Soil – A Renewable ResourceSoil – A Renewable Resource

Chapter 13: Food, Soil, Conservation, Chapter 13: Food, Soil, Conservation, and Pest Managementand Pest Management

March 2009March 2009

What is Soil?What is Soil?

• “Soil is a thin covering over most land that is a complex mixture of eroded rock, mineral nutrients, decaying organic matter, air, and billions of living organisms”

• Produced by physical, chemical, and biological weathering

Soil HorizonsSoil Horizons

Layers in Mature SoilsLayers in Mature Soils

• Infiltration: the downward movement of water through soil.

• Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower layers.

• The soil type determines the degree of infiltration and leaching.

Fig. 3-24a, p. 69

Mosaic of closely packed pebbles, boulders

Weak humus-mineral mixture

Dry, brown to reddish-brown with variable accumulations of clay, calcium and carbonate, and soluble salts

Alkaline, dark, and rich in humusClay, calcium compounds

Desert Soil(hot, dry climate)

Grassland Soilsemiarid climate)

Fig. 3-24b, p. 69

Tropical Rain Forest Soil(humid, tropical climate)

Acidic light-colored humus

Iron and aluminum compounds mixed with clay

Fig. 3-24b, p. 69

Deciduous Forest Soil(humid, mild climate)

Forest litter leaf moldHumus-mineral mixtureLight, grayish-brown, silt loamDark brown firm clay

Fig. 3-24b, p. 69

Coniferous Forest Soil(humid, cold climate)

Light-colored and acidic

Acid litter and humus

Humus and iron and aluminum compounds

Soil PropertiesSoil Properties

• Particle size: clay, silt, and sand• Soil texture: relative amounts of each different

particle size • Porosity: how well water infiltrates the soil• Soil Moisture: how much water is retained in the

soil• % Organic Matter• Percolation Rate – how fast water infiltrates the

soil

Fig. 3-25, p. 70

0.05–2 mmdiameter

High permeability Low permeability

WaterWater

Clay

less than 0.002 mmDiameter

Silt

0.002–0.05 mmdiameter

Sand

SOIL EROSION AND DEGRADATIONSOIL EROSION AND DEGRADATION

• Soil erosion is the movement of soil components, especially surface litter and topsoil, by wind or water.– lowers soil fertility – overload nearby bodies of water with eroded

sediment. – increases through activities such as farming,

logging, construction, overgrazing, and off-road vehicles.

TYPES OF SOIL EROSIONTYPES OF SOIL EROSION

– Sheet erosion: surface water or wind peel off thin layers of soil.

– Rill erosion: fast-flowing little rivulets of surface water make small channels.

– Gully erosion: fast-flowing water join together to cut wider and deeper ditches or gullies.

Sheet erosionSheet erosion

Rill erosionRill erosion

Gully erosionGully erosion

Global Outlook: Soil ErosionGlobal Outlook: Soil Erosion

Figure 13-10Figure 13-10

Soil Erosion in the U.S. Soil Erosion in the U.S.

• Soil erodes faster than it forms on most U.S. cropland, but since 1985, has been cut by about 40%.– 1985 Food Security Act (Farm Act): farmers receive a

subsidy for taking highly erodible land out of production and replanting it with soil saving plants like grasses and trees for 10-15 years.

DesertificationDesertification

• “Occurs when the productive potential of drylands falls by 10% or more because of a combination of natural climate change that causes drought and human activities that reduce or degrade topsoil.”

– Natural oscillating process that has been accelerated by human activities

– Affects 1/3 of world’s land and 70% of all dry lands.

Fig. 13-11, p. 280

Very severe (>50% drop)

Severe (25-50% drop)

Moderate (10-25% drop)

Causes and Consequences of Causes and Consequences of DesertificationDesertification

Fig. 13-12, p. 280

Causes Consequences Overgrazing Worsening

droughtDeforestationFamineErosionEconomic lossesSalinizationLower living standardsSoil compaction

Natural climate change

Environmental refugees

Salinization and WaterloggingSalinization and WaterloggingSalinization results from repeated irrigation in dry climates where salts gradually accumulate in the upper soil layers.

Waterlogging occurs when farmers apply too much irrigation water to leach salts deeper into the soil.

Figure 13-13Figure 13-13

The Effects of Soil SalinizationThe Effects of Soil Salinization

Figure 13-14Figure 13-14

Fig. 13-15, p. 281

CleanupPrevention

Soil Salinization

Solutions

Reduce irrigation

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

Flush soil (expensive and wastes water)

Stop growing crops for 2–5 years

Install underground drainage systems (expensive)

SOIL CONSERVATIONSOIL CONSERVATION

• Soil conservation involves reducing soil erosion and restoring soil fertility mostly by employing vegetation.

• Conservation tillage• Strip cropping/contour planting• Terracing• Alley cropping• Shelter breaks/windbreaks• Cover crops• Livestock rotation

Conservation TillageConservation Tillage

Strip Cropping/ Contour PlantingStrip Cropping/ Contour Planting

TerracingTerracing

Alley CroppingAlley Cropping

Shelter BeltsShelter Belts

Cover CropsCover Crops

Cover CropsCover Crops• Planting of a grass or grain that establishes well in fall and winter on a field shortly before

(early) or not long after (late) the main cash crop has been harvested

Cover Crops Benefit Ground and Cover Crops Benefit Ground and GroundwaterGroundwater

• Reduce nutrient concentrations in groundwater.

• Promotes root growth of subsequent cash crop especially in compacted soils.

• Especially effective against nitrogen.

Costs of Cover CropsCosts of Cover Crops

• Costs– Require extra management by the

farmer in order to perform well– Not always an available market/use for

the cover crop– Few programs advocate for them in MD

and VA – Requires farmers to incur the cost of the

cover crop (seeds) – Horton estimates this at $56 million/year in Chesapeake Bay watershed • In 2005, Gov. Robert L. Ehrlich Jr. provided

$5 million in grants to MD farmers to plant cover crops through the Maryland Agricultural Water Quality Cost-Share (MACS) Program .

Hairy vetch and winter rye at Clagett Farm

Livestock RotationLivestock Rotation• the movement of cattle or other grazing livestock from pasture to pasture• Benefits

– Prevents over-grazing of pastureland and excess soil erosion– Reduces the need for equipment intensive “hay” operations and the

expense of fertilizers and pesticides that go with them– Cattle require fewer medicines, antibiotics, and hormones– Rotation of livestock reduces the impact of animal waste and reduces

run-off of nutrients– Produce healthier meat products

In addition, converting crop land into pasture can broaden a farm’s economic base.

Costs Often means a reduction in gross sales

for the farmer Reduces the amount of land farmer

has for crop production

SUSTAINABLE AGRICULTURE SUSTAINABLE AGRICULTURE THROUGH SOIL CONSERVATIONTHROUGH SOIL CONSERVATION

• Fertilizers can help restore soil nutrients, but runoff of inorganic fertilizers can cause water pollution.– Organic fertilizers: from plant and animal (fresh,

manure, or compost) materials.– Commercial inorganic fertilizers: Active ingredients

contain nitrogen, phosphorous, and potassium and other trace nutrients.