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 nitrogen.

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 fertility.

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 answers. The 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.