Blog

Crop Yields and Taste

That modern agriculture is incredibly productive - much more than the past - is undeniable. These USDA data, for example, suggest we produce about 170% more agricultural output now than in the late 1940s. I have argued that these these increases in agricultural productivity are signals of improved sustainability. Some people believe the the productivity improvements have been accompanied with offsetting externalities or degredations in animal welfare. A different kind of critique is that modern crops - despite being more productive - aren’t as high “quality.” For example, this piece in Politico by Helena Bottemiller Evich, titled “The great nutrient collapse” discuses evidence that vitamin content of crops has fallen as yields have increased, and there is the often-heard complaint that tomatoes don’t taste as good as they once did.

There is some biological basis for these latter concerns. If a crop breeder selects plants for higher yields, they are selecting plants that are spending their energy and nutrients into producing bigger seeds and fruits, which is energy that could have gone (in lower yielding plants) to growing leaves or roots or other compounds that affect taste and vitamin content.

I had these thoughts in the back in my mind when I came across the Midwest Vegetable Trial Report put out by researchers at Purdue and other Midwestern universities. The report compares different vegetable varieties in terms of yield and other output characteristics. I noticed for a couple vegetables - green beans and sweet corn - there were also measures of taste for each variety. Granted, these were not full-on scientific sensory evaluations and they involved small numbers of tasters, but still I thought it would be useful to test the conjecture that higher yielding varieties taste worst.

Some researchers from University of Kentucky put together the green bean report. They compared the performance of 19 different varieties of green beans. The most productive variety (named “Furano”) yielded 785 bushels over six harvests, whereas the lowest yielding variety “Slenderette” only produced 233 bu/acre in six harvests. As the image below reveals, however, there was only a weak correlation between taste and yield. The correlation was negative (-0.26), but not particularly large. About 6.6% of the variation in yield is explained by taste. The best tasting variety “Opportune“ had a taste score of 4.1 (on a 1=poor to 5=excellent scale) and a yield of 557; the worst tasting variety “Bronco” had an average taste score of 2.3 and a yield of 543. So, the best tasting bean had better yield than the worst tasting bean. Overall, the results below provide some weak support for a yield, taste trade-off.

greenbean.JPG

The report also provided production and taste data on supersweet corn (this part was authored by Purdue researchers Elizabeth Maynard and Erin Bluhm). They compared 16 different types of bicolored supersweet corn (they also evaluated two varieties of white and two varieties of yellow, which I’m ignoring here). They had tasters rate “flavor” on a 1 to 5 scale. As the figure below shows, there is actually a positive correlation between flavor and yield, as measured by ton/acre. The correlation is 0.15, but the relationship is weak. The authors also report yield in a slightly different way, ears/acre, and by this measure the correlation is slightly negative (-0.09).

cornyieldflavor.JPG

These results don’t necessarily negate the idea that the taste of vegetables has declined over time as higher yielding varieties have been adopted, but they do suggest that in 2017, among the particular varieties tested and among the few tasters asked, there is only a very weak correlation between taste and yield for green beans and supersweet corn.

Trends in Farm Land Acreage

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 1.8%. 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 12% 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.

cum_acres.JPG

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.

acres_bycrop.JPG

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.

acres_composition.JPG

Given all the concerns expressed these days about mono-cropping, it might be interesting to look at the variation in planted acreage (in terms of the mix of crops planted) today than in the past. To see this, 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.

cropvariation.JPG

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.

New findings on agricultural productivity

The American Journal of Agricultural Economics has recently published several new and important papers on agricultural productivity.  Whether agriculture is becoming more or less productive is a critical question as it relates to sustainability (are we getting more while using less?), food security (can food production outpace population growth?), and consumer well-being (are food prices expected to rise or fall?). 

These papers focus on "total" or "multifactor" productivity rather than just yield.  Yield is a partial measure of productivity - it is the amount of output per unit of one input: land.  One can increase yield by adding more of other inputs such as water, fertilizer, labor, etc.  What we want is a measure of how much output has increased once we have accounted for uses of all inputs, and this is total or multifactor productivity.

The first paper by Matthew Andersen, Julian Alston, Phi Pardey, and Aaron Smith is worrisome.  They write:

In this paper we have used a range of data and methods to test for a slowdown in U.S. farm productivity growth, and the evidence is compelling. The results all confirm the existence of a surge and a slowdown in productivity but with some variation in timing, size, and statistical significance of the shifts. ... Over the most recent 10 to 20 years of our data, the annual average rate of MFP [multifactor productivity] growth was half the rate that had been sustained for much of the twentieth century. More subtly, and of equal importance, the past century (and more) of statistics assembled here suggest the relatively rapid rates of productivity growth experienced during the 1960s, 1970s, and 1980s could be construed as aberrations (along with the relative rapid rates of growth experienced during a period spanning WWII), with the post-1990 rates of productivity growth now below the longer-run trend rate of growth.

