Disease Suppressive Soil and The Impact of Temperature on Soil Characteristics

I'll start with the topic of carbon formation, carbon cycling. I'd like to talk about the effect of temperature during the formation of carbon, and then also how the end result or the end product of that, the difference in the carbon formation based on the difference in temperature, affects the crop that's going to be growing there next year.

Okay, so I'll try to condense this down into a few sentences. We know that humic substances in the soil are generally categorized as either fulvic acids, humic acids, and human. And actually, I spoke incorrectly. It's not. These are not the characterizations of humic substances in soil, but more of humic substances in mined humic soil salts, linardite, etc. And dry humays or lignite or whatever accepted terminology might be at the moment. So within the soil, when we have high temperature environments or high temperature soils greater than 60 degrees or even greater than 55 degrees Fahrenheit, as biology and fungi consume organic residues and lipids and everything else and convert them to humic substances when soil temperatures are warmer, the majority of the humic substances produced are in the form of fulvic acids. What we think of as fulvic acids, they are lower molecular weight compounds. They're very active, they're very strong chelation agents. When soil temperatures are cold, below 55 degrees Fahrenheit and perhaps even colder or frozen soil microbial activity never completely stops, but it slows down, as does molecular activity and atomic activity. And as a result of this slowing down, in colder temperatures, we form much higher concentrations of the more complex humic substances, such as humic acids. So these are much longer chain, more complex molecules that generally tend to degrade much slower. They have some slightly different properties and activities in the soil profile. And so the simplest way to think about this is to actually look at the various humalite or leonardite deposits in the Northern hemisphere and see how they shift. So as an example, the deposits in the Dakotas and in Alberta have a very high proportion of humic acid and a very low proportion of fulvic acid because they were formed in a very cold temperature environment. The deposits in New Mexico in the desert have very high proportion of fulvic acid and a comparatively low proportion of humic acid. The ratios are completely different, north versus south. And you see this gradual progression, north versus south, that is primarily an effect of temperature. The same process holds true in soils. Why this matters and why we should care is if we want to build soil organic matter and if we want to build humic Acid as the component of humic substances that remains viable in the soil for a very long period of time, then we should desire to have our microbial decomposition and the formation of humic substances happen in colder soils. So during the winter months, if we live in an environment where this is not possible and our soils Never go below 55 degrees Fahrenheit, this is one of the reasons why we need to accept the reality of the situation. We are never going to have high organic matter content soils. We can still have soils with very high concentrations of microbially active carbon, but we're not going to have high organic matter soils in these environments because the temperatures are not low enough to accumulate stable humic substances that last for very long periods of time, hundreds of years.

So that answers the question on the formation very well. Now, what would you expect the differences to be if there's more carbon formation? Let's say on the same farm you introduce and support and stimulate microbial activity in the fall to accelerate or to build a larger volume of the carbon during the winter compared to when you do that in spring. And now you plant the same crop, what would you expect the differences to be in the crops performance?

Well, it also depends, David, on the stage at which you terminate and incorporate that crop. So we have to consider that as well. So if we incorporate a crop, I would even suggest that is a primary, that's the primary determination of the effect that you'll have on the following crop. So if you incorporate a mature crop that has a very broad carbon to nitrogen ratio, which is going to be primarily digested by fungi, with that broad to carbon to nitrogen ratio, you will build these stable humic substances and you'll build organic matter, but you will deprive nutrients from the following crop at least for a period of six to eight weeks after that crop has been incorporated. Because the biology eats first and they need nutrients to break down that crop residue. If, on the other hand, you incorporate a cover crop that is immature and has a very narrow nitrogen to carbon ratio, that is primarily a bacterial food source, and that bacterial food source will not produce stable humic substances, you will not build soil organic matter with it, but you will provide a flush of plant available nutrients within two to three weeks after incorporation. So to go back to what I was speaking about a moment ago, if you want to build humic substances in the soil as efficiently and effectively as possible, the magical combination would be to incorporate either crop residue or a mature cover crop in the fall, as soil temperatures begin dropping. That's how you're going to build humic substances in the soil the fastest.

I like for you to talk about the nitrogen to sulfur ratio and the level of sulfur within the carbon or within the soil and how that affects the organic matter level and the importance of sulfur in that carbon formation. And are there any other key minerals that are needed for this carbon formation that maybe aren't generally talked about in mainstream agronomy?

Yeah. So to your first question, there's a biochemistry perspective and a chemistry perspective. From a biochemistry perspective, we could speak about the importance of lipids that are needed for the formation of stable humic substances. But if we just simply speak about it from a chemistry perspective, we know that when we have stable soil carbon, stable soil organic matter, this stable organic matter will have a carbon to nitrogen ratio of approximately 30 to 1. So that means that if we want to sequester 3,000 pounds of carbon in our soil profile, then the crop residue and fungi and the minerals of soil are coming from the atmosphere. We need somewhere in the nitrogen cycle to contribute 100 pounds of nitrogen. So in order to have a 30 to 1 ratio, if we have 3,000 pounds of carbon, we need 100 pounds of nitrogen to stabilize that. Then we also understand that in order for that nitrogen to be stable, we need to include all of the amino acids that are the stop amino acids in order to keep the proteins stable and prevent them from degrading further. So these stop protein or stop amino acids are the sulfur bearing amino acids, cysteine and methionine. So in order to keep the nitrogen stable, we need to have a 10 to 1 nitrogen to sulfur ratio. So if we have 3,000 pounds of carbon, that requires 100 pounds of nitrogen to remain stable. That means that to keep the 100 pounds of nitrogen stable, we need to have at least 10 pounds of sulfur in the soil profile. And so what we've observed happen is that the key descriptive term that I've been using in these sentences is stable. What is required to keep the carbon stable, what is required to keep the nitrogen stable? And what happens is when we have soils that don't have adequate sulfur, then essentially this ratio, these three elements, nitrogen, carbon and sulfur, will continue to be metabolized in the soil until they reach the lowest common denominator for stability. So if carbon or nitrogen or sulfur, it can be any of those three could be the lowest. But most commonly, we observe sulfur to be the lowest. So if you have 3000 pounds of carbon and 100 pounds of nitrogen, you need 10 pounds of sulfur. What happens when you only have 5 pounds of sulfur. When you only have 5 pounds of sulfur now you can only stabilize 50 pounds of nitrogen instead of 100. So the nitrogen level drops to 50 pounds and the carbon level drops from 3000 to 1500 pounds. And all that additional carbon, the great majority of it, will be volatilized and lost into the atmosphere as CO2 and off gas. So you've lost a lot of potential organic matter, you've lost a lot of carbon because you didn't have enough sulfur in the ecosystem.

