Soil Life: The Secret to Nutrient-Dense Crops
Co-Authored by: Charlie Dubbe, Head of Regenerative Partnerships, Agrology and Jay Radochia , Head of Agribusiness Development, Agrology
Dan Kittredge, founder of The Bionutrient Institute, recently shared a surprising revelation with Koen van Seijen on the "Investing in Regenerative Agriculture and Food" podcast. He revealed that in a multi-year study across 25 crop types, he and his team found only one clear predictor of increased nutrient density (the total quantity of minerals, antioxidants, and polyphenols) in crops.
Despite what you may predict, there wasn’t a clear link between increased nutrient density and the crop being grown in a regenerative or organic-certified system. There was no connection between increased nutritional quality and whether the crop was grown locally, came from a farmer’s market, or a supermarket. Even more surprisingly, nutrient density wasn’t correlated with the levels of macro or micronutrients or carbon in the soil, nor was it correlated with specific regenerative practices, such as no-till, cover crops, biodynamic, etc.
According to the Bionutrient Institute's research, the only factor consistently predicted increased nutrient density was soil respiration, a key indicator of the amount of life in the soil. In his own words - “the only thing that we found that correlated with nutrient levels was soil life... The mode we used to discern that was soil respiration” (minute 35 in this podcast).
This supports the conclusion that growers, consumers and the supply chain partners are coming to - to grow healthy, nutritious crops, we need healthy soils that are full of life. Healthy soils, with robust, balanced and diverse communities of soil biology, improve nutrient cycling, nutrient mining (where microbes gather and deposit vital nutrients into the rhizosphere), and stimulate the production of plant metabolites. All of these activities result in an increase in a crop’s nutrient density, flavor profile, and shelf-life.
Without the working communities of bacteria, fungi, protozoa, nematodes, etc. the nutrients that our crops need are often locked up in non-plant available forms. As the soil microbes digest organic matter, prey upon each other, live and die, they transform nutrients into plant-available forms and also respire carbon dioxide. This is why the total efflux of CO2 coming out of a soil is a remarkably accurate indicator of overall microbial life and activity within that soil.
There is even an amazing part of the soil food web called the rhizophagy cycle where plants actually eat the microbes themselves (bacteria, fungi, algae, etc), absorb the nutrients out of their bodies, and then release them back into the soil unharmed. It starts with the plant roots “farming” microbes by releasing energy-rich exudates into the rhizosphere. These symbiotic microbes scavenge nitrogen and other nutrients from the surrounding soil, absorbing them into their bodies. Plant roots then “swallow” these microbes, extract the nutrients from their cells, and release them back into the wild to continue their nutrient scavenging.
In addition to providing consistent and balanced nutrition to plants, soil microbial communities also provide a myriad of other important functions that create a healthy soil system. They are responsible for building and maintaining soil aggregate, which improves soil structure, aeration, and stability. They are the primary driver (along with plants) of carbon sequestration: processing carbon into more stable forms via the liquid carbon pathway. They also play a role in improving and buffering the small hydrological cycle in agrisystems: improving water infiltration, retention, and distribution in soils. As our friend Francois Visser often reminds us - "Best of all, they work for free. All they ask for is food, water and shelter."
When I listened to this podcast, I was excited to hear Dan explain that respiration was the only clear indicator of increased nutritional quality in crops. This supports my stance that regenerative agriculture must center around outcomes - specifically soil health improvements. Without soil health at the center of the conversation, we can become lost in a dogmatic battle over which set of practices/certifications/self-identifications is best. Furthermore, defining carbon as the only important outcome to measure and manage is akin to focusing solely on calories as the only measure of a healthy diet. Carbon is just a part (albeit a very important one) of the broader biological system in healthy soils.
The research team at The Bionutrient Institute found that across multiple seasons, and 25 crop types including roots, leaves, fruits and grains, there was a wide range of nutrient variation. In terms of mineral content, the nutrient density within a single crop type varied between 2x-10x in mineral content and varied between 20x-40x in polyphenols and antioxidants. This means you would have to consume 15 grapes grown within a poor soil health context to receive the same amount of nutrition from a single grape grown in healthy, living soil!
Image source: The Bionutrient Institute
Beyond nutrition, better crops can improve our health
Beyond basic nutrition, a robust and diverse soil microbiome also provides plants with improved biochemical communication and stimuli that help plants produce their own medicinal compounds known as secondary plant metabolites (SPMs for short). This is where the line between nutrient density and the medicinal content of food becomes a bit blurry. This is the type of health building nutrition that led Hippocrates to say, “Let food be thy medicine, and let medicine be thy food.”
As I point out in this article on Linkedin, these secondary plant metabolites are what make our food flavorful and medicinal. These biochemicals serve as the plants’ natural defense mechanisms against pests and disease, allowing growers to reduce their use of pesticides, insecticides and fungicides by growing disease resistant crops. SPMs are produced when plants encounter biotic or abiotic stress, and they help plants resist everything from fungal pressures, pest outbreaks to drought conditions.
These same compounds that are medicinal in plants are also highly medicinal in humans. Their curative effects in humans include anti-inflammatory, anti-cancerogenic, antioxidant, antibacterial, and antifungal effects, just to name a few. A robust soil microbiome acts as the catalyst for the production of these compounds in plants by enhancing nutrient absorption and signaling mechanisms. If you're curious to learn more about Secondary Plant Metabolites and their role in boosting immunity in plants and humans, check out this article on Linkedin or this webinar with John Kempf and Dr. Elaine Ingham.
