, we will want to note any hybrids that do relatively--and consistently--better than other hybrids under dry conditions. But since we don't know what next year will bring, we also need to include in our comparisons relative hybrid performance under better conditions, even if those come from last year or from 50 or 100 miles away.
In other words, use data from low-yielding comparisons done under drought conditions only if you expect those conditions in 2013. Otherwise, expect better conditions next year and, accordingly, use mostly data from better-yielding trials to choose hybrids.--Emerson Nafziger