APES Soil & Agriculture Review

Soil Provides:

- food

- clothes

- shelter

- energy

Why Do We Care About Soil?

- filters water

- recycles nutrients

- buffers against floods

- sequesters (isolates) Carbon

- maintains biodiversity

Formation of Soil

formed by WEATHERING and EROSION of bedrock

- takes 2,000 YEARS to make 10 cm of topsoil (practically a nonrenewable resource)

Erosion

MOVEMENT OF SOIL from one place to another

- occurs when plants (roots) are removed from ground caused by over cultivating land, overgrazing land, deforestation

- WIND: led to the Dust Bowl of the 30's

- WATER: formed Grand Canyon, makes shaped rills that feed into deep gullies

- ICE: glaciers receding form U shaped gullies

gully: water-worn ravine

Anthropogenic (human activity) Causes of Erosion

- burning ditches

- ATV use

- logging

- farming

- overgrazing of livestock

- monoculture

- construction

Soil Mixture

- 5% organic matter

- 25% water

- 45% mineral particles

- 25% air

5 Characteristics of Soil

- charge

- texture

- structure

- porosity

- permeability

Charge of Soil

NEGATIVELY CHARGED (anion)

- clay and organic matter are more negatively charged

- soil can hold onto positively charged (cation) nurtients

- a change in pH from acid deposition can change the soil's ability to hold onto nutrients

Cation Exchange Capacity

ability of a soil to ABSORB and release cations (positively charged mineral ions)

- CEC is used as a measure of SOIL FERTILITY

it quantifies the amount of negatively charged particles that can hold onto nutrients

Soil pH

determines which plants will grow; controls which nutrients are available for plants to use

3 primary plant nutrients:

- NITROGEN

- PHOSPHORUS

- POTASSIUM

also called MACRONUTRIENTS because plants need them in large quantities

3 primary plant nutrients

other nutrients:

- IRON

- MANGANESE

called MICRONUTRIENTS because are needed in small amounts

Nitrogen

Importance:

- stimulates above ground growth

- produces rich green color

- influences quality and protein content of fruit

- plant's use of other elements is stimulated by presence of Nitrogen

taken up by plant as NH4+ and NO3-

replenished naturally by rhizobacteria (root-colonizing bacteria that benefits both itself and the plant mutualism) on legume roots

fertilizer from manure or chemical reaction

Phosphorus

Abundant in:

- strong root system

- increases seed yield and fruit development

- parts of root involved in water uptake (hair)

major role in transfer of energy

taken up by plant as H2PO4- and HPO4-2

fertilizer is made from rock phosphate

Potassium

Potash

Important in vigor and vitality of plant

- carries carbohydrates through plant

- improves color of flowers

- improves quality of fruit

- offsets too much Nitrogen

found naturally in feldspar and micas

Acid Deposition & Soils

Carbon dioxide in atmosphere dissolves in water to form Carbonic Acid (H2CO3)

- makes precipitation slightly acidic

- pH of 5-6 is normal

Oxides of Sulfur and Nitrogen from burning fossil fuels can reduce pH of water making rain more acidic

- pH of 5.6 or lower is considered acid deposition

Soil Buffers

buffers: substances in soil that help neutralize acid precipitation

- help resist changes in soil pH, lakes, streams, ponds because they dissolve into water runoff

ex.

- Limestone

- Calcium Carbonate

- Calcium Bicarbonate

Soil Texture

determined by size and type of particles that make up the soil

- SAND: largest particle size; good infiltration, poor water/nutrient holding

- SILT: medium particle size; medium infiltration, water/nutrient holding

important component of river beds for fish spawning

- CLAY: smallest particle size; slow infiltration, good water/nutrient holding

- LOAM: combination of all types; ideal soil type

Soil Structure

layers, each called a HORIZON

layers all together, called SOIL PROFILE

- O HORIZON: organic layer, contains leaf litter, humus, decomposed organic material

