soils science - agronomy soil conservation pesticides and alternatives chapter 3 december 2006...
TRANSCRIPT
Soils Science - AgronomySoil ConservationPesticides and Alternatives
Chapter 3
December 2006
"Land, then, is not merely soil; it is a fountain of energy flowing through a circuit of soils, plants, and animals." - Aldo Leopold, A Sand County Almanac, 1949
Physical Properties and Use
Plants - agriculture and forestryBuilding-bearing strength and drainageWaste disposal - good drainage
Functions of Soil
“Allows” water to infiltrate, not runoffStores WaterProvide nutrients for plantsDecompose materials
Recycle nutrients Return carbon dioxide to atmosphere
Store carbon - reduce atmospheric CO2
SOIL
Air 25%
Mineral Matter 45%
Water 25%
Organic Matter 5%
Component definition: Mixture of mineral matter, organic matter, water, and air.
Example:
What is Soil (page 212)NOT DIRT - dirt is a four letter word!Mineral particles - non-living - 45%Organic matter - 5%
bacteria and other microorganisms partially decomposed plants - humus macroinvertebrates
Pore space - 50% air spaces water filled spaces
Soil Formation - “ingredients” (page 211)
1. Parent Material - rocks - raw materials Types of parent material
• Bedrock
• In PA, most is not the bedrock
• Transported materials:
– glaciers
– water (alluvial)
– erosion and gravity (colluvial)
2. Time3. Organic material4. Climate
5. Topography (slope and location on slope)
Variables determining kind of soil (page 211)
Climate affects rate, type of weathering Temperature fluctuation - freezing and thawing water plant roots - physical and release chemicals Chemical reactions: eg limestone running water glaciers
"Each soil has had its own history. Like a river, a mountain, a forest, or any natural thing, its present condition is due to the influences of many things and events of the past." - Charles Kellogg, The Soils That Support Us,1956
Soil Color
Color determined by minerals and oxygen availability
Red, yellow, brown hues - good aerationGray or olive - poorly aerated, poor
drainageMottling - seasonable wet; poor drainageOften dependent on parent material
Soil Texture - mineral particles (213)
Relative amounts (%s) of sand, silt, and clay Contrast sizes - chart 213
Affects infiltrationAffects water holding capacity (drainage)Indirectly affects fertility - adhesion ions to
clay“Strength” for building - clay soils not good
Clay
Less than .002 mmHolds waterForms aggregates - provides soil structure -
“sticky”Excess clay - poor drainage and compaction Derived from shalesGood adsorption of ions
Silt
.002 to .05 mmOptimal amount of soil water retention and
soil air circulationThe best soils have between 50% and 70%
silt
Sand
.05 to 2 mm1000 times larger than clayRapid infiltration/low water holding
capacityGood strength for building
Soil Texture Classes
Proportion of sand, silt, clay See page 214
Soil texture triangle
Soil Structure - (215)Aggregates - individual particles are
“glued” together to form larger piecesProvides pores Examples
granular platy massive - eg. very clayey soils
Why different soil structures Result of soil texture classes Result of organic matter
Granular
Platy
Blocky
(Angular)(Subangular)
Wedge
ColumnarPrismatic
Examples of Soil Structure
Organic Content1 to 20%Determines structure - aggregates of soil particlesColor - darker, more organicFertility (chemistry) and pH - high ion exchange
Soil Density
Largely due to soil texture and organic content
Degree of aggregation importantAffected by human useDense soils - high strength, low porosity,
low permeability, poor for plant growth
Soil and WaterInfiltration and porosity
must have pores - “loose” soils Dependent on soil aggregates, which in turn
depend on• soil texture (think of sand vs. clay)
• organic material in soil
Water holding capacity – ability of soil to hold water like a sponge holds water Increased by organic matter Loam has food capacity to hold water
Putting it all together
Summarize the chart on page 216
Soil Profile (216)Soil Horizons - Stratified horizontal layersUsed to classify the soilO: partially decomposed organic materialA: topsoilB: subsoilC: Parent materialBedrock
Classifying and Naming Soils
Age of soilSpecial features (eg. Fragipans)water related characteristicstexturehorizons - types and depthsCounty Soil Surveys -
Soil Conservation Service of USDA