The second paper by Alejandro Plastina and Sergio Lence provides a deeper understanding behind the causes of productivity growth.  They present a straightforward way to decompose multifactor productivity into six different factors: technical change, technical efficiency, allocative efficiency, returns to scale, output price markup, and the input price effect.    They write:

Technical change is the major driver of TFP growth over the long run, and there is evidence that technical progress in the 1990s and 2000s was much slower than in the 1970s. This is a relevant result for policy makers, and begs the question of what is actually causing the slowdown in technical change. This is the first study to show technical regress in the agricultural sector during the farm crisis of the 1980s.

Another novel result is that annual changes in TFP bear no significant correlation with annual rates of technical change but instead are highly correlated with the markup effect, followed by the returns to scale component and allocative efficiency change. These findings suggest that evaluating the effects of research, extension, and other variables on each of the components of our measure of TFP change (rather than solely on an aggregate TFP index) can shed light on the actual channels through which those variables affect agricultural productivity growth in the United States and therefore contribute to policy design.

Finally, there is Julian Alston's fellow's address from last year's AAEA meetings.  In addition to providing an excellent literature review, he makes several important points.  He argues that agricultural research is significantly under-funded relative to the benefits it provides in increased productivity:

Evidence of remarkably high sustained rates of social payoffs to both private and public investments in agricultural R&D testify to a significant failure of government to fully address the underinvestment problems caused by the market failure. Moreover, if anything, in high-income countries like the United States, agricultural R&D policies seem to be trending in the wrong direction, making matters worse.

and

a reasonable first step would be to double U.S. public investment in agricultural R&D—an increase of, say, $4 billion over recent annual expenditures.4 A conservatively low benefit-cost ratio of 10:1 implies that having failed to spend that additional $4 billion per year on public agricultural R&D imposes a net social cost of $36 billion per year—an order of magnitude greater than the annual $1–5 billion social cost of $20 billion in farm subsidies.

Alston also points out that the main beneficiaries of productivity growth are consumers, and the farmers may or may not benefit.  He writes:

It seems inescapable that the agricultural innovations that made food much more abundant and cheaper for consumers did so to some extent at the expense of farmers as a whole—more than offsetting the effects of growth in demand for output from the sector. This finding is reinforced when we pay attention to the details of the timing. Specifically, the periods of the most rapid decline (or slowest growth) in [net farm income] seem to coincide with the periods of most rapid increase in farm productivity—the 1940s to 1980s, especially 1950–1980, as identified by Andersen et al. (2018)—consistent with the hypothesis that agricultural innovations have reduced net incomes for U.S. farmers as a group.

This suggests something of a paradox.  Farmer groups have often been some of the biggest supporters of agricultural research and are proponents of productivity growth, while consumers have been skeptical if not hostile toward many productivity-enhancing technologies on the farm.  Yet, it is likely food consumers that have received the lion's share of the benefits from increases in agricultural productivity through greater food security and lower food prices.  

Wizards and Prophets

I've been reading Charles Mann's latest book Wizards and Prophets, which was released earlier this year.  Overall, I've enjoyed the book.  The subtitle, "Two Remarkable Scientists and Their Dueling Visions to Shape Tomorrow's World" is an apt description for much of the content, which describes food, agricultural, and environmental problems through the lens of Norman Borlaug and William Vogt.  The history is informative, and Mann gives a fair comparison of the underlying philosophical differences, which he attributes to Borlaug and Vogt, driving much of the debate today around food, agriculture, and the environment. 

I am very much in the "Borlaug-wizard camp" (which advocates for innovation, science, research to solve food security and environmental problems) but I came away with a better appreciation for the Vogt-ian, prophet point of view (focused on resource constraints, ecological limits, need to reduce consumption, etc).  

While I thought the book was well done and well worth reading, Mann gets one aspect of this debate wrong.  Because I've seen other writers make the same mistaken point, it's worth delving into a bit.

Throughout the book, Mann refers to the Borlaug way of thinking as "top down" and the "hard way," and he contrasts this with Vogt's approach which he depicts as "bottom up", "localized", etc.  This is exactly backward. 

Mann aptly describes a core belief among the prophets: that there are finite resources on earth and just like any other species, we will grow exponentially until we exhaust our resources, and then our population and civilization will collapse. The analogy is a jar filled with few fruit flies given a fixed amount of food.  Initially, the flies have ample resources and they multiple rapidly.  However, at some point the population becomes too large for the fixed food supply, and the population collapses.  The fruit fly population follows something like an S-shaped curve over time.

