3. soil screwed up (great)

TO SCREW UP (AND FIX)

THE SOIL

9/29/2013 Guru IBESS SOIL SYSTEM 1

http://www.nbclearn.com/portal/site/learn/changing-planet

Withering Crops





Bad results: Mineralization

• If detritus is lost, soil organisms starve

• Soil will no longer be kept loose and nutrient-rich

• Humus decomposes, breaking down the clumpy aggregate

structure of glued soil particles

• Water- and nutrient-holding capacities, infiltration, and

aeration decline

• Mineralization: loss of humus and collapse of topsoil

• All that remains are the minerals (sand, silt, clay)

• Topsoil results from balancing detritus and humus

additions and breakdown


The importance of humus to topsoil 9/29/2013 Guru IBESS SOIL SYSTEM 4

Bad results: Soil degradation

• Turnover of plant material produces detritus

• When humans cut forests, graze livestock, or plant crops, the soil is

managed or mismanaged.

• Soil degradation: occurs when key soil attributes required

for plant growth or other ecosystem services deteriorate.

• Some reports on soil degradation are incorrect or outdated

• 75% of the land in Burkina Faso was said to be degraded

• But agricultural yields have increased due to soil and water

conservation


Bad Soil: Erosion 1. Erosion: the process of soil and humus particles being

picked up and carried away by water and wind

1. Occurs any time soil is bared and exposed

2. Soil removal may be slow and gradual (e.g., by wind) or

dramatic (e.g., gullies formed by a single storm)

• Vegetative cover prevents erosion from water

• Reducing the energy of raindrops

• Allowing slow infiltration

• Grass is excellent for erosion control

• Vegetation also slows wind velocity


Splash, sheet, and gully erosion • Splash erosion: begins the process of erosion

• Raindrops break up the clumpy structure of topsoil

• Dislodged particles wash between other aggregates

• Decreases infiltration and aeration

• Sheet erosion: the result of decreased infiltration

• More water runs off, carrying away fine particles

• Gully erosion: water converges into rivulets and streams

• Water’s greater volume, velocity, energy remove soil

• Once started, erosion can turn into a vicious cycle

• Less vegetation exposes soil to more erosion


Causes of erosion: overcultivation • Plowing to grow crops exposes soil to wind and water

erosion

• Soil remains bare before planting and after harvest

• Plowing causes splash erosion

• Destroying soil’s aggregate structure

• Decreasing aeration and infiltration

• Tractors compact soil

• Reducing aeration and infiltration

• Increasing evaporative water loss and humus oxidation

• Rotating cash crops with hay and clover is sustainable


Erosion 9/29/2013 Guru IBESS SOIL SYSTEM 9

The other end of the erosion problem • Water that does not infiltrate enters streams and rivers

• Causing flooding

• Sediment: eroded soil carried into streams and rivers

• Clogs channels, intensifies floods, fills reservoirs

• Kills fish and coral reefs

• Damages streams, rivers, bays, estuaries

• Excess sediments and nutrients from erosion are the greatest

pollution problem in many areas

• Groundwater is depleted

• Rainfall runs off and does not refill soil or ground water


Desert pavement • Another devastating feature of wind and water erosion:

differential removal of soil particles

• Lighter humus and clay are the first to be carried away

• Rocks, stones, coarse sand remain

• The remaining soil becomes coarser

• Deserts are sandy because wind removes fine material

• Desert pavement: occurs in some deserts

• Removal of fine material leaves a thin surface layer of

stones and gravel

• This protective layer is easily damaged (e.g., by

vehicles)


Formation of desert pavement 9/29/2013 Guru IBESS SOIL SYSTEM 12

Drylands and desertification • Clay and humus are the most important parts of soil

• For nutrient- and water-holding capacity

• Their removal results in nutrients being removed

• Regions with sparse rainfall or long dry seasons support

grasses, scrub trees, and crops only if soils have good water-

and nutrient-holding capacity

• Erosion causes these areas to become deserts

• Desertification: a permanent reduction in the productivity of

arid, semiarid, and seasonally dry areas (drylands)

• Does not mean advancing deserts


Desertification 9/29/2013 Guru IBESS SOIL SYSTEM 14

Drylands

• Desertification is a process of land degradation

• Due to droughts, overgrazing, erosion, deforestation,

overcultivation

• It is extremely serious because it is permanent

• Dryland ecosystems cover 41% of Earth’s surface

• They are defined by precipitation, not temperature

• They receive minimal rainfall

• Droughts are common—they can last for years

• Rainfall causes vegetation to return so drylands are

not desertified


Preventing soil degradation

•Several farming strategies to prevent soil

degradation:

• • Crop rotation

• • Contour farming

• • Intercropping

• • Terracing

• • Shelterbelts

• • Conservation tillage


Reducing soil erosion • Contour strip cropping: plowing and cultivating at right

angles to contour slopes

• Shelterbelts: protective belts of trees and shrubs planted

along plowed fields

• The U.S. Natural Resource Conservation Service

(NRCS)

• Established in response to the Dust Bowl

• Regional offices provide information to farmers and

others regarding soil and water conservation practices

• U.S. soil erosion has decreased through conservation

• Windbreaks, grassed waterways, vegetation to filter runoff


Recent soil conservation laws • The U.S. has continued to pass soil

conservation legislation in recent years:

• • Food Security Act of 1985

• • Conservation Reserve Program, 1985

• • Freedom to Farm Act, 1996

• • Low-Input Sustainable Agriculture Program, 1998

• Internationally, there is the UN’s “FAR”

program in Asia.


