DaveTheGardenGuy

Getting Dirty is Good For You!

    We know that productive garden soil contains between 100 million and 1 billion bacteria per gram (about a teaspoon full).  We also know that many of these bacteria have important roles to play in the Soil Food Web and are to a great degree orchestrated by plants through plant root exudates.  What we don't know is what roles many of the different bacteria play.  We know about a small fraction of them that help with nutrient cycling, disease suppression, and are important to water dynamics in the soil but the greater number by far and their related interaction with other organisms is currently beyond our understanding.  In 2007, Christopher Lowry, a neuroscientist now at the University of Colorado found that certain strains of soil-borne bacteria sharply stimulated the human immune system.  One bacteria, however, Mycobacterium vaccae, has been found to have amazing benefits to us directly.

    Mycobacterium vaccae, a bacteria that is common in soil, has been found to activate a specific group of neurons in our brains that produce serotonin.  Serotonin is found in the brain and the blood and is a very important neurotransmitter which helps regulate a whole host of functions including:

• metabolism
• appetite
• sleep
• aggression
• anger
• mood
• anxiety
• behavioral arousal
• motor activity
• coping responses to stress

    Many antidepressants work by serotonin pathways or serotonergic systems.  Antigens derived from the bacteria, which is non-pathogenic and saprophytic in nature, altered stress-related emotional behavior in mice.  The tests and results of studies in London and Bristol showed that the bacteria caused an increase in serotonin metabolism within the prefrontal cortex.  The conclusions from the 2007 studies included "a novel hypothetical framework for investigating the relationships among immune activation, serotonergic systems, and mental health."  This added to previous work showing "unexpected improvements in quality of life scores" to clinical cancer and inflammatory disorder trials.  Another trial using the soil bacteria to treat psoriasis showed Mycobacterium vaccae "gave long-lasting clinical benefit to most patients, with minimal side effects."

    Related to M. vaccae are two scary bacteria:  M. leprae and M. tuberculosis which cause leprosy and TB.  M. vaccae, named after the cow, however, because it was first isolated from cow manure, is ubiquitous in fertile soil and thrives anywhere soil is enriched with organic matter.  Christopher Lowry said that the effect of M. vaccae is "basically no different from all the SSRIs".  This is exciting:  SSRIs are antidepressants and include medicines such as Prozac, but whereas SSRI's are considered "blunt instruments" by many scientists for treating mood disorders, M. vaccae are selective and specific in their ability to excite certain neurons that produce serotonin and directly impact cognition and mood regulation as well as increase the ability to cope with stress and anxiety.

    In a 2008 article in Psychology Today, Daniel Marano explains that eating antioxidant-rich fruits and vegetables may only be half of a newly evolving story of health and that our society's displacement from the natural world has disrupted a deep and direct connection we have to the soil and it's resident organisms.  Indeed, the sharp rise in chronic asthma, inflammatory bowel disease, and other inflammatory, allergic, and immune disorders has resulted in "The Hygiene Hypothesis".  The bottom line is that we as a society have gotten too clean and the recent obsession with sanitation and anti-microbial products has caught up to us.  It's clear that we are a part of the Soil Food Web and removing us from the soil is to our detriment!

    Not only does M. vaccae promote the generation of serotonin in our brains, but also norepinephrine.
Perhaps more important, it induces the neurogenesis, or creation, of more neurons that produce these two amazing  compounds in our brains.  Norepinephrine is just as important as serotonin and affects the amygdala part of the brain where attention responses are controlled, including the "fight-or-flight response and related heart rate, glucose release, and blood pressure responses.  Norepinephrine plays a large role in attention and focus and may be used for indications of attention-deficit/hyperactivity disorder, depression, and hypotension.

    Similar to the striking rise in allergic and inflammatory disorders, the rise in ADHD and Depression and the related increase in the use (and abuse) of drugs such as the psychostimulants Ritalin or Concerta as well as tricyclic antidepressants or newer SNRI's such as Effexor and Cymbalta point towards a modern society who's young kids do not get to play in the soil enough and one who has abused the use of antibiotics.  It would seem that exposing ourselves and especially our children to the soil in the garden could be a good thing indeed.  The Hygiene Hypothesis page in Wikipedia now has 39 references as well as plenty of supporting articles for further reading and external links.  It "has become an important theoretical framework for the study of allergic disorders" and both their increase since industrialization as well as their higher incidence in more developed countries lends credence to the theory which was first given a scientific background by David Strachan in 1989 and later made popular in the 2005 book by Richard Louv called "Last Child in the Woods: Saving Our Children from Nature-Deficit Disorder."  This is now a movement called No Child Left Inside and a Federal bill introduced to the House of Representatives on April 22, 2009, Earth Day.  The bill is currently languishing in a subcommittee on early childhood education due to opposition from a conservative american "think tank" called The Heritage Foundation.

