Plant and Insect Communications in Biological Cropping Systems

Hi friends, I'm John Kemp, hosting this podcast. I am passionate about developing regenerative agriculture systems that improve soil health, produce crops that are completely resistant to diseases and insects, and produce fruit of such an exceptional quality that we can have a legitimate conversation about growing food as medicine. I've discovered that there are many people with incredible knowledge and information about soil and plant systems and how to develop regenerative agriculture systems. However, much of this knowledge and this information is scattered. It's found all over the place, some of it has been published in peer reviewed publications, but there are many incredible stories and a lot of knowledge that has not been published and that hasn't been shared with many people. I started advancing EcoAgriculture in 2006 to bring this knowledge together in a more coherent fashion and incorporate it into products and growing systems that growers can easily put into practice. It's my personal mission to have these regenerative agricultural systems become adopted globally and become the mainstream, the status quo against which all other growing systems are compared. To help achieve this goal, I want to share the knowledge that we have learned in the last decade and make it available to everyone while we have developed products at AEA that embody the principles of regenerative agriculture systems and make them easier for growers to apply this knowledge and these principles can be applied anywhere and when they are applied properly, they will always increase farm profitability and resilience to climate stress. If you have any questions, suggestions, comments or ideas, topics that you would like for me to discuss, Please connect on LinkedIn or on Twitter where my username is visionbuilder7 or you can also email me at john kempf.com I would very much like to hear from you and to hear your feedback. Be sure to subscribe to this podcast and thank you very much for listening. Enjoy the show.

Greetings friends and welcome to the Regenerative Agriculture Podcast. On this podcast we explore the science and the practical application of regenerative agriculture ecosystems, how to regenerate soil health, regenerate crop health and quality, and how to increase overall farm profitability. Our goal is to give you clear, easy to understand and actionable information that you can implement on your operation. In this episode, I'm very excited to welcome Dr. Larry Phelan, currently from Ohio State University. Onto the show, Larry has done some intriguing research over the years looking at plant and insect communication systems and what might increase plant susceptibility to various insect pests, as well as looking at the concept of biological buffering and the capacity of plants to Absorb nutrients from the slow profile in the form of microbial metabolites. Larry, we're very excited to have you on the show. Thank you so much for joining us.

Well, the pleasure is all mine. Thank you.

Larry, you've done some fascinating work over the years looking at many different aspects of soil and plant ecosystems. What are some of your most memorable moments that have led you to where you are today and led you to some of the projects that you were working on?

Well, first of all, I want to start off by saying that all that we do is generated by the observations and the experiences of farmers. And so I actually, when I this area of research represented a pretty significant career change for me. I was actually trained as what's called a chemical ecologist, which means we would identify pheromones and plant attractants for insects as possible alternatives to pesticides. But as I was doing this and started talking to organic farmers, one of the things that kept coming up was that they had fewer problems with insect pests than their conventional neighbors. This is not true necessarily of all crops, but these were field crops that I was talking about here and was really intrigued by that and found there was not that much known about that in the literature. And so talking to them, we basically formulated hypotheses to try to understand what it was that they were observing. So first of all, we did document that what they were saying was actually true. And pretty consistently we're seeing lower levels of insect damage. And so, yeah, that just really changed the direction of my research. And so now we. About 20, 25 years ago, I switched and we started focusing on the soil and the microbial community and nutrient cycling and all kinds of things that I really didn't know that much about at the time. But you kind of have to go where the data takes you.

With some of the original research that you did comparing the insect pressure on the organic farms versus the non organic farms, this is actually something that I often hear these stories from organic growers, but I haven't uncovered a lot of research where people have actually tried to do a comparison and evaluate the differences. So what were. I guess the question I would have for you is what were the differences that you were seeing? What really stood out for you?

