Jeffrey Creque, Ph.D.

Oecos@earthlink.net

A Brief Introduction

to the Question of Soil Fertility (And how Soils Will Save the World)

• "The nation that destroys its soil destroys itself" -Franklin Roosevelt 1937

• "Do civilizations fall because the soil fails to produce - or does a soil fail only when the people living on it no longer know how to manage their civilization?"

-Charles Kellog, Soils and Men, the 1938 USDA Yearbook of Agriculture

• "Man, despite his artistic pretensions, his sophistication and his many accomplishments, owes his existence to a six-inch layer of topsoil and the fact that it rains."

Unknown

A little history…..

Jan Baptist van Helmont

• Van Helmont (1579-1644), a Flemish chemist, conducted an experiment to determine where plants get their mass. He planted a willow cutting in a pot, after first weighing the soil it contained, and gave the tree nothing but water for the next 5 years.

Photo: Sophie Nys

After 5 years, the cutting had grown to a tree weighing more than 75 Kg.

The soil in the pot had lost less than 60 g. Since the tree had received nothing but water, and the soil weighed practically

the same as at the beginning of the experiment, van Helmont concluded that the

increase had come from water alone.

Limiting Factors and Law of the

Minimum

Carl Philipp Sprengel (1787

–1859), a German

botanist, was the first to

formulate the ―theory of

minimum in‖ agricultural

chemistry.

This is the idea that plant

growth is limited by

whatever essential

nutrient is most lacking.

Limiting Factors and Law of the

Minimum. • This concept was popularized

by German chemist Justus von Liebig (1803-1873), who pioneered the production and use of artificial fertilizers in about 1845.

• At the time, it was believed that plants obtained carbon from the soil.

• Liebig showed that, in fact, plants receive all of their carbon in the form of carbon dioxide from the atmosphere.

• This is critically important and, oddly enough, provides the foundation upon which the organic farming movement stands.

How plants get their C

• Photosynthesis the phenomenally

complex process by which plants use

sunlight, water, and CO2 from the

atmosphere to produce sugars. Greatly

simplified, the process works like this:

6H2O + 6CO2 ----------> C6H12O6+ 6O2

In fact:

Carbon and Oxygen

together make up about

90% of the plant on a dry

matter basis.

Figure: Havlin et al, 2005.

Carbon and the Organic Movement

• At about the time (1924) Rudolph Steiner was delivering

the lectures that would provide the foundation for the BioDynamic Agriculture movement, which would ultimately make its way to Marin County, CA through the auspices of Steiner student Alan Chadwick and the Green Gulch Zen Center Farm,

• Sir Albert Howard was conducting his compost experiments in India, adapting traditional methods of soil quality improvement to the demands of tropical plantation agriculture.

• After reading Sir Albert‘s seminal works on the subject of compost making, soil fertility and agriculture, Lady Eve Balfour and Friend Sykes initiated the Soil Association of Britain, while at the same time,

• J.I. Rodale began the American Organic Farming and Gardening movement in the US.

• Key to the emergence of the organic farming

movement was the observation that soil organic

matter played a singularly important role in soil

fertility;

• That the ―chemical soup‖ view of soil fertility,

rooted in Liebig‘s law of minimum, was not

working.

• And in fact, appeared to be leading to increasing

problems of infertility in crops and livestock.

• All of this seemed to come to a dramatic head in

the events of the 1930‘s:

the catastrophic loss of

agricultural soils

South Dakota, 1934

Black Sunday April 14, 1935.

The dust storm that turned day into night. Many

believed the world was coming to an end.

Liberal, Kansas. April14,1935

It was this event that lead Congress to create the

Soil Conservation Service

Baca County, CO, Easter Sunday, 1935 Photo by N.R. Stone

A black blizzard over Prowers County, CO, 1937.

• (Western History Collection, University of Oklahoma)

The T value:

Soil loss tolerance

For a specific soil, the T value is the maximum

average annual soil loss per acre per year that will

permit current production levels to be maintained

economically and indefinitely.

