APES Unit 4, Module 20: Soil Composition, Properties, and Degradation

rock cycle

• no matter which rock you’re at, you can generate the other two

• fossil fuels at/core from sedimentary

• sedimentary, metamorphic, igneous 

succession 

• the process where a community develops slowly through a series of species

• earlier species alter the environment in some way to make it more habitable for others

• as the more species arrive, the earlier species are outcompeted and replaced 

• primary and secondary

soil formation

• primary succession

• where we develop ecosystems over time, soil isn’t present so starting with bare rock and it gets weathered

factors affecting soil formation

• time (hundreds of thousands of years)

• weathering 

  • physical

  • chemical

Physical weathering

• wind, waves, rain, streams, friction from other rocks, freezing and thawing (temp.)

Chemical weathering

• acid rain (pH changes) 

O horizon

• leaf /surface litter, dead, organic matter

A horizon

• topsoil

• mixture of soil types, lots of organisms, dark and rich

E horizon

• eluviation zone

  • the lateral or downward movement of dissolved or suspended material within soil when rainfall exceeds evaporation, aka infiltration

• not always in soil

• bleached

• no organic matter

B horizon

• long time to form

• less nutrients

• zone of illuviation (accumulation of minerals) 

• A and C

C horizon

• parent material

• weathered rock

• sometimes saturated with water

Bedrock

• impermeable

secondary succession

• does NOT follow primary succession

• is faster

• begins in an environment following destruction of all or part of a community but the soil remains intact

• ex.~ hurricanes, wildfires, deforestation, abandoned farmland, open area after fire

weathering vs. erosion

• erosion is more the physical movement of material from one plant to another and weathering is the break down of that material

• need both to create soil

soil properties

• composition

• permeability

• cation exchange capacity

• pH 

• fertility

soil composition

• the mixture of its four primary components: mineral matter (sand, silt, and clay), organic matter, water, and airgravel:biggest

  • sand 

  • silt: small

  • clay: very small, stick together

• 25% air

• 25% water

• 45% mineral

• 5% OM

permeability

• physical test

• measure of the soil’s ability to move water through it

• rate: amount of water per unit of time

• percolate

cation exchange capacity

• chemical test

• ability of soils to absorb and exchange cations (ion with + charge) 

• contribute the most to the chemical properties of soil

• agricultural soils require some level of clay to hold nutrients 

  • more than 20% holds too much water

clay

• negatively charged

pH

• chemical tes

• pH of most soils ranges from 4-8 

• it affects the solubility of certain plaint nutrients

• the optimum pH is 6-7 (plant nutrients are most available)

• soil amendments (ex.~ lime) can be used to achieve this pH

too acidic soil

• low pH

• an abundance of heavy metals are leached from the soil

• cations are exchanged for H+ ions obtained from carbonic acid or from the  plant itself

• cation exchange capacity happens too quickly

• net nutrient loss

too basic soil

• nutrients cannot dissolve in water

• don’t release many nutrients at all

infiltration and percolation

• measure of soil’s ability to move water through it

bulk density and compaction

• how much the soil weighs

• particle density: density of only the solid parts of the soil

• ex.~ brick= high density, low pore space

fertility

• a soil's capacity to sustain plant growth by providing essential nutrients, good physical structure, and favorable conditions for plant health

• N-P-K

• nitrogen: limiting factor in terrestrial ecosystems (nitrogen fixing bacteria to make nitrogen available)

• phosphorus: limiting factor in aquatic ecosystems

  • more phosphorus, more productivity, more algae blooms (eutrophication)

chemical soil tests

• pH, salinity, organic content, NPK content

• solutions: plant legumes, add lime for acidic soils

physical soil tests

• soil texture, permeability/ infiltration, moisture context

• solutions: add sand to increase porosity, aerate the soil

history of agriculture

• came about because we were farming a lot

• developed to support soils

need for fertilizers

• N,P,and K are necessary for life

• all amino acids contain N

• ever molecule in a cell’s membrane contains P, and ATP requires P

• K is necessary for metabolism

corn

• is one of the most nutrient demanding crops

• requires a lot of soil enhancement

benefits of fertilizers

• higher crop yield/ more crop per area

• increased soil fertility

fertilizer example

• manure

impacts of fertilizer

• cause eutrophication

• larger dead zones form in a gulf every summer

• over fertilization can lead to salinization of soils

  • too salty

• bacterial decomposition (dentrification)

