Photosynthesis is not a ‘constant’

Photosynthesis does not occur at a constant rate of speed. It varies from moment to moment dependent on the availability of light, carbon dioxide, water, temperature, chlorophyll concentrations, plant nutrition and genetics. This seems obvious on the surface, yet is almost always missed during research.

We understand that limitations on water, or nitrogen, or temperature extremes can have a pronounced impact on photosynthesis and consequently on plant growth and yield.

In contrast to this ‘downside potential’ of photosynthesis limitations, there is also an ‘upside potential’.

When environment and nutrition is optimized, plants can photosynthesize much more rapidly than what is ‘common’ or ‘normal’ (depending on how you define normal).

An extreme example is tomato production in greenhouses in the Netherlands, where yields are reaching up to 100 kg per square meter, equal to 890,000 lbs per acre. (No, that is not a typo, and it does not include an accidental additional zero.) Field grown fresh market tomato yields in the US range from 30,000 to 50,000 lb per acre, or about 6% of the yields in the greenhouses. To produce those results, lighting, CO2, and nutrition are all being managed very tightly.

This perspective on managing photosynthesis is very valuable when we think about how to increase yields and crop performance, and is often overlooked.

Very importantly, photosynthetic variability is completely overlooked in carbon sequestration research.

Research reports that this or that ecosystem can sequester xx amount of carbon. Grasslands at a certain level, forests at a certain level, farmland at a certain level.

The research, and the predictions coming from that research, contain the flawed assumption that the rate of photosynthesis is a constant from season to season.

Some fields/regions will photosynthesize less and sequester less carbon than the research indicates, because of a challenged environment.

Some fields and regions have the capacity to photosynthesize and sequester carbon at rates multiples higher than the research indicates.

As photosynthesis varies, so does root exudation, carbohydrate partitioning, disease resistance, insect resistance, crop response to microbial inoculants, fertilizers, and sprays.

All research evaluating the performance of products or practices on crops should contain the parameter, “what was the rate of photosynthesis in the plants contained in the study?” When this highly variable parameter is ignored, research does not translate consistently to other fields and farms.

Valuation of regenerative agriculture management

How do we value the ecosystems services that regenerative agriculture management contributes? How do we account the cost of ecosystem damages that present mainstream agriculture contributes? Some thoughts from Jerry Hatfield:

From the Regenerative Agriculture Podcast with Jerry Hatfield:

John: And because we can’t see into it very well, we struggle to understand how to value it. What is the true value of biology? And I think this is a particularly challenging question in the context of agriculture because our agricultural economics are screwed up. We have an agribusiness ecosystem that has developed in which our crops have generally become commodities, operating on very low margins, combined with the challenge that we have historically externalized many of our costs. We have externalized the environmental pollution that has been caused by some of the toxins and pesticides that we’ve used—fertilizers, nitrates in water, etc.

So, when we look at all these factors from a macro perspective, what is the value of regenerative agriculture? What’s the cost of it? And what’s the return?

Jerry: I’ve often given talks to people who’ve asked the value of carbon, and I tell them it’s priceless. But they don’t want to accept that answer.

I think we’re at the point in agriculture where we need to move away from just talking about agriculture and begin to think about agroecology. How does agriculture fit into the ecological system? What’s the value of its different ecosystem services? What is the impact of agriculture on water quality, on water quantity? What’s the impact on the biological services that we see within the soil? What’s the impact on the biological activity we see associated with that agricultural field? How do we even look at that landscape from a different perspective? So, I think that when we start looking at that context of agriculture, then we can really have a fruitful discussion about the value of regenerative agriculture.

In regenerative agriculture, as we improve carbon, we improve water. And we also improve nutrient cycling within the soil. And not only nitrogen, but phosphorus and potassium and all the micronutrients. All of those pieces are now linked together, and those things pay me dividends.

As an example, take a silt-loam soil with 2 percent organic matter in it, and assume five-foot-tall corn in the middle of August in the Midwest. This is using water at its maximum rate. That plant has about eight days of available water before it begins to be stressed.

