SoilsAgriculture_Ensci100_S2015

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Soils and Agriculture

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Figure: Brady and Weil, Elements of the Nature and Properties of Soils, 2004 Prentice Education Inc.

Soils An Interface where rock, water, air and life converge and interact

1.  Support Growth of Plants 2.  Recycle organic matter (nutrients and carbon are

recycled) 3.  A habitat for diverse organisms

4.  Major area of human interaction with earth’s surface (e.g. agriculture)

5.  Involved in the Hydrologic Cycle-helps purify water

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Soils- Why do we care? Main functions of soils

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What is a soil?

Figure: Brady and Weil, Elements of the Nature and Properties of Soils, 2004 Prentice Education Inc.

Soil is a complex and dynamic mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and billions of living organisms (mostly microscopic)

Soil is a continuum of materials at earth’s surface

–  Soil is separated from Non-soil at the… •  Top - vegetation, leaf litter, organic debris -and- •  Bottom - bedrock – parent material that

supplies grains and minerals contained in soil

—  We divide soils into zones (called horizons)

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O horizon Leaf litter

A horizon Topsoil

B horizon Subsoil

C horizon Parent

material

Mature soil

Young soil

Immature soil

Soil horizons

Bedrock

Soil Profile and Formation

See Fig. 9.6

Regolith

Time

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O horizon Leaf litter

A horizon Topsoil

B horizon Subsoil

C horizon Parent

material

Bedrock

Soil Horizons

See Fig. 9.6

Regolith

• O horizon- mostly organic material/decomposing vegetation

• A horizon- topsoil, leaching occurs dissolving/draining earth materials to lower levels (e.g. Fe)

• B horizon- zone of accumulation, clays and other material drained from surface accumulate

• C horizon- weathering parent material (rock/gravel etc).

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Soils develop over time Soil horizons - layers of soil (change with depth), they become apparent as soil develops, as materials are moved to deeper depths Organic matter addition happens at surface layers. The characteristics of each Horizon are defined By zones of accumulation and loss. Eluviation is the process of removal or distribution i.e., leaching (zone of leaching: horizons O-E) Illuviation is the process of deposition or accumulation (zone of accumulation: horizon B)

Figure: Brady and Weil, Elements of the Nature and Properties of Soils, 2004 Prentice Education Inc.

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Soil: Formation Rate

Soil can be a renewable source, but formed slowly, on timescales of 1000 years

•  1 inch (2.5 cm) typically takes 200-1000 years

to form

•  Erosion rate is approx 15 to 16 times faster than formation in the US – So every year a fraction of an inch is eroded

Grain Size and Surface Area:Vol

How does the surface area to volume ratio change as the diameter of particles get larger?

SA:V listed for ratio large to

small: Clay > Silt > Sand What grain type would adsorb

more contaminants on its surface?

Clay 9

Diameter (size) large to small: Gravel > Sand > Silt > Clay

What types of sediment are there? Sediments are defined in part by the

percentages of clay, silt and sand

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Soil Fertility •  Soil Fertility is… a measure of nutrients

found in soil for plant growth

•  Review: plants need 16

essential nutrient elements!

•  Macronutrients (large amounts needed) –  C, H, O, N, P, K, S,

Ca, Mg •  Micronutrients

–  Mn, Cu, Cl, Mb, Zn, Fe, B

Ways that soil gains nutrients: •  Nitrogen fixation

•  Most N in form of stable N2

•  Bacteria “fix” N and make it available as H-bound or C-bound forms

•  Organic matter decomposition •  Animal wastes •  Weathering of parent material •  Fertilizers

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The Nature of Soil Erosion •  Soil erosion – process by which soil particles are detached, transported

and redeposited elsewhere •  It is natural, but we are witnessing accelerated rates of erosion. •  Factors:

–  Precipitation –  Soil Conditions –  Surface Cover (vegetation) – Winds –  Topography

•  CAUSES:

–  WIND –  WATER

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Accelerated Erosion •  Affects agricultural

lands •  Caused by human

disturbance and climate

•  can accelerate 10-100 times faster than natural erosion

•  Results in loss of nutrients and necessary materials for plant growth

•  e.g. “dust bowl”

Soil Conservation Methods

14 Fig. 7-14, p. 153

Desertification

•  Lands in danger are arid and semiarid •  Due to prolonged drought, human activities,

altered vegetation •  Often results in dust storms. Dust might carry

pesticides, contaminants.

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Soil Degradation Caused by Irrigation Practices

Fig. 7-7, p. 144

Less permeable clay layer

Salinization 1. Irrigation water contains small amounts of dissolved salts.

