You would think by now that those of us working in the conservation field would have a really good handle on the value of topsoil. Again, you would think. In the abstract, I think we would all say that we “value” topsoil. However, in the 80 years since we’ve identified soil erosion as an issue in the U. S., we have been unable to even begin to quantify the value of topsoil in real numbers; until recently. Thanks to the leadership of Iowa State University Professor, Rick Cruse, we’ve moved one step closer to identifying the value of one ton of topsoil. A huge breakthrough in the work of soil conservation!
According to his research, Cruse says that if you lose a ton of soil this year, it affects your yield for every year into the future, not just the next year. In other words, once you lose a ton of topsoil, that soil is gone forever. And as my mom says, “forever is a long, long time”.
Dr. Cruse explains that erosion of topsoil affects our land investment in two different ways. First, erosion causes a direct loss of crop nutrients. In today’s market, every ton of eroded topsoil has an average nutrient value of $2.10 (nitrogen and phosphorus alone). If a farmer is losing 5 tons/acre/year he is losing $10.50/acre annually in nutrient value. Secondly, erosion causes a decline in soil health, which can cause yield loss both now and into the future. Soil only regenerates at a rate 1/10 to 8/10 of a ton per acre per year, with an average rate closer to 1/4. When a farmer loses an amount greater than the level of regeneration, he is losing present & future yields. In general, soil erosion costs about $0.07/ton in productivity this year as well as every year in the future. Of course, if the price of corn doubles in value, then this loss also doubles.
What about field averages….
I wanted to test out this concept closer to home. Recently I chose a field in Iowa and modeled the soil erosion of that field using Agren’s SoilCalculator. (See Figure 1) SoilCalculator calculated this field’s average erosion at 7.3 tons/acre/year.
Using Dr. Cruse’s estimates, I calculated that the farmer would lose $28.11/acre of yield potential and $153.42/acre of nutrients for a total loss of $181.52/acre over a ten-year period. On a 150 acre farm, the total loss to the farmer would be $27,210 over a 10 year period. Depending upon financial circumstances, the estimated financial loss should be enough to motivate the farmer to implement more conservation practices. (See highlighted values in Figure 2)
What about the most erosive part of the field…
Since erosion is not distributed evenly across the field, the farmer may want to evaluate those areas of the field where erosion is the worst and costs the most money. Using the calculations above, the loss to the farmer would be 17.4 tons/acre/year on the most erosive 20% of the field. Erosion on as little as 20% of a field could cost the farmer $365.68/acre in nutrient value and $66.99 in lost productivity over this same 10 year period. This is a total loss of $432.67/acre. That adds up to $12,980 on 30 acres in (20% of 150 acres). With this financial information, the farmer might then choose to focus on the worst 20% of the field by installing site specific conservation practices like a terrace or grass strip.
By identifying the value of a ton of topsoil and understanding the distribution of soil erosion, a farmer can start making informed decisions on specific problem sites. Precision Conservation is applying conservation practices in the right place, at the right time, and at the right scale. With precision conservation we are taking another step toward being able to identify the value of a ton of topsoil, pinpointing where and how much erosion is occurring, and where farmers should target their efforts. Imagine a farmer targeting his conservation efforts to achieve the best return on investment and also solving the biggest environmental problem. I think that is what we refer to as a WIN/WIN!