Soil: A Foundation of Agriculture

Importance of Soil

Soil supports all of Earth's terrestrial ecosystems, and healthy soil is vital for agriculture. When we abuse soil, we hamper its ability to sustain our production of food and fiber. Because every one of us relies directly on agriculture for the meals we eat and the clothing we wear, the quality of our lives is closely tied to the quality of our soil.

loam

Soil with a relatively even mixture of clay-, silt-, and sand-sized particles.

topsoil

That portion of the soil that is most nutritive for plants and is thus of the most direct importance to ecosystems and agriculture

B horizon (subsoil)

Frequently the second major soil horizon, composed primarily of mineral material with very little organic matter.

C horizon (parent material)

The least weathered horizon and is similar to the parent material initial step in soil formation

soil erosion is a global issue and has influenced by people

human activities move over 10 times more soil than all natural processes combined.

contour farming

process in which furrows are plowed sideways across a hillside, perpendicular to its slope and following the natural contours of the land. In contour farming, the side of each furrow acts as a small dam that slows runoff and captures eroding soil

waterlogging

saturation of soil with irrigation water or excessive precipitation so that the water table rises close to the surface occurs when overirrigation saturates the soil and causes the water table to rise to the point that water drowns plant roots, depriving them of access to gases and essentially suffocating them.

the best soils for plant growth and agriculture tend to be

silty soils with medium-sized pores, or loamy soils with a mix of pore sizes.

soils with very fine particles have

small pore spaces because particles pack closely together, making it difficult for water and air to pass through—so in clay soils, water infiltrates slowly and less oxygen is available to soil life.

ways to alleviate salinization

stop irrigating and wait for rain to flush salts from soil A better solution may be to plant salt-tolerant plants, such as barley, that can be used as food or pasture. A third option is to bring in large quantities of less-saline water (if available) to flush the soil. However, using too much water may cause waterlogging.

ways the erosion can be a problem

tends to occur much more quickly than soil is formed. Erosion also tends to remove topsoil, the most valuable soil layer for living things can be difficult to detect and measure

Sustainable approaches to fertilizing crops with inorganic fertilizers target

the delivery of nutrients to plant roots and avoid the overapplication of fertilizer.

Weathering

the physical, chemical, and biological processes that convert large rock particles into smaller particles. Physical weathering results from wind, rain, freezing, and thawing. Chemical weathering occurs as water or gases chemically alter rock. Biological weathering involves living things; for example, lichens (p. 83) produce acid that eats away at rock, and trees' roots rub against rock

things vital for plant growth

water, soil, nutrients

ways to minimize erosion

we can erect physical barriers that capture soil. In the long term and across large areas, however, the growth of vegetation is what prevents soil loss. Vegetation slows wind and water flow while plant roots hold soil in place and take up water.

Soil structure is a measure of the

"clumpiness" of soil. An intermediate degree of clumpiness is generally best for plant growth. Soil can be compacted by excessive foot traffic or by repeated plowing; this compaction reduces the soil's ability to absorb water and inhibits the penetration of plants' roots.

soil

A complex plant-supporting system consisting of disintegrated rock, organic matter, air, water, nutrients, and microorganisms.

Dust Bowl

A drought in the 1930s that turned the Great Planes very dry. prompted the U.S to fight erosion

shelterbelts

A row of trees or other tall perennial plants that are planted along the edges of farm fields to break the wind and thereby minimize wind erosion.

The simplest way to categorize soil horizons is to recognize

A, B, and C horizons corresponding respectively to topsoil, subsoil, and parent material. However, soil scientists often recognize at least three additional horizons (Figure 9.4). Soils vary by location, and few soil profiles contain all six horizons, but any given soil contains at least some of them.

salinization

Accumulation of salts in soil that can eventually make the soil unable to support plant growth. inhibits crop production; it currently lowers yields on roughly one-fifth of all irrigated cropland globally, costing more than $11 billion each year.

soil forms slowly

Although soil is a renewable resource, it forms so slowly that for all practical purposes we cannot regain soil once it has been lost. Because forming just 1 inch of soil can easily require hundreds or thousands of years, we would be wise to conserve the soil we have.