Soil ChemistryFertility - Ion exchange important
nitrogen (nitrates) phosphorus potassium
pH: 6.5 to 7.0 is best ion (nutrient) uptake many add lime (“sweetens” soil) effect of rainfall PA slightly acid soil
What is happening to our land?The “dirty thirties” (219)
abuse of land- intensive, monoculture farming Dust bowl
Every Year - worldwide 7.4 M acres ruined by erosion 4 M acres turned into deserts - removal of
natural vegetation 8 million converted to other uses - development
Response
Soil Conservation Service - 1935 now Natural Resources Conservation Service
County Conservation Districts Assist farmers Monitor soil erosion from:
• developments, highways, effects on waterways
Causes of soil degradation
Water erosion Types of erosion (217)
Wind erosionSalt building up in soil from excessive
irrigationLoss is “slow” but nearly permanent
1 mm year = 25 mm in 25 years 500 years to replace this
Erosion (pages 220 to 222)
Movement of soil by wind or water to new location
Problems caused by erosion Reduced high quality farmland Sedimentation of waterways Smothering of wetlands and coral reefs
Worldwide: 1% of world cropland is lost each year
Soil Erosion
Sheet and rill erosion buried crops at the base of a hill
Sediment loaded runoff from a field
Causes of Sources of Erosion
Causes of erosion – not using BMPs in Agriculture (60 % in U.S.) Construction Logging
Off-road vehicles use
Amounts in U.S.
Many areas exceed replacement limit: max 1mm/yr
50 million boxcars of soil lost per year 500,000 trains, 100 cars long
Agricultural Losses: Account for 60% of impaired river miles in U.S.
Desertification
Causes Natural or human caused local climate change Erosion or salinization of topsoil due to excess
irrigation (severe on 21% of world’s irrigated land)
Land Resources-Developed Countries
Less cultivated land than 100 years ago Why is there much less cultivated land?
Astounding 400% increase in yield per acre Improved crop varieties Fertilizers Pesticides Irrigation
Developing Countries
Many reaching limits of potential croplandLoss of tropical forests
Tropical Soils: fertility rapidly depleted Erosion a BIG problem Negatively affects rivers and offshore coral
reefs
Soil Conservation - Three Basic Approaches
Managing ground coverManaging TopographyReduced Tillage Systems
Providing Ground Cover
Cover cropping (don’t let the soil bear!) – protect soil in the “off-season”
Mulching
strip cropping/ contour farming and grassed waterways
Farming on contour of hill Alternating crops down slope Grassed waterway
Conservation Tillage: Minimum Tillage Systems (223)
Less frequent plowingOnly plow where planting will occurReduces
Erosion Water loss Fertilizer leaching into waterways
Cons: Purchase different equipment May delay planting May require more herbicides (weed killers)
Managing Topography (pg 221-22)Contour plowing (221)Strip-croppingCrop rotation: planting series all year – land
not ever fallowCover crops: grasses or legumesPerennial speciesDon’t farm on steep slopesFarm Act of 1985: made U.S. first major
food producer to make soil conservation a national priority
Conservation tillage
Leaves at least 30% of last years crop residue on soil surface
Preserving FarmlandAccomplished through the purchase of
agricultural conservation easements (also known as the purchase of development rights) on eligible Lehigh County farm properties.
As of June 2005, more than 175 farms totaling over 15,000 acres have been secured with perpetual agricultural conservation easements
Why Preserve Farmland
Pennsylvania's #1 industry, agriculture local supplies of fresh food protect surface and ground water resources air quality wildlife habitat scenic beauty and open space
How do we farm - options
Traditional – small scale, primarily human energy, less yield per acre
High intensity – high use of fertilizers/energy/water “Factory farms” –
OrganicIPM
Feeding the World (232-233)Population growing - primarily in
developing countries about 80 million more each year
More than 800 million lack food - but, now, sufficient food is grown to feed all
Future: about 9 billion by 2050 Will it be possible to provide food and water
for 9 billion mouths?
The “Green Revolution” (235)
Began in the 1970’sTwo key contributors:
High yield “miracle” crop varieties: rice, wheat, corn
Intensive fertilizer use“Miracle strains” rice, wheat, etc.
