Unit Two

“Soil, Agriculture, and the Future of Food”

The role of soil

• Soil is composed of eroded rock, organic matter, water, gases, nutrients, and microorganisms

• Soil is quasi-abiotic• Soil is a renewable resource; once nutrients

are depleted, it takes many years for those levels to be replenished

Humans and soil

• Due mainly to unsustainable farm practices, soil has been and is being depleted of nutrients that are required by plants for healthy growth

• Once a landscape’s soil has been depleted of nutrients no plants will grow in that area. Once there are no plants, this allows for massive amounts of wind and water erosion because there are no plants to hold the soil in place

• The above situation is called a “Dust Bowl”

Humans and soil cont’d

• A second scenario that can lead to “dust bowl” conditions is: Cattle Grazing

• Ranchers allow cattle to overgraze a landscape to the point most or all plants are removed thereby allowing for large scale wind and water erosion

• A third scenario that leads to “dust bowl” conditions is Deforestation: the complete removal of trees and other types of woody plants

Soil Degradation Causes

History of Agriculture

• Up until 10,000 years ago humans were hunter-gatherers and were nomadic (transient)

• At approximately 10,000 years ago when temperatures began to increase globally, various cultures began to plant seeds and domesticate animals, and this resulted in them settling in one area for extended periods of time

• People soon realized they could selectively breed desirable expressions of traits to generate higher yield with better flavor

The Industrial Revolution

• In the 1800’s, mechanization led to increased productivity and therefore led to increased harvests etc.

• Along with the advances in mechanization came increased irrigation, the introduction of synthetic fertilizers, and finally chemical pesticides that reduced competition from weeds and herbivory by insects

Contemporary Human Impact

• In general, humans modify and alter the earth/soil in many ways:

– Industrialized Agriculture (harvesting machines & crop planting methods)

– Construction (houses, offices, roads)– Flood Control– Resource Extraction

Soil as a System

• Soil composition:

– 50% mineral matter (Fe, Zn, Cu, P, N, C, Mg etc.)– 5% organic matter (plant leaves, decomposing

animals etc)– 45% pore space (air and water found here)

Soil Formation

• It takes hundreds, if not thousands, of years for soil to form

• Parent Material – base geological material in a particular location

• Bedrock – numerous rock layers that compose the Earth’s crust

• Weathering – process by which parent material is broken down into smaller pieces by wind and water action that eventually forms soil

Soil Formation cont’d

• Five factors that influence soil formation:

– 1. climate– 2. organisms (mainly micro….)– 3. topography (change of elevation)– 4. chemical composition of parent material– 5. time

Types of Weathering

• Physical - wind, rain, thermal expansion and contraction, and water freezing

• Chemical – compounds that cause rock composition to change

• Biological – tree roots and lichens

Soil Profile

• Soil profile shows the vertical variations in chemical composition of soil; the vertical sections are called Horizons

• They are listed from surface layer downward:O – Organic (leaf litter)A – Topsoil (crucial for agriculture & ecosystems)E - EluviationB - SubsoilC – Weathered Parent MaterialR – Unweathered Parent Material

Soil Characteristics

• Soil Color

• Soil Texture – fine/small or rough/large grains– Clay - smallest– Silt - medium– Sand – large

– Loam:even mixture of the above three particle sizes

Soil Characteristics

• Soil Structure – degree of clumpiness• Soil pH – acidic or basic

Soil Degradation• Desertification – loss of more than 10%

productivity due to human activities• Several human activities lead to Desertification:– Overharvesting via monoculture systems– Overgrazing– Deforestation

• If plants are unable to grow in soil, there is nothing to hold the soil in place

• If nothing holds the soil in place, wind and water erosion easily moves soil away

Overgrazing

Deforestation (Borneo)

Soil Conservation

• Both Overgrazing and Deforestation can be reduced and/or eliminated by using the “Rotational Island” approach

• Overharvesting can be reduced and/or eliminated by implementing one of the following methods:– Crop Rotation– Intercropping– Terracing– Shelterbelts

Soil Conservation

• Both Crop Rotation and Intercropping are forms of Polyculture

• Terracing reduces soil lost due to water erosion

• Shelterbelts reduces soil lost due to wind erosion

Intercropping

Terracing

Shelterbelts

The Fertilizer Issue

• In theory, fertilizers are a good way to supply plants/crops with the required nutrients they need for growth

• Fertilizers are especially useful when one is planting in an area where the soil has minimal nutrients

• The problem arises when people over apply fertilizer and the excess is deposited in waterways due mainly to the action of surface water

Worldwide Fertilizer Use

Agriculture & Bioengineering

• Food can be genetically modified to enhance desired traits: size, taste, color, disease resistance etc.

• Transgenic individuals are bioengineered to possess DNA from another species: Salmon

• Much of the food we eat is bioengineered• Society must proceed cautiously with this

advancement….. We do not have enough data to fully understand all the consequences of these practices

Bottom Line

• Sustainable (safe and healthy) practices need to be implemented to mitigate the negative impact humans have on the lithosphere due to the variety of ways we modify the surface of the Earth

• All things in moderation!!!!!