2. Evaporation and transpiration leave salts behind.

3. Salt builds up in soil.

Waterlogging 1. Precipitation and irrigation water percolate downward.

Transpiration

2. Water table rises.

Evaporation

Waterlogging

Occurring in Australia

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•  Waterlogging = Low to zero OXYGEN à anaerobic bacteria live and respire CH4 (methane) •  Methane adds to GHG accumulation in atmosphere.

Fig. 7-15, p. 154 17

Why should we be concerned about soil degradation?

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Population Growth à Need more food to feed the world!!

Agriculture and Food Supply

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Global  Trends  in  Food  Availability    

•  In  many  parts  of  the  world,  food  produc5on  has  been  transformed  from  small-­‐scale  diversified  opera5ons  to  vast  farms  growing  one  or  two  crops  

•  global  food  supply  problems  have  more  to  do  with  distribu(on  than  with  supply  (but  both  are  s(ll  important..).  

•  We  con5nue  to  produce  surpluses,  but  hunger  remains  an  urgent  problem.  

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Food  is  Unevenly  Distributed  •  FiBy  years  ago,  hunger  was  one  of  the  world’s  most  persistent  problems.  Today,  it  is  a  problem  regionally.  

•  The  world’s  popula5on  has  more  than  doubled,  from  3  to  >7  billion,  but  food  produc9on  has  risen  even  faster.    •  While  the  average  popula5on  growth  in  the  past  50  years  has  been  approx.  1.5  %  per  year,  food  produc5on  has  increased  by  approx.  2+%  per  year.    

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Hunger  Around  the  World  Has    Not  Been  Eliminated  

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Chronic  Obesity  is  a  Growing    Problem  Worldwide  

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Nutri9onal  content  and  calories    

•  A  good  diet  is  essen5al  to  keep  you  healthy.  •  You  need  the  correct  nutrients,  as  well  as  enough  calories  for  a  produc5ve  and  energe5c  lifestyle.    

•  The  United  Na5ons  Food  and  Agriculture  Organiza5on  (FAO)  es5mates  that  nearly  3  billion  people  (almost  half  the  world’s  popula5on)  suffer  from  vitamin,  mineral,  or  protein  deficiencies.  

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How Is Food Produced? •  Sources :

–  Croplands (approx. 75% of world’s food) –  Rangelands (approx. 15% of world’s food) –  Ocean fisheries (approx. 10% of world’s food)

•  A small # of edible plant species (<15) supply the world w/(most (approx. 90%) of world’s food calories; mostly wheat, rice, and corn

Corn production in the US has tripled since 1960

•  Most agriculture production in US occurs in the mid-west

•  In the US less land is cultivated now then 100 yrs ago, but food production has more than doubled

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Agricultural  Inputs  

Soil  is  the  founda5on  of  food  produc5on,  but  there  are  many  other  cri5cal  factors.      • Agriculture  is  also  dependent  upon:  

•  Reliable  water  resources    (2/3rd  of  water  use  in  US).  •  Nutrients.  •  Favorable  temperatures  and  rainfall.  •  Produc5ve  crop  varie5es.  •  The  mechanical  energy  to  tend  and  harvest  the  

crops.  

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How Productivity of Farmland increased without additional deforestation

•  Shift to High-Input agriculture where you increase –  irrigation efficiency –  synthetic fertilizer use –  pesticides use

•  Selective breeding –  high-yield grains

•  Controversial: environmental and socioeconomic concerns!

•  Decrease in genetic diversity

•  Genetically Modified (GM) foods –  Isolating genetic material of cells (DNA) and

reproducing them in crop species to increase yield

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Producing Food by Green-Revolution Techniques

1.  High-yield monoculture

2.  High inputs of fertilizer, pesticides, water

3.  Increased intensity and frequency of cropping: multicropping

Rice, Wheat, Corn

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Producing Food by Green-Revolution Techniques

Rice, Wheat, Corn • Key scientist cited as father of the Green Revolution: Norman Borlaug:

- cited as the “father of the green revolution” - agricultural engineer; began work in 1940s - won Nobel Peace Prize (1970) for increasing food supply; - his work began in Mexico (new high yield crops and modern agricultural approaches)

•  Privately funded efforts to increase food supply: Rockefeller and Ford Foundations initiated 1943

•  Initially, focus on feeding Mexico •  Post 1960s, methods implemented in other nations, India etc.

