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Sunday, March 27, 2011

It's the Soil...

Usually in these pages I write about water - rainwater harvesting - because access to water is so important to sustainable community gardens. The tsunami in Japan showed the sheer power of water to destroy, the need for water to avoid a nuclear disaster and how this resource can be made unusable by radiation.
                                Rainwater Harvesting System at the River Garden in the Bronx

Soil is equally important in a community garden. A fragile resource that can be lost through erosion, contaminated by heavy metals and chemicals and depleted of nutrients, oxygen and beneficial soil organisms if the soil is not cared for properly.

Most community gardens are in urban areas and on land that may have been contaminated by a prior use. There has always been a concern about potentially toxic chemicals or heavy metals that might still be present in the soil and end up being absorbed by community gardeners through the skin, by inhalation or through eating the vegetables grown in this soil. I am not aware of any poisonings or sicknesses caused this way. Community gardeners have always been advised to have their soil tested to know if special precautions need to be taken.

            Witch Hazel flowering in early March at the Jacquline Denise Davis Garden in the Bronx

The heavy metals of concern are Arsenic, Cadmium, Chromium,Nickel and Lead. An excellent heavy metals fact sheet published by the Environmental Sciences Analytical Center @Brooklyn College gives some interesting facts about the soils they have tested. The median levels of the five heavy metals results found in urban soils primarily taken from NYC gardens are anywhere from 2X the levels of Nickel to 20X the levels of Lead as found in rural soils in NY State. That sounds bad but even with these numbers there are best management practices for gardeners to follow to avoid any problems. Also, soil tests are based on mixed samples taken at different depths and from random spots in the garden. A soil test that shows high levels of Lead for example could have been taken from a spot that is contaminated by lead based paint chips from an adjacent building or from remnants of the building formerly occupying the site of the garden.

"Native" soil in a Bronx community garden

In my experience, most community gardeners grow in soil that has been brought in by a truckload and confined in a raised bed and are not planting edible plants in the existing soil. In addition, plants will be less likely to uptake lead in soils that includes 5 to 10% organic matter (compost). Slightly acidic soils with a pH of 6.5 to 7  and soils with the proper amount of phosphorus will bind the lead particles in the soil and make it  less available to plants. Gardeners who realize the importance of healthy soil spend time building up the nutrients and soil organisms. This is another example of sustainable gardening and yet another reason to preserve gardens. 

Soils that have been improved over years of stewardship are not easily replaced. A community garden destroyed or moved to a different location is not the same community garden. The centuries old villages destroyed by the tsunami will be difficult to rebuild in a short time and land contaminated by radiation from the still unfolding and worsening crisis at the nuclear power plants in Fukushima, Japan may not be usable for years, even decades. Soil, water  and community gardens are resources to be preserved and protected and not abused because of carelessness or for profit.

      A recently completed RWH system at the Belmont Little Farmers community garden in the Bronx 

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