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Soil Health – We All Love It, But What Is It Worth?

By   /  July 17, 2017  /  Comments Off on Soil Health – We All Love It, But What Is It Worth?

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If your field or pasture has been plowed, sometimes the topsoil is called the plow layer. Soil scientists call topsoil the A horizon when they describe the soil layers through the depth of the soil.

Soil health gets a lot of air time. But have you ever thought about what it’s actually worth in dollars? That’s the question Tom Buman of Agren decided to answer. What he learned is that we can put a dollar value on healthy soil as well as the cost of erosion.

Tom worked with a group of scientists to calculate the value of nutrients including the cost of fertilizer, the nitrogen, phosphorus, and potassium the soil is providing. They looked at the topsoil, the upper 6 to 9″ of soil. This is the soil that is richest in organic matter and darkest in color. By determining the nutrient content of the soil and how much it would cost to apply those same quantities of nutrients, they were able to estimate one aspect of the soil’s value.

Next, Tom worked with Rick Cruse of Iowa State University to see how nutrients in soil translate into value based on production. Rick and his team took soil cores at 40 locations in each of numerous Iowa fields on 7 different farms. Then, they used precision data provided by combines harvesting those fields to track corresponding yields at those exact locations. They also looked at yield data from 2007-2013 to get a bigger picture.

The fields Rick was tracking were all planted with corn-soybean rotations, but represented different intensities of tillage. One set of fields was tilled with each planting, one used no-till planting for soybeans, and the third used no-till planting for both corn and soybeans. All the farmers used similar inputs as far as fertilizer and pesticides.

What Rick saw was that the more tillage done, the more topsoil was lost. Less topsoil resulted in lower yields and lost income.  Based on the rates of soil loss, he calculated that 6.1 tons of topsoil would be lost over a ten year period from each acre of the regularly tilled corn/soybeans field, 4.2 tons from the tilled corn/no-till soybeans, and 0.1 tons from the no-till corn/soybeans.

Based on the value of the soil’s nutrients and the value of production, Rick and Tom calculated that over a ten-year period, soil losses from conventional tillage would cost $354.94 per acre ($35.49 per acre each year) in lost production and nutrients. For the fields tilled corn/no-till soybeans, the cost would be $231.81 per acre ($23.18 per acre each year) and for the no-till fields, the cost would be $6.83 (68 cents per acre each year).

Topsoil has eroded from high spot in the field, leaving lighter subsoil visible. Photo courtesy of Ray Weil.

Tom pointed out that the less topsoil you start with, the harder you’re hit by even a small loss. In other words, if you only have 3” of topsoil, dropping 1/2” of topsoil, means a big drop in production. If you have 10” of topsoil, the drop of ½” of soil won’t be as big a hit, but it will still lower your bottom line.  That topsoil is the soil richest in organic matter, so a drop in topsoil is measured as a drop in organic matter. Losing 1/2″ of topsoil means losing a good portion of your organic matter.

This pasture was cropped before being put into pasture. Higher areas lost topsoil, leaving less fertile soil with lower pH. Cattle prefer the grasses in the lower areas, avoiding the sedges and other grasses growing on the less productive hills. Uplands may be less productive because of rockier or shallower soils. In this case, and in many similar cases, though, years of plowing and the resulting erosion caused the reduction in fertility and production. Photo courtesy of Ray Weil.

Soil scientist and author Ray Weil noticed this on a nearby farm. Cattle are now grazing fields that were once cropped. The higher spots experienced erosion, and now have less topsoil. Ray also discovered that the pH is lower on the eroded hill tops, and the cattle are avoiding the broom sedge and other grasses that are growing there.

Maybe you don’t till your fields, or plant row crops, and maybe all your land is in rangeland and pasture. You still want to consider organic matter as a measurement of your soil health. The way to keep organic matter is by avoiding erosion. Because organic matter is lightweight, it is quick to blow or wash off any uncovered soil.

Keep your soil covered with dense vegetation to avoid losing productivity. To make sure you’re doing your best, it might be worth monitoring. There is still a way to go in determining the value of that topsoil and the soil health that we prize. But seeing the calculated loss of production makes its relevance that much clearer.

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About the author

editor and contributor

Rachel’s interest in sustainable agriculture and grazing has deep roots in the soil. She’s been following that passion around the world, working on an ancient Nabatean farm in the Negev, and with farmers in West Africa’s Niger. After returning to the US, Rachel received her M.S. and Ph.D. in agronomy and soil science from the University of Maryland. For her doctoral research, Rachel spent 3 years working with Maryland dairy farmers using management intensive grazing. She then began her work with grass farmers, a source of joy and a journey of discovery.

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