  • largest producer of N2O, which contributes to enhanced greenhouse effect (troposphere), 250x more heat trapping

  • creates climate change

organic fertilizers

• source: plant matter or manure

• advantages: less expensive, often doesn’t need transporting

• disadvantages: takes longer- decomposition, nutrient levels fluctuate, pathogens

synthetic fertilizers

• source: manufactured (soil or liquid)

• advantages: nutrients are quickly available, nutrients are targeted to crop

• disadvantages: requires fossil fuels to manufacture, can run into local water bodies

  • natural gas is needed

no-till farming

• fertilizer pollution solution

• leaving the old crop roots behind to decompose

intercropping

• fertilizer pollution solution

• plant corn (nutrient depleting) with soybean (nutrient replenishing)

contour farming

• fertilizer pollution solution

• reduces runoff/ erosion

• farm horizontally along the same elevation

slow release fertilizers

• less water soluble

• little pellets

• slowly dissolve

anaerobic methane digester

• fertilizer pollution solution

slash-burn agriculture

• problems:

  • burn forest to reduce weeds and tree trunks

  • reduced fertility by changing organic content/ nutrient content

  • CO2 is released from burning

  • rains wash soil (that is uncovered) away- loss of topsoil

• solution:

  • alley cropping

pesticide

• developed to manage pests, unwanted things

• DDT=broad spectrum, bioaccumulating

• narrow spectrum= kills only target species

benefits of pesiticides

• saves humans lives

• increase food supplies and lowers food costs

• increase profit for farmers bc. it increases yield

• work- faster and better than alternatives

problems with pesticides

• “pesticide treadmill”: creating a perpetual problem, the 1% that survives from pesticides so you need to use more

• bioaccumulation: the buildup of toxic substances within a single organism over its lifetime

• biomagnification: the increase in the concentration of these substances as they move up the food chain from one trophic level to the next, leading to higher concentrations in top predators

• persistence: doesn’t break down easily

• less than 2% of insecticides and 5% of herbicides reach their target organism

• kills beneficial insects

Selective herbicides

• kills only certain type of plants

  • Weed-B-Gone

Broad-leaf herbicides

• kill broad-leaf plants

• dicots

• agent orange

• round-up

• atrazine

irrigation

• 70% of human freshwater use is for this

• the supply of water to land or crops to help growth, typically by means of channels

furrow irrigation

• cuts furrows between crops and fills them with water

• inexpensive

• 1/3 of water lost to evaporation and runoff

• risk of soil erosion too

• getting water close to crops

• ditches w/ water

flood irrigation

• floods the agricultural field w/ water

• water-logging

• 20% of water lost to evaporation and runoff

• methane

spray irrigation

• more efficient then furrows and flood (<25% water loss)

• more expensive and requires energy

• salinization

salinization

• when salt in groundwater remains after water evaporates and overtime salinization can make soil toxic to plants

• causes:

  • overirrigation

  • misuse of salt containing fertilizers

  • self-containing lime

  • road salts

• solutions:

  • flush soil with water

  • decrease use

  • drip irrigation helps to reduce amount of evaporation

  • use vegetation that removes salts (barley oats)

  • cant plant crops that like salt

drip irrigation

• expensive

• 5% is lost to evaporation

• targeted to release water at the plant

problems of irrigation

• salinization leads to water-logging

  • repeated irrigation can reduce crop yields by causing salt buildup in the soil and water logging crop plants

• water loss

animal agriculture

• developed countries consume more meat than developing countries

CAFOs

• concentrated animal feeding lots

• quick and efficient method

• high density of animals

• typically fed grain instead of grass

• less expensive product as a result of how it’s raised

problems with CAFOs

• large amounts of waste (1 CAFO= 2,000 tons of manure annually)

