Organic Soil Management

Soil, soil testing, composting and soil supplements

Some Thoughts from Wendell Berry

“We learn from our gardens to deal with the most urgent question of the time: how much is enough?”

“The soil is the great connector of our lives, the source and destination of all. It is the healer and restorer and resurrector, by which disease passes into health, age into youth, death into life. Without proper care for it we can have no community, because without proper care for it we can have no life.”

More Wendell Berry

“Odd as I am sure it will appear to some, I can think of no better form of personal involvement in the cure of the environment than that of gardening. A person who is growing a garden, if he is growing it organically, is improving a piece of the world. He is producing something to eat, which makes him somewhat independent of the grocery business, but he is also enlarging for himself, the meaning of food and the pleasure of eating.”

“Eating is an agricultural act.”

The Golden Rule of organic soil management

Feed the soil not the plant

Soil Provides 4 Major Functions

1. Habitat for fungi, bacteria, insects, mammals, etc

2. Recycles raw materials

3. Medium for plant growth

4.Foundation for engineering projects

What does soil do for plants?

1. Provides oxygen in spaces between soil particles

2. Provides water in spaces between soil particles

3. Supplies and holds nutrients4. Provides temperature modification

(insulates roots from heat and cold) 5. Provides anchorage for root to stabilize

plants

Physical Properties of Soil

Soil Color

Soil Texture

Soil Structure

Soil Color

Generally color is a reflection of:1. Parent material from which the soil is

derived(bed rock)2. The amount of organic matter (the more

organic matter the darker the soil)3. The degree of oxidation and/or saturation

of the soil (wet cold soils slow oxidation of organic matter and are dark, warm well drained soils are lighter colored)

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Factors that give soil color

1. Organic matter

2. Weathered mineral material composing the soil

3. Quantity and condition of iron present

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Dark Color in the A Horizon

• Usually indicates the presence of organic matter

• This is a characteristic of the A horizon

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Sub-soil Color Determination

• Quantity and condition of iron

• Red colors = usually associated with unhydrated iron oxides and indicate a well drained soil

• Yellow colors = largely due to hydrated iron oxides and generally indicate a somewhat more moist condition than red colors

Soil TextureSoil is composed of minerals derived from the

bedrock and organic matter (OM). The mineral portion is identified by its texture. Texture is the proportion of sand, silt and clay in the soil. Sand: the largest, visible to the naked eye. Silt: sized between sand and clay, visible through low power microscope.Clay: can only be seen by electron microscope.

Clay Particles Under Electron Microscope

Particle Type Diameter (mm) Number of Particles per

gram

Specific surface area (cm2/g)

Clay < 0.002 90,260,853,000 8,000,000

Coarse sand 1.00-0.50 720 23

Fine sand 0.25-0.10 46,000 91

Medium sand 0.50-0.25 5,700 45

Silt 0.05-0.002 5,776,000 454

Very coarse sand 2.00-1.00 90 11

Very fine sand 0.10-0.05 722,000 227

Table 1–1. Particle type, number of particles per gram, and the average surface area per gram.

Sandy Soil

Assets: sandy soil has excellent aeration, drainage and tills easily. It warms earlier in the spring. Deficits: sandy soil erodes easily. It has a low capacity for holding water and nutrients

Clay and Silt SoilsAssets: clay soil erodes much less than sand. It has a high capacity for holding water and nutrients.Deficits: clay soil is hard to till and warms slowly in the spring. It has poor aeration and slow drainage.Silt soils: have intermediate characteristics between sand and clay soils.

Super Saturated Marine Clay Soil

More Marine Clay Soil

What Kind of Soil do I Have?

Take 1/3 cup of soil, moisten it and roll it into a ball. If that is difficult or it falls apart easily you have a sandy soil. The more it stays together you have a silt or clay soil. A wet clay soil will “ribbon” out between your fingers if you squeeze it hard; the longer the ribbon the more clay.

Another Test

Take a quart glass jar and fill it 1/3 full with soil from the garden. Remove pebbles, sticks and plant material. Add 1 tbs. of dish detergent or Borax and fill with water to 1 in. of top and shake for 5 minutes. Let it sit for at least 2 days. There will be a sand layer on the bottom followed by a silt and a clay layer. Measure each layer and divide by the total height to get the percentage of each.

Soil Structure

Soil particles clump together to form aggregates that range from pin head the pea size. Good soils have a granular structure. Silt and clay soils tend to clump together. Decomposed organic matter, fungi, soil microbes and plant root excretions promote good soil structure. Good soil structure prevents erosion and increases pore space that allows root penetration, water availability and aeration.

Pore Space

Good agricultural soil is 50% solid material (45% sand, silt and clay and 5% OM) and 50% pore space (50% water and 50% air). Clay soils have high water holding capacity due to huge number of pores (between clay particles) and drain slowly. Sand soils are the opposite, there are fewer pores due to large size of sand and it drains quickly.