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Green Revolution 1: First Green Revolution: developed countries

–  Since 1950, mechanism behind majority of food production, major increase in food productivity

–  HYV = Higher Yield Varieties of corn, wheat, and rice used

•  however these grains generally require higher amounts of nitrogen (N)…therefore more fertilizer use

–  System did not work well in developing nation. Selectively bred crops didn’t transfer well. A new breed of cereals (corn, wheat, and rice) needed…

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Green Revolution 2: Second Green Revolution: developing countries

–  Genetic research

–  Produced rice & wheat specially bred for tropical & sub tropical climates

–  Fast growing, allowing multiple cropping in a year

–  High-yield varieties used fit to local conditions, technologies and agricultural practices

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Green Revolution: Years 1960-2005

Get MORE Grains…

Use MORE Land

Use MORE Fertilizers

Use MORE Pesticides

…To a point

Source: UNEP/GRID-Arendal http://maps.grida.no/go/graphic/agricultural-trends-production-fertilisers-irrigation-and-pesticides

Developed nations and international oversight groups (World Bank, etc) put less effort into ensuring ongoing development of Green Revolution in Africa- Food production not able to keep up with population growth.

Increase use of fossil fuels for farm equipment and fertilizers (leads to air pollution) Increase dependency on irrigation (not necessarily efficient forms of irrigation) Increase dependency on pesticides Contamination of groundwater, waterways with fertilizers, pesticides, and farm animal wastes Concerns of contamination of food with pesticides Increase use = soil degradation Having a worlds agriculture based on a limited number of species (monoculture approaches) of organisms makes the worlds food supply more susceptible to failure due to pests, drought, climate change, and environmental degradation

Disadvantages of the Green Revolution

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You Can be a Locavore

•  A locavore is a person who consumes locally produced food.

•  Supporting local farmers can have a variety of benefits, from keeping money in the local economy to ensuring a fresh and healthy diet.

•  Maintaining a viable farm economy can also help slow the conversion of farmland into expanding suburban subdivisions.

•  Farmers’ markets are usually the easiest way to eat locally

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You Can Eat Low On The Food Chain

•  Because there is less energy involved in producing food from plants than producing it from animals, one way you can reduce your impact on the world’s soil and water is to eat a little more grains, vegetables, and dairy and a little less meat.

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You can become an informed consumer.. And use your purchasing

power to support or oppose issues

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Interesting new sources of information are becoming available to assist you in making informed consumer decisions. For example, apps like “buycott” that you can use to scan food labels…

Fer9lizer  Boosts  Produc9on  

•  Plants  require  small  amounts  of  inorganic  nutrients  from  soil.    

•  Fer5lizers  are  used  to  ensure  a  sufficient  supply  of  these  nutrients.  

•  The  major  elements  required  by  most  plants  are  nitrogen,  potassium,  phosphorus,  calcium,  magnesium,  and  sulfur.  

•  Much  of  the  doubling  in  worldwide  crop  produc5on  since  1950  has  come  from  increased  inorganic  fer5lizer  use.  

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Over-fertilizing is Also a Common Problem

•  Growing plants can use only limited amounts of nutrients, and the nutrients not captured by crops run off of fields or seep into groundwater.

•  Excess fertilizers contaminate drinking water and destabilize aquatic ecosystems.

•  Nitrate levels in groundwater have risen to dangerous levels in many areas where intensive farming is practiced.

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Modern  Agriculture  Runs  on  Oil  •  The  food  system  in  the  United  States  consumes  about  15-­‐20%  of  the  total  energy  we  use.    

•  Approximate  energy  use:  –  Energy  is  used  in  producing  nitrogen  fer5lizers  from  natural  gas.  

–  Energy  is  used  for  machinery  and  fuel.  –  Energy  is  used  for  irriga5on,  synthe5c  herbicides,  and  other  fer5lizers.  

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Pes9cide  Use  Con9nues  to  Rise  

•  Biological  pests  reduce  crop  yields  and  spoil  as  much  as  ½  of  the  crops  harvested  every  year  in  some  areas.    

•  Modern  agriculture  largely  depends  on  toxic  chemicals  to  kill  or  drive  away  these  pests.    

•  Indiscriminate  pes5cide  use,  however,  also  has  caused  many  problems  

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Conclusion  •  Food  produc5on  has  grown  faster  than  the  human  popula5on  in  recent  decades,  and  the  percentage  of  people  facing  chronic  hunger  has  declined.  

•  Increases  in  food  produc5on  result  from  many  innova5ons  in  agricultural  produc5on  like  the  green  revolu5on  and  the  development  of  GMOs.  

•  These  changes  bring  about  environmental  problems  such  as  soil  erosion  and  water  contamina5on  from  pes5cide  and  fer5lizer  applica5ons.  

•  Consumers  can  influence  farm  produc5on  by  choosing  what  food  they  buy  and  where  they  buy  it.      

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