    It is now clear that exposure to bacteria, and especially during neo-natal development helps to adequately develop regulatory T cells.  In 2007, Keven Becker of the Gene Expression and Genomics Unit at the National Institute on Aging wrote an article that supports a link to Autism, also on the rise, to the hygiene hypothesis and shows etiological links between autism, asthma, and inflammation disorders.  He hypothesizes that "immune pathways altered by hygiene practices in western society may effect brain structure or function contributing to the development of autism."

    More recently, Dorothy Mathews and Susan Jenks of the Sage Colleges in New York tested live mice by feeding them live M. vaccae and found that they could "navigate a maze twice as fast and act with less demonstrated anxiety behaviors as control mice".  Mathews said in a May 25 2010 Science Daily article that "learning environments in schools that include time in the outdoors where M. vaccae is present may decrease anxiety and improve the ability to learn new tasks."  This is a pretty good reason to promote school gardens!

    So what then, do all these medical maladies have to do with gardening, horticulture, and landscaping?... the point here is that we as organisms co-evolved on this planet along with and as a part of the soil ecology over millions of years.  Over the past 100 years or so we have become increasingly detached from the soil that supports us and our efforts to further cut us off from bacteria and microbes by the use of antibiotics and antibacterial products has led to increases in diseases and disorders.  It's time we realize the health benefits of our natural connection to the Web of life and rejoice in the practice of getting dirty.  The next time you breath in the steamy aroma of fresh turned earth, compost, and manure, think of all the wonderful biology making it's way into your personal ecosystem.  Contemplate the increased biodiversity you now harbor and be glad.  While there are still valid concerns over other bacteria such as certain strains of Escherichia coli, for the most part, the little soil that sticks on the fresh veggies you eat may actually be covered in organisms that are very good for you.  -Yet another great reason to grow your own food and if you don't have one, start a garden today!

Great Gobs of Glomalin!

Now we've all heard about how organic material breaks down into humus.  Humus is the not-so-secret component of "Black Gold"... that earthy well composted organic material that binds soil particulates into aggregates, makes gardeners proud and teary eyed to behold,  and feeds our precious soil food web.  Humus is broken down into two distinct kinds: active humus and stable humus.  Many fertilizers contain a mined humate called Leonardite, the result of thousands of years of the decomposition of ancient freshwater marshes.  For the longest time, humic acids were thought to be the main carbon constituent of soils.  Now, after breakthrough research by Sara Wright in 1996 and further study by her and others, what might be the soil's most important component has been identified.

 Most people have now also heard about Mycorrhizal fungi -fungi that extend and improve plant root's abilities to breakdown, make available, transport, and absorb many minerals and nutrients that would not otherwise be available to the plant were it not for this symbiotic relationship. Once the spores germinate, these fungi can only survive about three days before they must become associated with plant roots or they perish.  Many organic fertilizers contain inoculants of these amazing organisms and their benefits can be dramatic. They are broken down into two groups: Endomycorrhizae and Ectomycorrhizae.  Endomycorrhizae, as the name implies, grow and can produce spores inside the roots of plants and Ectomycorrhizae, which coat the outside of the roots of some plants.

It has also been known that the soil food web is to a large part orchestrated by plants.  This is done through plant root exudates, the study of which is still in it's infancy and our understanding is, and may remain, very limited.  When you consider the importance of soil bacteria, realize that there are an estimated 60,000 species, most of them having not yet been named, studied, or their role understood, and then think of the growing list of plant root exudates that help orchestrate their behavior, you start to appreciate the intricate web we are delving into.  This is a good moment to feel awed at the complexity of an ecology we so often take for granted.  Just as it was amazing for us to realize that the overwhelming  majority of plant tissue is not derived from the soil, but from the air ( CO2) and water (H2O), it is likewise amazing to realize that a large portion of the hydrocarbons produced by plants through photosynthesis are not held in the plants, but exuded through their roots into the soil food web! The area around the roots where all this action takes place is called the rhizosphere.  It's not so surprising then, to think that the endomycorrhizae fungi might likewise also have exudates.

What if I told you that there was a substance in the soil... a substance that was produced by certain fungi in symbiotic relationships with plants... that hold one of the main answers to our planet's health and is able to combat global warming?  As Landscapers and Gardeners we're in a position to both appreciate and play a big part in increasing the amount of glomalin in our soils.  Amazingly, this material  makes up a whopping 27% of soil carbon!  Depending on heat and moisture, glomalin can last from seven to twenty-four years.  Many soil microbes only last for 20 minutes. fungal hyphae may last from days to weeks.  The durability and longevity of glomalin makes it very important for soil health and as a carbon sink.  As a glycoprotein, carbon is stored in both it's sugar component and it's protein component, making it 30-40% carbon, up to 24 times as heavy as humic acids, and soils can contain four times as much glomalin as humates!  It provides more nitrogen and carbon to the soil than do hyphae or other soil microbes and can be found in quantities of over 100 mg/g in some soils.  It's durability is also the reason it took so long to identify it.  To find glomalin, you must put a soil sample in a bath of citrate and then heat it at 250 F for an hour!

