Pictured Above: ROOT DOWN. Advancing Eco Agriculture founder John Kempf believes uncultivated plants are absorbing a majority of their nutrient requirement via the rhizophagy cycle. He says it’s also possible for cultivated plants, when managed properly, to do the same thing.

Nitrogen management is one of the most important tasks no-tillers face each growing season, due to both the expense and the nutrient’s importance to plant growth. 

No-tillers and strip-tillers in particular have devoted more attention to improving nitrogen (N) efficiency by tissue testing, splitting applications, creating in-field test strips to measure optimal rates, and even changing up the form of N applied to balance economics and yield response.

But in recent years, a previously little-reported process involving soil biology is providing farmers with the knowledge to produce cash crops with a reduced N rate with little or no yield loss. 

This process — which emerged mostly through the research work of James White, plant biologist and pathologist at Rutgers University — is called the rhizophagy cycle. The founder of Advancing Eco Agriculture, John Kempf, says this cycle is a complete revolution in the industry’s understanding of agronomy and plant nutrition. 

NO-TILL TAKEAWAYS

  • Re-establish microbial populations with seed treatments and inoculants.
  • Give careful consideration to the amount and salt index of your fertilizers.
  • Take a look at products like compost teas and vermicompost to build soil life.
  • Consider plant-sap analysis as a way to manage inputs efficiently.

What’s in a Name? 

So what exactly is the rhizophagy cycle? According to White, it’s the process that happens at the growing root tip, where the growing point of the root cells are elongating and growing very rapidly. Entire microbes, bacteria and fungi are actually taken up directly into the root.

In the root, as the engulfed microbial cell moves back through the root system or past the root tip, the root releases reactive oxygen that strips the cell membranes off the bacteria in the microbial cells.

These naked cells are taken apart and the cellular components sometimes are moved up through the plant’s vascular tissue, and in some cases entire naked cells are absorbed directly by the plant root cells through a process called endocytosis.

All the nutrients contained in the bacteria are then utilized by the plant as a nutrient source. Yet, some of these bacteria survive this process. When there is a large enough concentration of bacterial cells formed further back from the root tip, they trigger the formation of root hairs, Kempf says. 

The growing root hairs secrete the mucilage and the exact nutritional requirements that these naked bacterial cells need to reform their own cell membranes. Then the bacteria are moved back into the soil environment.

Many of the signaling compounds that move out of the root system of these root hair tips know what the plant’s nutritional requirements are. The plant has signaled to them that it may need more phosphorus (P) or some other nutrient, and the bacteria go out and extract more minerals from the soil mineral matrix and hold them within their cells for follow-up root tips to consume those bacteria and provide the plants with the nutrients that it needs.

White believes uncultivated plants are absorbing the majority of their nutrition through this process, and it’s also possible for cultivated plants to absorb the majority of their nutrition the same way when managed properly. 

“This tells me that plants are not vegetarians,” says Kempf. “Plants are farming bacteria and microbes, feeding them and extracting nutrients from them much the same way that we farm livestock. This gives us a scientific explanation of how some farmers are able to produce higher-yielding crops than the regional averages with no fertilizer applications. 

“It’s a result of soil biology tapping into the soil and extracting nutrients, making nutrients available for the crop in very large quantities. We have all this bacteria living inside the growing root tips and then their minerals and nutrients being consumed and being utilized by the plants.”

DROPPING IN AND OUT. These photos (left to right) show the accumulation of bacterial cells and endophytes at a growing root tip, and how they move into and through the roots and provide minerals and nutrients to be consumed by the plants.

Click to enlarge

Kempf says his company, applying what has been learned from White and other researchers, has been able to help farmers cut N application rates by 30-70%, with a few able to drop N applications on corn completely. But he doesn’t advise most growers to quit N cold turkey. 

He advises one farm in southwestern Kansas that has been growing continual dryland corn on corn for the last 5 years that, paired with good rainfall of late, allowed them to push to 200 bushels an acre consistently with no N inputs. “There’s no compost or manure applications. One hundred percent of the nitrogen supply is coming from microbial delivery, from nitrogen fixation from the air through this rhizophagy process,” Kempf says. 

Over the last decade, using sap analysis on thousands of farms, Kempf says he’s learned the majority of nutritional imbalances growers experience in crops are not the result of adding too little of something, but the opposite — adding excesses of some nutrients in a way that creates deficiencies of other nutrients.

The two most common excesses that create the greatest yield challenges and quality challenges are nitrogen and potash. Kempf is focused on developing a completely different approach to nitrogen management for optimal crop performance.