Well, again, keep in context that this was 20, 25 years ago. There's been a lot more research in organic systems now, but at the time, you know, organic farming was considered very unscientific and more new age and not amenable to large scale production and all of that. And so I was working With a lot of organic farmers that were basically doing their own research, you know, not necessarily replicated research like we would do at the university, but trying different things and seeing what worked on their farm. And so this is the context in which we got started. And so I actually received a lot of criticism at the time that what I was doing was not very productive or not the direction that I should be going as an untenured faculty member particularly. But what we did was we went to these, in this case, these were corn, soybean farmers, and the organic producers were, I think, all the ones we worked with also raised animals, had animals integrated into their system as well. And first of all just did census of using, looking at their corn, looking at the levels of European corn borer damage in their fields versus their conventional neighbors. And as I'm sure you and many of your listeners have already often heard, I kept hearing this idea that if we have a healthy soil, then we're going to have a healthy plant, and insects don't like healthy plants, and so that's why they don't see the damage. And so again, I saw that as, although that in itself is not a very scientific statement, we could reformulate that as a hypothesis that we could test empirically. And so what we did was to collect soils from these organic farms and then go right across the street to a conventional neighbor, collect their soils, brought these soils into the greenhouse and planted them to corn, and either fertilized each of them, either with an organic fertilizer like manure or compost, or with a chemical fertilizer. And so what we were interested in figuring out was first of all whether the insects could tell a difference in these plants. And if they could tell a difference, was it associated with that, what I would call the short term effect of the type of fertilizer you use, or that long term effect of that history of management and how that impacted the soil community. And so after setting these plants up and letting them grow to a certain stage, we then released European corn borer females that had been mated into the greenhouse. And again, all of this was replicated and randomized and we just let them loose and see where they would lay their eggs. And what we found, very consistently we actually repeated this experiment, I think, with four or five different pairs of farms or soils from farms. Consistently we found if the plant was growing in a soil from an organic farm, irrespective of the fertilizer we applied, they received relatively few eggs. Whereas if that plant was growing in a plant or a soil from a Conventional farm. Sometimes they would receive a lot of eggs, and sometimes they would receive only a few eggs. And so this gave rise to this concept that I call biological buffering. So the way we envisioned this, and this was kind of our working hypothesis, was in that in those organic systems where you have a recurring influx of organic matter, either in terms of COVID crops or plant manures, or animal manures into those soils, you create this soil community which is beneficial to the plant. And so when nutrients then go into that system, they get absorbed by this microbial community, and then they release those nutrients very slowly over time. And as a result, we hypothesize that those plants are in better mineral balance than when you are putting down high levels of nutrients. Why this would be important is that plants are almost always limited by nitrogen levels. And so they don't have mechanisms for dampening the levels of nitrogen that they take up. They're going to take up whatever they can get. And in this context of putting down inorganic, highly soluble nitrogen sources, often these plants are taking up much higher levels of nitrogen than they are really set up to deal with. And so we then hypothesize that in that situation, those plants would tend to accumulate the simple compounds. And so as you have a imbalance of nutrients, when you have an imbalance of nutrients, let's say nitrogen to potassium, if you think about those two elements, nitrogen, of course, is very important in terms of protein synthesis, and potassium is also important in terms of converting amino acids into protein. So if you have an imbalance, you have too much nitrogen relative to potassium, what happens is you get the buildup of free amino acids in those plants. And insects love free amino acids. That's a very digestible source of nutrients for them because they're also highly limited by nitrogen. And so in those situations where you have these imbalances, that plant becomes very nutritious for the insect. Whereas in the plant that is in better mineral balance, where they're getting their nutrients relatively slowly, that metabolic machinery of the plant is able to act more efficiently. And so as amino acids and sugars are produced in the plant, they're more immediately converted to the less digestible and more complex building blocks of the plant, like proteins and starches and cellulose and that sort of thing.

Larry, you've mentioned a couple of fascinating pieces that I'd love to unravel a little bit more. The idea of biological buffering. What you're describing, in essence, if I'm understanding you correctly, is the capacity of biology in the soil to absorb Large amounts of nutrients that are applied and kind of contain those nutrients within their cells and then release them over a period of time. Is that what you're describing?

Yeah. So, you know, even in this artificial situation that we created, where we put inorganic fertilizer into a soil that had an organic history, even in that situation, that organic soil, that soil from that organic farm had enough carbon lying around where those microbes could actually use that inorganic form of nitrogen and ends. And then you, in combination with the carbon that was there and then bring that into that microbial community. And then. Yeah, as they then die off, you know, and you have other organisms that are feeding on those microbes, they then allow for the mineralization of some of these compounds, these nitrogenous compounds, and then it becomes available to the plant. And so we did, to follow up on this, we studied the dynamics of nitrogen across the growing season in these organic and conventional corn fields. Just as we would have expected, when you look at a conventional system where you have in the spring, the farmers putting down relatively high levels of soluble fertilizer and really not much carbon other than maybe some plant residue, you see huge fluctuations in terms of the availability of that nitrogen. So of course, before fertilization, nitrogen levels are very low. The farmer applies the fertilizer. Now they shoot way up well above what the plant can use. And then over the course of the growing season, that nitrogen then declines. But if you look at that same pattern in an organic system, what we found was that the levels of nitrogen, of soluble nitrogen in the soil solution generally were lower overall. And they also didn't vary much during the course of the year. And so that plant was getting this kind of constant supply, steady supply of nitrogen throughout the growing season. And really what we found when we compared these farms was that overall there was no difference in terms of the production at the end of the year between the organic and conventional farms.

I'd also love to understand the insect attraction piece a bit better. You mentioned that when you have this surge of nitrogen supply on the non organic farms from the nutrient application period, you have an increased attraction because you have a nutrient rich food source. Why are insects, why can insects not utilize plants as a food source that don't contain as high levels of amino acids? Because don't they would also contain some level of amino acids? No.

Yes. Yeah. All plants are going to have some levels of free amino acids and they can also digest protein. Let's keep that in mind too. But that protein, it's going to take energy for that insect to digest that Protein. Furthermore, a lot of plants have defenses that involve the inhibition of enzymes that break down protein. In the insect, these are called proteinase inhibitors. And this is actually in terms of what we call inducible defenses. This is one of the mechanisms of many, or the responses of many plants to insect attack. They start the production of these proteinase inhibitors in order to reduce the insect's ability to digest that protein. It basically knocks out those. Those proteinases in the. In the insect. And so the insect, it doesn't necessarily starve, but it slows their development way down. Well, in that situation, if you've also given that plant much, you know, these high levels of nitrogen, and it's accumulating these free amino acids that now short circuits that plant defense system. So, in other words, the insect doesn't need those proteinases as much because it has. It's getting these free amino acids that it doesn't have to break down.

Got it. That was a piece that I had always not fully understood, because I've heard it described that insects don't have the capacity to digest complete proteins and that they're dependent on soluble amino acids as a food source. And that never quite made sense to me. It made sense from a theoretical perspective, but it didn't make sense to me that plants might have no amino acids versus one plant having very high levels of amino acids.

Yeah, it's a matter of degree. And even proteins, they vary in terms of their digestibility for insects, too. And of course, insects evolve enzymes that are going to be most effective and.