For no-tillers aiming for sustainable and profitable crop production, optimizing soil health and function is the ultimate endgame, says former NRCS soil scientist Ray Archuleta.
“Healthy soil doesn’t want to be disturbed, and it wants to be covered perpetually,” he says. “And remember: The soil and plant are one — they are not separate.”
In addition to the judicious use of cover crops and careful use of fertilizer and agricultural chemicals, a “checkup” can reveal a lot about a no-tiller’s most important resource.
Conducting an aggregate stability, or “slake,” test is a good way to assess soil health and compare fields with different histories, he says. Archuleta advises farmers to randomly select aggregates, or clods, from a field or fields and let them air dry, or microwave them until all the moisture is gone. When the aggregates are dry, drop them into a jar of water for each sample.
“What we want to see is an aggregate that does not fall apart,” says Archuleta, who now works for the non-profit Understanding Ag, which operates Soil Health Academy learning sessions across the U.S. “We want to see which one holds its integrity and withstands the force of pressure when the water rushes in to fill the pore spaces.”
Soil aggregates that fail the slake test are degraded and, typically, that’s what happens when conventionally tilled soils are tested.
That, Archuleta says, is a major issue for American agriculture because he estimates that as much as 80% of U.S. crop production soils are still “falling apart” as farmers transition away from conventional tillage.
The primary reason for this degradation, Archuleta says, is a humus deficit. Organic matter is essential to creating the biotic glues that hold soil particles together, as well as holding nutrients in the soil.
These cementing agents are the result of metabolic processes of earthworms, arthropods, bacteria and fungi and include glomalin, which is produced on spores of arbuscular mycorrhizal fungi, polysacharides and other carbon-based substances.
Because lost organic matter reduces aggregate stability, soil degradation increases as organic matter decreases.
The take-home message for no-tillers, Archuleta says, is that this all-important binding of soil particles must be constantly renewed by biological processes and can be destroyed by management choices that don’t regard soil as an ecosystem that depends on a host of interconnected factors.
“The moment you run that vertical till, you force air into the soil system and wake up these critters called copiotrophic bacteria,” he explains. “They have an incredible metabolic rate and they love carbon. They start eating your organic biotic glues. As they eat that carbon they die, mineralize and release nitrate. If you add excessive nitrogen fertilizer, that also encourages them.”
Copiotrophic bacteria are needed to decompose residue, Archuleta says, but are poor carbon managers and, in out-of-balance soil ecology, they can decompose the structure of organic matter too completely.
Tillage also brings weed seeds to the surface and that secondary succession is stimulated by the nitrate release of the copiotrophic bacteria.
“Your most powerful weed control is a living plant,” he says. “Weeds are nature’s scabs. They are the healers, the indicator species. They are telling you that you’re disturbing the soil too much and if you don’t fill the void, nature will fill the void for you. As Voltaire said, ‘Men argue, nature acts.’”
A continuous no-till system, on the other hand, leads to more fungal-dominated soil that is better for decomposing organic material, Archuleta says.
Soil should be treated as an ecosystem habitat that farmers protect with no-till and feed with a varied food supply created by plant diversity.
Microbes and Infiltration
Archuleta says low soil disturbance and high diversity mimics nature and promotes healthy cycles within a soil ecosystem. A healthy microbial community, for example, is essential to a successful water cycle.
“Microbes are connected to the water cycle,” Archuleta says. “Organisms create the glues. If you don’t have the glues to hold soil structure, water doesn’t enter the soil. Soils are subaquatic systems. Bacteria are aquatic, protozoa are aquatic, nematodes are aquatic and earthworms like moist conditions.
“The reality is that everything is connected. If the water doesn’t get into the soil, the water cycle is not complete.”
The biotic glues created by organic matter keep pores intact. More pores mean more porosity, and more porosity means more infiltration, Archuleta says, adding that if water is running off the field, the water cycle is not complete.
“The first thing no-tillers realize when they stop tilling is that the water cycle starts functioning,” he says. “People say, ‘I don’t have those wet spots anymore.’ You’re letting the glue-makers make their glue, you’re not bothering the habitat and, if you’re a really awesome farmer, nutrient cycling starts working.
“The water cycle, the bio community cycle, the water cycle, the nutrient cycle — they’re diminished on a majority of our farms and that’s why we have to haul in fertilizer. We’re leaking. The soil isn’t functioning because it’s diminished. The biology is diminished. You mess with one cycle, you diminish the rest of them.”
However, better soil health could have a positive impact on the nation’s environmental problems.
“We don’t have a runoff problem in this country, we have an infiltration problem,” he says. “Runoff is a symptom of poor soil function. The water isn’t infiltrating in the soil. I love buffer strips and believe they are important, but they’re a diaper if the rest of the ground above them is bare.
