More Soil Microbe Information
At the Growers 2023 Annual Meeting, I have a presentation titled A Pragmatic Look at Soil Microbes. Increasingly, the focus of agri-business is not on fertility inputs but on soil microbiology (and specifically on adding microbes to the soil). We agree that the health of the soil microbiology is very important to soil and plant health and long-term sustainability, which has led to me doing a lot of research into those living beings under the ground. The following article is a summarization of what I presented at the annual meeting, which itself was designed to be practical and helpful to the average farm.
Roots
I began by talking about what I have found about root systems and what their limitations are. Roots have traditionally been understood to be the primary way by which plants absorb nutrition from the soil. What I have found is that, while this is true in a sense, they are relatively poorly equipped to absorb all the nutrition a plant needs only by direct contact with those nutrients in the soil. The following are some reasons why:
All soils contain macro- and micropores (or empty space). Roots can grow into macropores, but even the smallest roots are too large to grow into micropores.
Nutrients are not evenly distributed in soil, meaning that there could be necessary nutrients in micropores and other areas that the roots imply cannot reach.
Root growth is highly energy intensive.
Plants can only absorb nutrients in an inorganic form, meaning that roots cannot absorb nutrition locked up in organic matter until it has been broken down by microbes.
Because of these limitations, plants rely heavily on the symbiotic relationship they form with bacteria and fungi in and around the rhizosphere. For example, certain types of fungi will create mycelium networks (those silky white strands you may see in soil) that are able to reach a far greater area of soil than roots can. These networks will break down and carry nutrition back to the plant. Interestingly, in a cubic foot of soil, there can be up to 2 kilometers (~3 miles) of mycelium strands.
Additionally, a healthy plant will allocate up to 35% of the sugars it produces by photosynthesis as root exudate. My question is this: Why would plants voluntarily give so much of the energy they produce to soil microbes if not because they rely on them so heavily for many things?
Nutrient Cycles
My Purpose for including nutrient cycles, specifically the nitrogen cycle, was to highlight both the importance of healthy soil microbes in keeping cycles going and to show the effect of applying chemical nutrients on the cycles. Our atmosphere is 79% nitrogenous gas, which is in a form unavailable to plants. However, nitrifying bacteria in the soil are able to convert it into ammonia, then nitrite. Plants and other microbes are able to absorb nitrogen in any of these three forms, and so the nitrifying bacteria are a sort of gatekeeper to nitrogen availability in the soil. Conversely, denitrifying bacteria will convert ammonia, nitrites, and nitrates back into atmospheric nitrogen. These bacteria are especially active (while nitrifying bacteria are not) in anaerobic soil. Therefore, it is in your best interest to keep your soil open and breathing.
The application of chemical nitrogen also disrupts this cycle. The pH and impurities inherent in most nitrogen fertilizers chase away earthworms and other macroinvertebrates that start the process of breaking down organic matter. This in turn makes it more difficult for bacteria and fungi to convert organic nutrients into inorganic forms. Additionally, nitrogen acts as a sort of steroid for microbes, causing them to be overactive. Since it takes 15 molecules of carbon for a bacterium to use q molecule of nitrogen, too much nitrogen application can quickly use up soil organic matter. When the nitrogen cycle is disrupted, a lot of other services that soil microbes provide will also be disrupted.
Food Nutrition
A large study done in 1999 compared the nutrients levels in fruits and vegetables from 1950 to those grown in 1955. This study has been cited by many others that look at food nutrition and is considered to be very important in this area of research. The study found that most of the main nutrients (including protein, minerals, and vitamins) had dropped by at least 10%, and often much more than that. Their conclusion was that this was largely a result of genetically selecting varieties for size and yield instead of quality. You see, 80-90% of vegetable matter is carbohydrate, so if we grow varieties that produce larger vegetables, most of that extra size will be carbs, not other nutrition. Furthermore, any time one trait is selected to express more it means that other traits will not be expressed. There is always a tradeoff in messing with genetics.
In Growers' 68 years of experience, we have also noticed a drop in nutritional value of both human and animal feed. While I agree that genetics does have something to do with it, I also believe that the way a food crop is grown, and the way the soil is handled, will affect its quality. This is where the Growers Program has insight to offer. I don't believe we are doomed to food with no nutrition but lots of size because we have seen many times that both yield and quality can be achieved. With proper soil health and balanced nutrition, a plant can produce a large and nutritionally rich crop.
There was more to my presentation, but I have and will be writing on those topics at other times. My emphasis throughout the presentation was on a couple of things: 1) The soil is a living system, and we need to treat it that way, and 2) I believe that soil health is the answer to economic and food sustainability. If you have any questions, please give me a call and I'll do my best to answer them.
This is an excerpt from the Late Fall Growers Solution (2023) written by Zach Smith, Product and Training Specialist.
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