Interesting how we hear somebody talk about sulfur and then we, then we go and we address sulfur and we forget about calcium. And then, you know, next year we might hear about calcium. So we apply calcium and forget about sulfur.

Yeah. And so I think that speaks to your second question of what other minerals are important. You can think of it almost as being the concentric rings on a target on a bullseye. Yes, managing sulfur and nitrogen carbon ratios is critical for this specific aspect. But then if you want to support the microbial population that is a part of this entire process, and then plant health and all that contributes to that, then of course those rings just keep expanding and expanding until ultimately you go to the outer edges, you include all the 64 elements that are known to be beneficial to living processes and to enzyme structures and so forth.

I've been really working a lot with soil borne diseases and I'd like for you to talk about presence versus expression, because if I'm understanding this correctly, there's very few soils who don't have the presence of pretty much every pathogen, but they're not expressed everywhere. Why and what are some of the key factors?

It is my understanding, based on doing a lot of research, reading hundreds of peer reviewed published papers on this topic, that there is very little correlation between the presence of a disease causing organism in the soil and the infection of a plant or a crop with that disease. So instead the question is, what is the correlation? So why? Let's just pick on Phytophthora verticillium or Fusarium or Pythm, you could pick any of those as an example and say that the presence of the organism is essentially ubiquitous. It is in soils throughout our agricultural production systems. And the only difference between those soils where it causes an infection and those soils on where it does not is not just in the cultivar and the variety, whether it's susceptible or not, although that can have an effect. But the biggest contribution, the biggest reason, is the other organisms that are present. It's the environment. It's the remainder of the soil microbiome that suppresses the potential pathogens and either prevents them from infecting the plant or permits them to infect the plant. So if we want to develop soils that can, that are called disease suppressive soils that can prevent the infection of these diseases, it's not a question of planting disease resistant varieties. It's not a question of growing a crop rotation that doesn't offer a host to the pathogen. It's simply a question of changing the soil's biology, changing the soil's microbiome. And when we change the microbiome, we can develop a disease suppressive soil that will prevent the infection of a plant, even when we plant a susceptible cultivar, even when we have a crop rotation that is considered to foster the hosting and the development of that specific organism.

So what I hear you saying is to build the microbiome in such a way that these soil borne diseases aren't able to proliferate.

Exactly. According to Don Huber, I don't recall if this was in a personal conversation or in one of the podcast interviews that I did with him, but he was very clear that when you have two fields, one field has a Fusarium infection, the other one does not. There is no difference in the population of infectious Fusarium in the field. The quantity, the concentrations of Fusarium organisms in each gram of soil are identical. It's not the presence or the absence of the cereum that causes the disease. It's the presence or absence of other organisms that causes the expression of the disease.

So with that, I mean, looking at something like Alternaria, for example, where Alternaria on a tomato leaf is a beneficial, it has a symbiotic relationship with the tomato plant. And my understanding is that Algernaria is in fact a very strong antagonist against mildews, which is why tomatoes are not as susceptible to mildews as maybe cucurbits are. But when people normally think of Alternaria, they think of little spots, they think of the disease. So what happened there? Alternaria was beneficial and now suddenly we need to kill Alternaria or we call Alternaria ADCs. So taking that as an example and a context, is that also happening in the soil borne diseases that we're talking about?

Yes, it's very similar to what is happening in the soil. So Alternaria solani, the organism that you're referring to, is known to be present on the leaves of essentially all of the solanaceous plants. So tomatoes peppers, potatoes, eggplant, etc. From the moment of germination, so the moment that seedling germinates, there are already Ulterior Solani on the leaf surface and they colonize that leaf surface throughout the plant's entire life. And it is only when their relationship with the plant changes because of the state of the plant's health or unhealth, which we call dis ease, that later in life when the plant is under stress, the Alternaria solani begins attacking the plant. Doesn't happen at the beginning. Why not? Because the plant is not susceptible to it and the plant is actually feeding. It has a symbiotic relationship with it. So yes, the same type of symbiotic relationship is present with soil microorganisms that prevent the infection of soil borne diseases.

Fusarium, Phytophthora, verticillium. The things that we call diseases, are they also beneficial that then in turn attack the plant?

I don't know if this is true for some of the umycetes, for and for all the organisms like Phytophthora we spoke about a moment ago, but my understanding is that that is the case for some of these organisms, such as Verticillium and Fusarium, where they're actually saprophytic fungi. They're decomposers. They decompose nonliving plant residue. So if you put hay or straw mulch out and it rains on a couple times and then you pull it up and you see this white mycelium going all the way through it, majority of that white mycelium in many soils will be verticillium functioning as a decomposer. So again, it's not the presence of the organism that produces an infection, it's the presence and the symbiotic relationship with other organisms.