T values range from 2 to 5 tons per acre per year.

Is something wrong with this picture…?

• Modern concepts of soil fertility recognize that matters are more complex than posited by von Helmont or Liebig, and that a host of chemical biological, physical and ecological factors, including photosynthesis, influence plant growth, health and yield.

• Nutrients are exchanged between the soil solution and the plant and between the soil solution and the soil mineral and organic matter component.

• Nutrients are exchanged as a function of ionic charge (+ or -), and so we can speak of both the cation exchange capacity (CEC) and the anion exchange capacity (AEC) of soils.

• these processes are a function of a host of complex biotic and abiotic processes, over time.

• Soil is much more than an inert material providing physical support to the plant,or a medium to contain a chemical stew of plant nutrients…….

• the relationship among root surfaces, soil

texture, organic matter, soil structure, and

electrically charged molecules (cations and

anions).

Figure: Havlin et al, 2005

―Soil is placenta‖ - Susan Englebry

Cation Exchange Capacity

• CEC is considered one of the most important properties influencing nutrient availability and nutrient retention in the soil;

• It represents the total negative (-) surface charge on soil minerals and OM available to attract cations in the soil solution.

• CEC is subject to change through management intervention; specifically, by the addition or loss of Organic Matter.

Texture vs Structure

• Soil Texture is a function of the relative proportions of soil inorganic fractions, consisting of sand, silt and clay.

• Soil texture is not readily subject to change by management intervention because it is largely a product of soil geology and landscape geomorphology.

Structure vs Texture

• Soil Structure refers

to the physical

arrangement of soil

peds and pore space.

• It is a function of soil

texture, soil

mineralogy, OM, and

management,

including crop, tillage,

moisture, etc.

pH

• Soil solution acidity and alkalinity

• pH = -log [H+] in solution

• Each unit increase in pH represents a 10X decrease in [H+], representing a decrease in acidity (an increase in alkalinity).

• The pH scale runs from 1 to 14, with A pH of 7 considered neutral.

• Soil pH varies widely, with ranges of 4.5 (acid) to 8 (alkaline) typical.

CEC, pH and Soil Texture Organic Matter

Humus

Figure: Havlin et al, 2005

Soil Nutrients

• N-P-K;

– Only part of the story…

mobygarden.wordpress.com/

N in the Plant

http://extension.missouri.edu/publications/DisplayPub.aspx?P=WQ259

Nitrogen: Selling Water by the River

• N is typically viewed as the most limiting factor; but is it?

• 78% of the earth‘s atmosphere (about 117,000 tons N/acre)

• Not in a form directly usable by plants;

• Sources include: – Symbiosis with Rhizobium bacteria and Actinomycetes on

leguminous and actinorrhizal species.

– Free-living soil microbes (eg, Azospirillum)

– Lightning-formed N-oxides

– Synthetic N fertilizers (Haber-Bosch process).

(for more information on N and Haber-Bosch, see: Enriching the Earth, by Vaclav Smil)

Haber-Bosch Process

The N-Cycle

Rhizobium Nodules on Soybean Roots

Frankia Nodules on Alder Roots

Phosphorus (P)

• Energy storage and transfer (ADP and ATP). Energy obtained via photosynthesis and metabolism of carbohydrates is stored in phosphate compounds.

• Essential for growth and reproductive development (seed and fruit, etc.) and root growth, and accelerates crop maturity.

• Globally, mineral P deposits are limited and essentially non-renewable.

• Organic sources of P include organic waste materials, including manures.

Potassium (K)

• K is involved in plant water relations, osmotic pressure in cells and across membranes. Regulates leaf stomatal openings and thus rates of transpiration.

• Highly mobile in the plant.

• Important for many crop quality characteristics due to its involvement in synthesis and transport of photosynthates to plant reproductive and storage organs, including grain fruit, tubers; and carbohydrates, proteins, oils and; fruit size, color, taste and peel thickness….