- A HORIZON: topsoil, contains organic materials and minerals

- E HORIZON: zone of leaching; light colored because minerals leached out

leach: drain away

- B HORIZON: subsoil; zone of accumulation- organic material and minerals accumulate

accumulate: gather/build up

- C HORIZON: weathered bedrock

- R HORIZON: unweathered bedrock

Humus

- provides nutrients/fertility for plants and soil dwelling organisms

- helps topsoil hold water

- makes root growth easier

- improves soil aeration

- improves buffering capacity; stabilizes pH

- plentiful in deciduous forests, grasslands, temperate rainforests

Soil Development

- plants

- animals

- fungi

- bacteria

create soil through their activities and adding organic matter when they die

moist soils with high organic content are higher in biological activity

Factors Affecting Soil Formation

- takes thousands of years

- occurrence of FREEZE-THAW and WET-DRY CYCLES

- average temperature

- moisture levels

- climate affects VEGETATION

- PARENT material

- topography: DRAINAGE patterns

- LIVING ORGANISMS: organic matter-helps form humus

Soil Porosity

amount of air around the soil particle

- number of pore spaces

- ability of a soil to hold fluid

Soil Permeability

ability of water to flow through a soil

- gravel: high permeability

- clay: low permeability

soil with high clay content are prone to flooding

Desertification

- dry, nutrient poor soils can be easily DEGRADED

- irrigation can cause SALINIZATION

- topsoil is eroded away due to shallow roots failing to hold the soil in place

- Africa (Sahara expands 31 miles a year)

- unsustainable farming in China

CAUSED BY:

- erosion

- soil compaction

- forest removal (deforestation)

- overgrazing

- drought

- salinization

- climate change

- depletion of water

leads to major FINANCIAL LOSS

Salinization

build up of salts in surface soil layers

- water evaporates and leaves salts behind; forming a crust on the soil

PREVENTION:

- avoid planting crops that need a lot of water

- use water with low mineral content

- use only required amount of water to avoid evaporation

REMEDIATION:

- stop irrigation and wait for rain to remove salt crust

- grow salt tolerant plants

Dust Bowl

"Dirty Thirties"

homesteaders began farming/ranching

- removed native grass

- used deep plowing to grow wheat

- increased supply caused decrease in price

- severe drought

- inappropriate farming practiced (deep plowing, bare fields) caused wind erosion

- wind removed top soil ("Black Blizzard")

- visibility as low as 1 meter

- families abandoned farms

*called "Okies"

* by 1940, 2.5 millino people moved out

* migrated from Oklahoma to California

Led to the soil conservation service, now called, Natural Resources Conservation Service (NRCS)

Soil Conservation Methods

CROP ROTATION: alternate crops grown in fields each season/year; returns nutrients, breaks cycle of disease, minimizes erosion, reduces pests

- legumes used to return nitrogen to soil

CONTOUR FARMING: prevent water erosion on steep hills; acts as small dam

- good for gradually sloping land

TERRACING:

prevent water erosion on extremely steep hills; cut steps in hillside

- labor intensive

used for longest time

INTERCROPPING:

planting different types of crops in alternating arrangements

- provides more ground cover

- reduces pests/disease

SHELTER BEDS/WINDBREAKS:

prevent wind erosion

- rows of bushes/trees planted along edge of field

REDUCED TILLAGE:

"No Till Farming"

reduces irrigation and fossil fuel usage

- drill small hole through O horizon into top of A horizon

- add seeds and fertilizer to close hole

requires increased usage of fertilizer and pesticides

Soil Contamination

CAUSED BY:

- corrosion of underground storage tanks

- application of pesticides and fertilizer

- mining

- oil and fuel dumping

- disposal of coal ash

- leaching from landfills

- direct discharge of industrial wastes into soil

- drainage of contaminated surface water into soil

Clean Up (remediation) Options

- EXCAVATE and dispose of contaminated soils

- THERMAL REMEDIATION: heating soil to volatize chemical contaminants for vapor extraction

- BIOREMEDIATION: microbial digestion of certain organic chemicals

- PHYTOREMEDIATION: using plants to extract heavy metals

Bioremediaton

PROS:

- low cost

- reduces soil erosion

- reduces amount of material that has to be taken to a landfill

- less habitat destruction

CONS:

