By John Kempf
Properly designed foliar applications are one of the most effective tools to rapidly build soil organic matter and regenerate soil health.
Yes, you read that correctly. Properly designed foliar applications harness the plant’s photosynthetic engine, accelerate carbon sequestration and build soil organic matter more rapidly than almost any other management tool.
Healthy plants are the engine that creates healthy soil. While healthy soil can produce healthy plants, that healthy soil was created by plants in the first place — plants that were photosynthesizing, sequestering carbon and building soil organic matter through root exudates and biomass accumulation in the soil profile. Without plants’ contribution to soil health, soil would consist only of decomposed rock.
However, not all plants have the same contribution to sequestering carbon, building soil organic matter and regenerating soil health, because not all plants are photosynthesizing at the same rate of efficiency. It is common for many crops today to be photosynthesizing at only 15 to 25 percent of their inherent photosynthetic capacity. While this can be measured in the laboratory, it can also be observed experientially in the field when we observe crops producing only 15 to 20 percent of the yields they are genetically capable of producing. We can also measure the sugar content of plant sap using sap analysis or Brix readings as an analog for photosynthetic efficiency. It is common to observe crops with Brix levels of three or four increase to as much as 12-16 or higher when supplied with optimal nutrition from foliar applications.
The volume of photosynthesis in each leaf will vary based on chlorophyll concentrations, leaf thickness and leaf size, all of which are heavily influenced by nutrition. As photosynthesis increases and larger volumes of sugar are produced in each 24-hour photoperiod, sugars are partitioned to the plant sugar sinks differently.
Plants have four primary sugar sinks: the growing shoots, growing roots, fruit/seed and root exudates. Sugars are moved to the different sugars sinks in different volumes at different stages of physiological development.
The ultimate drive for a crop is to successfully reproduce. Because of this, plants will do everything they can to move sugars into the seeds or fruit, even if that means they need to sabotage other parts of the plant to do so. This is why much of the current-day corn crop dies early, both from the top down and from the bottom up. Sugars and nutrients are being pulled from both directions in toward the center and into the grain.
When we consider the quantity of sugar produced over the course of an entire season on an annual crop such as corn, the sum total sugar production would be the equivalent of 100 percent. As an example, let’s say that an average corn crop produces a total of 18,000 pounds of carbohydrates per acre in a single growing season and yields about 180 bushels of grain. The 180 bushels of grain will contain approximately 6,500 pounds of carbohydrates, or 35 percent of the total. Another 35 percent, 6,500 pounds, gets used to build above-ground plant biomass. About 15 percent, or 2700 pounds, is used to build root biomass, and the remaining 15 percent is sent out through the roots as root exudates to feed soil biology.
This is what the carbohydrate distribution in a “normal” corn crop would look like today. We know from Charles Tsai’s work that modern corn genetics are capable of producing 1,100 bushels per acre from a biochemical/photosynthesis/epigenetic potential. Thus, if we are producing only 180 bushels per acre, these corn plants are photosynthesizing at only 15-18 percent of the crop’s inherent genetic potential.
As we begin using foliar applications we can increase a corn crop’s rate of photosynthesis from 15-18 percent up to, say 30 percent. This will have effect of doubling the quantity of sugars being formed in each 24-hour photoperiod. But will it also double the yields? Probably not. Here is why: as the sugar production increases, the plant is no longer in survival/reproduction-only mode, and it will begin to partition sugars to the various sugar sinks in completely different ratios.
When a corn plant is in “starvation mode” at 15 percent photosynthesis, it will move as much as 35% of its total photosynthate production to the grain to ensure that it can successfully reproduce. Once photosynthetic efficiency increases up to 30 percent, it is no longer in starvation mode, and a much smaller percentage of the sugars move into the grain because the plant recognizes it now has a surplus of energy.
For a corn plant at 30 percent photosynthetic efficiency, the total sugar production has doubled, from 18,000 to 36,000 pounds per acre. The carbohydrate distribution numbers will look completely different. Above-ground plant biomass will represent approximately 25 percent, or about 9,000 pounds. Grain will represent another 25 percent, and 9,000 pounds. Root biomass and root exudates each represent an additional 25 percent, for a total of 18,000 pounds contained under the soil surface.