Flowers are evolutionary adaptations that function to attract pollinators; the sweet smells and bright colors of flowers are signals that advertise the sugary nectar and protein-rich pollen within

Animals seeking nectar and pollen are drawn to flowers, and they end up transferring pollen from flower to flower as they visit them. This enables flowering plants to reproduce, set seed, and create fruits.

Weathering and the accumulation and transformation of organic matter are influenced by five main factors:

Climate: Soil forms faster in warm, wet climates, because heat and moisture speed most physical, chemical, and biological processes. Organisms: Plants and decomposers add organic matter to soil. Topography: Hills and valleys affect exposure to sun, wind, and water, and they influence how soil moves. Parent material: Its attributes influence properties of the soil. Time: Soil formation can take decades, centuries, or millennia.

O Horizon (organic layer)

Composed of the leaves, needles, twigs, and animal bodies on the surface

soil supports agriculture

Crop plants depend on soil that contains organic matter to provide the nutrients they need for growth. Plants also need soil with a structure and texture suitable for roots to penetrate deeply, which assists with uptake of water and nutrients, allowing for proper growth. Plants need soil that holds water and dissolved nutrients in a way that makes them accessible to plant roots. And plants also depend on living organisms in the soil. In particular, many fungi form symbiotic mutualistic associations with plant roots, called mycorrhizae (p. 78). The dense network of fungal tissue in the soil helps draw up water and minerals, some of which are passed to the plant, and the plant provides to the fungus the carbohydrates produced by photosynthesis. Wheat and many other crops rely on mycorrhizae for proper growth. Animal agriculture also depends on soil with all these characteristics; because animals subsist on plants, the livestock we raise rely indirectly on healthy soil.

Another approach is to embrace technologies that improve efficiency in water use

Currently, irrigation efficiency worldwide is low, as plants end up using only about 40% of the water that we apply. The rest evaporates or soaks into the soil away from plant roots (Figure 9.8a). Drip irrigation systems that target water directly toward plant roots through hoses or tubes can increase efficiencies to more than 90%

The composition of a region's soil strongly influences the character of its ecosystems.

In fact, because soil is composed of living and nonliving components that interact in complex ways, soil itself meets the definition of an ecosystem

E Horizon (Eluviation)

Made up of coarse sand, silt and resistant minerals, clays and oxides of aluminum and iron are leached (removed by water) and are carried to lower horizons by water, sometimes this horizon is not there

One of the most effective ways to reduce water use in agriculture is to better match crops and climate.

Many arid regions have been converted into productive farmland through extensive irrigation, often with the support of government subsidies that make irrigation water artificially inexpensive. Choosing other crops that require far less water could enable these areas to remain agriculturally productive while greatly reducing water use.

horizons of soil

O horizon- made of decomposing organisms/humus A horizon- mixed minerals and topsoil E horizon- zone of leaching or eluviation B horizon- subsoil and very little organic material C horizon- similar to parent material, least weathered R

Sustainable approaches to irrigation maximize efficiency

One of the most effective ways to reduce water use in agriculture is to better match crops and climate. Another approach is to embrace technologies that improve efficiency in water use

Although erosion is a natural process, people have made land more vulnerable to erosion in three ways

Over cultivating fields through poor planning or excessive tilling (plowing) Grazing rangeland with more livestock than the land can support Clearing forests on steep slopes or with large clear-cuts

pollination can happen in many ways

Plants such as grasses and conifer trees are pollinated thanks to the wind. many kinds of plants that sport showy flowers are typically pollinated by animals, such as hummingbirds, bats, and insects

bedrock

Rock that makes up Earth's crust; also the solid rock layer beneath the soil

silt

Sediment consisting of particles 0.002-0.005 mm in diameter silt is intermediate, feeling powdery when dry and smooth when wet.

sand

Sediment consisting of particles 0.005-2.0 mm in diameter. Sand grains, as any beachgoer knows, are large enough to see individually and do not adhere to one another.

clay

Sediment consisting of particles less than 0.002 mm in diameter. Clay particles, in contrast, readily adhere to one another and give clay a sticky feeling when moist.