Green Revolution led to High Intensity Agriculture
Definition: producing high outputs using “High yield” miracle crops AND high inputs of:
Water - irrigation Fertilizers - organic, inorganic Energy - fossil fuels (Energy inputs in lower intensity agriculture: human
and animal) Pesticides - herbicides, insecticides
1900 1930 1960 1990 2020 2050
Year
0.050
0.040
0.030
0.020
0.010Irri
gat
ed a
rea
per
per
son
(h
ecta
res)
Figure 13-18Page 294
2,000
1,500
1,000
500
0
Gra
in p
rod
uct
ion
(mill
ion
s o
f to
ns)
1950 1960 1970 1980 1990 2000 2010
Total World Grain Production
Year
400
350
300
250
150
Per
cap
ita
gra
in p
rod
uct
ion
(kilo
gra
ms
per
per
son
)
1950 1960 1970 1980 1990 2000 2010
World Grain Production per Capita
200
Year
Increase in Meat vs. Plant Based Diets: Fossil Fuel Inputs/Food Outputs
Food Type Kilocalories of fossil fuel input per kilocalorie of protein output
Feed lot beef 20-78
Pigs
Broiler chicken
Rangeland Beef
Sheep
Vegetables
35
22
10
10
2-4
Producing More MeatProducing More Meat
Kilograms of grain needed per kilogram of body weightKilograms of grain needed per kilogram of body weight
Beef cattleBeef cattle 77
PigsPigs 44
ChickenChicken 2.22.2
Fish (catfishor carp)
Fish (catfishor carp) 22
Fig. 13-25 p. 298
Fig. 13-25 p. 298
Biodiversity Loss
Loss and degradation of habitat fromclearing grasslands and forests anddraining wetland
Fish kills from pesticide runoff
Loss of genetic diversity fromreplacing thousands of wild cropstrains with a few monoculture strains
SoilErosion
Loss of fertility
Salinization
Desertification
Environmental problems of high intensity agriculture
Air PollutionGreenhouse gas emissions from fossilFuel issue
Other air pollutants from fossil fuel use
Pollution from pesticide sprays
WaterAquifer depletion
Increased runoff andflooding from land clearedto grow crops
Sediment pollution fromerosion
Fish kills from pesticiderunoff
Surface and groundwaterpollution from pesticidesand fertilizers
Overfertilization of lakesand slow-moving riversfrom runoff of nitrates andphosphates fromfertilizers, livestockwastes, and foodprocessing wastesEnvironmental problems of high
intensity agriculture
Human Health
Nitrates in drinking water
Pesticide residues in drinking water,food, and air
Contamination of drinking andswimming water with disease organismsfrom livestock wastes
Bacterial contamination of meat
Can Green Revolution Continue? How can the world feed another 3 billion hungry
mouths? Is there a limit to continually increasing yield?Environmental reasons for leveling off
Huge use of energy - petroleum soil erosion depletion/pollution water supplies Effects on humans and animals of pesticides and
fertilizers Costs an issue, especially in developing countries
Fertilizers: Organic vs. Inorganic
Video segment: Soil Sustainability – organic and inorganic fertilizers
Soil Fertility
Soil nutrients- chemicals needed by plants from the soil
Source in natural ecosystem decomposition minerals nitrogen fixation from air
Primary nutrients - NPK
Nitrogen -growth of plant leaves (chlorophyll) and stems
Potassium - stem development, fruit and flower formation
Phosphorus - fruit and flower formationSecondary nutrients - Ca, Mg, and SSoil testing - includes above and pH
Synthetic - chemical - fertilizers
Nitrogen - need high input of fossil fuelsPhosphate - phosphate rock, coal, natural gasPotassium - potash - from mines, extracted
from earthSoil quality: if only synthetic fertilizers, ,
organic matter in soil decreases, soil looses structure and ability to hold water
Organic Farming and GardeningNO chemical pesticides or chemical fertilizersOrganic Fertilizers
Made from dead plant materials or other non-chemical stuff Cottonseed meal, blood meal, fish emulsion, manure and
sewage sludge are examples of organic fertilizers. Compost
• kitchen garbage• leaves• grass clippings• manure
Organic Advantages Improve Soil
Increase water-holding capacity of the soil. Improve the physical structure of the soil which allows
more air to get to plant roots. Bacterial and fungal activity increases in the soil.