• high risk of disease

• water and feed for animals

• land degradation, land becomes infertile

livestock and methane

• about ¼ of US methane emissions come from out of lifestock

overgrazing impacts

• degrading soil so it’s no longer fertile or usable

• soil compaction: make it hard enough that all of that stuff cannot go through

• loss of vegetation

• more soil erosion leads to desertification 

solutions to overgrazing

• rotational grazing

• free range grazing

• anaerobic digestion

GMO

• gentically modified organism by selecting genes and inserting them into DNA of other organisms

benefits of GMOs

• drought, heat, or salt tolerant

• tolerate repeated application of herbicides

  • roundup ready crops

• have built in pesticies

  • Bt corn

• grows faster, bigger, better

  • aspartame

  • salmon

  • rice that contains medicines

environmental advantages to GMOs

• high yields per acre, less land needed

• low-till due to herbicide resistant crops-reduce soil erosion and water loss

• lower pesticide use

• salinity tolerance/ drought resistance decreases the need for water

environmental disadvantages to GMOs

• high dosage or application of herbicides

• insect resistance to Bt gene

• Bt pollen toxic to butterflies

• higher yields= higher fertilizer use

• lower genetic variability

• glyphosphate is listed in CA. as a probably carcinogen

economic advantages to GMOs

• monoculture is easier to farm

• higher yields per acre 

• lower pesticides requirement 

• healthier appearance, more desirable

• drought resistance, resulting in lower costs for irrigation

• increased nutritional value

• higher yield, higher profit

economic disadvantages of GMOs

• higher yields lead to soil depletion

• increased fertilizer demand to reach yield potential

• require investment in a new pesticide

• have patented seeds 

• have sterile seeds, committing farmer to annual seed purchases

• risk consumer rejection

IPM

• integrated pest control

• ecosystem based strategy that focuses on long-term management (not eradication) of pests

• minimizes the use of chemical pesticides individually tailoring a plan to the specific pests

• manage pests w/o eradication, we’re controlling

• if absolutely necessary, uses narrow-spectrum pesticides

• mixture of chemical, physical, and biological methods

benefits of IPM

• reduces need for pesticides

• reduces incidental killing of bees/ spiders, etc.

• reduces CO2 emissions from pesticide application

• reduces bioaccumulation of pesticides

• reduces genetic resistance to pesticides. 

drawbacks to IPM

• requires higher degree of management

• more labor intensive

• success can be weather dependent

• cost

toxicology

• a branch of science that deals with the study of adverse effects of chemical agents on biological systems

• how adverse effects affect certain living things

dose-response studies

• expose animals or plants to different amounts of a chemical and then observe a variety of possible responses including mortality or changes in behavior and reproduction

• test subject isn’t real population

• must specify “test subject/ population” on AP test

toxicity exposure

• acute: single dose causes reaction within 24 hrs

• subacute: repeated exposure for 1 month or less

• subchronic: 1-3 months

• chronic: 3 months, carcinogens

LD-50

• lethal dose that kills 50% of the test subjects 

• important for assessing the relative toxicity of a chemical and determines if the chemical is lethal

ED-50

• effective does that causes 50% of the animals to display the harmful but non-lethal effect

sublethal effect

• when scientists are interested in other harmful effects a chemical may have, including its acting as a carcinogen that could alter the behavior of an individual

threshold of toxicity

• the dose/ concentration below which no lethal effect or mortality are observed in the test group

• could have background mortality if you increase the dosage but no change is in the mortality or if the control group has mortality

  • can’t always say product, etc. is toxic

dose-response graphs

• ex.~ x= dose (hypothetical units), y= percent mortality

• log on x

• normal curve on y

• S curve

testing standards of dose-response studies

• in the US - effects of chemicals on humans and wildlife are regulated by the EPA

• the toxic control act of 1976 gives the EPA the authority to regulate many chemicals, excluding food, cosmetics, and pesticides

• federal insecticide, fungicide, and rodenticide act of 1996 - regulates pesticides, a manufacturer must demonstrate that a pesticide will “not generally cause reasonable adverse effects on the environment” 

safe concentration for humans

• taking the LD-50 and dividing it by 10

• 10% of the LD-50 value should cause few or no animals to die