How much yield is enough?

Last week, two colleagues and I published a paper in PLOS ONE titled “Commercial crop yields reveal strengths and weaknesses for organic agriculture in the United States.” The article presents an analysis of USDA crop yield data to compare organic and conventional farms in the US. We were pretty careful in the paper not to overstate our conclusions, since our goal was simply to see where organic yields were competitive (or not) with conventional crop yields. I explain more about why we did the study over at In that post, I wrote:

I’d like to address some things our paper is not. We are not saying that organic farming is better or worse than conventional farming, and our analysis simply can’t justify such a broad conclusion. Simply analyzing differences in commercial yields (as we have done) is insufficient to choose a “winner” with respect to farming systems. Lower yield is not, in itself, evidence that farming is “harming the environment.”

Not long after it was published, though, our study was used by Alex Berezow at the American Council on Science and Health to do just that. Our paper was used to support a questionable conclusion regarding sustainability:

Another justification for organic food is that it is more sustainable and environmentally friendly. Those myths, too, already have been exposed, but a new paper in PLoS ONE puts another nail into the coffin.

[The lower yield in organic agriculture] violates the very notion of sustainability. An inefficient food production system that cannot feed everybody is, by definition, not sustainable.

Yes, a society must absolutely be able to feed itself. And I agree that yield is a critically important factor to evaluate when discussing the sustainability of cropping systems. I even think it is reasonable to assume that there is some minimum yield threshold required to consider a set of cropping practices sustainable. But I don’t think defining that minimum threshold is as simple as “X percent less than my preferred cropping practices.” I disagree with the notion that organic farms are inherently less sustainable simply because they currently produce less yield per acre than conventional US agriculture.¹

To explain my reasoning, it is helpful to understand some terms that will be familiar to most students who’ve studied agronomy or pest management. The figure below represents the spectrum of possible crop yields ranging from next to nothing (on the left) to next to impossible (on the right). Primitive yield is basically what you would get if you planted the seed and walked away until harvest. No management, no fertilizer, no irrigation or pesticides or anything else. Just put the seed in the ground and wait. For many annual crops, the primitive yield is often very close to zero. On the far right of the spectrum is the theoretical yield. Defining this value is largely an academic pursuit because we will likely never observe it in the field (though our children might). Theoretical yield is a target for breeders & agronomists to strive for. We can predict a theoretical yield based on the physics of photosynthesis and the energy of the sun and the carbon dioxide concentration in the air and all the other factors that determine a plant’s ability to produce a marketable product. But the theoretical yield has no practical value to a farmer.


The region between these extremes is where farmers actually reside when it comes to crop production. The attainable yield is the crop yield that is actually possible, but only under extremely intense management. Yield contests like the one sponsored by the National Corn Growers Association are a fun way to estimate the attainable yield on a year to year basis. The attainable yield is as far to the right of the yield spectrum as we can get given our current knowledge and technology. The economic yield is pretty much what it sounds like; it is the level of yield that maximizes net economic return to the farmer. Economic yield depends not only on crop yield, but also the price a farmer will be paid for the crop, the cost of all the inputs, the response of the crop to those inputs, etc. The economic yield is a constantly moving target that most farmers are aiming for every year.

As we learn more about crop production and develop new methods and new technologies, we continually push the attainable and theoretical yield higher and higher. In general, the economic yield tends to move in the same direction (though with many more bumps along the way due to various external factors, including things like farm policy and labor availability). But it is always true that the economic yield is less than the attainable yield. It is simply not cost effective to produce the maximum possible yield on a large scale. Farmers would lose money and quickly go out of business if they constantly pursued the attainable yield. In the yield contests and experimental plots where attainable yield is actually achieved, only a few acres are devoted to this effort.

On a vast majority of farm acres in the US and elsewhere, farmers do not attempt to maximize yield. No agronomy professor worth their paycheck would advise a student to maximize yield at all cost. Farmers (both conventional and organic) make decisions every single year that reduce the yield potential of their farm. Below are some examples of production decisions that farmers I know personally have made:

  • Purchasing a lower yielding crop variety because it is more resistant to a common disease or pest in their area to avoid having to spray a fungicide.
  • Choosing a variety that matures faster so they can harvest earlier to plant a winter crop afterwards.
  • Saving seed from their previous harvest instead of buying certified seed to reduce input costs.
  • Sacrificing a small section of a field to try and manage a vigorous weed infestation.
  • Not irrigating a corner of a field because the labor and added headaches is simply not worth the trouble during the busiest time of the growing season.
  • Not using a pesticide simply because it is deemed “too nasty” and the farmer doesn’t want to handle it.

Every one of the decisions above are reasonable given the farmers’ personal situation, and every one of these decisions reduced the yield of that farm. Farmers are humans, with values. And they farm in a way that is consistent with those values. I don’t think anyone would criticize a farmer making any of these decisions for being inherently unsustainable because they did not maximize yield.²

Because I prefer to work with data and numbers rather than purely theoretical endeavors, I quantified the impact these types of decisions have on yield by looking at US corn yield from 2014 (the same year we used for our PLOS ONE study). In 2014, the average US corn yield was 171 bushels per acre. We can assume that figure is a reasonable estimate of economic yield (though obviously with many caveats). The winners of the NCGA corn yield contest in 2014 produced an astonishing 503 bushels per acre! Pretty remarkable. This provides a pretty good estimate for attainable yield


On average, conventional farmers are only producing around 34% of attainable yield. If we are going to evaluate agricultural systems by yield alone, is this 66% yield gap of US conventional agriculture acceptable? Should we criticize conventional farmers for not producing even more yield, even if it is not in their best interests economically or environmentally? Do we call conventional agriculture a “hoax” or a “scam” because farmers make value-based decisions that prevent them from attaining maximum yield? Certainly not. Why, then, should we criticize an organic farmer who grows crops in a way that doesn’t maximize yield?

