Soil is described in terms of physical and biological components. Both of these components are important in establishing a foundation of soil knowledge, essential for good, sustainable management.

Soil Components Courtesy University of Georgia Agriculture Education Dept.

Organic Matter Living – about 15% - living leaf Recently dead - produce nutrients, - dead leaf Long dead – stable, holds nutrients, humus- decomposed leaf

Air and Water Occupy the same pore space Essential for soil life

Soil Particles Sand – largest O20-40x Silt – medium o25x Clay – smallest.1 Pore space varies with size of particles

Soil Texture Courtesy USDA

Characteristics of the Various Soil Classes QualitySandSiltClay LoosenessGoodFairPoor Air SpaceGoodFair to GoodPoor DrainageGoodFair to GoodPoor Tendency to form clods PoorFairGood Ease of workingGoodFair to GoodPoor Moisture holding ability PoorFair to GoodGood FertilityPoorGoodFair to Good

Soil Horizon Courtesy of USDA

Soil Structure Categories Courtesy University of Georgia Agriculture Education Department

Factors which affect soil structure Organic Matter Content Soil Organisms Soil Colloids Tillage Freezing and Thawing Water Movement

Organic Matter Content May be increased by Adding manure Growing cover crops May be decreased by Tillage Hot, Humid environment

Soil Organisms Bacteria in soil have sticky substance on cell wall. This “glue” holds soil particles to bacteria and to each other. This binds soil particles into larger particles. Fungi produce thread-like structures called mycelia which bind soil particles and peds making larger particles.

Soil Colloids Very small particles with a weak electric charge. + o o- The charge causes water to bind to particles. As water evaporates, colloids and larger particles draw together, creating even larger particles.

Tillage Positive effect Creates air space in soil, allowing organisms needed oxygen Negative effect Disrupts the soil structure and kills the larger organisms such as earthworms. If done when too wet or dry, may destroy the soil structure of the tillage zone.

Freezing and Thawing As water in soil freezes it expands, pushing soil particles apart. This opens pore spaces for air. As water thaws, pore spaces tend to remain temporarily. This can be enough to encourage soil organisms, by allowing more oxygen.

Water Movement Positive + As water moves vertically through the soil some of the water is stored, and can be used by crops. Negative - Vertical movement of water can cause leaching of minerals. Vertical movement in soil freshly tilled may cause collapse and less pore space. Vertical movement in clay can result in a hard pan. Horizontal movement may cause erosion.

pH pH is the measure of the concentration of hydrogen ions. It is measure on a logarithmic scale going from 1-14 with 1 being the most acidic (most hydrogen ions) and 14 the most basic (least hydrogen ions). pH of soil is important because certain chemical reactions only occur in certain range. Not as important for organic systems, because they depend on biological reactions more than chemical reactions.

Soil Ecosystem Biological model of soil management as opposed to the chemical model is the major key to good soil management. More individual life forms in soil than live on the surface of the earth. 4 billion bacteria, 1 million fungi per teaspoon of soil Perform many functions to support plant life

Biodiversity Soil fertility is related to having a large number of different types of life forms. Different crops depend on different ecosystems. Annual field crops – bacteria dominated Woody perennials – fungi dominated

Producers-herbivores-predators-higher predators- decomposers Copyright Soil Foodweb Inc., Dr. Elaine Ingham, used with permission

How the soil food web benefits plant life Builds soil structure Disease suppression Improves nitrogen retention Mineralizes nutrients Produces plant growth hormones Improves crop quality

Builds soil structure Pore space from burrowing. Sticky substance from bacteria holds particles together. Fungal hyphae holds soil conglomerates together

Disease Suppression Population density – “good” organisms take up all the niches in the soil so there is no room for disease organisms. Antibiotics – some fungi produce antibiotics which destroy certain bacteria.

Improves nitrogen and other nutrient retention Waste given off by organisms contain nutrients. Soil organisms retain nutrients in their bodies. When organisms die the nutrients are released.

Mineralizes nutrients Organisms can take nutrients that plants can’t use and change them into a form that plants can use, such as nitrogen. Chelation – Some nutrients are in a form that is not available to plants. Soil organisms can add an organic molecule, changing their form and making them available to the plant.

Decomposition of plant toxins Natural plant toxins, such as phenols and tannin, can be detoxified when there is a diversity of soil organisms. Man-made toxins can also be detoxified by a diversity of soil organisms.

Produces plant growth hormones Some plant hormones, such as auxin, can be produced by some soil organisms. Auxin promotes root growth.

Improves crop quality Not well studied Relation between soil biodiversity and nutrient quality of food grown in soil More proteins, vitamins, anti-oxidants present when soil had a diversity of organisms present

Importance of Carbon Basis for all life Cells 70-95% water – the rest carbon compounds All organic compounds are carbon compounds

Carbon Cycle Courtesy of Windows to the Universe,

Importance of nitrogen Nitrogen is part of proteins and nucleic acids so is needed by every living organism Free nitrogen (nitrogen gas) makes up about 78% of the atmosphere but is not available to plants Plants must absorb nitrogen compounds from the soil

Nitrogen Cycle Courtesy of Hach Company

Summary Soil properties Composition of soil Texture – sand, silt, clay, loam Structure – pore space Soil biology, ecosystems Soil life produces nutrients, builds structure Trophic levels Soil nutrient cycles Carbon cycles through organic matter and carbon dioxide Nitrogen cycles through nitrogen gas and nitrogen compounds to proteins and nucleic acids