2-6- 1: Soil. A"er this lecture you should be able to. Explain the process by which soil, par9cularly topsoil is formed.

Size: px

Start display at page:

Download "2-6- 1: Soil. A"er this lecture you should be able to. Explain the process by which soil, par9cularly topsoil is formed."

Marion Dennis
6 years ago
Views:

1 2-6- 1: Soil A"er this lecture you should be able to Explain the process by which soil, par9cularly topsoil is formed. Describe the components of soil and classify various soil types. Iden9fy the different layers of a soil profile and describe their characteris9cs. Iden9fy and analyze what makes a soil workable. Explain the different factors that contribute to soil degrada9on.

2 An introduction to soil and agriculture Some farmers follow the five golden rules of the tropics Keep soil covered Use minimal or no 9llage Use mulch to provide nutrients to the soil Maximize biomass produc9on Maximize biodiversity Harvests have increased drama9cally Farmer experimenters experiment and educate others, leading to sustainable agriculture

3 A rich soil is much more than dirt Soil: solid material of geological and biological origin Chemical, biological, and physical processes change soil Giving it the ability to support plant growth In produc9ve soil, detritus feeders and decomposers cons9tute a bio9c community Facilita9ng the transfer of nutrients Crea9ng a soil environment favorable to root growth Produc9ve topsoil involves dynamic interac9ons among organisms, detritus, and mineral par9cles of the soil

4 Soil characteristics Most soils are hundreds of years old They change very slowly Soil science is at the heart of agriculture and forestry Soil is classified by profile, structure, and type Soil texture: rela9ve propor9ons of each soil type Parent material: mineral material of the soil Soil has its origin in the geological history of an area Weathering: gradual physical and chemical breakdown of parent material It may be impossible to tell what the parent material was

5 Topsoil formation

6 Classification of soil Soil separates: small fragments smaller than stones Sand: par9cles from 2.0 to mm Silt: par9cles range from to mm Clay: anything finer than mm Gravel, cobbles, boulders: par9cles larger than sand You can see the individual rock par9cles in sand Clay par9cles become suspended in water Clay is gooey because par9cles slide around each other on a film of water

7 Soil Composition What makes up soil? How do you tell the difference?

$s texture: Add soil and water to a test tube and let the soil se\le$ $Sand par9cles se\le first, then silt, then clay Scien9sts classify soil$

8 Proportions Sand, silt, and clay cons9tute the mineral part of soil If one type of par9cle predominates, the soil is sandy, silty, or clayey Loam: a soil with 40% sand, 40% silt, and 20% clay To determine a soil s texture: Add soil and water to a test tube and let the soil se\le Sand par9cles se\le first, then silt, then clay Scien9sts classify soil texture with a triangle It shows rela9ve propor9ons of sand, silt, and clay

9 Properties Soil proper9es are influenced by its texture Larger par9cles have larger spaces separa9ng them Small par9cles have more surface area rela9ve to their volume Nutrient ions and water molecules cling to surfaces These proper9es profoundly affect soil proper9es Infiltra9on, nutrient- and water- holding capacity, aera9on Workability: the ease with which soil can be cul9vated Clay soils are hard to work with: too s9cky or too hard Sandy soils are easy to work with

10 Soil Profiles Horizons: horizontal layers of soil from soil forma9on Can be quite dis9nct Soil profile: a ver9cal slice through the soil horizons Reveals the interac9ng factors in soil forma9on O horizon: topmost layer of soil Dead organic ma\er (detritus) deposited by plants High in organic content Primary source of energy for the soil community Humus: decomposed dark material at the bo\om of the O horizon

11 Soil Profiles Subsurface Layers A horizon (topsoil): below the O horizon A mixture of mineral soil and humus Permeated by fine roots Usually dark May be shallow or thick Vital to plant growth Grows an inch or two every hundred years E horizon: pale- colored layer below the A horizon Eluvia<on: process of leaching (dissolving) minerals due to downward movement of water

12 Soil Profiles Subsurface Layers (Cont.) B horizon (subsoil): below the E horizon Contains minerals leached from the A and E horizons High in iron, aluminum, calcium, other minerals, clay Reddish or yellow colored from oxidized metals C horizon: parent mineral material Weathered rock, glacial deposits, volcanic ash Reveals geologic process that created the landscape Not affected by biological or chemical processes

Soil classification Soil comes in an almost infinite variety of structures and textures Soils are classified by: Order: the most inclusive group Suborder, groups, subgroups,

13 Soil classification Soil comes in an almost infinite variety of structures and textures Soils are classified by: Order: the most inclusive group Suborder, groups, subgroups, families Class: best corresponds to the soil in ques9on Four major soil orders most important for agriculture, animal husbandry and forestry: Mollisols, oxisols, alfisols, aridisols

14 Important soil orders Mollisols: fer9le, dark soils of temperate grasslands The world s best agricultural soils Midwest U.S., Ukraine, Mongolia, Argen9nian pampas Deep A horizon; rich in humus and minerals With less precipita9on, minerals don t leach downward Alfisols: widespread, moderately weathered forest soils Well- developed O, A, E, and B horizons Typical of moist, temperate forests Suitable for agriculture if they are fer9lized Oxisols: soils of tropical and subtropical rain forests The B horizon has a layer of iron and aluminum oxides Li\le O horizon: rapid decomposi9on of vegeta9on Limited agriculture: minerals are in living plant ma\er Leached minerals form a hardpan, resis9ng cul9va9on Aridisols: soils of drylands (arid, semiarid, and seasonally dry areas) and deserts Unstructured due to lack of vegeta9on and precipita9on Thin, light colored Some areas may support rangeland animal husbandry Irriga9on leads to saliniza9on

15 Asking more of the land Increased popula9on pressures croplands and grazing lands to increase produc9on 15% of Earth s land was degraded in 1991 Now, land degrada9on is even worse 20% of cul9vated land, 30% of forests, 10% of grasslands were degraded between 1981 and 2003 Soils are degraded by erosion, salt buildup, and other problems Future produc9vity is undermined

16 The Russian Desert Southeastern Russia has undergone severe deser9fica9on Stable rolling grasslands have become dri"ing sands Deserts are growing by thousands of acres annually Failed communist agricultural policies Plowing the thin soil for crops Grazing sheep with sharp hooves that broke the soil The sand has buried over 25 towns Building barriers and plan9ng vegeta9on help limit moving sand and reclaim degraded land

17 Past Neglect 90% of all food comes from land- based agriculture Oceans and natural systems are being depleted Protec9ng and nurturing soil is the cornerstone of food produc9on and sustainability But it has been overlooked repeatedly The Greek, Roman, and Mayan empires collapsed The result of decreased agricultural produc9vity Brought on by soil erosion Plowing the prairie and drought caused the U.S. Dust Bowl

18 End- of- Lecture Objectives Explain the process by which soil, par9cularly topsoil is formed. Describe the components of soil and classify various soil types. Iden9fy the different layers of a soil profile and describe their characteris9cs. Iden9fy and analyze what makes a soil workable. Explain the different factors that contribute to soil degrada9on.

Soil Texture = %Sand, Silt & Clay in a soil.

Soils Soil Texture = %Sand, Silt & Clay in a soil. Soil texture is the single most important physical property of the soil. Knowing the soil texture alone will provide information about: 1) water flow