Look at the difference between these two corn crops! One is yielding 180 bushels per acre and is contributing 5,400 pounds of carbohydrates per acre below the soil surface as root biomass and root exudates. The second is yielding about 250 bushel per acre and is contributing 18,000 pounds of carbohydrates below the soil surface. The second crop is contributing three times more carbohydrates to soil organic matter.
But there is more. Crop residue is not all converted to stable humic substances in the soil profile with the same efficiency. About 25-30 percent of above-ground crop biomass that is incorporated into soil is converted to stable organic matter. Approximately 50 percent of root biomass is converted and about 70 percent of root exudates. There is a much bigger organic matter gain from the second crop that can be accounted for by only looking at the carbohydrate distribution, because a greater portion of the carbohydrate contribution is coming from roots and root exudates than from crop residue. This explains why healthy corn crops can build soil organic matter by as much as 0.25-0.35 percent per year or more. The popular wisdom during the ’60s and ’70s was that the fastest way to build soil organic matter was to grow corn. Today, we have the idea that the fastest way to lose organic matter is to grow corn. What has changed is our management practices and the nutrition available from soil reserves that can increase photosynthesis, particularly carbon dioxide.
The principle of increasing photosynthetic efficiency holds true for all crops, not just corn. Corn is only a convenient example, because it has been studied more.
How can we increase a crop’s photosynthetic rate from a low baseline to a much higher level of performance? Optimal photosynthesis requires these four things: abundant carbon dioxide, adequate water, sunlight and a suite of minerals that are directly or indirectly involved in the photosynthesis process. Carbon dioxide and water are often limiting factors, and we will look at what is required to provide a generous supply in a future article.
The key to rapidly producing plants with much higher levels of photosynthesis is not to rely on soil amendments and remineralization. These are valuable and important tools, but they are not enough, and they take too long. To “hack the system,” we need to harness the plant’s photosynthetic engine and accelerate its momentum quickly. The tool that can do this most effectively is foliar applications.
Generally within agriculture, we have not given enough credit and appreciation to the response foliars can deliver because we have not used well-designed foliars. Well-designed foliar applications are the shortcut to success that can allow us to almost immediately speed up plant photosynthesis and yield potential.
We need to begin thinking of foliars as a foundational part of regenerative agriculture systems. The proper use of a foliar application is to increase the volume of photosynthesis. A foliar that does not deliver this response was not as effective as it might have been. We should be able to measure an increase in sugar content on a sap analysis after a foliar application.
When we begin with a crop that has a low sugar content, and a low Brix reading, let’s say a reading of 3, we then apply a foliar application and the Brix reading jumps from 3 to 10. After a period of time, the Brix reading drops back down again, perhaps to a 4. We can apply a second foliar application, and it jumps back up to 12. Over time, it drops back down to a 5 or 6. Over multiple applications, the intent of foliar application is to increase the baseline photosynthesis to a high-enough plateau where the crop is completely disease and insect resistant and is no longer dependent on any foliar applications.
The amount of time before photosynthesis drops back down can vary from as little as 2-3 days to as long as 5-6 weeks. The healthier the crop, the less product needs to be applied in a folia and the longer the crop response will last.
When foliar applications are not properly designed, they not only have the effect of increasing photosynthesis — they can have the effect of depleting soil nutrients, because they allow plants to grow at a higher rate than the soils would normally maintain. Well-designed foliars increase photosynthesis, which results in increased microbial populations and organic matter, resulting in a larger supply of minerals available from the soil.
As crops with a high degree of photosynthesis begin regenerating soil health and rebuilding soil organic matter, the entire soil/plant ecosystem can arrive at such a high degree of health that foliar applications are not needed to maintain it. At this point we can have a legitimate discussion about sustainability. First, though, we need regenerative agriculture systems, and all true regenerative agriculture models must necessarily harness the plant’s untapped photosynthetic engine, because this is the only way we have of bringing new energy into an ecosystem.
Healthy plants regenerate soil and create healthy soil. Let’s use foliars to quickly develop healthy plants even when our soils remain temporarily unhealthy.
John Kempf is the founder of Advancing Eco Agriculture, a plant nutrition and biostimulants consulting company. John is the host of the Regenerative Agriculture Podcast, where he interviews top scientists and growers about the science and principles of implementing regenerative agriculture on a large scale. This article appeared in the July 2019 edition of Acres U.S.A.
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