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submitted by Matthew Welsh, Resource Conservationist, Natural Resources Conservation Service (NRCS), USDA
Measuring erosion occurring on the land can be done in a number of different ways. The type of erosion will dictate how that is evaluated. A common type of erosion in our landscape that is often not quantified is ephemeral gully erosion. This type of erosion is characterized as small channels formed by concentrated flow. They are small enough to be leveled back off by tillage and will reform in the same location after rainfall events.
Within crop fields, ephemeral erosion can not only cause the loss of soil but nutrients, crop inputs, and cause field conditions not conducive to normal implement operations. The value of this loss often is not fully understood. Take for example a typical ephemeral gully on a silt loam soil measured at 450 feet of length with a top width of 3 feet and 1 foot of depth at its deepest cross section, this gully would erode at a rate of 40 tons per year.
This is a truly astonishing number considering these typical fields may have multiple ephemeral gullies which could bring a yearly lose in hundreds of tons per year for these fields. Nutrients and organic matter are lost with every inch of the soil eroded away. A typical analysis of soil may contain 15-20 PPM of nitrate nitrogen; 150-250 PPM of Potassium, and 50-100 PPM of Phosphorus.
From USDA soil resources the cost of soil erosion is estimated at 44 billion in the United States. University of Wisconsin studies have found fertilizer value of Nitrogen, Phosphorus, and Potassium to total $12.80/ton of soil eroded. The combination of many hundred tons of soil loss from ephemeral gullies annually amount to thousands of dollars in economic loss, this is on top of losses incurred from sheet and rill erosion on uplands.
Healing and fixing these areas can occur as fast as these ephemeral gullies will form. First steps are identifying locations and determining the frequency of ephemeral erosion over the crop rotation.
Some locations where flows typically carve out ephemeral gullies will need to be evaluated for structural practices such as grassed waterways or sediment basins. In some cases, ephemeral erosion may only show up following years of low residue crops like soybean. These situations my allow for opportunities within the rotation to use a cover crop to provide residue coverage through the critical erosion period in the spring.
Temporary spring seedings of oats in these troublesome areas are also effective and in many cases the proceeding crop could be planted directly into the temporary cover. Whatever the method of treatment; it is critical to manage these areas and prevent the soil loss that is moving nutrients and soil carbon off the field and degrading our water resources all the while negatively impacting economic returns on the field.
