Soil as a ResourceSoil as a Resource

Key idea: Key idea:

Soil is an important Soil is an important resource that can be resource that can be

conserved and protected. conserved and protected.

The Importance of SoilThe Importance of Soil

The soil The soil is a living entity not just a is a living entity not just a substrate in which to grow plants. A living substrate in which to grow plants. A living soil is teeming with life, from earthworms, soil is teeming with life, from earthworms, centipedes and beetles to fungi and centipedes and beetles to fungi and bacteria. Healthy soil has food, air and water bacteria. Healthy soil has food, air and water to help plants grow. The more nutrients to help plants grow. The more nutrients available in the soil, the more the plant can available in the soil, the more the plant can take up. The more nutrients in the plant - the take up. The more nutrients in the plant - the more available for animals and humans. We more available for animals and humans. We should believe that for this reason human should believe that for this reason human health is affected by the health of the soil. health is affected by the health of the soil.

Soil FertilitySoil Fertility

Soil fertilitySoil fertility is the ability of soil to is the ability of soil to grow plants. grow plants.

Most of the plant's nourishment comes Most of the plant's nourishment comes from the soil. The nutrients are made from the soil. The nutrients are made up of minerals from the earth. Other up of minerals from the earth. Other nutrients come from dead plants and nutrients come from dead plants and animals, also broken down over time animals, also broken down over time by insects and organisms which live by insects and organisms which live in the soil.in the soil.

How Much Fertile Soil Is Available How Much Fertile Soil Is Available Out There?Out There?

How Much Fertile Soil Is Available How Much Fertile Soil Is Available Out There?Out There?

Analyzing the map above, we can see that Analyzing the map above, we can see that the land good for agriculture covers a the land good for agriculture covers a rather small surface on the world’s map. rather small surface on the world’s map.

About 25% of the dry land is suited for About 25% of the dry land is suited for some agricultural use, but most of this some agricultural use, but most of this surface lacks water resources. surface lacks water resources.

Only about 10% of the world’s dry land is Only about 10% of the world’s dry land is used for intensive agriculture. This means used for intensive agriculture. This means that there is enough water for irrigation, that there is enough water for irrigation, and the soil is fertile enough.and the soil is fertile enough.

Is This Amount of Soil Enough for Is This Amount of Soil Enough for the Needs of the Mankind?the Needs of the Mankind?

The answer to this question is NO!The answer to this question is NO! The population of the world grows The population of the world grows

rapidly, while the cultivated surface rapidly, while the cultivated surface at its best might stay the same. at its best might stay the same.

In reality, the surface covered with In reality, the surface covered with fertile soils shrinks every year, due to fertile soils shrinks every year, due to intensive agricultural practices.intensive agricultural practices.

What Threatens Soil Fertility?What Threatens Soil Fertility?

Soil fertility, or the ability to grow plants, is Soil fertility, or the ability to grow plants, is given by its content in organic matter, given by its content in organic matter, mineral matter, and water. mineral matter, and water.

Each type of soil, based on its content, is Each type of soil, based on its content, is suited for certain crops. Some soils are suited for certain crops. Some soils are best for planting potatoes, but not good at best for planting potatoes, but not good at all for corn, for example; this is because all for corn, for example; this is because different plants have different needs in different plants have different needs in nutrients and water. nutrients and water.

What Threatens Soil Fertility?What Threatens Soil Fertility?

Soils can loose their fertility in several Soils can loose their fertility in several ways:ways:

Soil depletionSoil depletion SalinizationSalinization ErosionErosionare the most common ways for soil are the most common ways for soil

loss. loss. We will analyze each one of them We will analyze each one of them

briefly.briefly.

Soil DepletionSoil Depletion Soil depletion occurs when the soil gradually Soil depletion occurs when the soil gradually

looses certain nutrients because of harvesting the looses certain nutrients because of harvesting the same type of crop year after year. same type of crop year after year.

Farmers often use chemical fertilizers to put Farmers often use chemical fertilizers to put nutrients back in the ground, but in a long run nutrients back in the ground, but in a long run this practice is not good for the environment. this practice is not good for the environment.

To prevent soil depletion, good farming practices To prevent soil depletion, good farming practices include: include:

-rotation of crops each year -rotation of crops each year -letting the fields lay fallow (uncultivated, -letting the fields lay fallow (uncultivated,

unused), in order to let some nutrients unused), in order to let some nutrients accumulate. accumulate.

