No. To make the math easy, let's assume those are 100 lb bags. You put down 20 lbs N, 23 lbs P, and 12 lbs K. The problem is that you put down 200 lbs. So, the percentages would be 10-11.5-6.

Putting down one bag of 20-3-12 and one bag of 0-20-0 is not the same as putting down one bag of 20-23-12. In addition, there are variables to consider such as the intended rate of application, and the amount of area to be treated. The source of nutrients in each bag is also a consideration. Simply stated, they are not even close to being the same. But this is a very good question. Thanks for asking!

As long as the two bags are spread over the same area as the single bag then the lbs of N-P-K are the same in both cases. There is ~50 lbs of other stuff in the two bag scenario, but NPK is the same.

-Mike

Mike: You are correct. The total pounds of N-P-K are the same in both cases, as long as the first two bags are spread over the same area as the single bag. I did my calculations as 50 lb. bags. Assuming there are no other nutrients included (secondary or micro), the rest of the material is just filler.

Wait a minute. If I apply 100 pounds of 20-3-12 and then apply 100 pounds more of 0-20-0, are you saying I suddenly only have 10-11.5-6 on the ground? How can I end up with less than 20 pounds of N by adding a different product?

Here are some common fertilizer ingredients.
polymer coated urea
ammonium sulfate
diammonium phosphate
sulfate of potash
magnesia
muriate of potash
sodium borate
copper sulfate
copper oxide
ferrous sulfate
ferric oxide
manganese sulfate
manganese oxide
molybdic oxide
zinc sulfate
zinc oxide

In my opinion the word, filler, is over reaching. Any atoms which are not N, P, or K are considered filler regardless of what they are. Ammonium sulfate, for example, has the nutritional ammonia molecule but it is carried to the party as a sulfate. Thus the mass of the sulfate ion is considered filler. Everything that is in the bag is accounted for by the guaranteed analysis on the label.

************* UPDATE **************
Here is the delema. I had a soil analysis and it reccomends I put down 50lbs of 20-3-12 and 50lbs of 0-20-0. The 0-20-0 is very expensive and I am trying to find out if I can put down somthing close to a 20-23-12 to save money.

No, dchall, you suddenly have two bags of 10-11.5-6 on the ground. If you blended the two bags before applying, that's what you'd have.

mistermower, for what you're trying to do, it will work. It's the engineer in me who is insisting on getting the percentages correct. Your analysis is telling you that you need 10 lbs N, 11.5 lbs P, and 6 lbs K. You can mix and match fertilizers however you want as long as you get those amounts of NPK on the soil.

Lol @ dchall: Spoken like a true aerospace engineer. As I stated in my post, my calculations are based on 50 lb. bags. My numbers are correct. You'll need to research and learn more about the manufacturing and packaging of synthetic fertilizer products to understand their reasons for using a filler to complete the weight of the bag. The filler carries no nutrient value. It's just another good reason why your promotion of organic feeding of turf is highly justified.

@ mistermower: Most every soil test result I have ever seen recommends applying fertilizer in lbs./Acre or lbs./1000 sq.ft. Are you sure it states to apply only 50 lbs. of each of those products? And since you are in zone 5, I will assume this is fertilizer you will be applying later instead of now? Fertilizing cool season grasses at this time of the year is not recommended.

Applying 20-3-12 and 0-20-0 provides exactly the same nutrient value as applying 20-23-12. The only difference is the amount of other "stuff" in the bag.

"You'll need to research and learn more about the manufacturing and packaging of synthetic fertilizer products to understand their reasons for using a filler to complete the weight of the bag."

It is entirely inaccurate to say that a bag of 46-0-0 has "filler." It is 100% urea. (NH2)2CO. Nitrogen weighs 14 and there are 2 of them, so 28. The whole molecule weighs 60. (28+4+12+16) The percentage of nitrogen by weight is therefore 28/60 = 46%. No "filler" there. Basically, the only "filler" used in most lawn fertilizers is binding agents that make some "slow release." All the other weight not listed in the N-P-K ratio is the other elements required to bind those nutrients into a solid. After all, Nitrogen is gas and would just float away on its own. It is a physical impossibility to apply 100-0-0 fertilize to a lawn.

It is entirely inaccurate to say that a bag of 46-0-0 has "filler."

If a 50 lb. bag of 46-0-0 contains 23 lbs. of Nitrogen, then what does the remaining 27 pounds consist of?

"************* UPDATE **************
Here is the delema. I had a soil analysis and it reccomends I put down 50lbs of 20-3-12 and 50lbs of 0-20-0. The 0-20-0 is very expensive and I am trying to find out if I can put down somthing close to a 20-23-12 to save money."

Get some Lesco starter fertilizer, Home Depot usually carries it. It is 18-24-12. If your HD doesn't have it, then obviously Lesco will.

Maybe I am using the wrong terminology here. Would my point make more sense if I used the term "carrier" instead of "filler". All the fertilizer people I have dealt with over the years have always used the term "filler" to describe the material in the bag that carries the nutrients.

Bill, I am quite familiar with the fact that 46-0-0 is 100% urea. No need for the chemistry lesson. I have been familiar with the periodic table and atomic weights for many years.

Ah yes, tiemco. Someone who knows how to stay on the discussion topic. :) Lol.

Nearandwest, I thought Bill and Dchall explained the whole filler issue very well but perhaps you didn't grasp it. If you want to define anything that isn't N, P, or K as filler, then yes the other stuff in the bag is filler, but in Bill's Urea example you will see that there is no way around that. As elements these three are all basically impossible to add to your lawn. Nitrogen is a gas, so it needs to be added in an ionic or molecular compound to be usable by grass. Phosphorus is a highly reactive element that is usually stored in water as it has a tendency to combust in the presence of oxygen. Potassium is a highly reactive metal that usually ignites when it gets wet. You can see how both of those need to be added in compound form, and in this way you will never be able to get a bag of any fertilizer with a 100 as one of the three numbers.

Lol.. first of all, I agree with the content of the posts by dchall, Bill, and tiemco. The statements are factual and correct. Again, I believe I used a term that was not contextually correct. However, it is a term that is widely used by those individuals who sell fertilizer to Golf Course Superintendents. The term "filler" is used by commercial fertilizer sales people to describe the bulk material in a bag of fertilizer that is used as the carrier for the nutrients contained in the bag. I, too, use the term "filler" to describe the "carrier" of nutrients in a bag of dry fertlizer. Golf Course Superintendents in the Carolinas have been using that slang term since the days of Palmer Maples, Whitey Wright, Frank Stump and Landon Miller.

If you search the organic or soils forum you'll find a discussion much like this. One of the writers claimed that she had spoken with her chemistry teacher and, since nitrogen was a gas, it had no weight in the bag. Furthermore, there could not be that much gas in the bag because the bag would obviously explode. It was a very disturbing discussion. That topic has probably fallen off the bottom of the list by now.

lol. I wish I'd seen that thread when it was active. Maybe the chemistry teacher could explain why water is so heavy when it's made up of two gasses.