Soil

Soil Formation1. The four major components of soil are: Water (25%) Air (25%) Organic matter (6%) Parent material (44%)2. Parent material is: Bedrock which provides mineral content of the soil, Ex:Sand, silt and clay• Quartz: SiO2

• Calcite: CaCO3

• Feldspar: KAlSi3O8

• Mica (biotite): K(Mg,Fe)3AlSi3O10(OH)2

3. How is soil made from parent material? Include the role of weathering and living organisms•Weathering (physical and chemical) creates small pieces•Dead organisms- decay and release nutrients and gases•living organisms also release nutrients and gases

Parent material can be native to the area or transported to the area by wind, water or a glacierEX: Calcareous soils in Miami-Dade County are derived from Miami limestone. Most of Miami-Dade County, part of Broward County, and Monroe County (including the Florida Keys). Broward also has marl and stone sand bedrock

4. Humus is: Organic matter Dead and decayed organisms, ex plant matter

5.How long does it take to make soil from bare rock? 10 000 years

Soil Profile1. Describe the 5 Soil horizons•O- Organic matter, leaf litter (duff), dead animals, decomposed litter•A- Surface soil, decomposed organic matter and minerals, humus (fertile)•B- Subsoil, leached nutrients •C- Parent rock, weathered large unbroken rocks•R (Bedrock)- mostly a continuous mass of hard rock

Soil Texture1. What is soil texture?

Soil Texture1. What is soil texture?

• Proportions of clay, sand and silt

Particle sizeSmallest - clay = less than .002mm

- - Silt = .002mm - .05mm largest - sand = .05mm - 2 mm

• Proportions of clay, sand and silt

Particle sizeSmallest - clay = less than .002mm

- - Silt = .002mm - .05mm largest - sand = .05mm - 2 mm

2. What is porosity?• Ability to hold water

3.What is permeability?• Ability of water to flow through the material (rate)

4. Compare permeability of sand and clay.•Sand high, clay low Water Water

High permeability Low permeability

5. What is a loam?•A loam has about = mixtures of clay, sand, siltand humus - best for growing crops.

6. How can soil texture be determined?•Determined by particle size and feel

Soil type1. What are the main Soil types? There are six main types of soil usually discussed in agriculture, distinguished by the size of the particle matter that makes up the soil.•Sandy (water/minerals easily flow)•Clay (no drainage)•Silty (fertile, good drainage)•Loamy (a mixture of soils)•Chalky (alkaline)•Peaty (acidic , undecomposed organic matter)

Table 10-1 p. 216

Texture Nutrient Infiltration Water-Holding Aeration TilthCapacity Capacity

Clay Good Poor Good Poor Poor

Silt Medium Medium Medium Medium Medium

Sand Poor Good Poor Good Good

Loam Medium Medium Medium Medium Medium

Refer to Fig. 10-15 p. 215Refer to Fig. 10-15 p. 215

Soil Erosion is the process by which soil and rock are removed from the Earth's surface by wind or water flow, and transported and deposited in other locations.Sheet erosion - surface water peels off fairly uniform sheets of soil.Rill erosion - fast flowing rivulets cutSmall channels in soil. Gully erosion - rivulets join together toCut wider, deeper ditches or gullies Two major impacts- loss of soil fertility and pollution of near by waters

Causes of soil Degradation1. DeforestationNo vegetation to hold the

soil, soil is removed, loss of soil fertility, pollutes and can silt up rivers, decline in fish, flooding can worsen

Management: prevent deforestation, manage forest harvesting, replant

Fig. 10-6a, p. 219

Stepped Art

(b) Clear-cutting

Muddy stream

UncutCut 1 year ago

Dirt road

Cut 3–10 years ago

Uncut

Clear stream

(a) Selective cutting

(c) Strip cutting

Clear stream

2. AgricultureOvergrazing- livestock are grazed on land in an unsustainable way (poorly managed) which leads to soil erosion and compaction of soil (due to the feet of the animals)•Solutions-Rotational grazing- land is not grazed on until the plants have had enough time to grow back, cattle supplied with other food sources, ex hay•Over grazing can lead to desertification

Soils DegradationSoils Degradation Desertification - combination of Prolonged drought and human activities Lead to a reduction in the productive potential of land.

Desertification - combination of Prolonged drought and human activities Lead to a reduction in the productive potential of land.