Regional soil differences and agriculture

Soil and soil profiles vary from place to place, with implications for agriculture For example, it may surprise you to learn that soils of the Amazon rainforest are much less productive than soils in Iowa or Kansas. This is because the enormous amount of rain that falls in tropical regions such as the Amazon basin readily leaches minerals and nutrients out of the topsoil and E horizon, below the reach of plants' roots. At the same time, warm temperatures in the Amazon speed the decomposition of leaf litter and the uptake of nutrients by plants, so only small amounts of humus remain in the thin topsoil layer. As a result, when tropical rainforest is cleared for farming, cultivation quickly depletes the soil's fertility. This is why the traditional form of agriculture in tropical forested areas is swidden agriculture, in which the farmer cultivates a plot for one to a few years and then moves on to clear another plot, leaving the first to grow back to forest In contrast, on the grasslands of North America, which have been almost entirely converted to agriculture (Figure 9.6b), there is less rainfall and therefore less leaching, so nutrients remain within reach of plants' roots. Plants return nutrients to the topsoil as they die, maintaining its fertility. This creates the thick, rich topsoil of temperate grasslands, which can be farmed repeatedly with minimal loss of fertility as long as farmers guard against loss of soil.

Soil color

Soil characteristic -can be used to indicate the organic content and fertility of a soil and/or the type of minerals and elements that are in the soil -Black or dark brown soils are usually rich in organic matter, whereas a pale color often indicates a history of leaching or low organic content.

R horizon

The bedrock, which lies below all of the other layers of soil, is referred to as the R horizon.

Ways to Prevent Salinization

The best way to prevent salinization is to avoid planting crops that require a great deal of water in dryland areas. A second way is to irrigate with water low in salt content. A third way is to irrigate efficiently, supplying no more water than a crop require

soil degradation

The loss of some or all of a soil's ability to support plant growth

leaching

The process by which minerals dissolved in a liquid (usually water) are transported to another location (generally downward through soil horizons).

humus

a dark, spongy, crumbly mass of material made up of complex organic compounds Soils with high humus content hold moisture well and are productive for plant life.

soil horizon

a distinct layer within a soil profile

slash and burn agriculture

a farming technique in which trees are cut down and burned to clear and fertilize the land

land degradation

a general deterioration of land that diminishes its productivity and biodiversity, impairs the functioning of its ecosystems, and reduces the services these ecosystems provide to us.

compost

a mixture produced when decomposers break down organic matter such as food and crop waste in a controlled environment

fertilizer

a substance that promotes plant growth by supplying essential nutrients such as nitrogen or phosphorus

protecting pollinators protects..

agriculture

Inorganic fertilizers have

boosted our global food production, but their overapplication has triggered increasingly severe pollution problems. Because inorganic fertilizers are generally more susceptible to leaching and runoff than are organic fertilizers, they more readily contaminate surface water bodies and groundwater supplies

Soil texture

determined by the size of particles

conservation tillage

encompasses an array of approaches that reduce the amount of tilling relative to conventional farming

no-till farming

farming that excludes the usage of tillage to avoid the negative effects of tillage such as loss of organic matter, soil erosion, etc, leaves roots holding soil

organic fertilizers

fertilizer composed of organic matter from plants and animals

Conservation Reserve Program

first established in the 1985 Farm Bill, pays farmers to stop cultivating damaged and highly erodible cropland, and instead to place it in conservation reserves planted with grasses and trees besides reducing erosion, the Conservation Reserve Program generates income for farmers, improves water quality, and provides habitat for wildlife.