A Brief Word About Soil Chemistry

Cation(CAT-eye-on) Exchange Capacity- the ability of your soil to hold and release various elements and molecules.Ion – a charged particle. Cation – a positively charged particle. Fe, Ca, Mg, K, H, Cu and Mn are all cations.Anion – (AN-eye-on)- a negatively charged particle. Tend to be soluble in water. Nitrogen (nitrates and nitrites).

More Soil Chemistry

Cations are attracted to negatively charged particles and anions to positively charged particles. The important thing to remember is that clay particles and organic matter (especially humus) are nearly always negatively charged. Cations will attach to OM and clay, be held in the soil and become available for plants through their roots: hence Cation Exchange Capacity (CEC).

Organic Matter (OM)

The golden rule of organic gardening: “Feed the soil not the plant” Question: feed it what?

Answer: OM!OM is living or previously living material. In the soil it is always in the process of decomposing until it becomes humus which is stable. OM is an important source of plant nutrients (CEC) and it improves soil structure. OM is living or previously living material, humus is really dead !

OM Continued - Humus

The breakdown of OM is dependent on moisture, temperature, the availability of oxygen and biological action (bugs, protozoa, microbes, fungi, etc.). Humus – the end product of OM decomposition. It is OM broken down as far as it can go and still be called OM. The more humus in your soil the more nutrients it can hold ( Cation Exchange Capacity).

Humus !

OM ContinuedOM must continually be replenished as

plant material is removed from the garden and as OM breaks down by adding leaves, seaweed, compost, crop residues, green manure, etc.

OM improves water retention, supplies and holds nutrients, helps maintain a balanced pH, improves soil structure and serves as a food source for the flora and fauna that make up the soil ecosystem.

OM ContinuedSandy soil has poor structure and low water

and nutrient retention. Solution? Add OM Clay soil has poor structure, drainage and

aeration. Solution? Add OM Some authorities suggest aiming for a 5%

OM soil content but a 8-10% for most sandy and clay soils is a better goal.

The Key Question“What can I, as a gardener

do to nourish the soil food web so that my plants will be healthy without artificial inputs?”

“What can I do to nourish the soil food web?”

All together! ADD OM! The soil food web is a complex, dynamic ecosystem composed of thousands of forms of life in numbers that are in the trillions per square meter of soil. In one sq. meter of soil are bacteria, fungi, protozoa, mites, arthropods, beetles, grubs, nematodes, spiders, worms, moles and many more. All of which are absolutely necessary for soil fertility and plant health. Without this rich soil ecosystem we would literally be buried in dead uncomposted waste.

The Soil Food Web

The basic aim of ecological soil management (organic gardening)is to provide hospitable conditions for life within the soil.

Teaming With Soil Life

Soil macro and microorganisms are the essential link between mineral nutrient reserves and plant growth. They are what permits nutrients to flow from soil to plant. The “macros” (earthworms, mites, beetles, arthropods, etc.) shred and consume organic matter into tiny pieces that are then further consumed by protozoa, bacteria and fungi who then make minerals and nutrients in a form that is available to plants.

Teaming With Soil Life

This is a symbiotic relationship in which fungi and bacteria exchange nutrients with plants. This takes place around in an area of 1/10th of an inch around root hairs known as the rhizosphere. The plant roots secrete carbohydrates and proteins that the micros need in exchange for minerals and nutrients (most notably nitrogen and phophorus) that the plants need.

Beneficial Soil Bacteria

Bacteria (blue) in soil

Contributions of Soil Bacteria

1. Make nitrogen and phosphorus available to plants.

2. Improve soil structure.3. Dissolve nutrients from bedrock.4. Out compete pathogenic bacteria for

nutrients.5. Some (streptomycetes) produce more than

50 antibiotics to protect plants.

Beneficial Soil Bacteria

1.Could be 10 billion in a teaspoon of soil. 2. Aerobic- decompose organic material and

tie up nitrogen in their membranes.3. Anaerobic- often pathogenic, prefer low

oxygen environment (compacted over saturated soils).

4. Largely unaffected by tillage, depressed by dryness, acidity, salinity, soil compaction & lack of OM.

More About Soil Texture

1.Bacteria and fungi are essential to soil aggregate formation.

2. Aggregates determine water retention, nutrient availability and aeration.

3. Fungal hyphae bind soil particles together. 4. Sticky bacterial exudates “glue” soil

particles together.

Mycorrhizal Fungi

From the Greek myco (fungus) and rhyza(root). 85- 95% of all terrestrial plants have symbiotic relationships w/ mycorrhizal fungi. A mycorrhizal hyphalstrand has a diameter of about 1/50 of a human hair, can grow several meters in length and enable a plant root to access much more soil than a root without mycorrhizal association.

