It takes nature thousands of years to produce a fertile soil. That same soil can be lost to erosion in only a few decades. Clearly, as we attempt to feed our expanding world population, care must be taken to prevent unnecessary erosional losses of this vital resource.

Soil erosion results primarily from uncontrolled runoff of surface water. In areas that have never been tilled, soil is protected by a cover of plants, and there is an approximate balance between the slow loss of soil by erosion and the development of new soil from underlying parent material.

Whenever the protective shield of vegetation is broken, however, erosion will follow. There, are, of course, natural events that can destroy the vegetative cover. These include droughts, plagues of insects, epidemics of plant disease, and fires caused by lightening.

Agriculture, however, has been a far more potent factor in causing erosional loss of soils. Some of the erosion resulting from farming is unavoidable. We must have food, and so we must break into the natural vegetative cover.


There are, however, farming methods that reduce the loss of valuable topsoil to erosion, and these methods are practiced widely. For example, farmers now plow and plant their crops in rows that follow contours so that rainwater is retained rather than allowed to run off. Efforts are made to reduce the amount of time between preparation of the soil for planting and planting itself so that the bare soil will not remain exposed to erosion for long periods.

Strip-cropping is also practiced. This technique involves planting alternate bands of erosion-resistant crops such as clover and alfalfa with open spaced crops like com. Soil losses in the erosion-susceptible com strip are trapped in the adjacent strip of denser crops. Where fields are temporarily not utilized, soil-holding “cover” crops are planted, not only to retard erosion but to improve the soil by adding nitrogen. Because ordinary grass in an effective retardant for erosion, overgrazing by cattle and sheep must be prevented.

One of the most troublesome erosional problems faced by farmers is the control of gullies. Gullies start in either natural depressions or plow furrows and generally extend themselves toward higher ground by a process called headward erosion. The gully head receives rainwash from a wide area.

This water converges so as to flow rapidly into the steep depression at the upper end of the gully, eroding vigorously as it enters the channel. It is this rapid erosion that causes the gully to cut ever farther in the headward or upslope direction.


To halt this destructive process, steps can be taken that prevent water from entering the gully. Normally this is done by excavating a shallow diversion ditch around the gully head to trap its potential water supply and “starve” the gully. Because gullies grow by headward erosion, disposing of old refrigerators and automobiles in these ditches has no effect at all in retarding their growth.