Q: Is there a way to nudge plants toward producing more exudates?
A: According to Dr. Christine Jones, 90 percent of all of the carbon contained in root exudates is stable in the soil. So, if you want to build soil organic matter in the long term, you have to build lots of root exudates in the soil profile.
And yes, there is a way to move plants in the direction of producing a higher percentage of exudates: simply increase photosynthesis levels.
What we consider to be common today is plants that are photosynthesizing at about 15 to 20 percent of their inherent photosynthetic capacity. In an outdoor agricultural environment, it’s very reasonable to expect to be able to triple that number — to go from 20 percent up to about 60 percent. In ideal conditions, you can go beyond that — if plants have ideal sunlight, ideal temperature, ideal carbon dioxide, and ideal moisture — those the four big variables. But getting up to 60 percent is not difficult to achieve.
But then what happens when you get triple the sugar production? Does that mean you get triple the yield or triple the plant biomass? Usually not. You might get 60 or 80 percent larger plants, depending on the crop, or you might even get double the plant size. And you might also get 60 or 80 percent increase in grain yield. But that increase in vegetative biomass and reproductive biomass isn’t enough to account for all the additional sugar that’s produced. All of that extra sugar goes out through the root system as exudates.
So, the easy way to increase root exudates significantly is simply to increase photosynthesis. When you increase photosynthesis, root exudates increase disproportionately — faster than anything else — and more stable soil carbon is built up.
From John Kempf’s Eco-Ag U session at the 2024 Acres U.S.A. conference.
