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Biological Approaches to Farming


Academic year: 2021

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Biological Approaches

to Farming

Reducing Fertilizer Use & Pollution


he thin skin of soil that envelops the earth’s crust is a basic and criti-cal resource supporting life on the planet. Yet, in a sense, we treat soil — that remarkable collection of microbes, min-erals and processes — as if we were still in the Stone Age. Research (and just plain common sense) indicates that excessive use of synthetic fertilizers and pesticides have had far-reaching ramifications for our environment and our own survival. The time has come to change course in the treatment and management of our irreplaceable soil and water resources. For all our infatuation with the latest in computers, phones and modern gizmos, basic human survival depends a lot more on clean water and our ability to sustain soil productivity.

Water quality is deteriorating at an alarming rate worldwide, and farming is identified as a significant source of surface and groundwater pollution. As a result, nitrogen (N) and phosphorus (P) runoff mitigation has become a ma-jor goal of the agriculture industry. The preponderance of modern agriculture production relies on intensive synthetic fertilizer use, frequent tillage and heavy irrigation practices, all of which are highly conductive to nutrient leaching. The industry has proposed a number

by Mike Amaranthus Ph.D.

& Larry Simpson


of Best Management Practices (BMP) in an attempt to maximize production while minimizing surface and ground-water contamination from agricultural runoff and leaching. These proposed practices vary with particular farm-ing conditions, but most encompass proper vegetative cover and improved efficiencies in irrigation and fertilizer programs. While these practices may help, other valuable tools are available right beneath our feet.

A GROWING PROBLEM The advent of widespread synthetic fertilizer use in farming across North America in the 1940s and 1950s began to short-circuit many of the natural biological processes that keep soils and plants alive and healthy. Why care? Soil biology is critical to capturing and stor-ing fertility in the ground. In the absence of a living soil, fertility, especially in the form of chemically derived nitrates and phosphates, can readily move into

surface waters and aquifers, creating a loss of soil productivity and significant detrimental impacts on water quality and aquatic life.

Only a fraction of synthetic fertilizers applied to North American soils are ac-tually utilized by the target plants. Much of these inputs result in the “mainlin-ing” of inorganic nutrients into soils and waterways. Our use of synthetic fertilizers can be analogous to the much-publicized use of steroids by certain ath-letes. The treated plants may grow and produce yields at unnatural rates in the short term, but unfortunate side effects

can become serious over time. In an Io-wa State University study, corn fertilized with anhydrous ammonia utilized only 29 to 45 percent of the nitrogen input. The unused balance can end up damag-ing surrounddamag-ing environments. Some of the unused nitrogen is volatized into the air, contributing to acid rain and global climate change, but much of it washes past the target crop roots, through the soil profile, into the groundwater and ultimately into neighboring streams, lakes or oceans. In the same Iowa State study, 49 to 64 percent of the nitrogen

applied to the corn crop was volatized or leached.

Phosphorus is a nutrient essential to most aquatic plant growth, and its lim-ited availability regulates most aquatic plant ecosystems. So when excess phos-phorus becomes available to aquatic plants such as algae, growth can burgeon out of control. Just one pound of phos-phorus can result in the growth of 350-700 pounds of green algae.

Excess amounts of phosphorus and nitrogen cause rapid growth of algae phy-toplankton, creating enormously dense populations, or “blooms.” Unconsumed algae ultimately sinks to be decomposed by bacteria in a process that depletes bottom waters of oxygen. Like humans, most aquatic life requires oxygen. When the oxygen in an aquatic environment becomes depleted (a condition known as hypoxia), fish, insects, crustaceans and most other species will die unless they migrate to other areas where the habitat remains suitable. Prolonged hypoxia can result in eutrophication, essentially the process described above in which over-abundant nutrients, especially phospho-rus, develop into a biologically devoid aquatic environment. The economic

Green algae lake buildup.


consequences of excessive algal growth due to nutrient pollution can be costly and severe, leading to increased water treatment costs, degraded fishing, boat-ing activities and negative impacts on tourism and property values.

Like phosphorus, the heavy use of nitrogen fertilizer can also cause an over-load of nutrients in the waterways into which it drains. Excess nitrogen simi-larly stimulates algae blooms that can create oxygen-starved water, fish kills

and aquatic dead zones. Nitrates and phosphates migrate downstream from Midwest farmlands, eventually reaching the Mississippi River and ultimately the Gulf of Mexico. Once in the Gulf, they stimulate runaway algae growth, which has formed a fish-smothering hypoxia zone that is sometimes as big as the state of New Jersey.

Health costs have also been linked to the excess use of synthetic fertilizers. In some places, such as Des Moines, Iowa, a “blue baby alert” is issued when nitro-gen runoff from surrounding farmland is heavy. This alert cautions parents to avoid giving tap water to children be-cause elevated nitrates in the water bind to hemoglobin in blood, blocking proper

distribution of oxygen to the brain. An-other human health issue can be created by blue-green algae blooms, which can produce toxins affecting the nervous system and liver of humans. Numer-ous states have experienced negative economic and human health impacts due to general declines in surface and groundwater water quality as evidenced by algae blooms and fish kills.