SalinizationSalinization Because agricultural land is in great Because agricultural land is in great

demand, many counties expanded their demand, many counties expanded their crops in arid (dry) areas, by using crops in arid (dry) areas, by using irrigation. irrigation.

As the desert’s dry air rapidly evaporates As the desert’s dry air rapidly evaporates the irrigation water, the minerals that the irrigation water, the minerals that have been dissolved in water are left have been dissolved in water are left behind, and accumulate on the soil behind, and accumulate on the soil surface, a process called surface, a process called salinization.salinization. . At . At some point, the soils lose their ability to some point, the soils lose their ability to sustain crop growth. It is very difficult to sustain crop growth. It is very difficult to restore soils lost through salinization. restore soils lost through salinization.

Soil SalinizationSoil Salinization

Soil SalinizationSoil Salinization

Soil ErosionSoil Erosion

Soil erosion occurs naturally, when the Soil erosion occurs naturally, when the top soil is removed by wind, or water. top soil is removed by wind, or water.

Human activity can accelerate the soil Human activity can accelerate the soil erosion many times. For example, on erosion many times. For example, on 2001 one estimate indicated that soil 2001 one estimate indicated that soil in the United States was being in the United States was being eroded at a rate 17 times faster than eroded at a rate 17 times faster than the rate at which it was formed. the rate at which it was formed.

Soil ErosionSoil Erosion

Soil Erosion- The Dust BowlSoil Erosion- The Dust Bowl In the 1930s several years without rain In the 1930s several years without rain

led favored dust storms. Tons of topsoil led favored dust storms. Tons of topsoil were blown off barren fields and carried in were blown off barren fields and carried in storm clouds for hundreds of miles. storm clouds for hundreds of miles. Technically, the driest region of the Plains Technically, the driest region of the Plains – southeastern Colorado, southwest – southeastern Colorado, southwest Kansas and the panhandles of Oklahoma Kansas and the panhandles of Oklahoma and Texas – became known as the Dust and Texas – became known as the Dust Bowl, and many dust storms started there. Bowl, and many dust storms started there. But the entire region, and eventually the But the entire region, and eventually the entire country, was affected. entire country, was affected.

Soil Erosion- The Dust BowlSoil Erosion- The Dust Bowl The Dust Bowl got its name after Black The Dust Bowl got its name after Black

Sunday, April 14, 1935. More and more Sunday, April 14, 1935. More and more dust storms had been blowing up in the dust storms had been blowing up in the years leading up to that day. In 1932, 14 years leading up to that day. In 1932, 14 dust storms were recorded on the Plains. dust storms were recorded on the Plains. In 1933, there were 38 storms. By 1934, it In 1933, there were 38 storms. By 1934, it was estimated that 100 million acres of was estimated that 100 million acres of farmland had lost all or most of the topsoil farmland had lost all or most of the topsoil to the winds. By April 1935, there had to the winds. By April 1935, there had been weeks of dust storms, but the cloud been weeks of dust storms, but the cloud that appeared on the horizon that Sunday that appeared on the horizon that Sunday was the worst. Winds were clocked at 60 was the worst. Winds were clocked at 60 mph. Then it hit. mph. Then it hit.

Soil Erosion- The Dust BowlSoil Erosion- The Dust Bowl

Abandoned Farm During The Dust Abandoned Farm During The Dust BowlBowl

Erosion and Soil ConservationErosion and Soil Conservation

To minimize or prevent erosion, farmers use can To minimize or prevent erosion, farmers use can use methods such as:use methods such as:

Windbreaks Windbreaks (are barriers against the wind) (are barriers against the wind) Contour farmingContour farming (reduces water runoff) (reduces water runoff) TerracesTerraces (also slow the speed of runoff) (also slow the speed of runoff) Strip croppingStrip cropping: farmers plant crops that leave : farmers plant crops that leave

bare ground, like wheat, with crops that remain bare ground, like wheat, with crops that remain green, like Alfalfa.green, like Alfalfa.

No till-No till- Once the seeds of a crop in the soil, the Once the seeds of a crop in the soil, the farmers leave the field untouched until harvest.farmers leave the field untouched until harvest.

WindbreaksWindbreaks

Contour FarmingContour Farming

TerracesTerraces

Strip CroppingStrip Cropping

ConclusionsConclusions

The soil is a vital natural resources The soil is a vital natural resources because it sustains all living things.because it sustains all living things.

Unlike many natural resources which Unlike many natural resources which once depleted cannot be once depleted cannot be replenished, the soil can be replenished, the soil can be preserved using wise farming preserved using wise farming methods.methods.