Table 26-2. Common sources of N in turfgrass fertilizers.

Source

  
 

Formula

Concentration 

  

Salt index per unit†

  

Acidifying effect†

  

Cold-water solubility§

  
 

Comments

N

  

P2O5

  

K2O

 

  

 

%

 

kg/L (lb/gal)

  

 

Ammonium nitrate

  
 
NH4NO3
 

33

  
 

0

  
 

0

  
 

3.2 H

  
 

62

  
 

1.74 (14.5)

  
 

Contains both ammonium ions that are adsorbed by soil colloids, and nitrate ions, that may be mobile in soils.
                               

Ammonium sulfate

  
 
(NH4)2SO4
 

21

  
 

0

  
 

0

  
 

3.3 H

  
 

110

  
 

0.68 (5.7)

  
 

Contains 24% S and has the greatest acidifying effect of the materials listed.
                               

Calcium nitrate

  
 
Ca(NO3)2
 

15

  
 

0

  
 

0

  
 

-

  
 

-

  
 

-

  
 

Ca-containing (19%) source of N; absorbs moisture rapidly.
                               

IBDU

(isobutylidene diurea)

  
 
[CO(NH2)2]2C4H8
 

31

  
 

0

  
 

0

  
 

0.2 L

  
 

- 

  
 

SS

  
 

Two urea molecules are linked by a C group resulting in a source of N dependent on hydrolysis for release.
                               

Milorganite

  
 

organic N complex
 

6

  
 

4

  
 

0

  
 

0.7 L

  
 

-

  
 

SS

  
 

N in this activated sewage sludge is released by microbial activity.
                               

Polymer (plastic-coated urea)

  
 

CO(NH2)2 + polymer
 

38

  
 

0

  
 

0

  
 

-

  
 

-

  
 

SR

  
 

N release is dependent on hydrolysis.
                               

Potassium nitrate

  
 
KNO3
 

13

  
 

0

  
 

44

  
 

5.3 H

  
 

(-23)

  
 

0.12 (1.0)

  
 

May slightly increase soil pH as it releases N rapidly.
                               

SCU (sulfur-coated urea)

  
 

CO(NH2)2 + S
 

32

  
 

0

  
 

0

  
 

0.7 L

  
 

-

  
 

SR 

  
 

Permeable molten S coating allows water to move slowly through the barrier, dissolving the enclosed urea; N release is dependent on microbial activity and hydrolysis.
                               

Urea

  
 
CO(NH2)2

 
 

45

  
 

0

  
 

0

  
 

1.7 M

  
 

71

  
 

0.74 (6.2)

  
 

This highly water-soluble N source contains the highest N concentration of any granular fertilizer; it may volatilize quickly if applied in hot weather.
                               

UF (urea formaldehyde or methylene ureas)

  
 
[CO(NH2)CH2]n

 

CO(NH2)2
 

38

  
 

0

  
 

0

  
 

0.3 L

  
 

- 

  
 

SS 

  
 

N is released from these various-size, "chain-like" polymers of urea as a result of soil microorganism activity.

† Expressed as the relative salinity of mineral salts per unit of nutrient compared to sodium nitrate (6.3). High = 2.6 or greater; moderate = 1.0 to 2.5; and low = less than 1.0.

‡ Units of CaCO3 required to neutralize 100 units of fertilizer (by weight).

§ SS = slowly soluble; SR = slow release.

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