The deviation below trend was 34.1 bushels, only rivaled in the last half-century by 1988 when yield dropped 33.8 bushels below trend. From this perspective, the 2012 drought was indeed the 'big one' with respect to non-irrigated corn yield.
One final issue is whether trend deviations should be computed in bushel or percentage form. If one computes percentage deviations from the non-irrigated corn trend then 2012 does not look quite as dire. The percentage deviation in 2012, -29.3 percent, is only the third worst of the last half-century and considerably smaller than the -44.5 percent shortfall in 1988.
There is no obvious answer which form of deviation is correct. If one believes that the corn trend is a constant bushel increase then the linear trend presented in Figure 2 is valid. If on the other hand one believes that the corn trend yield is a constant percentage increase then a log-linear trend model (take logarithm of yield before regressing on time index) should be used.
We lean here towards the linear trend formulation because the range of trend yield deviations in bushels does not expand across time as one would expect if a log-linear trend model is the better specification.
The 2012 drought in the U.S. devastated non-irrigated corn yields. Depending on the measure of trend deviation, the drop in yield relative to trend was either the worst in the last half-century or in the top three.
This is an important data point with respect to the ongoing debate about the drought tolerance of U.S. corn production. Regardless whether drought tolerance has actually improved, 2012 demonstrated in rather spectacular fashion that widespread drought leads to sizable reductions in non-irrigated corn yields relative to trend.
More directly, there is still no substitute for a cool, wet July in terms of U.S. corn production.
Source: Farm Doc Daily