I'm curious about this as well. I recently saw some 40-0-0 (or was it 43? whatever... it was up there), and it specifically said on the bag "not for lawn use". I chickened out and bought a bag of ~30-2-8 (or something in that range) with a significant portion of the N being slow-release type. That was a week or three ago, and the lawn has greened nicely.

But as my recent soil test indicated that I'm high in P & K, I'm still looking for the best way to apply N in spring and next fall.

I'm waiting for an answer on calculating my fertilizer application as well.

Couple things I have realized at this point. Different types of grasses require different amounts of nitrogen. My TTTF requires about 2.5 lbs of N per 1000 sqft yearly.

This is where I found my info to work with. http://www.lawnfertilizers.com/info/lawnrates.html

So if I plan to to fertilize 5000 sqft of TTTF once for the year with 46-0-0 it goes like this.

yearly N requirements / N percentage on bag = amount of N for 1000 sqft.

2.5/.46 = 5.43 lbs for 1000 sqft so 5.5lbs or 27lbs for the entire 5000 sqft yard.

My only problem now is figuring out how to set my broadcast spreader.

My tactic with urea is to set my spreader tight so that I have to make multiple passes in perpendicular patterns, which helps eliminate dropping too much in any one area. The spreader settings are just a guideline, IMO.

The hopper on my spreader is big, and urea alone is too small of an amount to go through it effectively, so I use a carrier.

I mix it with a bag of Milorganite to act as a carrier. When I do that I apply less urea so I don't exceed 1 # N per 1000 square feet. I've also used soybean meal as a carrier.

We calibrated spreaders in my turfgrass class. No two are really the same. Those settings are approximate. To really get it right is a pain, but you only need to do it once every season or two.

You need a scale and a container large enough to hold about 20 pounds of fertilizer. Remember, the distribution of the fertilizer changes as the level goes down. So it's always best to have it full to half full.

Load fertilizer in the container, put it on the scale and weigh it.(Make sure to weigh the container first and account for that.)

Pour that fertilizer into the hopper of the spreader.

Mark off an area on a driveway, a specific number of square feet. You will be sweeping it up afterwards, so don't make it too big. I would do about a 20'x20' area, or 400 square feet.

We're talking about a broadcast spreader here, right?

Set the spreader at a setting a bit lower than you normally use. If you use it at 7, set it at 3 or 4. That's because urea has at least twice the nitrogen in other fertilizers.

Begin walking at your normal pace from OUTSIDE of the market area. This is important. Too often, people squeeze the trigger on the spreader just as they start walking, and you can see that in the lawn a week later after a rain. Too much fertilizer gets deposited at the beginning of each "stroke".

Walk back and forth over the marked driveway, overlapping as you normally would.

Now empty the remaining fertilizer from the spreader into the container and weigh it again. If you had 20# of fertilizer to begin with and now you have 19#, you have just put down one pound of the granules, or about 1/2 pound of nitrogen.

A half pound of nitrogen over a 400 square foot area at that setting and walking at that pace. Extrapolate that to 1000 sq. feet:

.5 x (1000/400) = 1.25

You have applied the equivalent of 1.25 pounds of nitrogen per 1000 sq. ft. in your test -- and that is a good rate of application for a fall feeding.

Adjust your spreader settings up or down if needed, and do the test again. You don't have to sweep it up between tests because you're not weighing what you spread; you're weighing what's left.

If you are going to mix it with a carrier in your spreader, I have no clue how you'd calibrate, but this actually sounds more complicated than it is. Sweeping up the granules from your test is the worst part.

Thanks, Mulch Mama, sorry for late reply, crazy around here.
I need to calibrate my spreader, never done that. I did find a fairly cheap source of urea. Howard Johnson has 26-0-3, 26% urea non coated for 8.99 for 5K square foot bag. They also make Hummerts.

FWIW, I apply fert/seed/etc. based on the size of my lot. I know I'm treating (say) 20k sq ft, and if I want 1# per 1k sq ft, then I know I'm spreading 20lbs over the yard. I set the spreader (mine is tow-behind broadcast) for small--usually "3" on mine for small granular--and usually make about 4 passes around the yard by the time I used it all. Hasn't failed me yet.