Agricultural Soils

September 9, 2013

What is Soil?

» Soil – What is it?˃ Unconsolidated porous media

˃ Compromised of inorganic (clay minerals and oxides) and organic components (organic matter)

˃ Has distinct physical, chemical, and biological properties

» Soil is dynamic – modified over time by physical, chemical, and biological agents

Midwest Agricultural Soils

» Typically fertile, but poorly drained» Drainage is often facilitated by networks of

artificial, subsurface drains to enhance productivity ˃ about 1 m below the soil surface ˃ can rapidly move excessive water (and

soluble contaminants) to surface waterways

Sediment Movement

» Benefits of soil movement ˃ Nourishes floodplains˃ Creates deltas and islands˃ Replenishes wetlands

» Problems with soil movement˃ Loss of excessive amounts of fertile soil ˃ Decreases the depth of streams, rivers, lakes and

reservoirs+ This can increase water temperature, effecting

aquatic species ˃ Requires increased water purification

Erosion

» Erosion: the wearing away of the land surface by rain or irrigation water, wind, ice or other agents that abrade, detach and remove soil from one point on the earth's surface and deposit it elsewhere

» The cost of water and wind erosion in the U.S. is estimated in billions of dollars each year˃ reduced productivity

˃ soil pollution of water and air

» Soil erosion is a global problem

Organic Matter» Organic matter (OM) improves soil productivity

through physical, chemical, and biological actions» Organic matter is a small fraction (2% to 4%) of

soil -- mainly present on the soil surface» Erosion gradually depletes organic matter which

decreases soil productivity

Effects of a Loss of Organic Matter» Soils tend to lose their physical structure hard,

compacted and cloddy» Soil aeration (water-holding capacity and

permeability) decreases˃ Less oxygen available for plant roots to grow ˃ Less water available for healthy plant growth ˃ Less water can soak into low permeability soils so run-off

increases

» Beneficial organisms are decreased » Suppress disease and break down organic residues˃ Do not function well at low soil oxygen and water levels˃ Reduces soil nutrient storage and supply ability

Impacts of Erosion on Air Quality

» Soil particles blown by the wind into the air have a major impact on human and animal health

» Particles suspended in air by wind are easily inhaled and accumulate in lung tissues causing major respiratory problems

» Concentrated levels of wind blown particles can also reduce visibility and increase the risk of automobile accidents

Factors Contributing to Soil Erosion» List all the factors that you can think of that

contribute to: Soil Erosion by Water Soil Erosion by Wind

Factors Contributing to Soil ErosionWater erosion Wind Erosion

Climate

Soil properties (aggregation/soil moisture)

Soil cover

Land management

Topography Soil surface roughness

  Unsheltered distance

  Wind velocity and turbulence

The Dust Bowl

» A period of severe dust storms » Caused major ecological and agricultural

damage » Affected American and Canadian prairie lands » 1930 to 1936 (in some areas until 1940)

The Dust Bowl» Causes

˃ Severe drought˃ Decades of extensive farming without conservation to

prevent erosion˃ Deep plowing of the virgin topsoil of the Great Plains

+ displaced the natural grasses that normally kept the soil in place and trapped moisture even during periods of drought and high winds

» During the drought of the 1930s, soil dried, turned to dust, and blew away eastward and southward in large dark clouds

The Dust Bowl

» At times the clouds blackened the sky reaching all the way to East Coast cities such as New York and Washington, D.C.

» Much of the soil ended up deposited in the Atlantic Ocean

» These immense dust storms—given names such as "Black Blizzards" and "Black Rollers"—often reduced visibility to a few feet

» The Dust Bowl affected 100,000,000 acres, centered on the panhandles of Texas and Oklahoma, and adjacent parts of New Mexico, Colorado, and Kansas

Reducing Soil Loss

» What are we currently doing to reduce soil loss?» Have we had any dust storms recently?

Wisconsin Dust Storm

» A massive dust storm that swept through central Wisconsin in late May, 2012

» Causes:˃ Partially the result of an increase in exposed

cropland in the region due to increased cultivation of the central sands region

+ The number of acres of cultivated cropland increased by almost 42 percent from 2005 to 2011

2012 Drought

» The severe drought that hit the Farm Belt did not create another Dust Bowl or widespread crop failure

» Expected average national yields in 2012 would have been records in 1991

» Soil conservation mostly controlled erosion, despite record heat and lack of rain in June and July

» Other reasons for reduced erosion˃ Improved seed quality˃ Improved planting practices ˃ Improved farming technology

Crop Residue

Tillage & Erosion » A tillage system that buries residue and

pulverizes soil leads to high erosion risk» A tillage system that preserves surface residue

and minimizes soil disturbance reduces erosion

Tillage Practices» Conventional tillage creates soil disturbance and mixing » Conservation tillage reduces soil disturbance to a

minimum and keeps more residue from the previous crop at the soil surface

Conservation Practices

» Contour planting» Strip cropping» Contour strip cropping» Grassed waterways

Contour Planting

Strip Cropping

Contour Strip Cropping

Grassed Waterways

Reading Assignment

» New Conservation Program Protest Most Highly Erodible Croplands

» Gullies in Long-term No-till Fields can be Troublesome

» The Fate of Our Nation's Soil Resource

» Linked on Assignment webpage» “Due” Wednesday, Sept. 11