It's the manure part that bothers people, leading them to eschew mushrooms. In fact, I'm not particularly thrilled about buying button mushrooms from the store, seeing all the growing media residue still clinging to them. Thing is, the manure, if used, was probably composted and possibly topped by a pasteurized,non-fecal casing soil to remove pathogens and interfering fungi in the process of being implanted with the fungus you'd be eating. That's better than you can say for the soils that grow many of your vegetables. Farmers often apply manure to their soil, allowing as little as 3 months for natural processes to kill off pathogens before harvesting the crop. So, wash your vegetables, as well as your mushrooms, before cooking or consuming them.
We could do better by the Bay than to spread manure on farmland. About 20% of Maryland farms are restricted in the types or amounts of manure they can use now because of the Phosphorus Management Tool (PMT) regulations. Phosphorus is an important pollutant to manage, but Nitrogen is also a growing concern, having negative impacts on at least 5% of affected ecosystems' endangered species. Much of the sandy soils in the Coastal Plain don't accumulate nutrients and pass them through quickly to aquifers and waterways. Rather than base manure application limits on soil phosphorus content, we should be looking at nutrient flows.
One of compost's key characteristics is that it holds on to chemicals, such as phosphorus, acting as a filter in the soil to limit the amount of nutrients that make it through to the Bay. The same can be said of biochar and mycelium, but to an ever greater degree. Blaming the PMT on the decline in the number of Maryland farms ignores the whole issue of nutrient pollution, while the PMT ignores the flow of nutrients from the soil. Adopting a more rigorous protocol for reducing nutrient pollution seems to be warranted, but we need to avoid burdening small farms with added costs and management effort. Options in the PMT for measuring reductions in actual pollution to waterways, rather than strict limits on fertilizers, could be the way to go.
Of all the methods mentioned, I think mycelium is the most promising (though farming with biochar would do enormous good). In Mycelium Running: How Mushrooms Can Help Save the World, Paul Stamets discusses implanting bunker spawn in trenches to filter runoff from areas of concentrated pollution. I'm starting to do this on my own property as I acquire mycelium in my various experiments. Oyster mushroom mycelium is supposed to be good for this use. Once the mycelium is established it can flourish, if fed new wood chips occasionally. The great thing about it is that farmers could harvest and sell the highly nourished oyster mushrooms that would grow out of these mycofilters.