Glomalin is named after the order of fungi that produce it: Glomales.  This Arbuscular mycorrhizal fungi creates glomalin in order to give rigidity and strength to it's hyphae so as to better bridge gaps between soil particles and to help transport soil solutions.  As the older hyphae outlive their short lifespan, and new hyphae are produced near the root tips, they release the glomalin in the soil.  It's interesting to note that tilling soil greatly reduces the amount of glomalin in soils.  Also interesting is that higher concentrations of CO2 in the air promotes rapid glomalin production.  This may be one of the major (and overlooked!) feedback loops the Earth has to regulate CO2 content in our atmosphere -and yet another reason to be awed and amazed by the abilities of plants!  Between a 3 year study on shrubs and a 6 year study on grasses in San Diego, Wright and scientists from Riverside and Stanford showed that when CO2 levels reached 670ppm (the level we will attain by 2050 given current trends), Glomales hyphae grew three times as long and glomalin production increased 500%.   Wright says that the same increase can come from good soil management techniques.  Longer hyphae can help plants reach and absorb more water, protect soil from erosion, and increase the fertility of soils.  These are all important traits for plants to survive in a warming climate.

Why is this not headline news?!  Here we have a major component of healthy top soil- the precious material that we all depend on for our survival, perhaps a key feedback loop in regulating our planet's CO2 levels, and an element of soil fertility that may prove more important to our future in the long run than the Haber process of fixing ammonium nitrate.  This discovery is fifteen years old and yet when I ask my fellow gardeners and landscapers if they've heard of glomalin, I get raised eye brows and an inquisitive look... This has to change.  This knowledge is precious.  Hats off to Sarah and her team!  I hope you all go out and include glomalin in your discussions regarding soil fertility and carbon sequestration.

(photo by Sara Wright)

Our Most Precious Resource?

I took a class last Thursday with the Marin Master Gardeners and the guest speaker and UC Berkeley Soil Scientist, Steve Andrews.  Steve took us through a wonderful and most entertaining review of soil morphology and additional insights into soil ecology and plant nutrition.  -Truly a a divine experience!  This was a longer version of the class he presented to the Bay Friendly Landscape Professional class I attended last year.  Steve told us that there may be an advanced soil class in the near future.  While at Cal Poly, SLO, I took the soil science classes, and all the topics Steve brought up were reminders of those classes, but that was back in the late 80's and Cal Poly was still somewhat stuck in the old agribusiness mentality of soil as a sterile medium, fertilizers being measured out by the acre and recommendations based on economic returns on investment -without comment about the soil ecology and how it might be affected.  It is so nice to hear a modern soil educator so passionate about our most precious resource, our LIVING soils.

Which is more precious?  Fresh Water, or Soil?... that's a hard one.  We need both.  They are intertwined in the web of life.  One creates the other.  As our species has evolved on Earth, our various civilizations have thrived and crashed primarily based on how we have treated these two resources. Their interaction along with the ecologies they support give rise to the world we hold so dear.  Our understanding of these interactions will be the basis of our survival.  Learning about soil is one of the first steps in learning about life, a big step towards our species making the changes necessary in our practices, and a huge leap towards any individual's concept of where they fit into the web of life - a strong dose of awe that can lead to a better intellectual and even spiritual questioning of how and why we are here.  Perhaps our greatest calling is to be good soil stewards.

A good resource for soil can be found at the WSS, the Web Soil Survey.  This is information provided by the National Cooperative Soil Survey operated by the USDA natural Resources Conservation Service.  Maps and data are available for more than 95% of our nation's counties!  Amazing to type in an address and get so much information: soil complex percentages, elevation, slope, mean annual precipitation, temperature, and frost free period plus depth to water table, etc.  Then you can search for a use and see the results.  

 During our class we got to do a textural ribbon test.  This is done by getting a soil sample damp and pressing it between the thumb and fingers and pushing it through into a ribbon, the length of which determining the relative amounts of sand, silt, and clay.  This exercise, along with rubbing a smaller, wetter sample in the palm of the hand to determine it's grittiness or smoothness can be a good indicator of the soil textural class as depicted on the Soil Pyramid.  The Sand, Silt, and Clay are the "Soil Separates".

 The relative sizes of these are:

Sand: 2mm -.05mm

Silt: .05mm - .002mm

Clay: smaller than .002mm.  (Cant be seen by the unaided human eye!)

"Garden Nirvana!" - the area in the middle of the pyramid (this sounds almost masonic!) where the concentrations of the three soil separates find their sweet spot in the textural class of  LOAM.