Two Mycorrhizal Types

Ectomycorrhizae (ecto=outside)- associated with forest plants: pine, beech, spruce, fir, oak and birch.

Key for bringing nitrogen to trees.About 5% of plants form ecto. relationships

but that includes 25,000 tree species. Forms mycelial relationships between same

and different tree species.Often forms mushrooms.

Two Mycorrhizial Types

Endomycorrhizae (endo= inside)- associated with vegetables, grasses, flowers shrubs and fruit trees.

Major source of nitrogen and phosphorus for plants.

About 80% of plants form endo. relationships.

The Big PictureSupply the soil ecosystem with the same requirements all life needs

1. Food2. Air3. Water4. Shelter

Teaming With Soil Life

What can gardeners do to promote a healthy soil ecology?1. Provide food: add OM, mulch and especially compost (more on this later)2. Provide air: promote good soil structure, don’t compact soil3.Provide water: the soil should not be saturated or too dry4. Provide shelter: OM for the “micros” and mulch for the “macros”

Teaming With Soil Life

What should gardeners avoid doing to promote a healthy soil ecology?1. Do not apply synthetic fertilizers: they suppress and kill fungal and microbial life2. Do not apply synthetic pesticides, fungicides, and herbicides, they kill fungal and microbial life 3.Keep tilling to a minimum: it disrupts the entire soil ecological community

16 Essential Plant Nutrients

Macro Nutrients Derived from air and waterCarbon(C)Oxygen(O)Hydrogen(H+) Derived from minerals in soil Nitrogen(N)Phosphorus(P)Potassium(K+)Sulfur(S)Calcium(Ca++)Magnesium(Mg++)

16 Essential Plant Nutrients

Micronutrients derived from minerals in soil Iron(Fe++)Boron(B)Manganese(Mn++)Copper(Cu++)Zinc(Zn++)Molybdenum(Mo)Chorine(Cl)

Von Liebig’s Law of the Minimum

If the least used nutrient is not present, it will not do any good if all the other nutrients are present.

Some Observations

The synthetic fertilizer you buy at the big box store provides NPK in large amounts that harms the soil ecosystem and is highly soluble. What the plants can’t use leaches away. It provides none of the remaining 13 macro or micro nutrients. A soil with adequate OM, good texture and structure will provide all 16 nutrients (with a little help from you) on a slow release basis.

How can you help?

Provide CompostCompost is a microbe-laden material that inoculates the soil, activating its biological processes. A healthy compost pile needs the same ingredients as a healthy soil ecosystem: OM, air, water and a rich, varied collection of micro and macro flora and fauna. You are optimizing the same process that takes place in the soil. The compost needs adequate air. It needs to be moist (like a squeezed out sponge) but not saturated and located in a sunny spot.

How can you help?

Compost ContinuedIt is important to have a good carbon(brown)

to nitrogen(green) ratio of the materials to be composted. Nitrogen allows the mix to heat and decompose the carbonaceous materials. Too much carbon and the process slows, too much nitrogen and nitrogen is lost to the air or leached by water. The ideal ratio is 30 parts carbon to 1 part nitrogen.

A word about soil amendments

Microbial activity in the soil is related to soil temperature. Microorganisms become inactive or dormant in cold or frozen soils. Gardeners in the spring should consider using some organic nitrogen supplements to stimulate plant growth. Examples are bloodmeal (12-0-0), alfalfa meal (2.6-0-2.3), soybean meal (7-0.5-2.3) and fish meal (10-6-1)

Other Amendments

Depending on your soil test, a number of other amendments are helpful and stimulate the microbial life in the soil.Granite meal (0-0-5) enjoyed by microbes, source of K, improves soils structure Greensand (0-1-7) source of K, many trace minerals, improves both sandy and clay soils Bone char (0-16-0) excellent source of P and much cheaper than bone meal

Soil TestsOrganic fertilizers and supplements, including

lime and wood ashes, should not be applied until a soil test is taken. Adding unneeded supplements or too much of any supplement can often cause more harm than doing nothing. Too much of one nutrient can result in another nutrient becoming unavailable. For example: too much P can cause a deficiency of Zn and S; too much Ca or Mg can cause a deficiency of many nutrients; too much K can cause a deficiency of Mn and B.

Soil pH

Soil pH refers to the relative acidity (sour) or alkalinity (sweet) of soil on a logarithmic scale of 0 to 14. 0 to 6.9 is acidic, 7.1 to 14 is alkaline and 7 is neutral. The ideal soil pH for nearly all garden vegetables is between 6.2 and 7 (slightly acidic). In that range the maximum amount of macro and micro nutrients are available. Again, a soil test is imperative; never apply lime or wood ashes without knowing the pH of your soil.