I'm new to this list and forum forum but not to the topic on other lists. Also, whether it matters or not, I'm not a lawn pro; but I have been around organic for a while and learned quite a bit that may help some of y'all to understand why they work. Unfortunately I can't be brief on anything, but I'll try, so stand by.
As has been said here, with organic management you feed the soil and not the plants directly. I don't want to demean anyone's education, but if you haven't been in school in the past year or so, some things have changed in the world of soil science and chemistry. I believe the discoveries explain the mystery of organic fertilizer.
In the recent past it had been thought that there were perhaps tens or maybe hundreds of different kinds of microbes in the soil. This reasoning was due to the ability to grow these microbes (fungi and bacteria) in a laboratory petri dish. More recently with DNA analysis, they have discovered there are 25,000 different microbial species in farm and garden soil and up to 45,000 species in forests. What this discovery means is that the ability of the soil microbes to manufacture nearly any organic soil food or disease is nearly unlimited. Obviously there is a limit but for us to comprehend the number of combinations and permutations is nearly unlimited. Whereas when we thought there were only a few or few hundred microbes, we could get a handle on that - and the handle we had did not indicate that there was much of any value in those microbes. Now we know that the microbes have developed a symbiotic relationship with plants that goes to great care to ensure the survival of both plants and microbes.
We also know that microbes need both sugar and protein to live. That's not news. But what is news is that the huge diversity of microbes have the ability to manufacture exactly the proper plant food, deliver it exactly at the proper time, and in the proper amount, all with very little waste. All we have to do is feed the microbes that sugar and protein.
Normally plants get their first level of sugar directly from the plants. Plants manufacture plenty of sugar through photosynthesis. The excess is made available to the microbes that might live inside the plants, on the leaf surfaces, attached to the roots, or in the root zone. Protein historically has been provided by dead animals or plants laying on the surface of the soil. First level microbes provide a decaying or rotting service that feeds protein to all the rest of the soil microbes. It is all done from the surface of the soil. As species after species "exudes" wastes and themselves die, the proteins are exchanged from one species to the next all the way through 25,000 to 45,000 different species. Somewhere along the food chain (now called the soil food web), plant food, medicines, enzymes, growth regulating hormones, and everything the plants need are made available.
That's the basics.
Someone mentioned that compost is not a very good fertilizer. That's exactly correct. Compost is a better source of microbes for soils that need a quick dose of living organic matter. These soils included soils that have been hit with a fungicide, pesticide, or herbicide. It also includes soils that have been underwater for a few days such that many of the formerly living microbes have been killed. The good microbes also need air to survive. So the time to apply compost (in thin layers of 1/3 inch) is after a chemical spill or a flood. But as someone else said, the soil has amazing recovery ability and will restore the species in time. The compost just speeds up that process for your clients. Plus compost should be about the most expensive thing you ever apply in an organic program. It should be a high profit item for y'all, but just not needed that much. Our local compost guru claims to have only used compost twice in his 30 years of manufacturing and selling it - and he says the second time he didn't really need it. That speaks volumes to me.
Someone mentioned that you have to use a lot of organic fertilizer to get any value. If you're measuring pounds of materials, that is also a correct statement. Organic fertilizers are heavier than synthetics. A normal application rate for organic fertilizer is 10-20 pounds per 1,000 square feet. So a 50 pound bag covers somewhere between 5,000 and 2,500 square feet. With synthetics the same coverage would weigh about 10 pounds. However with synthetics you have zero protein. The nitrogen is in the form ready to feed the plants. So the soil microbes get no benefit.
For those of you concerned about the cost, it is not more expensive to apply organic materials. If you'll look at the ingredients of organic fertilizers, you'll see a list of protein sources. They include corn meal, corn gluten meal, alfalfa meal, soy bean meal, canola meal, milo, feather meal, cottonseed meal, and most other materials commonly found in animal or dog food. You can get that stuff at the feed store in 50 pound bags for about $5. Buy in huge bulk and you can find it for half of that or less. Compare that price to the same materials sold in commercially marked bags in the same stores for $30 for 30 pounds. Maybe you professionals cannot apply a product marked "FEED" on a lawn, but we homeowners sure can. I use whole ground corn meal.
If you want to test this yourself, dump a half a bowl of dog food on a turf somewhere where the grass is not otherwise fertilized. Wet it down so it melts into the soil and the squirrels don't run away with it. Then come back in a month and see what happened. Dog food is too expensive in bulk, plus it has sodium in it. Don't need that. Shoot, even used coffee grounds make a great fertilizer. Lots of low budget organic gardeners get free coffee grounds from Starbucks and other savvy coffee shops.
Someone mentioned Milorganite. Several years ago they sent out a bad batch or two that had some heavy metals in it. Now they test the biosolids before the Milorganite folks get it to ensure there are no metals. Then the sludge is incinerated at over 1,000 degrees to turn it into the near ceramic quality you see in the bag. It is pretty sterile. And I don't like the smell either.
Someone else mentioned manure smelling bad. Well, duh! Manure is supposed to be composted so it doesn't smell bad. After the microbes get through with it, compost smells fresh like a forest floor. It smells incredible! But uncomposted manure has NO place in organic gardening (IMHO).
Someone mentioned organic fertilizers contaminating runoff waters. If it is a proper protein based fertilizer, it does not run off or contaminate anything. Manures might, but they have a different role when properly used. They are for growing microbes, not direct fertilizing.
Here's a list of things an organic program can do that no chemical can do. The beneficial microbes in the soil do the following.
1. Decompose plant residues and manure to humus.
2. Retain nutrients in humus.
3. Combine nitrogen and carbon to prevent nutrient loss.
4. Suppress disease.
5. Produce plant growth regulators.
6. Develop soil structure, tilth, and water penetration/retention.
7. Clean up chemical residues.
8. Shift soil pH to neutral and keep it there.
9. Search out and retrieve nutrients in distant parts of the soil.
10. Decompose thatch and keep it from returning.
11. Control nitrogen supply to the plants according to need.
12. Pull minerals out of inorganic soil components for plants.
13. Provide the exact chemical nutrients to the plant that the plant has evolved with rather than man's cheapest chemical approximation.
14. Provide exactly the required quantity of nutrients that the plant needs.
15. Provide the nutrients at exactly the right time that the plant needs them.
No chemical can do any of that. To be fair, no single microbe can do all of that either. In fact, it could be that it takes 100 different species, one working right after the other, to do any one item in the above list - sort of like a microbiological assembly line. But at least it's real easy to get all the right microbes. The biology of the soil is very complicated.
At the same time, many chemicals inhibit the microbe's natural abilities to do these things. Herbicides, fungicides, and pesticides are all designed to kill various biological life. As a byproduct, they often kill off the beneficial microbes that are doing 1 through 15 above. Any break in the assembly line can interrupt the process, damage the mini ecosystem, and lessen the benefit of the organic methods.
Organic fertilizers can give every bit as successful looking a lawn as a synthetically fertilized one. And I enjoy letting my 5-year old barefoot daughter help daddy through out the corn meal.