> My numbers may be off, but it is my understanding that we have upwards
> of 350 million acres of farmland, so this represents about 1/7th of a
> ton per acre. Sustainable compost demand would be more in the 5 to 10
> tons per acre annual range. To bring soil humus up to ambient, which I
> claim is a sustainable level, would require upwards of 200 tons per
> acre. This represents a "topsoil debt" as high as 7 trillion tons of
> compost.
>
All farmland should not receive compost. Some farmland is used to
produce cattle, and it would not be appropriate to use compost in a
feedlot or on grazing land. Agricultural acreage figures often include
forests, as well as just about any piece of land that is zoned
agricultural, much of which is not cultivated.
>From an economic, and possibly even an environmental perspective, the
only land that should receive compost inputs is the land that is
cultivated, to allow for incorporation. Why put compost on top of hilly
grassland, where it can easily be eroded?
Much of the intensively cultivated land is next to the cities, producing
flowers, vegetables, fruits and nuts. Urban organics can benefit these
lands, provided they are clean enough. Farmers that are located next to
urban areas are finding that theses resouces are much more than a drop in
the bucket.
I work with farmers on the fringe of San Jose, California, who are using
yard trimmings collected in the Bay Area. There is a shortage of
composting infrastructure in the city, so much of the material is going
out to farms uncomposted. Farmers are composting the material on farm,
using methods ranging from the Luebke Controlled Microbial Composting
Method to the "let it sit a couple months, and try to keep it moist"
method. And some growers are landspreading uncomposted yard trimmings,
even on vegetable row crop ground. Most of the hauling cost is covered
by the companies that grind the material, but farmers are not getting any
money to take it, and farmers who live further from the city are
starting to pay part of the hauling.
Karin Grobe, Santa Cruz, California