- slow

- vegetation may be hazardous

- hazardous waste to dispose

- only effective to root depth

- may introduce exotic species

- hard to grow specific plants

Soil Tests

pH:

- measured hydrogen ion concentration

SALINITY:

- measures salt content

ORGANIC CONTENT (humus):

- analysis that indicated organic content

ION EXCHANGE CAPACITY:

- measures ability to absorb and release cations

NITROGEN, PHOSPHORUS, POTASSIUM, SULFUR:

- measures levels present

Physical Soil Tests

SOIL TEXTURE (soil sieves, particle soil analysis) percent of sand, silt, clay

POROSITY:

- amount of water the soil can hold due to pore space

PERMEABILITY/PERCOLATIN RATE:

- speed of infiltration of water into soil

MOISTURE CONTENT:

- amount of water in the soil at a given time

Soil Remediatoin

TOO ACIDIC: add lime

TOO BASIC: add sulfur

NEED NITROGEN: plant legumes or add manure

NEED PHOSPHORUS: add bone meal

NEED POTASSIUM: add burnt crop residue

Hunter Gatherers

1st humans were hunter gatherers

agriculture began 10,000 years ago

- selectively breeding

- traditional agriculture: produce just enough to eat

- groups began to settle in order to farm

- starvation was common

- poor nutrition

7.6 million people starve to death every year

33% of the world is starving

Industrial Revolution

boosted yield of crops

- better transportation of crops

- improved harvesting

- synthetic fertilizers

- chemical pesticides

- increased irrigation

- beginning of monoculture

Green Revolution

more effective farming techniques (1940-1970)

- HIGH YIELD crop varieties through crossbreeding

- increased IRRIGATION infrastructure

- wide use of PESTICIDES and FERTILIZERS

- MONOCULTURE becomes dominant (field planted with only one crop)

BOTTOM LINE: the green revolution meant more food made on less land

depends on large amounts of synthetic fertilizers, chemical pesticides, irrigation, fossil fuels, and new strains of artificially selected crops

- GOOD: yield increase prevented damage for deforestation and preserved biodiversity

- BAD: population growth continues so agricultural land use increased pollution, erosion, salinization, desertification

Mechanization

machinery to do the work of separating grain/seed instead of doing it by hand

Monocultures Increase Output, but at Cost

MONOCULTURE: large expanse of a single crop

- more efficient, increases output

- devastates biodiversity

- susceptible to disease and pests

- narrows human diet: 90% of food comes from 15 crop species and 8 livestock species

SLASH AND BURN: cutting and burning of forests to create fields

- ash acts as fertilizer; soil is depleted of nutrients and then move to new area

- devastating decreases in biodiversity

Pros and Cons of Monoculture

PROS:

- planting and harvesting are more efficient

- more cost-effective

CONS:

- since crop shares the same genetic make up, there is an increased risk of decimation by one type of pathogen or pest

- fewer ecological niches; decreasing biodiversity

- depletes soil of nutrients; use of fertilizer increases

Seed Banks

institutions that preserve seed types as a king of living museum of genetic diversity

Undernourishment

people receive less than 90% of their daily caloric needs

Over nutrition

receiving too many calories

can lead to:

- DIABETES: problems with body dealing with sugars

- HYPERTENSION: (high blood pressure) build up of pressure in arteries; leads to heart disease, stroke, aneurysms, kidney disease

Malnutrition

shortage of nutrients the body needs

can lead to:

- ANEMIA: lack of iron, low energy and fatigue

- RICKETS: not enough calcium in bones and lack of vitamin D

- VITAMIN A DEFICIENCY: poor vision

- SCURVY: lack of vitamin C causing loose teeth, black/blue spots on skin, swollen gums

- GOITER: results from lack of iodine; causes large growth on neck

- KWASHIOKOR: diets lacking protein or essential amino acids; results in bloated stomach, mental and physical disabilities

- MARASMU: protein deficiency and insufficient calories; results in wasting or shriveling of body

Future

world population is to hit 9 BILLION or more by 2050

to feed everyone, we need to:

