soil science

APLD Brochure: An APLD Guide to Sustainable Soils Available on the APLD website

This brochure is a really good basic summary of soil - and we all know its all about the soil!  

"The bottom line is that soils should be valued and preserved, because, literally, life depends upon it."

Recommendations for Designers include:

  •  Design for your soils. Aim to restore the site's soil back to its native composition. In most cases, avoid overbuilding soils into something beyond what is natural for your area.
  • Know the biology of your soils by sampling and testing the soil using a competent soil biology lab.
  • Do not till or physically disturb a healthy, mature soil. Physical disruption severely damages or destroys the mature soil food web. 
  • Physical soil compaction during construction has a long-term damaging effect on soils and is difficult to remedy after the fact. All efforts should be made to protect soils prior to and during any construction phase. 

The brochure also has a nice summary of the role soils play in sustainability:

  • Soils are the foundation of the ecosystem.
  • The living systems occurring above and below ground are determined by the properties of the soil. Soils store and cycle nutrients needed by these living systems, supporting life all the way from microbes to humans. A healthy, diverse ecosystem is critical for life, and it begins with the health of the soil.
  • Soils store carbon
  • Soils manage water.  Water enters the soil through the channels created by vegetation and the activities of organisms such as earthworms. It fills the empty pore spaces and is taken up by plants. Healthy soils have sufficient open pore space to absorb the water and allow it to infiltrate the soil, recharging the groundwater. Wetlands, also known as hydric soils, manage large quantities of water and also serve as buffers and filters in addition to supporting a vast array of wildlife.  

On the other hand, degraded soils exhibit erosion, which occurs when soils are not covered by vegetation, and rainfall both compacts the soils, forming a crust on the surface, and carries the top layer of sediment away. Compacted soil compresses the pore spaces so that air, water, and plant and animal life cannot penetrate.

  • Soils filter, buffer, degrade and detoxify potentially harmful chemicals
  • Soils influence climate.  Soils moderate temperature fluctuations, as soil heats more slowly than air and can absorb more heat on a hot day. Soils absorb heat during the day and radiate heat at night. Darker soils, which tend to have higher organic content, absorb the most heat. Soil temperature affects plant growth, which in turn affects climate.

Soils and Water

Our soils have changed.
When considering the loss of the eastern deciduous forest (75% gone) and the transition from native prairie / savanna plant systems to the mono-crops of industrial agriculture, we are looking at an incredible change within our soils. The depth and bulk of our current root systems no longer exist as they did two hundred years ago. Trees have extensive root systems in the top 24" of soil, and can reach five to eight feet or more in depth. The prairie existed on a root system depth between two and three feet, with some plants reaching four to six feet deep. The extensive root systems of our original "ground cover" opened up the soil, allowing for a deep penetration of precipitation and the slow exhale of moisture back up into the atmosphere through plant transpiration.
Not any more: corn, soybeans, wheat and other annual crops have temporary root systems in the 12 to 18 inch range. Perennial turfgrass, our American lawn, covering an area about the size of Wisconsin, has a root system of around six to twelve inches in the best of conditions. Precipitation run-off is now something we have to plan for after almost every rain.
Garth Conrad, APLD Garth Conrad Associates, LaPorte, IN


More Soil Basics - what are the roles of soil?

I recently joined the Soil Science Society of America.  They have published a fabulous book called 'Know Soil Know Life" - designed as a textbook for middle/high school students.  Here's some of the points they make.

Soils Overview - Provided by the Soil Science Society of America

Soils are complex mixtures of minerals, water, air, organic matter, and countless organisms that are the decaying remains of once-living things. It forms at the surface of land – it is the “skin of the earth.” Soil is capable of supporting plant life and is vital to life on earth.

Soil is formally defined by the Soil Science Society of America as : "the unconcolidated mineral or organic material on the immediate surface of the earth that serves as the natural medium for the growth of land plants".    The second part of the definition is "the unconcolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time.

So, then, what is DIRT?

 Dirt is what gets on our clothes or under our fingernails. It is soil that is out of place in our world – whether tracked inside by shoes or on our clothes. Dirt is also soil that has lost the characteristics that give it the ability to support life – it is “dead.”

Soil performs many critical functions

in almost any ecosystem (whether a farm, forest, prairie, marsh, or suburban watershed). There are seven general roles that soils play:

1. Soils serve as media for growth of all kinds of plants.

2. Soils modify the atmosphere by emitting and absorbing gases (carbon dioxide, methane, water

vapor, and the like) and dust.

3. Soils provide habitat for animals that live in the soil (such as groundhogs and mice) to organisms (such as bacteria and fungi), that account for most of the living things on Earth.

4. Soils absorb, hold, release, alter, and purify most of the water in terrestrial systems.

5. Soils process recycled nutrients, including carbon, so that living things can use them over and

over again.

6. Soils serve as engineering media for construction of foundations, roadbeds, dams and buildings, and preserve or destroy artifacts of human endeavors.

