Welcome to the 2004 Massachusetts Envirothon Workshop

Soils Overview Workshop

Part II Tom Cochran

USDA-NRCS Franklin Co., MASome material courtesy of Jim Turenne

USDA-NRCS, Rhode Island

Climate

Rain water allows chemical reactions to occur on the exposed surfaces of the minerals that compose the rock.

Some of the elemental molecules leave the surface of the minerals and go into solution. (i.e. iron, calcium, magnesium, aluminum, potassium, etc.)

This weakens the crystal structures of the rocks and particles begin to break off, and cracks begin to form in the rock matrix. The particles and the minerals in solution begin to form the soil.

Climate (continued)

Temperature also affects soil forming process.When rain water enters the cracks and freezes, the water expands with enough force to fracture the bedrock, forming boulders, stones, and/or cobbles.

Prolonged cold temperatures slow organic matter decomposition causing an increased percentage of soil organic matter. Saturated conditions also slow the decomposition process.

In western Massachusetts, we get approximately 40 inches of rainfall per year.

There are 80 130 frost-free days in the Berkshire Mts., and 150-> 195 frost-free days in the Connecticut River Valley.

OrganismsOrganisms including bacteria, fungi, earthworms, nematodes, arthropods, moles, groundhogs, man, etc. alter the soil by their actions.

One teaspoon of soil often contains millions of bacteria and fungal organisms. These microbes decompose organic materials deposited at the soil surface and are responsible for the dark colors of the surface horizon. Without them we would be living on dead organic matter.The by product of their respiration process is the catalyst for the formation of light colors in saturated zones of soil bodies.

Arthropods, nematodes, moles, groundhogs, and man stir the soil and promote the presence of structure in the soil body.

Soil fungi

Earthworm BurrowsEarthworm Burrows

middens

Middens: piles of residue around the mouth of earthworm burrows.

TopographyTopography affects the water flow on and through the soil, which affects the soil formation processes.

Soil types can often be found on the landscape in a predictable pattern because of the topographic soil forming factor.

Topography (continued)

TimeOver time, the affects of climate, topography, and organisms continually alter the parent material and soil particles, which results in the formation of recognizable soil profiles.

It takes 500 years to form one inch of topsoil.

It takes thousands of years to form a weakly structured subsurface horizon like we have in New England.

It takes tens of thousands of years to form the well structured clay subsurface horizons of the south and mid-west.

Soil Horizonation

Over a long period of time, the other four soil forming factors combine to create soil bodies with unique sets of horizons and characteristics.

Thousands of different soil series exist in the US and more are continually identified as new areas are mapped and old mapping projects are updated.

Each soil series has a unique set of horizons and characteristics. These horizons and characteristics are a product of soil forming processes.

Not every soil body is affected by the same soil forming processes.

Soil Forming Processes

Translocations – Movement of ions and compounds from horizons above to horizons below.

Transformations – Chemical and physical alteration of soil material.

Additions – Anything that is added to the soil. Organic matter, fertilizer, and ions in rain water represent additions to the soil.

Losses – Minerals, ions, and organic matter are removed from the soil profile. Leaching and erosion are the main loss processes.

There are four processes that guide horizon formation:

The major horizons are as follows.

O = organic matter on the soil surface that is in various states of decay.

A = the surface of the mineral soil that is composed of mineral and organic material.

E = the horizon between the surface and subsurface that has some part of it removed and transported to the subsurface by the flow of precipitation through the soil. Clay, iron, aluminum, and humus are most often the materials removed.

B = the subsurface zone where materials from the horizons above are deposited by the water that continually moves down from the surface.

C = A zone of partially weathered rock.

R = bedrock in its unchanged state.

An E horizon can develop in this area.

Bedrock can lie below the C horizon. In this position, the bedrock is called an R horizon.

Soil CharacteristicsHorizon characteristics are used to name and classify soil.

Soil taxonomy defines diagnostic horizons that have certain properties, which reflect the soil forming processes that created them . There is a set of surface and subsurface diagnostic horizons.

The main clues for identifying diagnostic properties of interest include texture, color, structure, consistency, and profile position.

Your soil judging worksheet will ask you to identify the soil forming factors and the soil diagnostic features that are evident in each of the soil bodies to be judged.

TextureTexture is often the first characteristic soil scientists determine. It is the relative proportion of sand, silt, & clay sized particles in

the fine earth fraction of a soil horizon. The fine earth fraction is all of the individual particles that are

smaller than 2mm in diameter. Everything larger than sand is excluded.

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2mm sand particlemagnified 133x

Silt Particle

Clay particle

The three main methods for measuring texture are

Pipette method – laboratory procedure used by the National Soil Survey Lab in Lincoln, NE. It is time consuming and very accurate.

Hydrometer method – a reasonably accurate simple laboratory procedure often used in soil survey field offices to test the accuracy of the feel method.

Feel method – method used by soil scientists in the field, which involves feeling the soil with your fingers.

Requires practice and occasional calibration with the hydrometer method .

Soil survey scientists continually compare how they perceive various field samples using the feel method. This ensures consistent results from one scientist to another.