Moving from flies to people, the issue is typically described in a Malthusian manner.  As the graph below shows, as we add more labor to a fixed amount of land, diminishing marginal returns kick in and the amount of food available per worker eventually falls.

malthus1.JPG

If this resource-constrained view is a core belief, how do you solve the problem?  Adherents to this point of view typically urge folks to consume less or use less resource-intensive systems/products or to constrain population in some way.  But, most individuals don't want less.  Particularly folks in the developing world - they want to have and consume the things those us in the developed world enjoy, whether it be meat, air conditioning, ipads, or MRIs.  Yes, persuasion may result in a few people cutting back, but not on a scale that matches the magnitude of the problem.  Thus, the only fully effective way for the prophets to accomplish their goal (preventing catastrophic collapse) is to force or constrain the population to adopt outcomes few individuals would choose on their own.  Thus, the call for policies to mandate a cap on the number of children one can have (as occurred in China), restrictions of resource use, taxes, bans, etc. In other words, top-down planning is required to constrain growth and population, which is often manifested in "one size fits all" or highly non-localized policies.  Just recall of all the clamoring by Vogt-type adherents when Trump decided to pull out of the Paris accord that had global (i.e., non-local) prescriptions to fight climate change [note: I'm not advocating for or against the Paris accord, only noting that it is non-local and more-or-less top-down).  

The wizardly Borlaug view, by contrast, operates via entrepreneurial innovation and individual decisions of whether to adopt or not.  When Borlaug worked for the Rockefeller foundation, he/they had no "power" to force individual farms to adopt their new seeds and production practices, rather as Mann himself reveals, the early Mexican adopters took on the new seeds precisely because they saw for themselves via Borlaug's demonstration plots that they could achieve higher yields.  Yes, the types of seeds and production practices developed by Borlaug et al. spread far and wide, but it is was largely because they "worked" not because it was mandated from on high.  And, the adoption was much more adapted to local conditions than Mann lets on.  Producers in different locations ultimately used different varieties, different irrigation and fertilization techniques, etc.  As time has gone on, precision agriculture has led to even more localization of management decisions.  

The promise and hope of the Wizard is that innovation can get us off the curve shown in the graph above and move us to a new, higher outcome, as shown below. 

malthus2.JPG

This isn't a denial of resource constraints, it is a recognition that innovation allows us to get more with the same or fewer or even different resources.  But, for those innovations to be adopted, they must pass the market test.  Real life-farmers and consumers need to choose to adopt them (or not). This is precisely the opposite of top-down.

Here's what I wrote a while back when Nassim Taleb referred to GMOs as a "top down" technology. 

Taleb makes reference to the Hayek bottom-up vs. top-down planning. He says GMOs are the top-down sort. I’m not so sure. Real life farmers and people have to be willing to buy varieties that have the GMO traits. No one is forcing that outcome. It is true that competition will limit - to some extent - the diversity of plants and genetics that are observed because some plants aren’t tasty or aren’t high enough yielding. But most plant breeders keep all kinds of “ancient” varieties precisely for the purpose of trying to breed in new traits to today’s varieties (and folks working on synthetic biology are creating their own, new strands of DNA, creating new diversity). Geography also increases diversity. Iowa grows a lot of corn, Oklahoma doesn’t because it isn’t our comparative advantage. I see little reason to believe that a single GMO variety will perform well in all locations. So, yes individual companies are planning and creating new varieties, but it is all our local knowledge of what works in our places and conditions that determine whether particular genetics offered by a particular company are used. We do not have a seed czar or a DNA czar.

How to Feed the World

That's the title of a new book edited by Jessica Eise and Ken Foster that was just released last week.  The book is a collection of essays primarily from my colleagues in the Department of Agricultural Economics here at Purdue, but it includes contributions from Purdue faculty in other academic disciplines as well.  I had the privilege of writing the afterward.  

Here is the table of contents:

Chapter 1. Inhabitants of Earth- Brigitte S Walforf
Chapter 2. The Green, Blue, and Gray Water Rainbow- Laura C Bowling and Keith A Cherkauer
Chapter 3. The Land that Shapes and Sustains Us- Otto Doering and Ann Sorensen
Chapter 4. Our Changing Climate- Jeff Dukes and Thomas W Hertel
Chapter 5. The Technology Ticket- Uris Baldos
Chapter 6. Systems- Michael Gunderson, Ariana Torres, Michael Boehlje, and Rhonda Phillips
Chapter 7. Tangled Trade- Thomas W Hertel
Chapter 8. Spoiled, Rotten, and Left Behind- Ken Foster
Chapter 9. Tipping the Scales on Health- Steven Y Wu
Chapter 10. Social License to Operate- Nicole J Olynk Widmar
Chapter 11. The Information Hinge- Jessica Eise
Chapter 12. Achieving Equal Access- Gerald Shively

eisebook.JPG