How much can you increase photosynthesis levels beyond what is considered ‘normal’ today? Beyond what is common?

How much higher might national corn yields be, if the right incentives were aligned to produce the desire for higher corn yields? Could we have a 350 bushel national average yield? Don Huber suggests we had the capacity to do so with knowledge that existed in the 70s if we had the collective desire.

From our interview on the podcast episode here.

John: What is the potential for plants to increase the volume of photosynthesis?

Don: The potential is 100 percent. I mean, fivefold, tenfold—depending on where we are now and what plant we’re talking about. There a number of different ways to do that.

I mentioned plant morphology, but you can also do it by increasing light intensity. You got a lot of leaves on a garden plant—a mature corn plant at tasseling time—that aren’t getting very much sunlight. They’re not photosynthesizing at their potential because of that lack of sunlight. That’s where morphology comes in.

Plant spacing—we can increase the number of ears on a corn plant. There is tremendous work being done at Purdue, for instance, in corn breeding/genetics—they’re producing five and six ears on a corn plant. If you increase the efficiency of that plant, you don’t need as high a population. You can minimize that crowding and that shading effect.

We can reduce the allelopathic effect of our plants. To increase the population in corn, it’s very critical to have even germination. If you delay germination six to eight days, you automatically reduce the size of your ear by the allelopathic effect—that auto-intoxication effect of the root exudates on an adjacent plant—by as much as 80 percent.

John: Wow!

Don: When the John Deere MaxEmerge planter came out, I remember how it was almost an instant success because it increased the soil-seed interface—the contact that gave you that uniform emergence, to minimize that allelopathic auto-intoxication suppression that you otherwise had from those higher populations. We got an increased corn population and maintained full yield potential without the allelopathic chemicals reducing the overall production potential of that particular plant.

There a number of things we could do if we needed to. Right now we’re concerned about a surplus. The biggest thing is that necessity is still the mother of invention. But there’s plenty of potential there.

In one of our brainstorming sessions at Purdue we asked Charles Tsai what the biochemical genetic potential of a corn plant was. And a couple of weeks later, when we were all together, he said “I’ve got your answer.” We were shooting for 350, 400 bushels in our research. We knew that a lot of our better farmers—back in the late ’70s—had the potential for 550 or even 600 bushels. We were trying to design some systems for them to achieve that on a field basis.

And Charles sat down, and we said “Well, is 600 bushels a realistic figure?” And he said “You’re all pessimists. The biochemical genetics of the corn plant are about 1100 bushels.” That’s what we could do if we managed the environment and the plant in a proper manner and provided the expression.

We probably won’t come close to achieving that until the necessity is there. The limiting factor is the innovation of man. And as long as we’re doing okay—as long as we don’t have that burr under our saddle to look at both the genetics and the environment—we won’t have the need to maximize the expression of that genetic material.

John: What yields did you end up achieving on your yield trials?

Don: We could get 400 bushels. We had farmers that were getting 350. Of course, the average was still 75 bushels. They were doing three or four or five times what the average was on a major piece of land. They were able to do it because they recognized that they were managing an ecology. They started out with the soil. They had a beautiful soil.

I remember visiting Herman Warsaw’s farm. You could take a steel probe and you didn’t have to lean on it. You just pushed it in the soil three feet. He had that system working very well. In some of his neighbors’ fields you’d get the probe down three or four inches and you’d have to really put some pressure on it. To get it down a foot and a half you’d be driving it in.

I can’t tell you how many of the old ping tubes are still sitting out there in the field. Those were tubes that you could drive into the soil to collect soil samples—at three and four feet. And we had to get it into our soils using a sledgehammer. Then the problem was pulling it out. You would tear the metal off of the tube with a jack, and finally you’d just crimp it over so that it wouldn’t tear up the tire, and then you left it. A lot of them are still sitting out there in those fields because we didn’t have that concept— the soil wasn’t a major part of the management program. In general, we would look at the nutrients and forget that all parts of the ecology needed to be managed—to have better percolation, to have biology, to have air exchange—and most things have to take place if you want to capitalize on the genetic potential of the plant.

John: What were the plant populations that growers were using to achieve 350-plus bushels per acre?

Don: You had the old Pioneer 3532 seed—a hybrid that picked up 95 percent of its nitrogen by tasseling time and then merely recycled it. On sandy soils it was a great hybrid because you couldn’t maintain your nitrogen availability in those sands. It would take it up and store it, but it had a yield potential of about 125 bushels at 24,000 plants, which was our standard at the time. But you could increase the population of that particular variety because it didn’t have the allelopathic effects from the root exudate with high population. It had a fixed ear. So, as you increased the population, you still maintained that same ear length. It wasn’t big like your higher-yield hybrid, but it was very stable and it tolerated high populations. So they got the yield up by increasing population.

With our other varieties—our high-yielding varieties that were hybrids—there you had a flex ear that related to the environment more dynamically. The higher the yield potential, the more nitrogen you want as ammonium. For the 3532 variety a 50-50 ratio of ammonium/nitrate was optimum for it. And you get into the higher yield and the 250- to 300-bushel yields, you want 75 to 80 percent of your nitrogen as ammonium and only 10 to 20 percent as the nitrate source of nitrogen, because you want as much photosynthesis as possible to go into the kernel. When the plant utilizes nitrate nitrogen—and most plants can utilize either form equally well—it takes 15 to 20 percent of your photosynthate to reduce nitrate nitrogen back to the amine form so that the plant can utilize it.

And so the higher your yield potential, the more ammonium nitrogen you want—to provide those amino acids for that growth, and your enzymes and everything—and less nitrate nitrogen. We always found that there was a benefit to some nitrate nitrogen because it serves as a buffer—both to limit the drain on carbohydrates—if you have a high uptake of ammonium nitrogen, nitrate will tend to balance that—but also as a stable form of nitrogen. If you run short, then you can use some of that photosynthate.

If you have molybdenum and your other nutrients available, you have part of the function of your nitrate and nitrite reductase enzymes. Again, you have a different physiological pathway. And if you’re saying, “Well, I’m going to get most of mine from an ammoniacal source,” you may forget that you also have to have molybdenum for some of those other enzymes that aren’t quite as dynamic or quite as involved as they are if you’re relying more on the nitrate source.

Those are some of the things you could do to enhance that overall photosynthetic efficiency—the form of nitrogen is going to influence your soil biology and your buffering capacity in those areas.