Beyond Chemicals

While I see a need to have soil restoration promoted in the next version of the Calvert County Comprehensive Plan, there are already many elements of the plan and ongoing institutions promoting soil conservation. The Comprehensive Plan includes "Sediment flows from development and farming" as a threat to the vision that

Our wetlands, streams, and forests support thriving plant and animal communities.

The corresponding action is "Develop soil conservation and water quality plans for farms."

When you look into the Best Management Practices of the Soil Conservation District, it appears that they have this whole issue pretty well in hand (at least among the farms on the list of cooperators). Many of these best practices lead to soil restoration in addition to soil conservation. At least one of the BMPs, however, is potentially counterproductive - that is, perpetuation of chemical fertilizers.

Photo by Paul Riismandel (CC BY-NC-SA 2.0)

The problem with chemical fertilizers is that they can reduce the soil biota population below a critical level where the microorganisms make the soil ecosystem work in the plants' favor. This results in the need to use more fertilizer to achieve the same results as in previous years and the soil undergoes a death spiral until it is no longer economical to farm.  Many of the trace nutrients used by plants are generated by the proliferation of soil microorganisms and could be uneconomical to add directly as we do commonly applied macronutrients like Nitrogen, Phosphorus, and Potassium (N, P, K).

It may be possible to restore soil humus by intensive farming methods while still using chemical fertilizers, but a surer method is to farm organically using biochar, compost, and organic fertilizer, as necessary. The goal should be to eliminate fertilizers altogether in favor of creating humus which is self-regenerating as long as crops are grown successively and rotated from year to year. Our farmers, large and small, need to learn to do this if for no other reason than that chemical fertilizers are a nonrenewable resource. A better option, still, is to grow perennial food crops. While we're at it, let's take advantage of soil carbon restoration for its role in cooling the planet.

Eco-solution for E. Coli

When I became aware, a couple of years ago, that roof runoff may contain some heavy metals that could potentially find their way into your food garden, I took a bucket of biochar and dumped it into the bottom of my rain barrel. Problem solved. What I didn't realize is that I was solving another (bigger) problem of roof runoff - e. coli bacteria.

To be honest, my quick fix may not have solved the problems; (a) because I didn't really have a problem - my rain barrel feeds my ornamental rain garden, and (b) the biochar filter inside a rain barrel should probably be a little more meticulously constructed and maintained.

Now that I am about to set up a rain barrel that will be used to spray my mushroom logs and save money on my water bill, I definitely need to think about the contaminants in the water. The draft Certified Naturally Grown standards for mushroom growers does not address roof runoff specifically, but does cover surface water. Could a biochar filter be used to meet the CNG standard? Let's explore.

The water standards for mushrooms are the same as for irrigation water. A study done at Rutgers University found that the major concern for roof runoff is e. coli contamination, rather than heavy metals (though lead and zinc warrant measurement). This bacterial contamination could stem from dead animals and feces, particularly in gutters (but also in rain barrels and on the roof, itself). Occasionally, the study found e. coli in excess of the limit coming from a roof in their study.

It turns out that biochar captures and sequesters e. coli bacteria, as +Kathleen Draper points out, referring to research done at McGill University showing that biochar filters out e. coli. The excellent thesis by Shoieb Akaram Arief Ismail shows how large pore biochar with particle sizes up to 2 cm (such as the wood based product that I make with my pyramid kiln) is a significantly better e. coli filter (a couple orders of magnitude) than sandy soil alone.

Granted, the filtering action in this study took place over 24 hours, but some reduction of e. coli could be expected by less than a minute of residence time in a rain barrel partially filled with biochar. The practical limit is how badly the water flow would be reduced by the filter. This can be discovered empirically. The biochar should be rinsed thoroughly prior to adding to the rain barrel in order to prevent washout of fine particles which could clog the outlet. In addition, gutters should be cleaned regularly and the biochar filter changed annually when the rain barrel is scrubbed clean for the season.

The rain barrel volume you are sacrificing to the filter may require a larger barrel. I got a good deal on a 65 gallon barrel, which I think will do just fine. Even a 55 gallon barrel should be big enough. For my homeys, Baltimore is having a truckload sale of them and Calvert County has a half-price deal for residents that comes with a free workshop, both in April.