Fortunately, there are many exam-ples in which water quality has been

improved by limiting nutrient loads, including Lake Erie, Lake Geneva, Swit-zerland and Lake Endine, in Italy. Eu-trophication in these lakes was reversed by implementing measures that reduced nutrient pollution. These examples dem-onstrate that a phosphorus reduction of 70-90 percent is required to significantly reverse eutrophication and improve eco-logical health to a body of water.

LIVING SOIL: RESERVOIR OF FERTILITY Truly healthy soil contains a prodi-gious abundance of biological activity. One heaping tablespoon of healthy soil may contain billions of soil organisms. Just an ounce can contain numbers of

organisms equal to the earth’s entire human population! An acre of healthy topsoil can contain a web of life that includes 900 pounds of earthworms, 2,500 pounds of fungi, 1,500 pounds of bacteria, 130 pounds of protozoa, 900 pounds of arthropods and algae, and in most cases, even some small mammals. These soil organisms are like billions of miniature bags of fertility, each storing plant nutrients in their body tissue while slowly converting them into available forms of plant nutrients.

Scientific research confirms that fal-low, tilling and compaction — all com-mon in agricultural areas — reduce or eliminate the soil’s mycorrhizal fungal populations. Furthermore, high levels of synthetic fertilizers can have a devastat-ing effect on the soil food web. Many synthetic fertilizers are essentially salts that suck the water out of beneficial bac-teria, fungi, protozoa and a wide array of other soil organisms. Yet these are the or-ganisms that form the basis of the food web, creating, conserving and processing nutrient capital in the soil. The destruc-tion of large segments of living soils often leave growers stuck on a treadmill requiring the continual and increasing use of chemicals to compensate for the loss of natural fertility.

Thousands of research studies docu-ment that beneficial soil organisms play key roles in the conservation, mobiliza-tion and transportamobiliza-tion of nutrients from soils into plants. On those farmlands in which beneficial organisms have been eliminated, tasks such as supplementing nutrients and pest and pathogen control must now be done by farmers. Over time, input costs have gradually esca-lated due to an over-reliance on increas-ingly expensive chemical approaches to agricultural land management. Often solving one problem synthetically causes three others later.


Prior to World War II, growing op-erations were largely biologically based. Most had been successfully and sustain-ably managed for generations. It has only been since the late 1940s that the syn-thetic approach has been utilized on a large scale. Within these last 60 years,

se-Tomato trial: without mycorrhizal inoculation and fertilizer; fertilizer only; and fertil-izer and mycorrhizal inoculation. The addition of mycorrhizal fungi reduced nutrient loss and increased yield.


rious problems have become clearly evi-dent. However, there are biological tools that can decrease the need for chemi-cal fertilizers in agricultural operations. Among these are those crucial groups of microorganisms that keep soils fertile and healthy: bacteria and fungi.

Incorporating nitrogen-fixing plants into farm management practices adds nitrogen and organic matter to soils in a less leachable form. An excellent example is the use of rhizobial bacteria inoculant when planting nitrogen-fixing plant spe-cies such as legumes. Eighty percent of the earth’s atmosphere is nitrogen, yet despite this abundance, plants are un-able to absorb it as a gas from the air. That’s where symbiotic, nitrogen-fixing bacteria associated with the roots of certain plants come in. These bacteria are capable of utilizing the vast pool of atmospheric nitrogen by converting it to an organic form that plants can use. A legume cover crop can add and store as much as 200 pounds of nitrogen in an acre of soil.

In their natural environments, most plants, including more than 90 percent of all crop species, form a root associa-tion with specialized fungi called mycor-rhizae. Mycorrhizae literally means “fun-gal roots.” In this mutualistic association, root-attached fungal filaments extend into the soil, helping the plant by gather-ing water and nutrients and transportgather-ing these materials back to the roots.

Miles of fungal filaments can be pres-ent in a small amount of healthy soil. The plant’s association with mycorrhizal fungi increases the effective surface ab-sorbing area of roots several hundred to several thousand times. In return, the plant feeds the fungus sugars produced by photosynthesis. Scientific studies with hundreds of various plants indicate that the mycorrhizal relationship can improve nutrient uptake, yields, drought tolerance and root biomass. This symbiosis is truly a win-win association for the plant, the fungus and potentially for the farmer.

Crop inoculation with arbuscular mycorrhizal (AM) fungi can be an im-portant component of farming practices that reduce nutrient runoff while main-taining plant crop quality and yield. AM fungi are a specialized group of micro-organisms that colonize the roots of

most plants, establishing this mutually beneficial relationship. Attached to the roots, they develop a dense mass of tiny fungal filaments that reach out into the surrounding soil, dramatically enhanc-ing the plant’s ability to acquire mineral nutrients and water.