• Manure can be a good organic source of K (especially sheep and goat). Globally, there are large natural deposits of K salts, associated with old lakes or seas…..

• Wood ash is a good source of K, along with Ca, P, Mg and trace minerals.

Some Other ‗Minor‘ and ‗Micro‘

Nutrients

• Sulfur: important in protein synthesis;

• Calcium: important in cell wall structure and

permeability. Nutrient uptake. Cell division.

• Magnesium: Primary constituent in chlorophyll;

protein synthesis; plant metabolism.

• Micronutrients

• Fe, Zn; Cu, Mn; B; Cl; Mo; Ni

• Average soil C:N:P:S ratio = 140: 10: 1.3:1.3.

A Marin County Organic Garden Soil Analysis

5 Marin County Agricultural Soils, Farmed Organically

Fertility as an Alternative to

Fertilizers

• Bootstrapping Fertility: using the Garden‘s

own biological and ecological processes,

rather than relying upon ―inputs.‖

• How is this possible if we are continually

removing nutrients from the Garden?

The Garden as Biological Sink

• Carefully managed, the Garden becomes a

biological sink, drawing fertility to it in the form of

birds, insects, spiders, small animals and solar

energy.

• Manage the garden as an organism or an ecosystem

and remember:

• Biological systems are ―open‖ systems, and

• Solar energy is, for our purposes, infinite.

Regolith: Bottom-up (and

bottomless) Soil Formation

http://www.landforms.eu/orkney/regolith.htm

Organic Matter: Top-down Soil

Formation

• Photo by Jim

Turenne, photo

location - A kettle bog

that was cut open by

wave action at Nauset

Beach, Orleans Mass.

Photos by Jim Turenne

The Soil Environment

Credit: USDA, S. Rose and E.T. Elliott

Conservatoire: ―Every Pip‖ • To bootstrap fertility it is critical to embrace Alan

Chadwick‘s concept of ―Conservatoire,‖ or conservation, in the Garden.

• For example, weeds pulled up by the roots and laid along the garden path will rapidly lose nutrients and water via oxidation and volatilization.

• how garden detritus is handled is at least as important as how the living plants in the garden are managed.

• Each plant removed from its place in the garden represents energy, nutrients and water that can either be recycled (via composting, etc.) to further build garden fertility, or cast aside to serve as one more avenue of loss from the garden ecosystem, requiring replacement by outside inputs.

The Rhizosphere

Mycorrhizae

(―fungi-root‖)

• can increase plant root absorbing surface

area by 10X.

• enhanced P and water uptake are among

the many benefits of mycorrhizal

association.

• Mycorrhizal glomolin makes up 30 to 60%

of soil organic C.

The Rhizosphere:

the plant-fungal-bacterial-soil

relationship

http://www.morning-earth.org/graphic-e/biosphere/Bios-C-PlantsNew.html#soillife

http://www.soq.wur.nl/UK/Research/Joint%20research/

Endo-mycorrhizae

finely-branched arbuscule inside root: grasses, grains,

vegetables, herbs—most flowering plants

http://www.morning-earth.org/graphic-e/biosphere/Bios-C-PlantsNew.html#soillife

Soil Structure:

Air, Water and Cultivation

• Unlike soil texture, soil structure can be changed by management practices, both for better and for worse.

• Cultivation is fundamentally a destructive process, but, if applied correctly; at the right time, for the right reasons, in the right way and at the right moisture content, cultivation can lead to improvement in soil structure if subsequent management, including cropping and amendments, are appropriate.

• The flush of growth that arises from newly cultivated soil is the result of the break down of soil organic matter and soil structure, resulting in the rapid release of plant-available nutrients.

• This is not sustainable unless supported by use of the appropriate soil forming, soil conserving, and soil repairing tools.

• ―Intensification of agricultural production is

an important factor influencing greenhouse

gas emissions, particularly the relationship

between intensive tillage and soil C loss.‖ -Reicosky and Archer, 2007. Soil & Tillage Research 94:109-121.