The Importance of Context:
In regenerative farming, context is key. Each farm (and sometimes even each field) requires a unique, tailored approach to maximize soil health by taking into account the myriad of factors that make up its context. These factors can include (but aren’t limited to) soil type and soil characteristics (compaction, aggregation, water infiltration, SOM, etc.), management history, existing microbial composition and biomass, crop production systems, agricultural equipment available, irrigation systems, farm financial constraints and opportunities, pest and disease pressures. And this is just the tip of the iceberg in terms of a farm’s comprehensive context. This is why “one size fits all,” prescriptive solutions to guiding farmers in their transition to regenerative are deeply misguided. Each farm needs its own tailored approach, and the best way to find out what works best for your farm is to experiment with a few different approaches.
This is where Agrology can help. The researchers at the Bionutrient Institute chose respiration to be the easiest, simplest tool for revealing the amount of biological activity and life in the soil. If the goal is maximizing the life in your soil, Agrology’s real-time continuous monitoring of respiration and carbon flux should be a key tool in the tool-kit. Like a continuous Haney soil health test, Agrology’s system can provide clear feedback from the soil’s microbial communities. This ground-truth data helps tie practices to real outcomes (as opposed to models which merely estimate them), and can act as a guidance system when growers are experimenting with different sets of practices, biological inputs, and regenerative strategies.
Every grower who is embarking on a transition towards regenerative farming only has so many dollars to spend on that transition. Agrology can help optimize that spend by measuring and comparing the changes in respiration profiles from different small plot experiments (for example biochar in one block vs. compost in another, roller crimper vs. mow). Once a grower has found the tailored regenerative program that works best for their context, they can feel confident scaling it across their acreage, and have a clear, quantified understanding of how that program will increase soil life and ultimately the nutritional quality of their crops.
Approaches to Measuring Soil Respiration:
So, if respiration is to be the guide post by which farmers can measure their progress in soil health improvements, then how best should we measure soil respiration? And how do we determine which soils are healthy and which are not?
Traditionally, farmers have relied on lab tests like the Solvita burst test or the Haney Soil Health test to measure soil respiration. These methods are a great starting place, however they have some limitations. Dr. Elaine Ingham (of the Soil Food Web School) has expressed her concern around the disturbance to the microbial communities that results from the sampling, transport, and sieving (and/or grinding) of the soil samples. Additionally, these tests dry down the soils completely and then remoisten them under lab conditions, which doesn't necessarily reflect the real-world environment. Most importantly, these tests provide only a snapshot of microbial activity at a single point, missing the natural fluctuations that occur throughout a season. Ideally microbial activity is measured in-field, and as continuously as possible, which brings us to the next option for respiration monitoring: soil chambers and gas flux analysis tools.
Image Source: Solvita CO2 Burst Test
Continuous measurement of respiration in-field has mostly been the domain of academics, who have the expertise and research budget to deploy systems such as the LI-COR 8100 series. These systems are great, and are highly accurate and precise in their monitoring of soil respiration, however they are not practical for the average farm due to their cost and complexity.
This is where Agrology aims to innovate with our Arbiter System. The Arbiter is a continuous gas-flux measurement technology optimized for the intensity and variability of commercial farming. Unlike the Solvita Burst and Haney Tests, it tracks CO2 levels continuously, allowing farmers to see how soil microbial activity changes throughout a season (and even throughout a single day) and how their soil biology responds to different regenerative practices, products, and conditions.
In addition to monitoring soil CO2 respiration, the Arbiter also measures carbon concentrations in the canopy. This dual approach not only tracks the respiration emitted by microbial activity, but also how much carbon plants are able to reabsorb through photosynthesis, offering a more complete picture of the health and productivity of the carbon cycle in the real-world context of that field.
But what sets the Arbiter System apart is its practicality. It’s built to withstand the tough conditions of farming, can be easily moved, and is fully integrated and automated offering a scalable solution that doesn’t require a soil scientist to operate. Additionally, Agrology presents raw data and processed insights in easy to understand charts and alerts on a mobile app and online Grower Portal. This empowers growers to turn their soil health and climate data into actionable insights, helping optimize their spend on their regenerative programs to maximize the soil health gains. We also partner with internationally respected carbon project developers to use Agrology’s data to differentiate and expound agricultural carbon insetting and offsetting programs.
In Summary
The ultimate goal of Agrology is to empower a new generation of farmers to prioritize soil health as the foundation of agricultural success. By providing clear, continuous data on soil respiration, we aim to support growers in refining farming practices that improve soil vitality, crop resiliency to pests and diseases, and nutrient quality of the final product.
Nutrient density is deeply connected to soil health, ecosystem health and human health. Regenerative agriculture should be a commitment to revitalizing our soils, our agricultural communities, and our future in farming by putting human health at the center of our food system. Please comment with your opinions, stories, lessons, strategies, and questions. As Dr. Allen Williams and John Kempf put it in this provocative podcast, none of us have experienced ideal soils, plants or ecosystems that are truly abundant, but we do know what’s better. So let’s not be too proud of ourselves, let’s observe and measure better, and let’s learn from each other how to reconnect with our land and ensure its richness for generations to come.