you just grow more cover crops. But i agree that all manure, including human manure, ought to be recovered.

Well the kind of agriculture they're talking about isn't sustainable in the first place. Organic isn't by default sustainable.

Am I missing something? Nitrogen starts as a gas. Where is the complete nitrogen cycle treated accurately in these links?

If you are not familiar with the nitrogen cycle, one review is at:

http://www.physicalgeography.net/fundamentals/9s.html

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I did see statements such as: "Are these really alternatives to fertilizers? I think not. Although these adaptations may help improve nutrient use efficiency of crops (that amount of the nutrient pool in the soil that crops take up), aside from legume nodules they fail as fertilizer alternatives due to conservation of mass, which here can be stated as “nutrients exported from a field must be replaced by an equal import of nutrients.” Nutrients are not created in the field through any mechanism, natural or not. Even nitrogen from legumes is imported from the air. "

Please notice the statement: " Nutrients are not created in the field through any mechanism, natural or not. Even nitrogen from legumes is imported from the air."

To me (H.Kuska) this quote has no meaning as earlier he had stated " aside from legume nodules they fail as fertilizer alternatives ." His attempt to use "conservation of mass" is too limited - he has to do so with the entire nitrogen cycle which includes the air.

Please see how important the addition of the air is in the "accounting" from the following quote from my nitrogen cycle link above is:

"Almost all of the nitrogen found in any terrestrial ecosystem originally came from the atmosphere. Significant amounts enter the soil in rainfall or through the effects of lightning. The majority, however, is biochemically fixed within the soil by specialized micro-organisms like bacteria, actinomycetes, and cyanobacteria. Members of the bean family (legumes) and some other kinds of plants form mutualistic symbiotic relationships with nitrogen fixing bacteria. In exchange for some nitrogen, the bacteria receive from the plants carbohydrates and special structures (nodules) in roots where they can exist in a moist environment. Scientists estimate that biological fixation globally adds approximately 140 million metric tons of nitrogen to ecosystems every year."