The Shape of Yields to Come

great pumpkin
A pumpkin fit for Linus. This behemoth weighed 2,624.6 pounds (1,190.5 kg), claiming a new world record October 9, 2016 for Belgian grower Mathias Willemijns at the Giant Pumpkin European Championship in Ludwigsburg, Germany. How much further up can humans push the yield curve? Image credit: Thomas Kienzle/Agence France-Presse/Getty Images

An article in AgFunder News published February 1, 2018 reported that a bag of corn had a yield potential of about 500 bushels per acre. In 2017, the US average corn grain yield hovered around 176 bushels per acre, 2 bushels above 2016 and far away from the AgFunder News report. Meanwhile, in 2015 David Hula of Charles City, Virginia produced 532 bushels per acre; the year before, Randy Dowdy of Valdosta, Georgia marked 504 bushels per acre. This caught many experts off guard, sending them back to their research plots to figure out what they were doing. A few even criticized the yield figures as faked.  In fact, the biophysical limit for corn grain yield was estimated by Matthijs Tollenaar in 1985 at ~1,320 bushels per acre using optimized, yet realistic, levels of quantum efficiency, grain fill duration, harvest and leaf area index parameters. At the time Tollenaar published his estimates, Herman Warsaw had just produced a (then) record-breaking 370 bushels per acre on his Illinois farm.

If you have never heard of Herman Warsaw, I invite you to watch a three-part film about him produced by the Office of Agricultural Communications at the University of Illinois in 1986. All told, the film is less than 30 minutes. And yes, it is dated, having the pedagogic look and intonation of flicks you may have been forced to watch in some long-ago high school class. But Herman Warsaw’s challenge to question, study, and judge carefully the factors limiting production remain timeless. He was also an early conservation tillage adopter who relied on non-inversion chisel plowing for residue management and soil building on his farm. Warsaw, Hula, and Dowdy all produced their record breaking yields with no appeal to big data or drones, and in Warsaw’s case, before the advent of precision soil management and GPS guidance. Herman Warsaw passed away in 1989 just prior to the twin revolutions in plant breeding and genetics. Since then, technology has advanced light years. Yet as recent US average corn grain yields admonish, the yield curve, though an increasing function, is a stubborn thing that is not easily borne aloft.

Precision soil sampling is one path for building crop yields. Herman Warsaw stressed high soil test levels for plant-essential nutrients like potash and phosphate. The film shows him manually pushing a steel probe into the soil, as if underlining his commitment to sound nutrient management. The AgFunder News article also stresses soil testing, albeit using more modern automated systems. Yet there is one very peculiar fact about the Hula and Dowdy production systems that is different from that of Herman Warsaw: both rely heavily on fertigation for in-season nutrient management. In other words, Hula and Dowdy are by-passing their sandy, relatively nutrient-sparse southeastern Coastal Plain soils by doing tissue testing and focusing instead on feeding nutrients directly to the plant. I know this isn’t music to soil scientists, but this approach overcomes many inherent physical and chemical factors in a growing medium that for all practical purposes, can’t be changed, or requires long-term devotional soil building to nudge up the metrics. It also calls into question the scientific orthodoxy saying that “the answer lies in the soil”.

Or does it?

There is nothing wrong with soil building, cover crops, organic matter, rotational or strip cropping, and the like. Each may have its place in the production system, depending on the interest and goals of the operator. Crop failure and/or under-performance are crucial factors when devising a management plan. In the film, someone is heard asking Herman Warsaw why he didn’t plant all his corn at the highest population density so that he could be producing 370 bushels on every acre. His reply was that the risk of crop failure and/or crop losses would be too great because not all his land is equally endowed and the weather in any growing season was too uncertain. By varying plant population and hybrids across his operation, corn yields would come out better, on average, he contended. The bottom line is, a lot of things must line up just perfectly even to reach 300 bushels per acre, let alone 500. This is one reason operators must continually calibrate their inputs and adapt agronomic practices year-to-year to stay solvent.

To use a music analogy, farming is like conducting a hundred-piece symphony orchestra wherein each piece must have perfect balance and pitch to achieve the desired effect. Every single off-note, errant staccato, or minor second, puts the whole movement out of sync in some small yet not inconsequential way. To give an example in farming, ground conditions often are not amenable to heavy equipment traffic during the critical periods of plant growth when yield potential is being formed or ‘sinks’ are actively filling. This period also usually coincides with field operations like side-dressing, cultivation, and pest control prior to the plant canopy closing in. After then it is up to the gods, who may be crazy or not. It stands to reason that operators would like to harness the plant-soil-water realm for as long as possible to mitigate risk, the gods be damned. This is where modern technology and human ingenuity both come into play. Operators are questioning time-honored orthodoxy and figuring out how to produce big corn, soybeans, pumpkins, you name it.  We should not stand in the way because they challenge our cherished ideas or threaten our professional conceits. Aerial and over-and under-canopy programmable machine detection and delivery systems are evolving rapidly, driven by the unrelenting need for reducing uncertainty, increasing control, and maximizing efficiency. This is how we will reach 500 bushels per acre and beyond. It is how we will continue managing to feed the world’s population even as living standards rise.

I don’t want to downplay the importance of soil mineral nutrition, and soil testing generally, but so often this is not what is limiting yield. Drainage, growing degree days (GDDs), relative humidity, evapotranspiration-water balance mismatch, plant nutrient uptake, and a host of other biophysical factors can down-rate yield regardless of the level of mineral nutrients or their placement in the soil. Going back to the symphony analogy, these are the musical mishaps that, collectively, determine the shape of yields to come, and whether this year will be record busting or simply a bust.

Each season promises a new beginning for the farmer, a clear ground upon which he or she will leave fresh tracks, so inscribing a record of their deeds. He’s hoping that your tracks lead to bathtub-size squash, 20-row ears of corn, triple-digit soybeans, and gluten-full wheat.


Reetz, H.F. 2000. Producing high corn yields-Herman Warsaw’s challenging legacy. Better Crops vol. 84. International Potash and Phosphate Institute.$webindex/768E8C2C854019AE852568EF00543357/$file/00-1p20.pdf

Tollenaar, M. 1985. What is the current upper limit of corn productivity? Proceedings of the Conference on Physiology, Biochemistry and Chemistry Associated with Maximum Yield Corn. Foundation for Agronomic Research and Potash and Phosphate Institute. St. Louis Missouri, 11-12 Nov. 1985.

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