7. Soils act as a living filter to clean water before it moves into an aquifer.

Biochar is the New Black

More from the NYS Arborist Meeting in January:

Mr. Hendrickson, the guru from Bartlett Tree Research, mentioned a magic ingedient in passing that I didn't know anything about - biochar.  It turns out that biochar has a rich history (no pun intended) as a soil amendment that "magically" makes plants and trees grow and that even helps soil structure and health.

Here are some facts:

Biochar is formed from organic material (otherwise know as garden waste) by pyrolysis: a thermochemical decomposition of organic material at high temperatures (390 - 570 degrees F) in the absence of oxygen.  It involves the simultaneous change of chemical composition and physical phase, and is irreversible. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating".  In general, pyrolysis of organic substances produces gas and liquid products and leaves a solid residue richer in carbon content, char - aka biochar.  Pyrolysis differs from other high-temperature processes like combustion and hydrolysis in that it doesn't involve reactions with oxygen or water.

Biochar as a soil amendment has an ancient precedent - "terra preta", discovered in the 1950s by Dutch soil scientist Wim Sombroek in the Amazon rainforest.  It still covers 10 percent of the Amazon Basin.  As the nonprofit U.S. Biochar Initiative explains, “biochar has been created and used by humans in traditional agricultural practices in the Amazon Basin of South America for more than 2,500 years.  Dark, charcoal-rich soil (known as terra preta, or black earth) supported productive farms in areas that previously had poor and, in some places, toxic soils".  

Over the past 10 years, researchers have been investigating terra preta, now called biochar, as an agricultural resource. Typically when biomass decomposes or burns, virtually all of the carbon stored in the plant is released into the atmosphere as carbon dioxide, a greenhouse gas that contributes to global warming.  But when biochar is produced, roughly half of the plant’s carbon is retained as stable carbon in the biochar.  The other half is released as wood gases, which can be used as an energy source. This biochar cycle puts carbon from the atmosphere back into the earth, puts it to positive use in the soil and increases the amount of time it stays there.

Here's why biochar is "magic":

  • It provides a combination of moisture management and a way to store microbial food and plant fertilizer.  When there is an excess of water, food and fertilizer, biochar stores them.  When there is a deficiency, it slowly releases them back into the soil, where the plant or microbes can take advantage of them.
  •  It persists in the soil for years, greatly reducing(eliminating?) the need for re-application.  It is much more persistent in soil than any other form of organic matter that's applied to soil.  This is referred to as "stability" by the soil scientists.
  •  It is highly adsorbent.  It sops up humic acid, a food for soil microorganisms, and humic acid itself binds to fertilizers, keeping them from leaching out of the soil.

"What is special about biochar is that it is much more effective in retaining most nutrients and keeping them available to plants than other organic matter such as for example leaf litter, compost or manures. Interestingly, this is also true for phosphorus which is not at all retained by 'normal' soil organic matter". (Lehmann, 2007) 

from Cornell webpage; references as cited on that page

  • It is also highly adsorbent of water.  In conditions with greater than 60% relative humidity, it absorbs water.  And in conditions less than 40% relative humidity, it releases water.  So it is an enormous stabilizer of relative humidity in soil, which means less watering.
  • It is a way to "recycle" organic waste, and the off-gas can be used as fuel.
  • You only need a little, and it can be added as a soil amendment to existing planting beds, like tree wells.

But there are caveats as well:

  • The vast majority of research has been into biochar's effects on agricultural soils and crop yields.  Until very recently, there has been little research on biochar in urban and suburban soils, trees and shrubs.  Agricultural crop research goes a lot faster than urban tree growth research - that will take years.
  • All biochar is not created equal - it matters what organic matter was used to make it and whether it has been tested for contaminants and properly de-watered.
  • This is not a plug - but Bartlett uses biochar as part of their soil improvement and root invigoration treatments.  Bartlett Tree Research Laboratories is collaborating with the Morton Arboretum to look at the effects of adding biochar to existing tree wells in Chicago.
  • Mr. Hendrickson said that Bartlett has a supplier that they have vetted extensively.  

Here are some of the initial findings that Bartlett Tree Research Laboratories and the Morton Arboretum have publicized for biochar:

  • Biochar can have a measurable positive impact on both soil quality and plant growth.
  • Biochar works best in combination with compost.  Biochar itself doesn't provide nutrients, but compost does.  So when you mix them together, you're "charging up" the biochar with nutrients.  Their research also suggests that biochar improves the performance of compost - i.e. when the two are blended, trees and shrubs show better growth than with either of the two alone.
  • More is not necessarily better - in fact it can be deleterious.  (like anything!) Their research is trying to determine the optimal amount, but they already know that a little bit goes a long way.
  • Biochar may also promote disease resistance - this is only preliminary greenhouse-based research but will be looked at in future studies.

To find out more: is an interesting website - this link will lead you to a story about the Morton Arboretum work on tree growth using biochar

And, of course,Cornell has a lot of expertise - this link will provide you with both information and lots of references