Sally Brown

November 17, 2014 | Connections

Connections: Dirt Cheap

Sally Brown

Sally Brown
BioCycle November 2014

How it roils my soul, that expression ”dirt cheap.” We have been getting a really sweet deal since we started putting seeds in the ground many thousands of years ago. Very rarely, however, have we considered the cost of preparing the seed bed, aka the soil. We count on soil for so many things, food being the most prominent. Water storage and purification and nutrient transformations are just a few of the others. These services are essential and the soil that provides them is critical. This is why dirt is not cheap. It is incredibly labor and time intensive to produce. But traditionally, humans haven’t been the ones doing the work.
Soil is formed through a complex interaction of biological, physical and chemical processes — summed up in every introductory soils class as the five factors of soil formation: 1) Parent material; 2) Climate; 3) Topography; 4) Time; 5) Organisms (we would fit into this category).
The interaction of those factors is really fascinating if you want to study soil formation. For me, the critical part is the time frame. An academic paper by David Montgomery (Montgomery, 2007), author of ‘’Dirt: the Erosion of Civilizations,” estimated the rate of soil formation as 0.058 to 0.083 millimeters (mm) per year. In other words, about 437 years for each inch of soil. From where I sit, that counts as a lot of work. That same paper estimated the rate of soil erosion in the U.S. as between 0.2 and 1.65 mm per year — meaning we are currently losing that same inch of soil at a rate of 15 to 142 years per inch. Now you don’t have to be an expert at unit conversions or math to realize that we are losing the soil much faster than we are making it. Something tells me this is where Montgomery came up with the title of his book.
Our current accounting system doesn’t put much value on the soil. There is no real consideration of the time and effort involved in making it. The best we have come up with is the U.S. Department of Agriculture’s Conservation Reserve Program (CRP) that pays farmers not to farm sensitive soils to reduce their potential for erosion. The program pays about $130 per hectare (2.5 acres) per year to let the soil rest. For an investment of about $58,000, over the course of those 437 years, an inch of soil will be formed on that hectare of land. For lands not deemed sensitive enough, in fact for soil in general, there are no subsidies or budget to help or encourage us to protect it.
As noted, people fall into the organism category of the five soil forming factors. In fact humans can greatly accelerate the formation of soil, and make lovely soil at that. A recent article in the San Francisco Chronicle describes how adding compost to rangeland soils helps lock up carbon. From a soil’s perspective, locking up carbon is synonymous with building soil. The added carbon not only adds depth to the soil profile, it helps hold the inorganic portions of the soil in place. A high carbon soil is the same as a soil that is resistant to erosion.
The article describes the Marin Carbon Project in Marin County, California, where scientists have shown the power of compost to sequester carbon in soils — a key component of building healthy soil. While sequestering carbon is one of the great things that soil can do, I personally would rank growing food and filtering water higher on the benefit list. The article also talks about economics. The reporter points out that the cost of bringing waste to a composting facility, composting it, and then applying it to farmland can be a significant barrier to municipal officials and farmers alike.

Incentivizing Soil Building

This is where our current accounting system is really falling short. Compared with the USDA’s CRP, the financial incentives for how we manage our residuals — the best and fastest tool out there for soil formation — are nonexistent. There is no financial incentive in this country to build soil with residuals. Our residuals accounting system is currently based solely on comparative costs of collection for landfill versus collection for composting. We are thinking of the cost per truckload rather than the cost of losing our soils. Granted, it is really tough to wrap your mind around 437 years to build an inch of soil, especially when we’ve always thought of soil as dirt cheap. It is also tough when you are working in the framework of annual budgets and the fear of angry ratepayers. And because we have not subsidized this critical form of soil protection, widespread use of compost by farmers is often cost-prohibitive.
Getting the ratepayer in the same room with the farmer might make the conversation easier. However, our challenge is even greater because we have not yet started to consider the interrelationships between the urban and agricultural sectors and their associated costs and benefits. In other words, the farmer never talks to the solid waste manager or the ratepayer. The team in charge of waste management in a municipality has no way to integrate the costs of soil loss into their spreadsheet. And despite all the known benefits, the farmer has a hard time justifying the costs of using compost instead of synthetic fertilizers when his or her profit margins are tight enough.
The USDA’s CRP provides a financial incentive for letting land rest. What if that same $130/hectare were available for using compost? If the USDA would provide that same $130 per hectare for compost use, our world would be very different. The Marin Carbon Project has put an important spotlight on the role of composts for preserving soils. Putting a dollar figure on that will go a long way to turning it into normal practice. In reality, dirt is far from cheap.
Sally Brown is a Research Associate Professor at the University of Washington in Seattle and a member of BioCycle’s Editorial Board.


Montgomery D.R. Soil erosion and agricultural sustainability. Proc Nat Acad Sci., 2007; 104(33):13268-72.

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