“Plants are not vegetarians. They’re farming bacteria and microbes, feeding them and extracting nutrients from them much the same way that we farm livestock…” – John Kempf


“It’s common to think of nitrogen as one of the nutrients that we need a lot of. But when you do the math on what crops require in terms of physical quantity, they need as much calcium as they do nitrogen and potassium,” he notes. “And in fact, you get an equivalent yield response and a much greater quality response from calcium applications as you do from nitrogen applications. 

“You also get the same speed of growth response from calcium as you do from nitrogen, but we don’t give calcium the same credit or consideration, which I think is something that we’re really missing out on.”

Two ‘N’ Models

One concept growers should be aware of, Kempf say, is William Albrecht’s principle that plant nutrients should be available, but not soluble. Studies from universities have shown only about 40% of N applied to crops is actually absorbed by the plant, with the rest lost through leaching or nitrification. If growers could move that number to even 80%, it would cut their nitrogen requirements in half.

Kempf says there are two different models of plant nutrition being practiced by most farmers. The first is that plants have the capacity to absorb simple ions from the soil’s water solution to acquire calcium, magnesium, nitrate, potassium and so forth. “And it is true that plants do have the capacity to absorb simple ions from the solution,” he says. 

The second model, Kempf argues, is being used by growers who are producing extraordinarily high-yielding and high-quality crops. It holds that plants absorb the majority of their nutrition in the form of microbial metabolites from amino acids, amino sugars, organic acids and essential fatty acids — “all these cellular fractions that are absorbed directly from living microbes as well as directly from decomposed microbial cells.

“The way plant nutrition is actually designed to work is for plants to absorb this form of nutrients rather than simple ions,” he says. “The first model being used in mainstream, broad acre agriculture relies on glorified hydroponics, and that’s not how plant nutrient absorption in healthy soil actually works.”

Kempf uses the example of plants or trees growing out of bare rock or a cliff face. “Where’s the soluble nitrogen and phosphorus and potassium in that environment? It doesn’t exist. Who fertilizes the forest? No one. These wild plants are absorbing nutrients using this second model from microbial symbiosis rather than in the form of simple ions. Our domesticated plants have this same capacity.”

Which ‘N’ is Best? 

There are four different primary forms of nitrogen that plants can absorb: Nitrates, amino sugars and amino acids, urea and ammonium. And then in addition, of course, plants can absorb actual living microbial cells as well. 

While plants can absorb these primary forms directly, all of them have different effects within the plant based on how the plant metabolizes and uses them, the energy that they contribute to the plant, Kempf says. “So when we think about nitrogen utilization efficiency, different forms of nitrogen contribute energy to a plant or extract energy from a plant to differing degrees.

“Amino sugars or amino acids are the most energy efficient, and they contribute the most energy to a plant. Urea is next in line, then ammonium and lastly nitrates. Nitrate nitrogen actually draws a great deal of growth energy from a plant,” Kempf explains.

Conventional wisdom with N applications is that the majority of N gets converted to nitrate and plants absorb it, producing a rapid growth flush. But there’s more to it, Kempf says: 1 pound of N is not a pound of N. Some growers need to apply an equivalent rate of 1.2-1.5 pounds an acre of N to raise a bushel of corn. But other growers apply 0.5-0.7 pounds.

He explains the issue this way, using the example of N sources on the opposite side of the spectrum (amino sugars or acids and nitrates): “When a plant absorbs nitrate nitrogen, it’s picked up through the roots and moved up into the leaves. And once it’s in the leaves, it then gets converted to an amine nitrogen, and of course we have the nitrate reductase enzyme.

“In this conversion process, each molecule of nitrate to be converted to amino acids requires three molecules of water. So immediately, there is a water requirement for nitrate conversion that is not present for ammonium or urea conversion or amino sugars for that matter,” he says. “In addition, there’s also energy required for this conversion process to happen.”

When a corn plant absorbs 80% of its total nitrogen requirement in the form of nitrate, it requires 16% of its daily photosynthetic energy just to convert nitrates to amino acids.”

Kempf says that is a tremendous energy drain on the plant and it slows down the plant’s available sugars for growth and reproduction. Amino sugars and acids have the opposite effect, Kempf says, by contributing energy to the plant. 

“So this is why sometimes when growers switch from conventional nitrogen applications to organic production that pounds of nitrogen required to grow a bushel of corn appear to drop,” he says. “Now their nitrogen is coming from cover crops, or manure applications or compost applications.” 

To sum it up, Kempf says his observations and learning have led to this foundational premise: the only reason to apply nitrogen is when the capacity of soil biology to deliver the need of nitrogen has been destroyed. “And unfortunately,” he notes, “that’s the case for many agricultural soils. And the counterpoint is also true — that the fastest way to degrade the soil’s ability to provide nitrogen is to apply nitrogen. 

“In essence, the more nitrogen you apply, the more you’re creating an addiction where the soil biology is unable to overcome the surplus nitrogen in the soil profile and sequester and fix and make available to the crop what it really would have the capacity for without that surplus application.”