“The battle is in the soil. Do you really think that tiny buffer is going to hold back 99% of the bare soil?”
Adjacent fields with identical soil types can have radically different water infiltration rates, leaving a long-term, conventionally tilled field in a drought situation while an undisturbed field has ample moisture.
And Archuleta points out that infiltration ability doesn’t just affect water. He cited an example of fields with the same soil type in which a tilled field leached 17 kilograms of nitrate per hectare, while an adjacent forested area leached just 2.1 kilograms per hectare.
Healthy soil structure is also a no-tiller’s best protection against weather extremes, Archuleta says.
While residue and growing plants insulate the soil from high and low temperatures, a functioning soil ecosystem utilizes rainfall more efficiently.
“I grew up thinking that if I disturbed the soil, I was going to let more air in and that would let more water in,” he says. “Soil wants to do two things with water. It wants to hold it and it wants to filtrate it. The organic matter holds it and the big pores let it filtrate. But if you get in the way and you disturb the soil, you mess up the water cycle.”
Cover Crop Benefits
According to Archuleta, even tile systems won’t function properly if soil isn’t healthy with open pores throughout its profile.
“If you want to regulate and help your tile drainage system, plant cover crops. They store the nutrients and help keep the pores open,” he says. “We want wormholes to go all the way. That’s what a healthy soil system does. But the only way to hold your nutrients is in the body of a microbe and the body of a plant.
“When you destroy carbon, you’re headed to haul it back in — you can’t do that and be sustainable for farming in the 21st century. The use of cover crops is not just about controlling erosion. It’s about storing your nutrients and feeding the soil biology.”
Cover-crop roots also secrete allelopathic chemicals that act as natural herbicides, as well as transferring nutrients through arbuscular mycorrhizal fungi. Archuleta prefers multi-species cover crops to monocultures and says manure should be used in conjunction with cover crops because it raises the vitamin content of plants, particularly B vitamins.
Cover-crop residue also helps regulate temperature and moisture in the soil. At high temperatures, Archuleta explains, most of the soil moisture is utilized to cool plants down rather than for growth.
“We can create our own drought,” he says.
Archuleta says cover crops can increase the enzymatic activity in the soil by introducing root exudates that are novel to a particular system. He isn’t opposed to using native species as cover crops, but emphasizes that “planned diversity” is important.
While any cover crop may be better than bare soil, he suggests that no-tillers select species that contribute to what a particular system needs and fit the natural ecosystem — whether they are native or not.
“We don’t want to just throw seed out there just to throw seed,” Archuleta says. “You have to do it cautiously. We want to design these cover-crop mixes to meet your goal because each plant has a different chemical signature.
“You have to know your context and have a thought process and a goal. For example, if your goal is to put lots of carbon into the soil system, you may choose cereal rye. But you have to know what those cover-crop species do for your system.”
How Cover Crops Can Improve Soil Health
While there are many cover crops available to farmers, here’s a rundown of 10 popular species and the benefits they offer.
Buckwheat is a non-legume broadleaf that germinates quickly and is among the first species to come out of the ground after seeding. It extracts soil phosphorus and attracts beneficial insects.
Cereal rye is a cool-season annual grass and is very winter-hardy. It can be seeded later in fall than other cover crops and will still produce a good amount of biomass in spring. It’s easy to establish and has an extensive soil-holding root system.
Crimson clover is a winter annual legume that grows rapidly and can fix generous amounts of nitrogen. It has good shade, heat and drought tolerance and is a good soil builder.
Hairy vetch is a cool-season legume that goes dormant over the winter, yet regrows in the spring and provides needed spring nitrogen through nitrogen fixation. It is useful for erosion control and weed suppression.
Oats germinate quickly, come up fast, improve soil biology and can sharply reduce the cost of a multi-species cover crop mix. The cool-season annual grass winterkills, can tolerate brief periods of flooding or ponding and is good for weed suppression and reducing soil erosion.
Radishes scavenge nutrients and quickly establish a good cover. The radishes die off over the winter, so they don’t have to be terminated in the spring.
Rapeseed/Canola is a cool-season brassica that grows quickly and can provide large amounts of biomass. It has good drought tolerance and the deep, fibrous root system is good for loosening the soil.
Sorghum-sudangrass is another fast-growing warm-season grass that can balance out other species in a mix while producing large amounts of biomass.
Sunflowers provide favorable soil conditions while attracting insects that encourage pollination. They have deep tap roots that can break up compaction as well as smaller, hairy secondary roots.
Winter lentil is a cool-season, winter-hardy legume species that thrives in low-moisture areas. Similar to hairy vetch, it can fix atmospheric nitrogen and provides good ground cover to reduce erosion and weed pressure.
Look for Earthworms
Archuleta says the presence of earthworms is a good indicator of soil health, and he wants to find them in abundance.