Several insights I gleaned is that in most soils, soil pore space, roughly 50% by volume in soil, is filled with air and water, always in flux, and is where the concept of "field capacity" as it relates to water saturation occurs.  This is also where gas exchange occurs and most of soil chemistry.  5% of most soils is comprised of organic matter and humus which, consisting of relatively 80% of that 5%, is the magical "glue" that binds soil into aggregates and peds, the macro structures of soil conglomerates.  The ability of humans to enhance or destroy soil structure is key to the survival of civilization.  These concepts: soil texture, a constant in an anthropocentric time frame, and soil structure, a fragile system that can take thousands of years to create ("pedogenesis") -or destroyed in a very short time frame, form the basis of modern soil classification.

Clay is also where all the action is.  Clay, being .002mm or smaller in size, has both chemical properties an electrical properties.  The negative charge of clay particles allows soils to hold onto cations -important plant nutrients.  The negative clay surface also allows the soil to interact with active nutrient absorption systems that plants (and a plethora of other organisms) have evolved.  The sheer mind boggling expanse of this surface area is hard to comprehend.  Clay particles, which are so small they are not visible to the naked human eye, are comprised of layers, 1:1 or 2:1 of tetrahedral and octahedral layers.  This layering allows an amazing surface area.  Steve pointed out in our class that a single teaspoon of clay can have the relative equivalent surface area of a football field.

Clay can also be the source of life as we know it on this planet.  A.G. Cairns-Smith, in a paper in 1966, postulated that clay was the scaffold upon which life arose.  Clay affords the protection, the repeating layers, the proper distances between those layers, the chemical charge, and the structure to create repeating compounds as well as the affinity for organic compounds and an ability to organize them.  Chemist James Ferris and colleagues at Rensselaer Polytechnic Institute, during research sponsored by NASA, created an experiment where they "induced clays to act as scaffolds in the formation of RNA, the polymer that carries the genetic message enabling protein synthesis".  Harvard University geneticist Jack Szostak, who later mixed clays, RNA nucleotides, and lipids was able to show that the clay not only absorbed the RNA, but quickly formed lipid vesicles. "This spontaneous self-assembly of RNA-containing vesicles, though a long, long way from synthesizing life, is perhaps the closest anyone has come to forming a cell-like entity from scratch". (p.158, Gen-e-sis, Robert M. Hazen, 2005)

The miracle of life may well have evolved in the chemically charged, too-small-to-be-seen, layers of clay.  This concept lends a new perspective to the idea that soil supports life.  Other impressive soil life concepts from the present day include:  a gram of soil contains a population of between 100 million to 3 BILLION bacteria, roughly a million fungi, perhaps miles of mycelium...  and a plethora of virus, anthropods, isopods, etc. -a truly wonderous soil food web with feedback loops and interactions with the macroecology of vertebrates and plants. -too much to go into in this little blog!

We also briefly looked at the Munsell color chart, an expensive and very accurate color system created by Albert H. Munsell and adopted by the USDA for soil research in the 1930's.  It uses Hue, Value, and Chroma to determine the exact color- based on human visual perception.  Soil color can show us clues to mineral concentrations, especially in the B soil horizon where soil elements accumulate due to leaching over time.  As Steve pointed out, the color of soils can also have a legal application in the process of saving our wetlands from overdevelopment.

 Soil as it relates to gardens and gardeners -agriculture- is a huge topic.  I will explore more of this awe inspiring topic and how we fit into the soil web in later blogs.  Fertilizers and their use being the next topic of discussion for the Sloat Garden Center Seminar series (Feb. 20 in Kentfield and Feb 27 in Mill Valley, Miller) and the Marin Garden and Landscape Meet Up group meeting.

That having been said, I can't express enough my main take-away from the class, and almost every gardening class I've ever been involved with:  The magic bullet:  Compost.  Compost adds life, it adds buffers, it adds humus.  Compost can take almost any soil ill and correct it over time, creating a more complex (and thus stable) food web, maintaining better water holding capacity while improving drainage, water infiltration and filtration, soil nutrient availability through chemical and biological actions, as well as a myriad of other benefits including the breakdown of toxins.  As our Co-Horts pointed out, one of the main MMG mantras is " Compost Compost Compost - Mulch Mulch Mulch!"  This is truly the key to improving humus content and soil life.

Steve Andrews also pushed another take-away:  Don't fall into the media-driven trap of regular fertilizing without proper soil testing and taking the plants needs, the season, and climate into account.  This falls right into place alongside the practices of IPM - using the synergistic approach and monitoring before taking action, knowing the biotic and abiotic situation and the possible affects of those actions.

So go forth and spread the good word of Compost, Mulch, and the wonder of Life; in, from, and dependent on -our precious Soil.