That’s not very much. But if there’s 4 percent organic matter, the plant can go for thirteen days without water. You’ve got five more days of available water for that plant to perform to its optimum, without stress. The probability of getting rainfall during a five-day period across the Midwest is still pretty good. My point is that this is one of the ways regenerative agriculture produces value.

The other thing we see is that when we enhance nutrient cycling, we have a greener plant—a more photosynthetically efficient plant—so that more carbohydrates go into that plant. This not only improves grain production—it also continues to feed that root system so that it becomes more effective all the time.

That’s where yield stability comes from. We will become less affected by the weather variation that is going on—the longer periods of time between rainfall events.

You’ll always have parts of a field that are low yielding. The high-yielding parts of that field are always really good soils. The low-yielding parts are always those really poor soils that have low water availability and low nutrient availability.

Losing a thousand pounds of carbon per acre per year

From the Regenerative Agriculture Podcast with Jerry Hatfield:

John: When I think about the differences between sustainable agriculture and regenerative agriculture, the approach we’ve taken in our work is that regenerative agriculture is all about helping plants get to peak photosynthesis, produce an abundance of carbohydrates, and move those carbohydrates into the soil, where you have a very functional carbon cycle working. You’re constantly accelerating plant health and constantly accelerating soil health.

What I’ve realized is that when we think about the entire soil-plant system—as an ecosystem—you have photosynthesis, which is the way you bring new energy into the ecosystem, and you have soil biology, which processes that energy into soil. And that total energy flow—voltage, if you will—is reflected in the carbon cycle, the carbon exchange.

How does the carbon cycle shift and change when growers begin managing soils and crops differently—with regenerative management, rather than with present mainstream management?

Jerry: We do a lot of work in corn-soybean systems. Over the past seventeen years, looking at the exchanges of carbon between the plant, the atmosphere, and the soil, we’ve shown that our typical corn-soybean system is losing a thousand pounds of carbon per acre per year. This is with maybe a deep rip in the fall and field cultivation in spring, and the only thing taken off the land is the grain of corn and soybeans.

And think about the average life of a producer. Farming forty years, they’ve lost 40,000 pounds of carbon—twenty tons. It’s a slow loss, but that slow loss is impacting the aggregate stability of their soils. The farmer realizes he’s losing productivity, that it’s different than it was before, but he doesn’t come to the realization that it’s the cumulative effect of what he’s been doing over his farming career.

That’s a dynamic that we need to consider when we talk about why fields become variable overtime. But on the other hand, we can change that system quickly. And I think this is the framework that we need to be talking about. When we go to a system where we add cover crops, and we reduce the tillage intensity by going to strip-till or no-till, we find that within one year we can change that negative carbon balance into a positive carbon balance. Then we can put more dividends from that plant back into the soil biology. We go from a negative to a positive carbon balance.

John: In a single year? That is amazing.

Jerry: Yes, and even more amazing is that over a two-year period we doubled the microbial biomass in the upper twelve inches of that profile. And these are not test plots. These are 160-acre fields, and they’re sampled at 150-foot grids. So there are a large number of samples coming out of those 160 acres. We were able to improve the biology very, very quickly.

And we’ve already begun to change the upper surface of that soil. The cover crop is giving us a longer period of time in which to take carbon dioxide out of the atmosphere—converting it into carbohydrates, putting it back into the soil, and feeding that soil biology.

I always tell producers that biology wants four things. It wants food, water, air, and shelter. These are the basic necessities of life that you and I want. We should start thinking about biology from that perspective. They want a food source, just like you and I like to eat every day. In a lot of our systems we were only growing a crop during the summer. There was a long period of time on either end of the growing season when we weren’t feeding the soil biology. It had to exist on what was there, and that’s pretty much a starvation diet. If we didn’t eat three months out of a year, we’d probably be fairly thin.

Cover crops utilize a lot of solar radiation. If we don’t have a crop growing, that sunlight is just going into the surface of the earth and isn’t doing anything for us.

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