Likening earthworms to factory workers that help build the carbon-based glues that maintain soil structure, he points out that those workers cannot exist and thrive under harsh conditions. In extremely high temperatures in unprotected soils, for example, earthworms die and bacteria begin cannibalizing each other to survive.
“Go out there, smell your soil and count your earthworms,” Archuleta suggests. “You should have 1.5-3 million earthworms in an acre — anywhere from 40-150 earthworms in a square foot. If you don’t, that means some of the biology is missing.”
Earthworms can change the soil in just 48 hours, according to Archuleta. Living roots take a little longer — about 30 days — but also have a profound impact by “leaking” enzymes from root debris and border cells. The enzymes stimulate the nitrogen (N) cycle and are part of a communication process between roots and microbes.
“They’ll send these chemical messengers and they’ll trigger the right biology to get soil processes going,” Archuleta says. “If you’re having problems decomposing some of your residue, you need to put different root exudates out there.
“Vertical tillage won’t solve the problem — it will just mask the symptom. You need to put different cover crops out there that will leak different enzymes. That will stimulate the biology and bring earthworms into the system.”
Protecting Soil Life
Mycorrhizal fungi are another important component of the soil ecology, Archuleta says, and the management practices employed by farmers can have a dramatic effect on their health and relative abundance.
Tillage is especially detrimental because it diminishes the hyphae — the branching filamentous structure of the fungus — as well as reducing the spores necessary for propagation.
One of the reasons Archuleta favors perpetual cover is that fallow periods also reduce spore populations, as does poor soil drainage.
Other practices detrimental to the mycorrhizae are stubble burning, which kills spores on the soil surface, and the use of those fungicides that are toxic to the fungi, he says.
Although a holistic approach to soil health and crop production can reduce the need for herbicides and pesticides, those agricultural chemicals appear to have little effect on the mycorrhizae when applied at recommended rates.
Archuleta notes that research results have been uneven and inconclusive regarding the use of mycorrhizal inoculants, but he is not opposed to them.
However, he points out that certain cover crops and corn are particularly good at promoting mycorrhizal spores in the soil.
Rethink Soil Testing
Because soil biology is the key force behind nutrient cycling, Archuleta believes soil-testing methods should be focused on biology as well. That’s why he’s a proponent of the Haney soil test.
“Our old tests are based on reactive chemistry,” he explains. “The Haney test is based on biology, which uses nature’s green chemistry. This is biomimicry, or mimicking nature ion the field.”
The Haney test gives growers an overall soil health score based on seven parameters. The first is what’s called the Solvita 1-day carbon dioxide burst, which measures how quickly microbes respire.
What that means, Archuleta says, is the higher the soil fertility — which is the “food” of the soil — the faster soil microbes release carbon dioxide when it rains. “The theory is if we can predict that we can help estimate how much mineralization is going to occur,” he says.
The second and third parameters are WEOC (Water Extractable Organic Carbon) and Microbially Active Carbon (%MAC), which is the efficiency of the microbes in processing WEOC.
The fourth parameter is Extractable Organic N, a metric which Archuleta admits was elusive to soil scientists because the old technology couldn’t account for this large source of water-soluble organic N.
“We’ve been missing over 50% of this nitrogen source with our current soil tests,” he explains. “When you use the conventional soil test on forests or pasture systems, you usually find low numbers of nitrogen in those soil ecosystems. Why? Because most of the nitrogen is in the organic form.”
The final parameters of the test include organic carbon-to-N ratio, as well as organic and inorganic N and phosphorus (P).
All seven parameters in the Haney soil test will help producers reduce N, P, and potassium (K) use, Archuleta says, especially because the standard soil tests can only pick up on nitrate N and some ammonia, while the Haney test can pick up on other forms of organic N, along with the nitrate N and ammonia. All N sources now can be accounted for.
That’s because the Haney test utilizes complex water analyzers and can get a direct read from the soil-water solution, with no guessing or model predictions involved.
Archuleta explains that the Haney test is a passive test — just like a blood sample is for humans. Just as a blood sample gives a direct read of various hormones, nutrients and other compounds in humans, the Haney test gives a direct read of all the solutes in the soil water.
“The Haney test does not use a soil analyzer,” he says. “It uses a sophisticated water analyzer that is more sensitive than soil analyzers.
"Why use water analyzers? Because the soil functions on water. The soil water is the blood of the soil. These instruments are very sensitive. It has the ability to pick up the water soluble organic carbon and water soluble organic N in the system.”
In using the Haney test, Archuleta says scientists have learned they’ve been missing 50% of N pools in the soil vs. the standard soil test. The standard soil test cannot account for organic N in the soil, which he says is even more important for no-tillers that use cover crops and animal integration, as these type of farming systems are healthier and have more measurable organic N.