Crop rotation • Alternating the crop planted (e.g., between corn and

soybeans) can restore nutrients to soil and fight pests and

disease.

Figure 8.16a


Contour farming • Planting along contour lines of slopes helps reduce erosion on

hillsides.

Figure 8.16b


Intercropping

• Mixing crops such as in strip cropping can provide nutrients

and reduce erosion.

Figure 8.16c


Terracing • Cutting stairsteps or terraces is the only way to farm extremely

steep hillsides without causing massive erosion. It is labor-

intensive to create, but has been a mainstay for centuries in

the Himalayas and the Andes.

Figure 8.16d


Shelterbelts • Rows of fast-growing trees around crop plantings provide

windbreaks, reducing erosion by wind.

Figure 8.16e


Tillage

• Plowing has multiple desirable effects:

–Weeds and weed seeds are buried / destroyed.

–Crop residue is turned under - decays faster

and helps build soil structure.

–Leached nutrients brought closer to surface.

–Cooler, darker soil is brought to top and

warmed.


Problem:

• Each trip over the field is an added

expense to the farmer, and at the same

time increases the amount of time the

soil is open to erosion via wind or water.


No-till planting • No-till agriculture: a technique allowing continuous

cropping while minimizing erosion

• Routinely practiced in the U.S.

• After spraying a field with herbicide to kill weeds

• A planting apparatus cuts a furrow through the mulch

• Drops seeds and fertilizer

• Closes the furrow

• The waste from the previous crop becomes detritus

• So the soil is never exposed

• Low-till farming uses one pass (not 6–12) over a field

• http://www.youtube.com/watch?v=I_7d0h2bSoY&feature

=related


http://www.youtube.com/watch?v=I_7d0h2bSoY&feature=related

http://www.youtube.com/watch?v=I_7d0h2bSoY&feature=related

Apparatus for no-till planting 9/29/2013 Guru IBESS SOIL SYSTEM 27

Conservation tillage • No-till and reduced-tillage farming leaves old crop residue on

the ground instead of plowing it into soil. This covers the soil,

keeping it in place.

• Here, corn grows up out of a “cover crop.”

Figure 8.16f


Conservation tillage

• Conservation tillage is not a panacea for all

crops everywhere.

• It often requires more chemical herbicides (because

weeds are not plowed under).

• It often requires more fertilizer (because other plants

compete with crops for nutrients).

• But legume cover crops can keep weeds at

bay while nourishing soil, and green manures

can be used as organic fertilizers.


Reduces erosion Saves fuel Cuts costs Holds more soil water Reduces soil compaction Allows several crops per season Does not reduce crop yields Reduces CO2

release from soil

Can increase

herbicide use for

some crops

Leaves stalks that

can harbor crop

pests and fungal

diseases and

increase pesticide

use

Requires

investment

in expensive

equipment

Disadvantages Advantages

Trade-Offs

Conservation Tillage


Waterlogging and salinization

• Overirrigation can raise the water table high

enough to suffocate plant roots with

waterlogging.

• Salinization (buildup of salts in surface soil

layers) is a more widespread problem.

• Evaporation in arid areas draws water up

through the soil, bringing salts with it. Irrigation

causes repeated evaporation, bringing more

salts up.


Fertilizers • Supply nutrients to crops

• Inorganic fertilizers =

mined or synthetically

manufactured mineral

supplements

• Organic fertilizers =

animal manure, crop

residues, compost, etc.

Figure 8.18


Global fertilizer usages • Fertilizer use has risen dramatically in the past 50 years.

Figure 8.19b


Inorganic fertilizer • Can provide optimal amounts of nutrients efficiently

• But it lacks organic matter to support organisms and

build soil structure

• It can keep nutrient content high under intensive

cultivation (two or more cash crops/year)

• But mineralization and soil degradation proceed

• Additional fertilizer leaches into waterways

• Chemical fertilizers have a valuable place in agriculture

• Organic fertilizers may not have enough nutrients

• Growers must use each fertilizer as necessary


Soil conservation & Sustainable Ag • Sustainability means doing all we can to reduce erosion

• Soil conservation must be practiced at two levels

• Individual landholders can best preserve soil through traditional knowledge and

practices

• Public policies can lead to conservation or disaster

• Goals:

• Maintain productive topsoil

• Keep food safe and wholesome

• Reduce chemical fertilizers and pesticides

• Keep farms economically viable

• Sustainable options mimic past practices

• Contouring, crop rotation, terracing, little or no chemicals

• The U.S. Sustainable Agriculture Research and Education program

(SARE) (1988)

• Provides $5–12 million/year for building and disseminating knowledge about

sustainable agriculture


3. soil screwed up (great)

Education

Transcript of 3. soil screwed up (great)