Read this discussion over at herbicides/pesticides.
Physically, however it is done, phosphorous and nitrogen are required for the growth of plants optimally. We currently utilize many unsustainable, toxic, and soil-destroying mechanisms to push into plants these two elements.
The following short video discusses how to escape the dependency on increasingly toxic low quality phosphate rock with a recycling program that yields methane bio-gas--and the bio-gas 'waste products' are phosphorous-rich materials that can be applied to plants. It is being done in Europe in combined bio-gas/phosphorous fertilizer plants already:
City To Farm Composting Project
Betsy Kettle explains the City to Farm Composting Project. This is a different method of collection and processing urban food scraps that could potentially supply the farmlands around major cities with an odourless, leachate free compost. The security of the urban food supply may be dependent on growing locally without dependence on petrochemical-based fertilizers and minimal transport. Organic agriculture based on compost may be our future food security and also create a more sustainable agricultural system.
What about nitrogen? Well, do some selective planting of fast growing nitrogen-fixing trees, like tree lucerne, that provide nitrogen rich soils for other plants in the area. Cut these trees regularly and use those products for something else. The following arrangement is shown raising milk goats with tree lucerne cuttings because they are high in protein. In two parts, this is a short 20 minute documentary about the co-inventor of permaculture concepts, David Holmgren. The first few minutes solve the nitrogen issue:
Permaculture co-originator 'Holmgren', Pt1
'Eco-Centric', a story by reporter Tim Lee from the 2004 ABC program 'Landline' about permaculture co-originator David Holmgren, whose "pivotal role in developing permaculture has scarcely been recognised" http://www.holmgren.com.au.
Permaculture co-originator 'Holmgren' doco Pt2
Another way to create durable soils full of required minerals and other materials is to draw upon rediscovered Amazonian soil fertility strategies:
Unravelling Human Creation of Amazonian 'Terra Preta'/Dark Soil (Or, How to Make Permanent, Self-Renewing Soil); 7 min.:
This is a short excerpt from a BBC Horizon documentary entitled "The Secret of El Dorado". It recounts how a previously unknown highly populated area of Eastern Bolivian Amazonia extending into the Amazon River Basin gave the area a major urban/agricutural society. It completely disappeared as Europeans arrived. However, it left its 'terra preta'--the dark earth of the Amazon--that is still mined and carried off because it is so beneficial a soil. And it still self-replicates--long after the original human/indigenous creators have died off and their secret lost. We are slowly unravelling how to recreate this perpetual self-renewing soil. Some secrets of it are featured in this short video clip. One secret is slash-and-char instead of slash-and-burn. The charcoal mixed later into the soil creates a slow release of minerals instead of burned ash that is eroded away very quickly. Very smart. See the amazing differences of scale of yields by only varying the addition of charcoal! Watch the longer video below for more detailed information about other aspects of the terra preta.
BBC - Horizon - The Secret of El Dorado
New evidence that advanced societies flourished in the Amazon Basin before the arrival of Europeans. It was the most notorious wild-goose chase in history: the Conquistadors' search for El Dorado, a fabulous kingdom of gold that Indians said lay hidden in the jungles of the Amazon Basin. But now, at last, archaeologists have uncovered the truth behind that myth. They have found evidence of a huge society, as advanced as the Egyptians or the Incas, right in the heart of the rainforest. And this is more than the story of a lost world rediscovered. For it seems that the people of the real El Dorado possessed a secret with the power to transform our world and their secret in the soil could be the solution to solving famine in the Third World and other nations [by making local independent and autonomous agricultural sound for poor soil areas--because you can invent the soil out of nothing in a low-tech way!] once and for all.