SOIL RESOURCES AND SUSTAINABLE AGRICULTURE.

WHAT IS SOIL?

Soil is a mixture of mineral matter, organic matter, water, air, and organisms.

Weathering breaks down the bedrock into small particles.

Particle size:

  • Gravel: 2-64 mm.
  • Sand: 0.05-2 mm.
  • Silt: 0.002-0.05 mm.
  • Clay: less than 0.002 mm.

Sandy loam (clay and sand mixture) is the best for agriculture.

Humus is the partially decomposed bodies of plants and animals.

SOIL ORGANISMS

Soil is an ecosystem with its peculiar community of animals, plants, fungi and microorganisms.

Most animals stay close to the surface.

Burrowing animals and plant roots contribute to the turn over and aeration of soil.

There are many decomposers that return nutrients to the soil.

SOIL PROFILES

Most soils are stratified into layers called horizons.

Soils are classified according to the texture, color and composition of its horizons.

SOIL TYPES

Alfisols are produced under moist, deciduous forests.

Mollisols are formed under grasslands.

Both are very fertile.

LAND RESOURCES

Only about 10% of the earth's land area is currently in agricultural production.

Constraints to agriculture: steep slopes, shallow soil, poor drainage, low nutrient level, metal toxicity, excess salts, acidity.

Current ratio is 0.64 acre/person; by the year 2025 is projected to be 0.42 acre/person.

95% of the recent agricultural growth has come from improved crop varieties, increase, fertilization, irrigation and pesticide use.

Largest increases in cropland has occurred in South America and Oceania.

Asia and Europe have little opportunity to open new cropland.

The soils of tropical Asia, Africa and South America are generally infertile.

Most of the nutrients are in the standing plants and not in the soil.

LAND DEGRADATION

In the past 50 years some 1.9 billion ha (1 ha = 2.46 ac) of agricultural land has been degraded.

  • 300 million are strongly degraded.
  • 910 million are moderately degraded.

Causes vary from wind erosion, water erosion, salinization, waterlogging, nutrient depletion and toxic chemicals.

Every year

  • 3 million ha of cropland are ruined by erosion
  • 4 million ha are turned into deserts,
  • 8 million ha are converted to nonagricultural uses: roads, shopping centers, housing, etc.

EROSION

It is a natural process that redistributes the products of weathering, and it is part of soil formation and soil loss.

It is a disaster only when it occurs in wrong place at the wrong time.

It is estimated that 25 billion tons of soil are lost from croplands each year due to wing and water erosion, 1% of the cropland per year.

Erosion causes siltation of rivers, reservoirs, estuaries, wetlands and offshore reefs and banks.

Mechanisms of erosion:

  • Sheet erosion: layers of soil are removed from the surface.
  • Rill erosion: rivulets or small channels of running water.
  • Gully erosion: large channels of running water.
  • Streambank erosion: washing away of soil from stream and riverbanks often removing trees.

Plowing fields or overgrazing are responsible for exposing the soil to the action of water and wind.

United States has one of the highest rates of soil erosion in the world.

  • It exceeds soil formation on cropland by 40%.
  • About 1/2 of the soil that existed before the Europeans came has been lost.

Worldwide about 25% of the land has potential use for agriculture.

About twice as much as we now use.

China, India, Russia, and Ethiopia have high erosion rates.

Population pressure is responsible for the cutting of trees and plowing the grasslands with great effect on soil and loss of biodiversity.

Large expanses of land could be used more intensely with the proper input of fertilizers, high-yield crops and technology.

AGRICULTURAL RESOURCES

Water

Efficiency of irrigation water use is rather low in most countries.

High evaporation rate and seepage may cause the loss of up to 80% of the water intended for irrigation.

Waterlogging and salinization are the result of overwattering.

Fertilizers

Nitrogen, potassium and phosphorous often limit plant growth.

Overfertilization often occurs because farmers are not aware of the nutrient content of the soil they farm.

Many countries have reported dangerous level of nitrates in ground water in farming areas.

Eutrophication of lakes, streams and ponds result.

Climate

Greenhouse effect may cause increase yield due to the higher amount of CO2, but it may cause a decrease in precipitation at the center of continents and on the highlands.

Energy

Energy-intensive agriculture in industrialized countries:

Mechanization, fertilizer and pesticide production, food processing.

U.S. (260 million) uses about 12 times more energy per person than less developed countries (2.9 billion people).

Crop diversity

Local varieties are well adapted to the climate and soil of the region but they are being replaced by high yield varieties that are not as well adapted.

Ancestral relatives are disappearing due to loss of habitat.

Preserving genetic diversity becomes especially important as diseases and weed species proliferate and become insensitive to chemicals.

SUSTAINABLE AGRICULTURE

It is also known as REGENERATIVE AGRICULTURE.

Soil conservation

Soil can be renewed and replenish indefinitely with careful practices.

1) Managing topography:

  • Contour plowing reduces water runoff and erosion.
  • Strip farming is the planting of different crops in alternating strips along the land contours.

2) Terracing prevents erosion of steep hillsides.

3) Planting perennial species in unstable soils on sloping sides.

Providing ground cover

Annual crops generally cause high erosion rate.

  • Crop residues left on the ground.
  • Cover crops planted after the harvest and plowed under later on.
  • Mulch, heavy paper or plastic sheets.

Reduced tillage system

Plowing helps to control weeds, reduces competition, brings nutrients to the surface, improved drainage and aerated the soil.

Less plowing preserves the soil, improves water management, saves energy and increases crop yields.

  • Minimum till uses a chisel plow.
  • Conserv-till uses a sharp disc to cut a slot on the soil surface.
  • No-till drills the seed into the ground directly without plowing.

Low-input farming methods use less chemicals, involve more crop rotation and use less energy but the total revenue is less but the net income per acre is often higher.

Low-income farming is generally more sustainable.

Should the small farmer be considered or left at the mercy of multinational agricultural conglomerates?

  • Energy intensive.
  • Monoculture.
  • Chemical and hormone intensive.