AM fungi have been considered as a valuable tool to decrease fertilizer inputs because numerous mycorrhiza-inoculat-ed plant species have reachmycorrhiza-inoculat-ed similar or greater growth with a fraction of the fer-tilizer rate required by non-inoculated control plants. Recent research by the University of California examined the use of mycorrhizal fungi to increase nu-trient use efficiency and reduce nitrogen and phosphorus leaching. The authors found that mycorrhiza-treated plants had greater biomass than non-treated controls. Shoots from mycorrhizal-colo-nized plants averaged 30 percent higher nitrogen content and a whopping 300 percent higher phosphorus content than shoots of the identical plants without mycorrhizal root colonization.

Perhaps most importantly, the au-thors also documented a significant re-duction in the concentrations of nitrates, ammonium and phosphates found in the leachates of inoculated plants receiv-ing the full rate of fertilization. Nitrate, ammonium and phosphate losses via leachates were reduced 30 percent with mycorrhizal inoculation. This study has tremendous implications for more ef-ficient use of fertilizers while simultane-ously reducing water pollution in grow-ing operations. Farmers can save money on the use of fertilizers while minimizing surface and groundwater contamination from runoff and leaching.

Recent research published in the jour-nals Nature and Ecology emphasizes the important, newly discovered role mycor-rhizal fungi play in delivering nitrogen to plants. This information may lead to a reduced reliance on synthetic nitrogen fertilizers in agriculture. Root coloni-zation by mycorrhizal fungi improved nitrogen uptake for a variety of plant species by direct utilization of nitrogen in the form of organic amino acids. With this in mind, farmers may be able to har-ness mycorrhizal fungi for more efficient use of the organic nitrogen stored in existing soils, manures, organic

fertiliz-ers and crop residues, thus diminishing chemical fertilizer inputs.

The research authors found that ben-eficial mycorrhizal fungi transfer sub-stantial amounts of nitrogen to their plant hosts. The fungus facilitates use and conservation of nitrogen by absorb-ing amino acid molecules, which contain nitrogen, thereby minimizing the plant’s need for leachable nitrogen forms such as nitrates, which must be converted in the surrounding soil.

ESTABLISHING NATURAL, LIVING SOIL So, how do you re-establish ben-eficial soil organisms after they have been lost from the farm? The beneficial bacteria, Rhizobia, has long been avail-able as an inoculant for legumes and is usually applied as a liquid or peat-based form to the seed or plant. More recently, advancements in our under-standing of mycorrhizal fungi and their requirements has led to the production of high-quality, mycorrhizal inoculum at affordable prices. Mycorrhizal inoculum is currently available in granular, powder and liquid forms.

The most important factor for re-in-tegrating mycorrrhizae is to place myc-orrhizal propagules directly with seed or on or very near the root systems of target plants. Inoculum can be banded with seed or seedlings, sprayed in-furrow, watered into porous soils, or pre-mixed into soil. The form and application of the mycorrhizal inoculum depends up-on the needs of the farmer and the equipment used.


Over the last few decades a grow-ing reliance on synthetic fertilizers has developed throughout the agricultural industry. This trend depends heavily on chemical inputs rather than biology-based methods to solve crop produc-tion and land management challenges. While these practices have provided nutrients in the short term, the syn-thetic approach has resulted in a litany of long-term problems and expenses. It is a “Stone Age mentality” to keep bombarding our soils with practices that destroy its valuable biology. In ad-dition to the steadily escalating expense


of chemicals themselves, collateral costs include the major deterioration of many aquatic systems and increased health concerns.

It’s clear that the need to manage nitrogen and phosphorus biologically is especially urgent. Before the advent of synthetic nutrient sources and the fossil fuels that deliver them, biologi-cally sound practices proved successful and sustainable for thousands of years without detrimental impacts to wa-ter quality. In Stone Age times, man’s inability to heed the negative conse-quences of his actions can be attributed to ignorance and lack of sophistication. What’s our excuse today as we witness the deterioration of our soils, waterways and health due to flawed agricultural practices?

The modern farmer has many bio-logical tools with which to improve the health of the land and its people by putting the living soil back to work. A biological methodology works by incor-porating important soil organisms that

build and maintain soil fertility as a cor-nerstone of farm management. This ap-proach is now spreading rapidly across America as we begin to recognize the fact that rich, productive soils are dynamic, living ecosystems made up of a mixture of minerals, air, water, organic materials and a healthy population of beneficial soil organisms.

Mike Amaranthus, Ph.D., is adjunct associ-ate professor at Oregon Stassoci-ate University and president of Mycorrhizal Applications, Inc., web-site www.mycorrhizae.com. Dr. Amaranthus has authored over 60 scientific papers on mycor-rhizal fungi and their uses. He has received the Department of Agriculture’s highest honors for scientific achievement and been featured on several national television broadcasts.

Larry Simpson is director of education and training at Mycorrhizal Applications, Inc. He previously spent nearly 20 years specializing in organic soils and fertilizers in the retail lawn and garden industry, where he formulated and developed numerous innovative and success-ful natural/organic soil and fertilizer products, including some of the first to contain mycor-rhizal inoculants.

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