Safeguarding soil from depletion or

deterioration

Sustainable Soil Use “A nation that destroys its soil destroys itself” Franklin D. Roosevelt, 1937

The capacity of a soil to sustain biological productivity and diversity, maintain environmental quality, and promote plant and animal health

Anything that affects soil quality can affect sustainable use of soil

1. Soil Erosion

2. Salinization

3. Nutrient Removal

4. Urban Encroachment

5. Contamination / Pollution

(Limitations first, then some solutions)

Wind Erosion in New Zealand

Water erosion

Raindrop impact loosens soil particles--particles can then either move down hill and knock other particles loose, or enter soil pores, plugging surface soil and encouraging more erosion

Erosion is also associated with roads, landings, wildfires… other areas with bare soil

Since 1945 11 % of earth’s vegetated surface ( area of China + India) has been degraded so badly it will be very expensive or impossible to fix.

In many areas, subsistence agriculture is practiced.

But once the land is eroded, the soil is ruined for farming and may be abandoned

Nevertheless, populations are still increasing….especially in areas where subsistence farming is important

Bangledesh: population increasing and urbanizing

soil degradation from ↑farming intensity

↓SOM, ↓fertility; estimated cost of soil degradation is 7.7% of GDP (2007)

China 1/6 land area => serious erosion

Atmospheric scientists in Hawaii can tell within a few days when the spring plough starts in N. China.

It is estimated that 1/5 of the world’stopsoil has been lost since 1950!!

US Dust bowl of the 1930’s

Desertification:

The spreading of desert conditions due to land degradation

Hillel 1991

Earth's deserts and areas susceptible to desertification

Average soil formation rate:

Geologic or natural erosion rate:

or ~ 1 ton per acre

USDA tolerable soil loss per year:

or 5 tons per acre !!

~.25 mm per year = 2.5 Mg ha-1

11 Mg ha-1 !!

~0.03 mm per year or ~ 0.3 Mg ha-1

or ~>0.1 ton per acre !!

Did you know that in Texas ~60 tons of topsoil is lost to produce 1 ton of

cotton?

Average annual soil erosion in the US.

Erosion has declined but still exceeds the tolerable limit of 5 tons per acre per year.

USDA, 1995

Universal Soil Loss Equation (USLE) or

Revised Universal Soil Loss Equation (RUSLE)

Predicting Soil Erosion

A = RKLSCP

A = metric tons of soil lost per hectare per yearR = rainfall erosivityK = erodibility of soilL = length of slopeS = steepness of slopeC = cover typeP = erosion control practices

1. Soil Erosion

2. Salinization

3. Nutrient Removal

4. Urban Encroachment

5. Contamination / Pollution

Salt-affected soils are the 2nd largest cause of soil degradation (after erosion)

Globally it removes about 3 hectares of land from production every minute.

2. Salinization

The rising water table in a poorly-drained soil infuses the root zone with salts.

Irrigation with water containing salts and over-fertilization lead to salinization Hillel 1991

Lake Eyre, Central Australia

Murray River Basin, SE Australia

1. Soil Erosion

2. Salinization

3. Nutrient Removal

4. Urban Encroachment

5. Contamination / Pollution

If you harvest a crop you are removing nutrients from that ecosystem - for sustainable production they need to be replaced.

3. Nutrient Removal

Amounts of some nutrients removed by harvesting over a 50 year period compared

with weathering release of nutrients in temperate areas (kg/ha)

P K Ca MgDeciduous Forest Harvest

10-20 60-150 175-250

25-100

Corn-wheat-soybeans

1200 2000 550 500

Weathering Rates

5-25 250-1000

150-1500

50-500

4. Urban Encroachment

For example, LAS VEGAS

Las Vegas, 1972pop. 273,000

Las Vegas, 1992pop. 863,000Las Vegas, 2000

5. Contamination

FROM:

metals toxic organics over fertilization - nitrate, phosphate solid wastes

overfertilizing a lawn

toxicity symptoms in alder planted in mine tailings

Current population gain is 78 million people per year, or 214 000 /day = 8 904 /hour.

It is predicted that world population will level off at about 10 Billion.

In next 30 years humans will need as much food and fiber as they used in last 10 000 yrs.

“Soil degradation is among the fundamental causes of global unrest”

Rattan Lal, 2007, President of SSSA

Soil degradation Poverty

Our challenge is to produce and distribute enough food, energy and necessities for all, without ruining the resources used to produce them.

Prevent damage !! Do the right thing at the right place

Land capability classes

Keep vegetation on site,Use cover crops, Conservation tillage,Don't excessively fertilize,Avoid compacting soil,Use compost…..Build roads sparingly and

carefully

Use the best management practices

e: erosionw: waters: shallow, rockyc: climate

Reclaim or restore soils

Repairing Soil

stabilize land - prevent further erosion establish vegetative or other cover repair topsoil - add organic matter

For eroded soil:

Effect of a windbreak on wind velocity when planted perpendicular to prevaling winds.

Chiras et al. 2002

For wind erosion, prevent further loss.

Use windbreaks, or keep soil covered.

Decommisioning and restorating a logging road

For water erosion, keep soil infiltration high, control overland flow using vegetation, ditches, contour plowing etc.

After mining:

stabilize waste stabilize or remove toxic metals restablish vegetation even better: begin restoration with mining, recontour, clean wastes, replace topsoil, plant native vegetation

Active gold mineNew Zealand

With other types of contamination:

not always possible to repair- remove soil bioremediation - microbial degradation (oil) phytoremediation - using plants for reclamation

Restoration of mine tailings, Washington State

If nutrient are being depleted:

Urban encroachment

If soil develops salinity: install drainage leach slowly with clean water may need to add Ca to displace Na

replace nutrients with:compostorganic wastesfertilizers

use zoning to protect: floodplains, best soils, sensitive soils; reclaim soils