# Quick question

#### stevenf

##### LawnSite Bronze Member
Researching and Learning about Fertilizer and have a simple question.
How do you know what ratio to use for lawns when it comes to N-P-K? I understand the soil test will show whats lacking in what areas, but how do you know to use 28-0-8 rather then 20-0-8?

#### Marcos

##### LawnSite Gold Member
Researching and Learning about Fertilizer and have a simple question.
How do you know what ratio to use for lawns when it comes to N-P-K? I understand the soil test will show whats lacking in what areas, but how do you know to use 28-0-8 rather then 20-0-8?
Those numbers represent % of each nutrient, so for example if you have a 50# bag of 28-0-8, there would be 14 pounds of nitrogen in that particular bag.
The rest is up to preference.
It all depends on whether you want to apply the N @t .5 # / 1000 sq ft, .75 # / 1000 sq ft, 1# / 1000 sq ft.....or at a rate even higher.

Most common around here is 1# / 1000 sq ft.
At 1 # / 1000 sq ft, you get 14,000 sq ft of coverage out of that 14 lbs of N.

At .75 # /1000 sq ft, you get 18,666 sq ft coverage out of 14 lb N.

See how it's done?

OP
S

#### stevenf

##### LawnSite Bronze Member
I do, Thanks! Do you guys go thru the process of sending off each soil sample or do you use the cheap on-the-shelf testers?

#### Marcos

##### LawnSite Gold Member
Researching and Learning about Fertilizer and have a simple question.
How do you know what ratio to use for lawns when it comes to N-P-K? I understand the soil test will show whats lacking in what areas, but how do you know to use 28-0-8 rather then 20-0-8?
To take this question to a different perspective level, a 50# bag of 28-0-8 has more value than a 50# bag of 20-0-8 because it covers 4000 more square feet using the 1 lb / sq ft spreading rate.
You wouldn't want to pay as much for 20-0-8 as you would for 28-0-8.

But a 3 numeral analysis can be deceiving!
There's this thing coating some of the nitrogen (urea) known as 'sulfur coated urea', or 'SCU' on the label. That adds value, too because it helps prevent dessication during dry, hot spells.
And the turf fertilizer could have micronutrients included like iron & manganese.
I could confuse you even more & get into weed & feeds and such.........!

#### Marcos

##### LawnSite Gold Member
I do, Thanks! Do you guys go thru the process of sending off each soil sample or do you use the cheap on-the-shelf testers?
The stuff on the shelf is almost all junk!
Send 'em off to a land grant university.
LSU in your state is one of those.
I suggest that you go to their website to see what procedures they have for sending in soil samples.
They may require that you send their pre-labelled soil sample packaging material so as to prevent contamination or whatever.

#### grassman177

##### LawnSite Fanatic
you need a good understanding of turfs needs as it goes through the season, and how weather will also dictate what you use, ie not using high N in a dry period.

#### DA Quality Lawn & YS

##### LawnSite Fanatic
Yep...understand the turfgrasses prevalent in your area, weather patterns, soil structure, etc. Then do the nutrient calculations like explained above and select products that meet your turf's needs.