- put more land into agricultural production

- improve crop yields

- reduce consumption of meat

- harvest more fish

Feedlot Agriculture

(factory farms) also called Concentrated Animal Feeding Operations (CAFOs)

- huge warehouses/pens to deliver energy rich food to animals living at high densities

- 1/2 of the world's pork and poultry come from feedlots

BENEFITS:

- greater production of food

- minimizes land costs, improve feeding efficiency, and increase fraction of food energy that goes into the production of animal body mass

DRAWBACKS:

- contributions to water and air pollution

- poor waste containment causes disease

- heavy use of antibiotics to control disease; leads to disease strains (80% of antibiotics go to livestock)

Impact of CAFO's

- manure and wastewater contribute to pollutants (nitrogen, phosphorus, organic matter, sediments, pathogens, metals, hormones, ammonia)

- excess nutrients in water

- low levels of dissolved oxygen (kills fish)

- decomposing organic matter than contribute to toxic algal blooms

- runoff: degrade water resources; resulting in illness

- dust/odors: respiratory problems

- increased antibiotic resistant microorganisms

Sustainable Agriculture

does not deplete soil, pollute water, or decrease genetic diversity

ORGANIC AGRICULTURE: uses no synthetic fertilizers, insecticides, fungicides, or herbicides. No irradiation, GMOs, or sewage sludge

Farming Laws

FARM BILL (1990, 1996, 2002): provides subsidies to farmers for overproduction and/or crop losses due to weather conditions

1990 ORGANIC FOOD PRODUCTION LAW: designed to develop uniform national standards for being "organic".

USDA states that any food that is:

- genetically engineered/modified

- fertilized with municipal sludge

- zapped with radiation

...IS NOT ORGANIC

Types of Irrigation

CONVENTIONAL: spraying water over all plants; very little gets taken in by the plants, much is lose due to evaporation

CENTER-PIVOT IRRIGATION: water still not targeted to specific plants; most is lost

DRIP IRRIGATION: hoses are arranged to water specific plants; very little water is lost

Problems with Irrigation

- lead to desertification

70% of water withdraw is used for irrigation

- water never makes it to its original destination

- changes ecosystem

- Case Study: The Aral Sea

- waterlogging: over irrigation causes over saturation of soil, suffocates plant roots

- salinization: buildup of salts in surface soil layers; water evaporates and leaves salts: soil gets crusty

The Aral Sea

- 4th largest salt lake

- found between Kazakhstan and Uzbekistan

- Soviet Government diverted rivers that fed the sea to irrigate the desert in attempt to grow rice, melons, cereals, cotton (1960's)

- diversion of water exceeded surplus, causing sea to shrink and dry up

Irrigation Solutions

PREVENTION:

- do not plant water-guzzling crops in sensitive areas

- irrigate with low salt water

- irrigate efficiently, supplying only water that the crop requires

- drop irrigation targets water directly to plants

REMEDIATION:

- expensive and not very effective-increase drainage or add water to leach salts downward

Fertilizers

agriculture removes organic matter and nutrients from soil

- contain essential nutrients for plants (nitrogen, phosphorus and potassium)

TYPES OF FERTILIZERS:

- organic

- synthetic

Synthetic/Inorganic Fertilizers

- produced commercially by the Haber process (artificially fixing atmospheric nitrogen N2-->NH3)

- highly concentrated

PROS:

- easy application

- can be specially formulated

- easily absorbed by plants

Organic Fertilizers

- organisms' decomposed waste (manure)

- crop residues

- fresh vegetation

- compost

- reduces amount of waste

- improves soil quality

Advantage of Inorganic Fertilizer

- easily obtained, transported, stored, and applied

- more economical

- nutrients are concentrated

- only need small amounts

- computerized applications can release specific minerals needed by plants

- nutrients are immediately available to crop

- increases soil fertility

- have specific nutrient composition

- increases crop yield

- speeds up growing process

Disadvantage of Inorganic Fertilizer

- adds no humus or organic matter to soil; decreasing water holding capacity

- lowers oxygen content of soil; keeps nutrients from being take up as efficiently

