Soil & Agriculture

Who cares? You do!

• In India, one child dies every minute from severe acute malnutrition.

Case Study: The Dust Bowl

• In the “dirty thirties” a large area of cropland was abandoned due to soil erosion caused by poor farming practices and drought.

• Spurred one of the largest internal migrations in U.S. history.

But that was a long time ago, right? Wrong!• Modern Dust Bowl

Why is soil important?

•Our lives depend on it!

• It’s a habitat for other organisms

•Cleans and Stores Water

What is Soil?

• Thin layer on the Earth’s surface made of: rock, mineral nutrients, decaying organic matter, water, air, many organisms

• 4 Parts

• Mineral Particles (45%)

• Organic Matter (5%)

• Water (25%)

• Air (25%)

Structure of Soil

• Soil Horizons:

• O Horizon: surface litter, i.e. freshly fallen undecomposed or partially decomposed organic matter. Normally brown or black.

• A Horizon: topsoil layer of partially decomposed organic material (humus) and inorganic mineral particles.

•B Horizon: subsoil, mixture of sand, silt, clay, and gravel.

• Gravel—coarse to very coarse particles

• Sand—medium sized particles

• Silt—fine particles

• Clay—very fine particles

•C Horizon: parent material, often unweathered bedrock.

How is it formed?

•Weathering

• Chemical—minerals in rock react with other substances to form new materials

• Physical—cracking and breaking rock apart to form smaller particles

• Biological—plant roots can crack and break rocks apart

•Decomposition—complex organic matter is broken down into simpler forms of matter

What does this describe?

•A plant’s roots or animal cells undergo cell respiration and the CO2

produced diffuses into soil, reacts with H2O & forms carbonic acid (H2CO3). This eats parts of the rock away.

Properties of Soil

• Soil Texture

• Determined by type and relative amount of soil particles

• Soil texture can be described as:

• Gritty—sandy

• Sticky—lots of clay

• Smooth—silty (feels like flour)

•Porosity

• Volume of space per unit of soil

•Permeability

• Rate at which water and air move through the soil

Infiltration & Leeching

•As water moves down through the soil it dissolves minerals and organic matter. These dissolved materials are carried from the upper layers to the lower layers.

Is soil renewable? Are we using it sustainably? • It takes from fifteen years to

hundreds of years to form 1cm (.4 in) of soil.

• “Soil is being swept and washed away 10-40 times faster than it is being replenished”• According to David Pimentel in his study "Soil Erosion: A Food

and Environmental Threat"

• Erosion

• Materials are moved from one place to another. Caused primarily by water and wind.

Global Soil Stats

• Soil on 38% of the world’s cropland is eroding faster than it forms.

• Food production has decreased on 16% of the world’s croplands.

U.S. Soil Stats

•6.4 billion tons of soils are eroded from the U.S. each year

•On farmed land, soil is eroding 16 times faster than it is being formed.

Types of Soil Degradation

• Desertification

• A decrease in the productivity of arid or semiarid land by 10% or more.

• Moderate

• Severe

• Very Severe

• Salinization

• An accumulation of salts in soil due to repeated irrigation

What are we doing about it?

• Agriculture Adjustment Act (AAA)

• Subsidized farmers taking erodible land out of production and planting it with soil saving plants for 10-15 years

• Killed excess livestock

• Cut soil losses by 66%

• Agricultural Act of 2014

• Farm Bill

Soil Conservation

• Conservation-tillage (Used on 45% of U.S. farms in 2003)

• Minimum tillage farming—soil is undisturbed over the winter, special tillers break subsurface soil without turning over topsoil, crop residue, or cover crop.

• No-till farming—seeds, fertilizer, pesticide are injected into thin slits made in unplowed soil.

Terracing—converting slopes into flat terraces that run across the lands contour.

