At the risk of fostering an NPK mentality, I'm posting a link that specifically answer's your question. In the organic world, it would be more valuable to know how much protein there is and how readily available it is. For example feather meal is very high in protein but it takes months for it to decompose. Blood, on the other hand, is also full of protein but decomposes nearly overnight.

You would be time ahead if you forgot everything you ever knew about NPK and your nitrogen quota. Organic fertilizers simply feed the soil microbes. They turn the food into plant food.

Sawdust? Are you going to compost it or what? You may already know this but maybe other readers aren't aware. Sawdust not only has very little nitrogen, it actually requires huge amounts of nitrogen to decompose. If you bury sawdust in the soil, the fungi that decompose it will "absorb" all the nitrogen they need (or can get) from the surrounding soil. The sawdust decomposing fungi normally get their nitrogen from the atmosphere, but if you bury it, they steal it from the soil and it becomes unavailable to the plants. So with buried sawdust, no matter how you apply your "nitro quota," none of it goes to the plants until the wood is fully decomposed. This is an example of the organic program not working like a chemical program. Half of "going organic" is learning to forget what you think you already know.

Here is a link that might be useful: NPK of stuff

Thanks, dchall. I know not to pay all the attention to the NPK term of chemical fertilizers but I did want to make sure that my lawn received the right amount of effective nitro throughout the growing season since I was going to try not to rely so heavily on the soybean meal.

As far as the sawdust I think you misunderstood my poorly worded statement of "mixing it in". I was simply going to toss in a small bag full of untreated pine sawdust in with my grains before I rolled them out in the rotary spreader over the lawn as a means of using that organic material for something instead of just tossing it in the trash. I'm thinking of an effective rate of about 1/4 lb per 1000sqft!

I would like to experiment with composting my own mix but I just don't have enough ingredients laying around. I mulch mow (oops no greens!) and don't have much in the way of trees for their leaves (not much browns!). I'll probably just continue to stick to my periodic blast of compost tea and corn/milorganite/alfalfa/soybeans + weed hound!

Sawdust on the surface should be fine. It gets nitrogen from the air and really leaves a lot of fungi for you.

Regarding nitrogen from organics: If you grow leguminous crops like clover, they bring a special bacteria(um?) that lives on the roots. That bacterium is able to "absorb" or "fix" nitrogen "from the air" and store it for release later. I wish I knew more about how it stores it. I'm pretty sure it does not have a little compressed nitrogen tank, so it must be storing it in a biological form. All microbes store nitrogen in the form of protein (amino acids), but this one has a reputation for doing it better than others. Before I digress too far, the point is when you have a healthy herd of microbes, they will collect nitrogen from the air that you cannot measure. Thus a lawn of grasses mixed with Dutch white clover may never need to be fertilized.

There is a GardenWeb member (woodycrest) who cares for two, mixed-turf golf courses in Canada. When he started with these courses they had been cared for with chemicals and the soil was rock hard. The turf was bentgrass with plenty of dandelions. Besides these issues he had snow mold every spring. He started with cracked corn on the snow mold and some of the greens. Then he changed his mowing height and everything has gotten better, year after year. If I'm not mistaken he has used no chemicals in several years and now his primary tool is his reel lawnmower. The dandelions disappeared, and the turf has changed to bentgrass and Dutch white clover. He has a striking photographic record of his success. The golfers love having greens that will hold a high chip shot rather than bouncing the ball 40 feet beyond the green.

I got some sawdust on my lawn from a carpenter who was cutting wood out there. The grass took a turn for the worse in that spot. I won't do that again.

Was he building a deck? (was it treated lumber?)

I have a dead spot on my yard since 1997 from cutting treated lumber. I've tried every organic treatment I know of and nothing. It will have to be replaced with fresh soil.

I'm thinking anything cedar might also be of a detriment if I remember correctly because of a naturally occurring chemical that inhibits fungal development. Certainly not as detrimental as the copper based chemical of the old CCA treated lumber. In fact (not that I've tried) if you want a plant dead (like a tree/stump) then drill a few holes in it and stick some copper wire in it. Apparently it can be very effective.

dchall,

I have never heard of Nitrogen consuming fungi.
I thought the legume bacteria was unique and even those guys worked only for the host plant.
Then after part or all of the host plant dies, the nitrogen becomes available to the general soil.

Just how effective are these fungi and would they help in the long term by feeding them sawdust?

With the bacteria, at least, it isn't a preferential pathway. They won't produce nitrogen if they don't have to because it's a comparatively expensive process for them to do so.

Production is limited to just what they need, which then becomes available when they die. For the symbiotes, they'll feed their host plant as well, all of it becoming available when the host dies. That will be the limit of the amounts, however.

I haven't heard about the fungi, but it wouldn't surprise me greatly. Nitrogen sources, when limited, mean a major advantage for anything that can produce its own. I don't imagine the pathways are much different, though, as it's still going to be expensive to synthesize it out of atmospheric N2.

morpheuspa,

So you are saying that even the, nitrogen-fixing bacteria really won't bring in much (if any) atmospheric nitrogen for the root nodules of legumes if there is adequate nitrogen in the soil?

They shouldn't, no. People plant legumes to restore tapped-out soils because they don't require nitrogen fertilization.

If you fertilize, that pathway should shut down (I'd need to look up the genes, what blocks them, and whatnot, but that's fairly typical). Well, pathways never really shut down...but they do slow down to the point where they're mostly off.

This is very intereting to me :)
Is there a site which would give a good explanation of the 'expense' of N fixing from the air, vs. soil/material?
Including an explanation how this process occurs from the microbe's point of view?

Tons...I listed some below. The rundown below shows the use of 16 parts ATP (energy) to produce 1 mole of nitrogen, compared to 2 ATP used to produce 4 ATP when metabolizing glucose

A general idea. OK, but not a great resource:
http://www.whatislife.com/reader2/Metabolism/pathway/nitrogen.html

A little about the genes--particularly Regulation of Nitrogen Fixation in the below.
http://www.science.siu.edu/microbiology/micr425/425Notes/12-NitrFix.html

Thanks :)
This will be educational.
I appreciate it.