- does not have all micronutrients

- requires large amounts of energy for production, transportation, application

- releases nitrous oxide (greenhouse gas)

- over application can harm plants

- aquatic pollution

- expensive

- human health problems

Genetically Modified Organisms (GMO's)

crops whose DNA have been altered to create desire traits

ex. soybeans, corn, cotton, canola

Pros of GMO's

- increased nutritional content

- increased agricultural efficiency

- decreases fertilizers and pesticides

- increases production

- rapid growth

- increases shelf life

- diseases/pest resistance

- weather resistance

- genetically modified bacteria can take up pollution

- people want standardized food

Cons of GMO's

- not well understood

- cross contamination

- mutations

- creates "super-pests"

- mixed effect on biodiversity

- mulinational corporations harm small farmers

- copyright on living organisms

- not accepted by many

- exacerbating allergies in humans

Pests

any organism that damages valuable crops

WEED: any plant that competes with crops

PESTICIDES: poisons that target pest organisms

- INSECTICIDES: target insects

- HERBICIDES: target weeds

- FUNGICIDES: target fungi

Types of Pesticides

BIOLOGICAL: lady bugs, parasitic wasps

CARBAMATES: organic compounds that affect nervous system of pests; more water soluble than chlorinated hydrocarbons

CHLORINATED HYDROCARBONS: affect nervous system; can accumulate in fatty tissues

FUMIGANTS: spray pesticides used to sterilize soil and prevent grain infestation

INORGANIC: many act as poisons

- highly toxic and susceptible to bioaccumulation

ORGANIC/NATURAL: derived from plants (tobacco nicotine) and chrysanthemum (pyrethrum), usually chemicals a plant naturally uses to protect itself

ORGANOPHOSPHATES: synthetic, extremely toxic, low persistence

Effects of Pesticide Use

PESTICIDE TREADMILL: more pesticides used as a result of resistance; results in death of predators of pests and further INCREASE IN PESTICIDE USE

- some individuals are GENETICALLY IMMUNE to a pesticide; they survive and pass these genes to offspring

- evolutionary arms race: chemists increase chemical toxicity to compete with resistant pests

Biological Control

uses a pest's natural predators to control the pest

- reduces pest populations without chemicals

- BACILLUS THURINGIENSIS (Bt): soil bacteria that kills many pests

Alternatives to Pesticides

- FOOL 'EM: crop rotation, changing planting times, change location where you are growing

- HELP PEST'S PREDATORS: provide homes for predators, increase crop diversity

- GENETIC RESISTANCE: genetic engineering

- BIOLOGICAL CONTROLS: import natural predators

- INSECT PERFUMES: sex pheromones lure pests into traps

- HORMONES: use them to disrupt pests life cycle leading to fewer offspring

Pests Controlling Laws

FEDERAL INSECTICIDE, FUNGICIDE, RODENTICIDE ACT (1942): FIFRA

- EPA, USDA, FDA regulates the sage sale and use of pesticides

- EPA registers pesticides based on ricks/benefits and makes rules on label/package

FEDERAL ENVIRONMENTAL PESTICIDES CONTROL ACT (1972):

- amendment to FIFRA

- pesticides are categorized as "general" or "restricted" and the EPA regulates use

FEDERAL FOOD, DRUG, COSMETIC ACT (1996):

- EPA sets max residue levels for pesticides used in or on food or animal feed

DDT: insecticide

dichloro-diphenyl-trichloroethane

- first synthetic insecticides in the 1940's

- killed off malarial mosquitoes

Roundup: Glyphosphate

- nonpersistence (break down in a couple weeks)

Pros of Pesticides

Pros:

- kill unwanted pests that carry diseases

- increases food supplies

- more food means less expensive

- effective/fast-acting

- newer pesticides are safer

- reduces labor costs on farms

- food looks better

- agriculture is more profitable

Cons of Pesticides

- accumulate in food chain

- creates pesticide treadmill

- runoff

- destroys bees

- threatens endangered species

- affect egg shell of birds

- 5% actually reach pest

- 20,000 human deaths/year