Contour farming—crops are planted across slopes instead of up and down the slope

Strip Cropping—alternating row (corn) and cover (legume) crop

Agroforestry—crops planted between rows of trees

Soil Restoration

• Fertilizers

• Organic

• Compost (animal manure, plant material), bone meal, peat

• Inorganic

• Includes fertilizers produced by factories, which are composed primarily of N, P, K.

Agriculture

•Croplands—77% of the world’s food, mostly grains

•Rangelands—16% of the world’s food, mostly livestock

•Ocean Fisheries—7% of the world’s food

•Production has increased significantly since the 1930’s due to: technological advances, machinery, selective breeding, genetic engineering.

Industrialized-High Input-Agriculture

•Uses large amounts of: fossil fuel, water, fertilizer, pesticides

•Crops grown in monocultures

Fig. 13-21, p. 289

Trade-Offs

Animal Feedlots

Advantages Disadvantages

Increased meat

production

Need large inputs

of grain, fish

meal, water, and

fossil fuelsHigher profits

Concentrate

animal wastes

that can pollute

water

Less land use

Reduced overgrazing

Reduced soil

erosionAntibiotics can

increase genetic

resistance to

microbes in

humans

Help protect

biodiversity

Fig. 13-18, p. 285

Biodiversity Loss Soil Water Air Pollution Human Health

Loss and

degradation of

grasslands,

forests, and

wetlands

Erosion Water waste Greenhouse gas emissions from fossil fuel use

Nitrates in drinking water

Loss of fertility Aquifer depletion

Pesticide residues in drinking water, food, and air

Salinization Increased runoff and flooding from cleared land

Other air pollutants from fossil fuel use

Fish kills from

pesticide runoff

Waterlogging

Sediment pollution from erosion Greenhouse gas

emissions of nitrous oxide from use of inorganic fertilizers

Contamination of drinking and swimming water with disease organisms from livestock wastes

Desertification

Killing wild predators to

protect livestock

Fish kills from pesticide runoff

Surface and groundwater pollution from pesticides and fertilizers Belching of the

greenhouse gas methane by cattle

Loss of genetic diversity of

wild crop strains replaced

by monoculture strains

Bacterial contamination of meat

Overfertilization of lakes and rivers from runoff of fertilizers, livestock wastes, and food processing wastes

Pollution from pesticide sprays

Traditional-Low Input-Agriculture•Uses less: water, fertilizer, pesticide,

etc.

•Depends on human labor, draft animals

Aquaculture

• Fish farming—fish are raised and harvested in enclosed ponds

• Fish ranching—fish are raised, released, and then harvested when they return to spawn.

Fig. 13-24, p. 292

Trade-Offs

Aquaculture

Advantages Disadvantages

High efficiency Needs large inputs

of land, feed, and

waterHigh yield in

small volume

of waterLarge waste

output

Destroys

mangrove forests

and estuaries

Can reduce

overharvesting

of conventional

fisheries Uses grain to feed

some species

Low fuel use Dense populations

vulnerable to

disease

Tanks too

contaminated to

use after about 5

years

High profits

Profits not tied

to price of oil

Livestock & their Products•Chickens, pigs, sheep, cattle

• Eggs, meat, leather, wool, manure

Factory Farming

•High density livestock operations

Free Range Farming

• Lower density livestock operations

SOLUTIONS: MOVING TOWARD GLOBAL FOOD SECURITY

• People in urban areas could save money by growing more of their food.

• Urban gardens provide about 15% of the world’s food supply.

• Decrease food waste!

• Up to 90% of the world’s food is wasted.

Figure 13-26

Solutions: Steps Toward A More Sustainable Food System

•We will have to address production, processing, distribution, consumption and waste to achieve a sustainable food system

What can you do? Think About Your Own Consumption

• Diet & Ecological Footprint

• More energy, water and land is required to produce meat products than to produce plant products

• Therefore, high meat diets have larger ecological footprints than high plant diets

• Eating more chicken and fish and less beef and pork reduces the harmful impacts of meat production on the environment

• Eat a whole food, plant based diet and change the types of meat that you eat.

What can you do?