permaculture

["Wordgarden" <wordgarden@iinet.net.au>]

Most of the elements in plants are Carbon (carbohydrates) extracted from the
air and Nitrogen (in proteins), which can also be extracted by legumes etc.
from the air. And most of the bulk is water. An extremely small proportion
of the elements in
the soils are lost as food is removed from the farm.

So, yes, it is theoretically possible for farms with no external inputs to
be sustainable.

However, there is more to soil fertility than just the raw elements, as
"Lawrence F. London, Jr." <lfl@intrex.net> wrote. It is how available those
elements are to the plants, and the structure of the growing medium itself
that decides whether plants can be grown there for ever.

The humic content (from compost, worms, fungi, bacteria, vegetable material
in the soil)
makes the various elements available to the plants. Organic farming of all
kinds values soil fertility over importing raw elements (such as is found in
synthetic fertilisers). Soil fertility can certainly be achieved by growing
green manures for compost or to plough back into the soil.

Doing it this way needs extra time and effort to grow enough extra plant
material to plough back
into the soil.

One advantage of applying external input is that in certain areas certain
trace elements necessary for plant or human health are lacking. Adding ag
wastes and rock dusts from another place can ensure a balanced supply of
trace elements. And it is a much quicker way to increase fertility than
growing green manure in a worn out farm. (municipal sewage should be avoided
unless you want to import a lot of nasties, but it has uses. It could be
fermented for methane.)



--Robert