Jefferson’s Improved Moldboard Plow

ca 1788

Farmland after rain (right), showing waterlogging due to poor structure

resulting from cultivation, compaction and lack of soil cover. Different

management, including denser groundcover, on the adjacent paddock

(left) results in higher soil carbon, better structure and improved water

absorbing and holding capacity.

Patrick Francis, Australian Farm Journal

Carbon-rich topsoil from beneath perennial grass (left hand) compared to

adjacent carbon-poor soil (right hand). By holding more air, sustaining moisture

and having higher bioavailability of soil nutrients, carbon-rich soils benefit plants

and soil biota.

Photo: Lucy House, ‗Anabank‘, Baralaba

Rootzone Interactions:

http://www.nsfc.gov.cn/Portal0/InfoModule_480/24239.htm

3 rows of Corn. Peanut on right, Wheat on left,

Cover crops, intercropping, rotations,

leaf area index

Kathy Collins/Photodisc/Getty Images http://www.specialtycrops.colostate.edu/rmsofp/green_manure.htm

Atmosphere • The tangible condition of the air

within the boundaries of the Garden, and the intangible essence that one becomes aware of upon entering a Garden that has achieved this state.

• When Fertility, as a state, has been achieved in the Garden, the air is infused with more oxygen from the maximized photosynthetic activity of the plants, and with more CO2 from the active heterotrophs of the dynamic soil ecosystem.

• The scent of flowers and herbs and honey meld with the aromas of active growth and decay in a heady perfume that transports the garden visitor to an awareness of a heightened realm of human ecological possibility.

• The Garden is experienced, rather than observed.

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Atm

osp

her

ic C

O 2

( pp

mv

)

Year

Speaking of Atmosphere……..

The Keeling Curve: Remember van Helmont‘s Willow?

Good News: Excess Carbon Dioxide in the

Atmosphere Can Be Transformed Into Soil

Organic Matter Through the Processes of

Photosynthesis and Decay. Abe Collins, CarbonFarmersofAmerica.org

Remember the

lesson of van

Helmont‘s Willow:

(almost) everything

in that

wheelbarrow

came from the Air

‘… every one tonne increase in soil organic carbon

represents 3.67 tonnes of CO2 sequestered from the

atmosphere and removed from the greenhouse equation.’

‘For example, a 1% increase in organic carbon in the top 20

cm of soil (with a bulk density of 1.2 g/cm3) represents a 24

t/ha increase in soil OC which equates to 88 t/ha of CO2

sequestered.’ -Dr Christine Jones (2006), Australia

A soil OM increase of 1% equates to roughly 27,000 gallons

of increased water holding capacity in an acre foot of soil.

Soil OC comes from plants, and plant C comes from the air.

Increases in Soil OC can mean long term reduction and

storage of atmospheric CO2, while at the same time

leading to enhanced soil fertility and water holding capacity.

Can Soil Carbon Sequestration

Reverse Global Warming? • Land area under crop production in the world= 1.5 billion hectare

• Average bulk density of the soil = 1.3 ton/m3

• Average plow depth is 20 cm

• Increasing plow layer soil organic matter by 0.1%( at C content of 58% in

• OM)= 0.058%/yr

• If you multiply this out is about 2.2 billion tons of C/yr going into the world‘s arable soils. The total amount increasing in the atmosphere is about 3.2 billion tons/yr.

• Thus, increasing soil organic matter by 0.15%/yr should offset the increase in atmospheric CO2.This rate can be maintained for 25 to 50 years.

•

• In addition, we have pasture land and forest lands etc. Thus, there is a huge potential for soil carbon sequestration.

• The Marin Carbon Project

-Rattan Lal, pers.com, December, 2007

Are our Agricultural Ecosystems Nutrient

Limited (N,P, K….)

or

Energy Limited (Carbon)?

-END-

―Land, then, is not merely soil; it is a fountain

of energy flowing through a circuit of soils,

plants, and animals.‖ -Aldo Leopold