Soil degradation is caused by

forest removal, cropland agriculture, and overgrazing of livestock

Desertification

form of land degradation in which more than 10% of productivity is lost as a result of erosion, soil compaction, forest removal, overgrazing, drought, salinization, climate change, water depletion, and other factors. Most such degradation results from wind and water erosion.

sustainable approaches do not rely solely on organic fertilizers but

integrate them with the targeted use of inorganic fertilizer.

inorganic fertilizers

mined or synthetically manufactured mineral supplements

If we are to feed the world's rising human population, we will need to

modify our diets or increase agricultural production (or both)—and do so sustainably, without degrading our resources.

Plants require _______, _________, and ________ to grow

nitrogen, phosphorus, and potassium

Productive soil is a renewable natural resource;

once depleted, soil may renew itself over time. However, renewal generally occurs very slowly. Most farming and grazing practiced so far has depleted soils faster than they form, so it is imperative for our civilization's future that we develop sustainable methods of working with soil.

what type of fertilizer does sustainable agriculture embrace?

organic fertilizers, because they can provide some benefits that inorganic fertilizers cannot. Organic fertilizers provide not only nutrients but also organic matter that improves soil structure, nutrient retention, and water-retaining capacity.

intercropping

planting different types of crops in alternating bands or other spatially mixed arrangements helps slow erosion by providing more ground cover than does a single crop reduces vulnerability to insects and disease and, when a nitrogen-fixing legume is included, replenishes the soil with nutrients.

many crops rely on....

pollination

Soils with large particles are

porous and allow water to pass through quickly—so crops planted in sandy soils require frequent irrigation.

preventing salinization in the first place is better because

remedying salinization once it has occurred is expensive and difficult

deposition

the arrival of soil at a new location

irrrigation

the artificial provision of water to support agriculture If the climate is dry, or if too much water evaporates or runs off before it can infiltrate the soil, crops may require irrigation. By irrigating crops, people can farm in arid regions (Figure 9.7) and may maintain high yields in times of drought. Fully 70% of all fresh water that people withdraw from rivers, lakes, and underground aquifers is used for irrigatio

parent material

the base geological material in a particular location

parent material of soil

the bedrock underneath the soil

overgrazing

the consumption by too many animals of plant cover, impeding plant regrowth and the replacement of biomass

soil profile

the cross-section of a soil as a whole, from the surface to the bedrock Generally, the degree of weathering and the concentration of organic matter decrease as one moves downward in a soil profile.

what causes land degradation?

the cumulative impacts of unsustainable agriculture, deforestation, and urban development. It is manifested in processes such as soil erosion, nutrient depletion, water scarcity, salinization, waterlogging, chemical pollution, changes in soil structure and pH, and loss of organic matter from the soil.

pollination

the process by which male sex cells of a plant (pollen) fertilize female sex cells of a plant (ova, or egg cells)

crop rotation

the process in which farmers alternate the type of crop grown in a given field from one season or year to the next reduces insects and ultimately disease

The amount of water a crop requires also is influenced by

the rate of evaporation and by the soil's ability to hold water and make it available to plant roots.

erosion

the removal of material from one place and transport to another place by the action of wind or water

A Horizon

the topsoil layer that is a zone of overlying organic material and underlying mineral material

precision agriculture

the use of technology to precisely monitor crop conditions, crop needs, and resource use to maximize production while minimizing waste of resources

Plants can die in soils that are

too acidic or too alkaline, so soils of intermediate pH values (p. 27) are best for most plants. Soil pH influences the availability of nutrients for plants' roots. For instance, acids from organic matter may leach some nutrients from the sites of exchange between plant roots and soil particles.

terracing

transforms slopes into a series of steps like a staircase, enabling farmers to cultivate hilly land without losing huge amounts of soil to water erosion. Terracing also helps farmers conserve and make maximum use of water. Terracing is labor-intensive to establish but in the long term is likely the only sustainable way to farm in mountainous terrain.