Soil Formation

THE END PRODUCTS OF WEATHERING CALLED SEDIMENTS OR SOIL SOIL: a combination of sediment, rock minerals, and humus (organic material from biologic activity)

SOIL – THE PRODUCT OF WEATHERING AFTER THOUSANDS OF YEARS…

SOIL HORIZONS Layers that develop as a result of the weathering processes, biologic activity, and leaching (flow of water through rocks) O = Organic. It consists of fragments of leaf litter, twigs, roots, and other organic material lying on the surface of the soil. This layer is not present in cultivated fields. A = Topsoil. It is usually darker than lower layers, loose, and crumbly with varying amounts of organic matter. This is generally the most productive layer of soil. B = Subsoil. It is usually light colored, dense, and low in organic matter. C = Parent Material. Partially decomposed parent material The unconsolidated organic and mineral material in which soil forms.. R = Bedrock. The solid rock that underlies the soil and other unconsolidated material

Soil Development Size and thickness of each horizon depends on: Climate Vegetation/ Biologic Activity Slope (gradient or incline) Time

Soil Classification Different conditions lead to different soil types.

A - Horizon A : topsoil: upper layer of soil with a matrix of inorganic material; much organic matter (HUMUS) and many creatures; zone of greatest biological activity

What is Humus? Humus it the decayed plant and animal matter in the A horizon

B - Horizon B : accumulation layer: minerals leached from layer A, precipitate or accumulate here, sometimes forming an impermeable barrier

C - Horizon C : weathered rock: little organic material, perhaps large roots; directly above solid Rock

Changes that occur as a Soil becomes More Mature

Changes that occur as a Soil becomes More Mature 1 - Increased Depth

Changes that occur as a Soil becomes More Mature 2 - Development of Distinct Horizons

Changes that occur as a Soil becomes More Mature 3 - Additional Plant Growth

Changes that occur as a Soil becomes More Mature 4 - Increased Permeability and Capillarity

Changes that occur as a Soil becomes More Mature 5 - Increased Animal Activity

2 TYPES OF SOIL TRANSPORTED SOIL: SOIL CARRIED BY EROSION AND DEPOSITED ON THE BEDROCK (MOST SOIL IS TRANSPORTED) BEDROCK BENEATH ≠ SOIL ABOVE RESIDUAL SOIL: SOIL FORMED BY THE WEATHERING OF THE BEDROCK DIRECTLY BENEATH IT BEDROCK BENEATH = SOIL ABOVE

TRANSPORTED SOILS DUE TO …

What does Parent Rock mean with respect to Soil?

Parent rock is the original rock that the sediment which makes up the major part of the soil weathered from.

If a forest soil and a prairie soil have the same parent rock from which they are made, why will the two soils be different?

Forests and Prairies have different Organic Matter and different Climates associated with them.

Soil Conservation

Why is soil conservation important? "A nation that destroys its soil destroys itself." - President Franklin D. Roosevelt, 1937

First let us look at the problem of soil erosion. Sheet erosion is the removal of the thin layer of topsoil by raindrop splash or water run-off.

First let us look at the problem of soil erosion. Wind erosion is the detachment and movement of soil by wind.

First let us look at the problem of soil erosion. Gully erosion occurs when small streams unite and create a stronger flow, cutting a channel down which water flows during or just after rain

Worldwide, an estimated 26 billion tons of topsoil are washed or blown off cropland each year. Every year 6 million hectares of productive dryland become desert.

The soils of our planet have formed over thousands of years in conditions which have long since changed. The destruction of soils through man's misuse, however, can take place in just a few years, and in most cases this process is permanent or at best is difficult to correct.

What can be done? The most critical factor in protecting soils from erosion by water and wind is the maintenance of cover (plant residues, pasture and forest litter) in close contact with the soil surface.

The importance of groundcover

Soil Conservation Plowing Furrows Strip Cropping Terracing Cover Crops Wind Belts

PLOWING breaks up hard layers forming from leaching

Strip Cropping

Terracing

Terracing is one of the oldest and most efficient means of saving soil and water (Pipkin and Trent, 1997). A terrace is a flattened area that catches and temporarily stores or slows water run-off on moderate to steep slopes (USDA Soil Conservation Service, 1992). By slowing down the rate of surface water run-off, terracing can significantly reduce soil erosion. The art of terracing is an ancient soil conserving practice that has been used for many centuries to prevent soil erosion within agricultural land. In central China, for example, where steep slopes are underlain by erodible deposits of wind-blown silts, terracing has been a major factor in reducing soil loss (Skinner and Porter, 1997). Terracing has been used in China for centuries to 3

Cover Crops

COVER CROPS IN AGRICULTURE - AN OLD NEW CONCEPT History COVER CROPS IN AGRICULTURE - AN OLD NEW CONCEPT History. Cover crops were used by the Romans and Ancient Greeks as green manures, along with animal manures, to improve soil fertility. Since the Roman and the Greek empires occupied the semi-arid and arid regions around the Mediterranean Sea along Southern Europe, West Asia and North Africa, they used winter annual legumes such as vetch (Vicia spp.) and clover (Trifolium spp.) to fix nitrogen, recycle nutrients, add organic matter to the soil, and reduce soil erosion. Because rain in that region fell during the winter months (November through February), they took advantage of the rainy, mild season to grow the legumes and plow them under by the end of the rainy season at which time they seeded their main wheat crop. PRESENT USES OF COVER CROPS Cover crops have more uses in present agriculture than they had in the past. The expansion in use is the result of new species and varieties with better adaptation to adverse climatic conditions including high and low temperature, drought, flood and soil salinity tolerance, high biomass and nitrogen fixing efficiency, and resistance to pests. In addition, there have been great advances in management practices of these cover crops to meet the needs of changing agriculture, particularly in the area of sustainable agricultural systems which reduce soil and nutrient losses and conserve natural resources.

Wind Belts

Wind Belts

Furrows