• Mycorrhizal fungi make other nutrients more available to plants thrive in soil where the organic matter content is high.
Organically derived plant nutrients are slow to leach less likely to contribute to water pollution than synthetic
fertilizers.
Does not use fossil fuels - imitates natural cycles, so unending supply
Food does not contain pesticides
Disadvantages of Organic FertilizersUsually more expensiveRequires more knowledge and researchHarder to obtain in some cases
What do you see advertised on TV?
Pest Control-3.8
BUGS….can’t live without ‘em, but tough to live with ‘em
PestsWhat is a pest?
Why not a problem in a balanced natural ecosystems?
Examples grasshopper - $400 million each year in U.S. Boll weevil and cotton borer Many fungi on fruit trees Trees
• Hemlock wooly adelgid
• Gypsy moth
• Fungi-chestnut blight, dutch elm disease Transmit diseases - malaria, yellow fever, West
Nile virus, heartworm in dogs
What is a pesticide ( table on 251)What is a pesticide?
Rodenticides Herbicides - weedkiller - most used in U.S. Insecticides Fungicides
Some “natural” - derived from plants - rotenone and pyrethrum
First major production of chemical pesticides - during WWII from nerve gases
DDT organophosphates
Pesticide Use in the U.S.Trend in use:
0
5
10
15
20
25
30
1950 1970 1996
Billion $
Where are Pesticides Used - U.S.
Agriculture: 3/4Herbicides: 59% (Figure 12.5, 252)Household application:
12% of pesticides 23% of insecticides
Do you or your family use pesticides? For what reasons?
Chemical Pesticides -Variables(253-255)Variables - important in determining effect
on humans and environment Persistence (stability) in environment
• High: chlorinated hydrocarbons Biomagnification: Chlorinated hydrocarbons Effects on other organisms
• Broad vs. narrow Spectrum Pesticides
• Toxicity to non-target organisms
Pesticides - Their Good SideDisease Control
Malaria: 50 million humans saved Other diseases for which insects vectors
• Bubonic plague and Yellow fever
Often very and quickly effectiveHave in many cases increased food supplies and
lower cost of foodIf used properly relatively safe
newer pesticides safer
Pesticide Problems Evolution in action: “superbugs” – cannot be killed with the pesticide
(253) Broad spectrum vs. narrow spectrum pesticides Effects on non-target species Creating a new pest – by killing off the predators of an insect (255) Bioaccumulation – example is effect of DDT on birds of prey (254) Persistent in environment ; some not biodegradable
Such as DDT – even now found in high concentrations in human mother’s milk (254)
Effects on human health – many unanswered questions here!
Effects on Nontarget Species
Up to 90% of pesticides never reach targetEffects on other insects - honeybeesKilling beneficial predators (both insect and
non-insect) (see next slide)
Creating “New” Pests
Broad spectrum pesticides - eliminated natural predators and parasites that previously kept pest insects in check Examples: ladybugs, parasitic wasps, and
praying mantis What controls insect pests in nature? Yes, the
NATURAL predators that pesticides often kill off!
Creating “Superbugs”: Resistance & ResurganceInsects become resistance: evolution in actionPercentage crops lost to insects increasing! \
Genetic diversity results in pest resurgence Diagram page 253 Pesticide treadmill – more pesticides become
less effective, so use more, and then becomes less effective again, etc. , Etc.
Persistence(253-254)
Define: the length of time the chemical pesticide remains in the environment.
Vary with pesticidesSome pesticides biomagnify in fatty tissue
100% of people in U.S have detectable amounts of DDT or DDE
Some human mother’s milk: could not be sold due to high levels of some pesticides
The DDT Story (pg. 255 & 3.9)
Dichloro-diphenyl-trichloroethane Degradation product DDE
What were the benefits? Great reduction in malaria, yellow-fever
The decline of predatory birds- What happened??
