I hear a lot of talk about the impacts of federal farm policy on our food system. It is sometimes suggested that farm policy is to blame for “cheap food” and thus obesity (see this nice twitter response by Tamar Haspel) or that many of our purported modern day farm and food ills can be traced back to Earl Butz, who as Secretary of Agriculture in the early 1970’s encouraged producers to plant “fence row to fence row.”
One way to evaluate these sorts of claims is to look at how much (or little) crop acreage in the U.S. has changed over time. Here is data according from the USDA, National Agricultural Statistics Service on the amount of land planted to nine major commodity crops over time (note: vegetable acreage, which comprises only about 1% of all acreage is not included; nor is fruit or nut acreage, which is also a very small share of the total).
The figure below shows the cumulative acreage in the U.S. planted to nine major commodity crops over 93 year time period from 1926 to 2018. Over the entire time period, there was an average of 246 million acres planted to these nine crops each year. Seven out of the 10 highest planting years were prior to 1937 with the remaining three being in 1980, 1981, and 1982.
The coefficient of variation (the standard deviation divided by the mean) is only about 7.5%, implying relatively low variation over time (usually a figure less than 100% would be considered low variation). Since 1990, there have been relatively small year-to-year changes. Over the most recent 28 year time period, about 225.7 million acres are planted each year to these nine commodity crops, with a coefficient of variation of only 5.7%. This lower variation in recent years is interesting because farm policy has been much more market-oriented since 1996, and this is precisely the period over which there has been more stability in planted acreage.
Total land devoted to farming (or crop acreage) today is about 25% lower than the highs of the 1930’s and the early 1980’s. This is amazing in many ways given that the U.S. population is now 130% higher than it was in the 1930’s. Stated differently, twice as many people are now being fed on fewer crop acres.
Moving away from total acreage, it is instructive to look at the mix of acreage (see the two following figures). Here, we can see some significant changes in which crops are planted in the U.S. over time. For example, in 1926, there were only 1.9 million soybean acres but in 2018, for the first year in history, more acreage (89 million acres) was planted to soybeans than any other crop. Prior to that corn had been king every year except 1981-1983, when more acres were devoted to wheat than corn.
Another big change was a reduction in the number of acres planted to oats. Prior to the 1960’s, more than 40 million acres of oats were routinely planted each year. In 2018, only 2.7 million acres were in oats. Why the change? One big reason is that there aren’t as many mules and horses that need to be fed. Cotton also experienced a precipitous reduction in acreage from the late 1920’s to the early 1960s, stabilizing a bit thereafter.
The following figure shows the same data, but with acreage dedicated to each crop expressed as a percentage of total acreage in a given year.
Taken together, these three figures suggests the big change hasn’t been the total farmland planted but rather the change in which crops are planted to the acres. Moreover, this crop mix issue (the rise of soy and the decline of oats) probably had little to do with farm policy.
Given all the concerns expressed these days about mono-cropping and the supposed loss in farm/crop diversity over time, it is perhaps surprising to see that there is, today, actually more diversity in planted acreage (in terms of the mix of crops planted) today than in the past. To see this for clearly, I calculated the coefficient of variation across the number of acreages planted to each of the nine crops in each year. This gives a feel for how much crop variation there in a given year. Here are the results plotted over time.
The coefficient of variation ranges from about 87% to 138%. Comparing this to the coefficient of variation for total acreage planted (which was 7.5%), implies there is more variation in which crops are planted to which acreages in a given year than there is variation in the total planted acreage over time.
The figure above shows that the crop-mix variation (at least among these nine crops) has been increasing since the 1960s, and the variation is higher in the past decade than at any point in the preceding 80 years. In this sense, U.S. crop acres are move diverse today than has historically been the case.