Organic farming has demonstrable benefits that many organic growers believe are worth the yield trade-off. We can certainly have a reasonable debate on whether those benefits are indeed worth the reduced yield, but these value judgments really aren’t so different than the decisions that conventional farmers make every year. Organic farmers have done the same internal calculus as conventional farmers, albeit with a different set of values and tools and incentives (such as the organic price premium). Organic farms are only 12% further behind the attainable corn yield than conventional farms, but they get labeled “unsustainable” for not producing enough. Why is it that the first 66% reduction in yield is acceptable and touted as “feeding the world” but an additional 12% reduction is considered inherently unsustainable?

I don’t claim to be a major supporter of organic agriculture. It is no secret that I think some of the restrictions in the USDA organic regulations are fairly arbitrary from a scientific standpoint, and I think that allowing targeted use of some currently-prohibited substances could increase both productivity and sustainability of organic systems. But the organic systems that have evolved in response to those restrictions represent a unique opportunity to learn more about all kinds of agriculture. A variety of benefits have been documented in these organic systems. If our goal is really to sustainably feed the increasing world population into the future, we need to take every opportunity to learn about what works and what doesn’t, both with respect to yield and also all of the other aspects of sustainability.

As we stated in our paper:

“[A]gricultural systems should not be judged on yield alone. A primary goal for agriculture of the future should be to produce enough food to feed a growing population, and to do so while minimizing the negative impacts of that production.

“Examination of commonalities and differences between organic and conventional production practices in states with the best and worst yield ratios could be informative. Detailed knowledge of these specific production systems is necessary to investigate these comparisons, presenting an important opportunity for cross-commodity collaboration as well.”

Evaluating “sustainability” is difficult, but I think just about everyone can agree that there are two sides to the sustainability equation; yield is important, but so is biodiversity, economics, social wellbeing, environmental impacts, and a host of other factors. Producing massive amounts of food in a way that destroys the environment is obviously unsustainable. Protecting the environment to the extent that millions of people go hungry is also obviously unsustainable. I think any reasonable person will agree that the answer lies somewhere between these two extremes. Continual focus on only one side of the sustainability equation makes it impossible to find truly sustainable options. Yes, we need to continue increasing realized crop yields to feed the world population, especially in developing regions where the conventional yield gap is greatest. But dismissing the benefits of organic agriculture simply because it yields less than conventional farming (which also don’t come even close to maximizing yield) seems like a pretty unscientific position to me.

UPDATE – August 30, 2016 —

There have been a few people taking issue with my decision to compare both the organic yield and the conventional yield to a common number (attainable yield) instead of comparing them directly to each other. Here is why I made that decision:

Percentages are, by definition, relative. If the goal is to compare one thing to another, then certainly, using one of those things as the reference is reasonable. That’s what we did in the original analysis, because that was the objective. But that’s not always the goal. Consider this analogy:

Jane and John want to buy a new toy that costs $5.00. There are lots of ways they could try to get that money.

  • SCENARIO 1: They go search the couch cushions. Jane finds a $0.10, and John finds $0.05.
  • SCENARIO 2: They set up competing lemonade stands across the street from each other. Jane makes $4.00 and John makes $2.00.
  • SCENARIO 3: They go through the neighborhood raking leaves. Jane makes $8.00 and John makes $4.00.
  • SCENARIO 4: They buy lottery tickets, and both win! Jane wins $150 million, and John wins $75 million.

In all 4 scenarios John has 50% as much money as Jane. But that tells us nothing about who is closer to their goal of buying the $5 toy. In the first scenario, even though Jane has twice as much money as John, they are only 1 and 2% of the way to their goal. In the second scenario, neither has reached the goal but Jane is much closer (80% of the way) while John is still quite far behind (only 40% of the goal). And in scenario 4, a $5 toy would be a trivial cost to both of them. So which is more useful in this case? Comparing them to each other? Or comparing each of them to their common goal?

The point of this post was to ask the question “How much yield is enough?” Hence the title. Farmers have a shared goal. We can debate what that ultimate goal should be, but comparing them to each other is less useful and less productive than comparing them to the common goal for this purpose. It is not misleading or lying. It is an attempt to change the reference point, and change the conversation so that we stop taking sides.

¹ There are aspects of organic agriculture (as defined by USDA) that I believe are unsustainable over the long-term, but that’s another topic entirely… here I want to focus exclusively on the yield question.

² Granted, conventional farmers get criticized (quite loudly) for an entirely different set of reasons including doing too much to increase yield; like using fertilizer and pesticides and tillage. Everyone’s a critic.

³ The top 3 producers in the 2014 NCGA contest exceeded 503 bu/A. Geography was likely a factor, since these three producers came from southern states with a longer growing season (Virginia and Texas). However, the statewide corn yield for Virginia in 2014 was only 145 bu/A (less than the national average). The statewide irrigated corn yield for Texas was 202 bu/A, which is greater than the national average, but still significantly less than the 500 bu/A mark.

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