Banned in early 1970’s in developed countries
Effects of some pesticides on Human Health (Pg.260)
Acute (short term) - High dose exposure Farmworkers most susceptible Mostly children (1966: 22,000 reported) Think about your pets and pescticides sprayed on your
lawns!Chronic
Low doses Long time periods Difficult to assess actual health risks Potential hormone disrupters - rat experiments (read
257)• Extrapolation to humans??
How are Humans Exposed - Chronic?How get exposed
food (264)• children may get larger exposure & more
susceptible
• endocrine disrupters
• Nat Academy of Sciences: 4-20,000 cancer per year in U.S.
waterAgent Orange in Vietnam- 2,4 D
(contamination with dioxin) http://www.lewispublishing.com/orange.htm
How are Humans Exposed - Chronic?
How get exposed food (264)
• children may get larger exposure & more susceptible
• endocrine disrupters water
Agent Orange in Vietnam- 2,4 D (contamination with dioxin) http://www.lewispublishing.com/orange.htm
Who “protects” us? (265)What is “tolerance level”
“maximum amount of pesticide residue allowed in or on food or in drinking water” - EPA
• What must be considered– dose
– toxicity
– persistence
– age of people exposed
– most difficult: synergism
Can you reduce your risks?Follow directions when using pesticidesMinimize useBuy and grow organic organicWash all foodsDon’t demand perfection - see The Perfect
Apple (266)
What is Sustainability
Sustainability rests on the principle that we must meet the needs of the present without compromising the ability of future generations to meet their own needs.
What is Sustainability
Sustainability rests on the principle that we must meet the needs of the present without compromising the ability of future generations to meet their own needs.
See 244 and 245
“Sustainable” Agricultural
Organic FarmingIPM
Example of IPM: Attacking the Gypsy Moth
Integrated Pest Management (IPM)In many cases…50 to 90% reduction in pesticide use w/o reducing production
Replacing the Sledgehammer with the Replacing the Sledgehammer with the ScalpelScalpel High Technology/Education are Keys Precision of application of pesticides Mechanical cultivation and bug vacuums
Goal: select a combination of nonchemical methods but where necessary use less harmful and less persistent chemicals for pest control
Alternatives to Current PesticidesResistant plant varietiesDon’t use monoculture (279)Biological Controls
Beneficial insects - (276-280)• parasitic wasps, lady beetles (parasites)
Bacteria that infect specific insects (B.t.) High technology:Computer programs and
careful monitoring - spray at exact time Birth control: Sterilized males released (so
sorry ladies) Phermones- devastate the bugs sex life
Organic Farming and Gardening
Definition No pesticides No inorganic (chemical) fertilizers
Focus on soil “health” Build up humus in soil
Focus on consumers healthFocus on farm workers healthRodale Organic Research Farm
Why not use organic or IPM?
Farmers/gardeners may not have knowledge, skills
Must accept some loss of crops Lower yields Higher cost of production
• BUT, organic foods do sell for more!
Do you (or does your family) try to buy organic foods?
Why or why not?
Genetic Modified Foods
Insert genes into food or other crops Purposes:
Herbicide resistence (roundup resistant soybeans)
Increase vitamin or other nutritional content Create insect resistant crops
Phase 1Make Modified Gene
Identify and extractgene with desired trait
Identify and removeportion of DNAwith desired trait
Remove plasmidfrom DNA of E. coli
Insert extracted DNA(step 2) into plasmid(step3)
Insert modifiedplasmid into E. coli
Grow in tissueculture tomake copies
cell
gene
DNA
Plasmid
E. coliDNA
Geneticallymodifiedplasmid
plasmid
Phase 2Make Transgenic Cell
Transfer plasmidcopies to a carrier
agrobacterium
Agrobacteriuminserts foreignDNA into plantcell to yieldtransgenic cell
Transfer plasmidto surfacemicroscopic metalparticle
Use gene gunto inject DNAinto plant cell
A. tumefaciens(agrobacterium)
Plant cell
Nucleus
Host DNA
Foreign DNA
Phase 3Grow Genetically Engineered Plant
Transgenic cellfrom Phase 2
Cell division oftransgenic cells
Culture cellsto form plantlets
Transgenic plantswith new traits
Problems
Can genes spread to wild species – this could create wild plants that kill insects – and, overall, insects are good!
Potential and unknown effects on human health Note: foods with GMOs are not labeled