Solutions: Reduce1. Overgrazing2. Deforestation3. Destructive forms of farming,

irrigation, and mining

Solutions: Reduce1. Overgrazing2. Deforestation3. Destructive forms of farming,

irrigation, and mining

Soils: DegradationSoils: Degradation

Salinization - salts left on soil as irrigation water evaporates. Stunts cropgrowth and reduces crop yields.

Salinization - salts left on soil as irrigation water evaporates. Stunts cropgrowth and reduces crop yields.

• Waterlogging - farmers leach salts fromSoils by applying large amounts of water. if water does not drain, saline water sits in pools

and damages roots of plants. Solution- Drip irrigation, better drainage

• Waterlogging - farmers leach salts fromSoils by applying large amounts of water. if water does not drain, saline water sits in pools

and damages roots of plants. Solution- Drip irrigation, better drainage

Prevention Cleanup

Reduce irrigation

Switch to salt-tolerant crops(such as barley, cotton, sugar beet)

Flushing soil(expensive andwastes water)

Not growing crops for 2-5 years

Installing under- ground drainagesystems (expensive)

Preventing and cleaning up soil salinization

Industrialized Crop Production Causes Soil Erosion

• Industrialized agriculture, high-input agriculture (intensive) produces 80% of world’s food supply

• Uses heavy equipment and large amounts of fossil fuels, water, commercial fertilizers, pesticides, and financial capital.

• Primarily monocultures – single crop in one area.– Goal is to steadily increase crop yield, Ex Corn

Reduce Soil Erosion Due to AgricultureSoil conservation methods•Crop rotation- Crop rotation is the practice of planting different crops during consecutive growing seasons. By doing this the following benefits are applied to the soil and plants:

•Strip cropping with cover crop

Terracing

Terracing: Carving steep hills into terraces to retain water at each level and prevent soil erosionfrom downhill runoff. Contour farming: plowing rows to follow the curve of gently sloping land. Samebenefits as terracing.

Alley cropping: rows of crops are planted between a row of trees that provide fruit or fuelwood and reduceEvaporation and wind blown soil erosion

Windbreaks - use rows of trees to reduce wind erosion and help retain soil moisture.

Soil Degradation: conventional tillageSoil Degradation: conventional tillage Conventional-tillage - fields often Plowed in the fall and left bare over winter. This leaves it vulnerable toErosion, breaks soil structureSolution: Conservation tillageIdea is to disturb the soil as little as possible when planting cropsNo-tillage- leave last years crop, useSeed injectors

Minimum tillage - subsurface soil is loosened but not topsoil.

Conventional-tillage - fields often Plowed in the fall and left bare over winter. This leaves it vulnerable toErosion, breaks soil structureSolution: Conservation tillageIdea is to disturb the soil as little as possible when planting cropsNo-tillage- leave last years crop, useSeed injectors

Minimum tillage - subsurface soil is loosened but not topsoil.

Advantages Disadvantages

Reduces erosion

Saves fuel

Cuts costs

Holds more soil water

Reduces soil compaction

Allows several crops per season

Does not reduce crop yields

Can increase herbicide use for some crops

Leaves stalks that canharbor crop pests and fungal diseases and increase pesticide use

Requires investment in expensive equipment

CONSERVATON TILLAGE

• Water ManagementOver-watering a crop area will result in erosion of soil and possible flooded fields.  

• To counteract this farmers can plant crops native to the area that do not require external irrigation or employ minimal water techniques, such as drip-irrigation - the process of only watering  the crops themselves by using a hose with small holes at each crop.  

Case StudiesMEDC- USA pg 303 textbook (Dustbowel 1930s)LEDC- India see article

Types of SoilPodzols are soils with an ash-grey subsurface horizon, bleached by organic acids, on top of a dark accumulation horizon with brown or black reddish iron compounds.•Podzols occur in the Boreal and Temperate Zones•Soils are acidic (pine needles), little ground vegetation•Sandy not good for farming

Characteristics•Cool moist environmentClimate:•Evergreen so limited litter layer•Slow to decompose due to limited soil organisms (cold)Water:•Lots of water, snow melt•Water infiltrates through layers, leaches out nutrients (Fe, Al) that collect lower down the profile.

Soil horizons Soil horizons

Soil profile Soil profile

O horizonLeaf litter

A horizonTopsoil

B horizonSubsoil

C horizonParent

material

Mature soil

Young soil

RegolithRegolith

BedrockBedrock

Immature soil