12.2.1: Introduction- Wind and Water

The major forces that strip soil from fields are wind and water. Nature buffers these erosive forces by keeping a vegetative cover on the soil year-round. Of course, farming and gardening expose the soil because we have to have a way to get our desired crop seeds in the ground. In this section, we look more closely at erosion and its causes. In upcoming sections, we examine how we can farm differently to minimize the two soil robbers, water and wind.

So long! It’s been good to know you. This dusty old dust is a gettin’ my home. And I’ve got to be drifting along.

—Woody Guthrie, 1940

Wind

The dust storms that hit the Great Plains of the United States during the 1930s, centered in parts of Oklahoma, Kansas, and northern Texas, were responsible for one of the great migrations in our history. As Woody Guthrie pointed out in his songs, soil erosion was so bad that people saw little alternative to abandoning their farms. They moved to other parts of the country in search of work. Although changed climatic conditions and agricultural practices improved the situation for a time, there was another period of accelerated wind and water erosion during the 1970s and 1980s. (Ironically, some of the worst-struck areas during the Dust Bowl are now producing crops again when the Ogallala aquifer was tapped for irrigated agriculture, although the water will run out in a few decades). In 2025, we again have seen wildfires and dust storms claiming lives (traffic pileups) as strong winds blow over uncovered soils.

Figure \(\PageIndex{1}\): Sloan. 1936. Dust Bowl – Dallas, South Dakota. Retrieved from en.wikipedia.org/wiki/File:Dust_Bowl_-_Dallas,_South_Dako...

Figure \(\PageIndex{2}\): Modern day dust storm causes traffic accident in 2025

 

Water

The other major type of erosion is caused by rain storms and a lack of vegetation to cover and protect the soil. We've already discussed how managed grazing covers the soil with a protective blanket, but in some areas grazing and hay-making on pastured land have fallen by the wayside as farms concentrate their animals, truck hay into the farm, and focus machinery and management on growing annual grains like corn and soy to feed their concentrated livestock. In Northeast Wisconsin, for example, farmland in Brown County lost 70% of its hay/pasture land since 1990, having it converted to grains. This means land is tilled annually, and the result is that in springtime, erosion runs very high when this region receives rain on uncovered land before new crops grow and cover it. Up to 70% of the erosion occurs in just 17 springtime rain events. The soil washes into the bay of Green Bay, making it a new hypoxia hotspot.

The soil is gone from the landscape. Soil was formed in the Green Bay region just recently, after the last lobe of the glaciers retreated from the Midwest 10,000 years ago. The soil is young and fertile, but it is eroding more quickly than it can be built. In just the last 50 years, the region's farmers have reversed millennia of soil building.  As they plow and plant they send soil into Lake Michigan.

In many other areas around the world, land degradation has forced families off the farm to urban areas or caused them to seek out new lands by developing natural areas like rainforests. Fertile soils on slopes in southern Honduras are now severely eroded (Figure \(\PageIndex{2}\)) after years of slash-and-burn agriculture. Much of the land has been turned into pasture or abandoned, and the area has become depopulated.

Figure \(\PageIndex{3}\): Erosion on steep lands in Central America. Removal of the fine topsoil left mostly boulders behind. Sorghum plants show drought stress due to lack of rain and low water holding capacity in the soil.

Erosion Is A Natural Process, But ...

Erosion of rock and soil is a natural process that over the eons has caused the lowering of mountains and the formation of river valleys and deltas. And natural erosion is going on all the time as water, ice, and wind have their effects on rock and soil. One dramatic example of such erosion is the dust picked up by winds just south of Africa’s Sahara Desert—the Sahel region of transition from desert to savannah—traveling some 3,000 miles to South America and the Caribbean, and occasionally reaching the southeastern United States. This dust is thought to be a major source of phosphorus for the Amazon River basin, balancing losses that occur there. The problem in agricultural soils is greatly accelerated erosion that is especially severe when the soil is bare, unprotected by living plants, their roots, or residue mulch. Also, the breaking up of soil aggregates with tillage lessens rainfall infiltration into the soil, which worsens runoff and erosion.

Climate and soil type are important factors affecting erosion. Intense or prolonged rainstorms are major causes of water erosion and landslides, while drought and strong winds are critical factors in wind erosion. More extreme weather conditions as a result of climate change are therefore adding to the concerns of both water and wind erosion. Soil type is important because it influences the susceptibility to erosion as well as the amount that can occur without loss of productivity. We discussed how some soils (especially silts) with poor aggregation are more susceptible than other soils, especially those with good aggregation. This is reflected in the soil erodibility ratings, which soil conservationists use to plan control practices.