He stresses this is why no-tillers should consider using the Haney test, because the standard soil test works fine in “very destroyed, mineral-dominated soils” often seen in conventional tillage fields, where there’s very low dissolved water-soluble organic N.
“We finally have a soil test that is useful for pasture systems, forest systems, grassland systems or other ecosystems that do no soil tillage,” Archuleta says. “These systems have higher forms of organic systems vs. tilled systems.
“You cannot compare a conventionally tilled system vs. regenerative soil systems. They’re night and day. Conventional soil systems are very leaky and bacteria dominant. No-till systems are more fungal dominant and hold nutrients more tightly in the soil profile — more biotic glues.
“Once you start going into a soil health system, the old current tests start to fall apart, because these test were based on the wrong premise. These tests were not based on soil life — biochemistry — but on inorganic chemistry. The soil is alive."
Using Tools Wisely
All of these practices are tools and Archuleta encourages growers to consider the larger picture and use management tools wisely.
“Chemical fertilizer is a tool I have on the negative side if it’s used unwisely — and most of the time I see it used unwisely,” he says. “Chemical fertilizer is a salt and can, in large quantities, hurt our soil organisms.
“You can make a plant susceptible to disease because you put too much on. Fire is a tool, but in very hot fires, we’ve known it to destroy organic matter, oxidize it off and seal the soil. Nothing is for free.”
Archuleta says he’s changed his view of soil nutrients.
“When I walked out of school, I thought it was all about N, P and K,” he says. “I now think it is carbon. You fix the carbon cycle — although you may have to use nutrients to get there — and you stop disturbing that soil system.
“It’s all about carbon. Organic matter is 58% carbon. The root exudates are carbon. Once you bring the carbon, you’ve got the soil biology going. Those soil microbes are functioning, respiring, metabolizing. They are functioning — they are doing their business.”
While high organic-matter levels can be beneficial — more organic matter provides a better buffer to chemicals, Archuleta says — he warns that growers need to be careful about how they view organic matter.
“Organic-matter values change all the time," he says. “Focus instead on carbon flow and quality. Water-soluble carbon is critical to nutrient and water cycling.”
He gives the example of some bog soils that are 20% organic matter but not cycling on their own. It’s not the total carbon but the quality of carbon, he says.
“You can’t get any plants to grow on them,” Archuleta explains. “We have to determine what we want out of the function of our soils. It’s not just about organic matter — it’s about active water-soluble carbon, which increases internal nutrient cycling, which creates more aggregated soils with increased water-cycling capacities.”
Archuleta’s goal for no-tillers is to have a soil so healthy and effective at mimicking nature’s nutrient cycling that it doesn’t respond to N application. The key to achieving that is in soil biology. “Always remember that 90% of all nutrient cycling is biological,” Archuleta says.
“It is the biology in synchrony with the plants that makes the nutrients available. It’s a self-healing, self-regulating, self-organizing system.’”
No-tillers need to focus on soil health, rather than on the practices they use to grow crops, Archuleta says.
“We cannot have love affairs with tools. Cover crops are a tool. Manure is a tool. A no-till drill is a tool. But we need to go right for soil health. That is the goal,” he says. “We have to make that soil function.”
The 5 Principles of Soil Health
1. Soil Armor
Soil armor is important for reducing water and wind erosion, decreasing water evaporation, moderating soil temperatures, reducing the impact of energy from raindrops, suppressing weed growth and providing a habitat for surface dwellers, which are an important part of the soil food chain.
2. Minimizing Soil Disturbance
Minimizing soil disturbance, which can be biological, chemical or physical disturbance, enables the soil armor (surface plant materials/residue) to persist. Biological disturbance includes overgrazing of forages that reduce soil armor and below ground biomass. Physical and chemical disturbance occurs from tillage used to work the soil or bury crop residues and adding chemicals that stimulate microbial breakdown and lead to excessive carbon release into the atmosphere.
3. Plant Diversity
Prairie plant diversity aided and allowed soils to develop prior to the introduction of annual cropping systems. Plant diversity uses sunlight and water to sequester carbon and other nutrients, preventing leakages into ground and surface waters. Understanding the four crop types — warm-season grasses and broadleaves, and cool-season grasses and broadleaves — is necessary for designing cropping systems that improve soil health.
4. Continual Living Plant Roots
A continual living plant root either from the commodity crop, cover crop or forage crop provides carbon exudates to feed the soil food web, which is exchanged for nutrients for plant growth. This process is also important for soil aggregate formation, which increases soil pores for improved water and air exchange.
5. Livestock Integration
Lastly, livestock integration balances soil carbon and nitrogen ratios by converting high carbon forages to low carbon organic material, reducing nutrient transport from the soil, and promoting pasture and rangeland management in combination with cover crop grazing.