CROP ROTATIONS, COVER CROPS AND NITROGEN FIXATION. Alfalfa
can fix 180 pounds of nitrogen a year and many studies have shown that
corn following alfalfa needs little additional nitrogen. But nitrogen
fixation provides only 5% of our crops nitrogen needs. It is estimated
a farm would need a third of its area in legumes to do without supplemental
The argument is made that if all grain were grown
in rotation with nitrogen fixing crops, less total grain would be harvested
and more land would have to the cultivated to make up the difference.
The opposing argument is that 70% of the grain is being fed to animals. They
could be fed more of that nitrogen fixing forage instead. Also
we would be healthier if we ate less meat and more grain anyway. By
feeding less grain to animals and reducing total grain acreage there
would be room to grow more nitrogen fixing legumes.
OTHER NUTRIENT SOURCES. Deep rooted crops can bring nutrients
that have leached into the subsoil back up to where they can be used. Rock
powders such as granite dust and greensand can provide some slow release
Fish and seaweed extracts can provide a fertilizer
boost through foliar feeding. Soil nutrients are inexorably being washed
into the sea so this is a way to bring some of it back to the land. If
done properly it could be done sustainably.
If all the above methods of maintaining soil fertility
were used to their maximum extent, could unsustainable chemical fertilizers
be eliminated? I
sure don't have the answer, but suspect other sources of crop nutrients
will always be needed to feed the world's growing population.
It is ironic that 78% of the earth's atmosphere
is nitrogen gas yet nitrogen is often the limiting plant nutrient.
Is an artificial nitrogen fixation system which is solar powered possible?
Could genetic engineering increase plant nitrogen fixation?
CONCLUSIONS: These articles on sustainable agriculture
have only scratched the surface and have raised more questions than provided
reason is I don't have the answers. Developing a sustainable agriculture
or society as a whole could take generations. Yet I fear we no
longer have the luxury of time. The resources on which we base
our lives are non-renewable and are being depleted fast, the environment
which supports us is being degraded at an alarming rate and human population
grows without limit.
The organic farming movement has taken many steps
in the right direction. But
with all the focus on things like maintaining purity from chemical contamination,
certification rules and national standards we are missing the bigger
question of WHAT IS SUSTAINABLE?
A sustainable system of agriculture, in addition
to the established organic practices, may need that sewage sludge even
if it is not 100% pure. It may need some responsible chemical
pest control. It may need some artificial nitrogen fixation. It
may need some genetic engineering. I believe the search for what
is sustainable will lead us beyond the chemical vs organic debate.