What to Do Now? 

So how do no-tillers turn this field methodology into practical field application? Kempf says there are a few different considerations for regenerating the rhizophagy cycle in soils and delivering 100% of a crop’s nitrogen requirements.

One is re-establishing the microbial population. In natural ecosystems, he says, the presence of beneficial endophytic microbes — which live inside the plant and in the soil at the same time — are important. 

For more about the rhizophagy cycle and soil health, please go to www.No-TillFarmer.com/0821 to see John Kempf’s question-and-answer session with National No-Tillage Conference attendees earlier this year.

“When we have healthy plants, these endophytes should be transferred from generation to generation on the seed coat. But that cycle is interrupted when breeding work is done by cell culture, which unfortunately is the case for many of our modern-day varieties that have been disassociated with their previous generation of endophytes.”

That’s why seed treatments are beneficial, he says, “because when the correct microbial inoculants are used, we can re-establish these associated microbes on the seed, and immediately establish this beneficial microbial population that can supply the crops nitrogen and general nutrient requirements.”

This also plays out when it comes to plants defending themselves from pathogens that might want to infect the root. When planting occurs there is often a 1-2 week delay in recruiting beneficial microbes from the soil profile, just a big-enough window for pathogens to attack roots. But the organisms that colonize the interior of the roots, as well as the exterior of the roots, are the same as those that provide exceptional disease resistance, he says. 

“So if we have challenges with a phytophthora or verticillium or fusarium or rhizoctonia — or any of these soil-borne fungal pathogens — resistance to these pathogens can be a perfect 100% when we have these associated endophytes,” Kemp explains. 

Most no-tillers have heard of mycorrhizal fungi and how important they are to soil and plant health and growth, but there are other bacteria and fungi that are important that are just beginning to be understood, Kempf notes. 

“In our consulting work, we have actual inoculants that we use because we know they are consistent and reliable and repeatable,” he says. “If you want to develop your own, I’m seeing some very intriguing and generally quite reliable results from either vermicompost, compost teas and the Johnson-Su bioreactor.” 

Watch the Additives

Another area to look at, he adds, is the overuse of fungicides, herbicides and insecticides and how that affects the soil’s microbial populations, because the effects have become negative in ways researchers are just starting to learn, he says. 

“And,” he adds, “we’re still connecting a lot of dots to understand whether soils are actually capable of delivering or supplying all of the endophytes and organisms that the seedlings are trying to recruit. My personal guess is that we have, over the last 40 years, destroyed so much of what has existed that we don’t even know what a really healthy microbial population might have looked like several decades ago.” 

Fertilizer sources are another area to consider, Kempf notes. 

TINY CONVEYORS. The graphic above explains the rhizophagy cycle process that happens at the growing root tip, where microbes, bacteria and fungi are taken up directly into the root and provide nutrients to the plant that were gathered in the rhizosphere.

Click to enlarge

“When we apply any soluble, ionic fertilizer, that oxidizes microbial cells in the soil profile. Most of the products used have a relatively high salt index and high electrical conductivity has an immediate direct negative impact on the soil microbial population,” he says. “It kills microbes that it comes into immediate contact with, and after it is diluted with soil water it still shuts off the microbial release process for nutrients. 

“When soil biology recognizes that the soil has a surplus of available nitrogen from applied nitrogen, they’re not going to exert any energy to sequester nitrogen from the air. Why would they? They don’t need to. There’s already an abundance of nitrogen in the soil profile. So the very act of constantly applying fertilizers determines that our soils will constantly be dependent on continued fertilizer applications.” 

Kempf isn’t suggesting growers stop all fertilizer applications right away because in most soils that would be a disaster. “But what I am suggesting is that you only apply what is needed, when it’s needed, and no more. 

“And when you do apply nitrogen, you should also buffer it in ways that allow the soil microbial population to rapidly convert it from the ammonium or nitrate or urea form that it was applied into amino sugars and to amino acids, because these amino sugars and amino acids are available but not soluble. They don’t leach. And yet plant roots can still absorb them.”

A Different Measurement Tool

Another way no-tillers can move in a new direction with nutrient management is using plant sap analysis to measure how much nitrogen the crop is actually absorbing from the soil and how much it really needs.

In Kempf’s opinion, many of the soil analysis tests currently used to establish N availability “are worse than useless” because they don’t accurately reflect what the crop actually absorbs from the soil.

After running tens of thousands of tests and comparing soil analysis vs. plant sap analysis, “I personally am not comfortable ever making recommendations for nitrogen applications exclusively based on soil data, because the soil data doesn’t correlate with what the plants are actually telling us,” he says. “Those numbers don’t correlate in any way, shape or form.”