1. Slow Release = Controlled Release eg CRN = Controlled Release Nitrogen

2. Why Use Slow Release Fertilizers?
More uniform growth response
No growth surge
Longer growth response
Less chance of burn
Less leaching of nitrate
Labor saving

3. Uncoated Slow Release Fertilizers
Urea formaldehyde (UF)
Methylene urea (MU)
Isobutylidene diurea (IBDU)
Natural organics

4. Ureaform and Methylene Urea
Very similar materials chemically
Mostly granular, some liquids
about 40% N, 70% WIN (28% N for liquids, all soluble)
Formed by reacting urea and formaldehyde = chains of alternating C and N
Main difference is chain length, and as a result, mineralization rate

5. Products Formolene 30-0-2 FLUF 18-0-0 Nitro 26 CRN 26-0-0
Nitroform (Powder Blue, Blue Chip)
CoRoN (25% of total N is urea)

6. Different Chain Lengths
Methylene Urea
N-C-N
N-C-N-C-N-C-N
N-C-N-C-N-C-N-C-N-C-N
N-C-N-C-N-C-N-C-N-C-N-C-N-C-N
Urea Formaldehyde
N-C-N
N-C-N-C-N-C-N-C-N-C-N
N-C-N-C-N-C-N-C-N-C-N-C-N-C-N
N-C-N-C-N-C-N-C-N-C-N-C-N-C-N-C-N-C-N
N-C-N-C-N-C-N-C-N-C-N-C-N-C-N-C-N-C-N-C-N-C-N

7. Ureaform and Methylene Urea
Designed to release N for 8-12 weeks
Contains unreacted urea, fast greening
Requires soil microbial activity
temperature sensitive, soil at 78o F is four times as active as soil at 42o F
moisture sensitive
Seasonal response

8. Mineralization
The decomposition of complex, N-containing organic molecules and the resulting release of NH4

9. MU, UF Chain Length Determines Solubility The longer the chain, the less soluble it is, and the slower it will be mineralized. Some may be so long that they are essentially insoluble, and won’t break down.

10. N Release from UF, MU Determined by Solubility Test
Water soluble vs Water insoluble fractions:
CWSN, cold water soluble N, is soluble at 25o C, is quickly available to the turf. Includes unreacted urea and short chain molecules
CWIN, cold water insoluble N. What remains insoluble at 25o C. Longer chain, N is released slower, over a period of several weeks
HWIN, N insoluble at 100o C. Longest chain, N released over months or years

11. How Much Dissolves at 25o C?
100 grams
CRN in
71 grams
out
Stir
= 29 grams (29%) CWSN
and 71 grams (71%) CWIN

12. How Much Dissolves at 100o C?
71 grams
CRN in
22 grams
out
Stir
Thus, in 100 g of CRN, there are 22 g HWIN

13. Activity Index, AI
Basically the fraction of CWIN that goes into solution in hot water. It estimates the slow-release value of the fertilizer
CWIN - HWIN CWIN
Fertilizers with a higher AI have increased N solubility, better slow-N release characteristics.
UF should have an AI of > 40%
X 100%

14. Summary CWSN - 29% CWIN - 71% HWIN - 22%
Activity Index = CWIN - HWIN CWIN = 71% - 22% %
X 100%
X 100% = 69%

15. CRN Sources* Vary Which Will Give Longer Response?
36%
HWIN
71%
HWIN
Formolene
38-0-0
Nutralene
40-0-0
51%
CWIN
18%
CWIN
*Both from
Agrevo
13% urea
11% urea

16. WSN vs WIN % WIN must be stated on label
Expressed as % of the product, not the nitrogen
Example: FLUF contains 18% N, and 4.5% WIN. This means that =13.5% of the N is WSN. What % of the N is WIN? 4.5/18=25%

17. IBDU Urea is reacted with isobutyraldehyde
Only a single chemical product is formed, not a bunch of different molecules. 31% N, 90% WIN
Different sized granules available
N release depends on solubility and hydrolysis (IBDU molecule reacts with water and breaks apart), releasing urea.
No free urea in IBDU, may need to add

18. IBDU start here Urea breaks down quickly to NH4
IBDU is relatively insoluble, so only small amounts are available at any one time
Release sensitive to soil moisture, temperature
Release also depends on granule size and contact with soil. Smaller granules release N faster than larger granules

19. Liquid Slow Release Fertilizers
Chemistry similar to UF, MU
Micro-suspension of MU (FLUF)
CoRoN, N-Sure; 28%N, 7% as urea and 21% as short chain MU or small ring structure.
Get quick and slow release
Foliar application?
Is slow release slow enough?

20. Liquid Slow Release Fertilizers
Easily handled, applied
Can be formulated with P and K
Some have short storage life
Require specialized delivery system
Volume of liquid used in application is not enough to move the material down into the root system - must irrigate in

21. Coated Slow Release Fertilizers
SCU, sulfur coated urea
Polymer coated urea

22. Sulfur Coated Urea Solid urea core, coated with sulfur and wax
30-38% N, depending on coating thickness
Coating is not always perfect, having cracks, thin spots, holes, etc.
Release determined by 7 day dissolution test; 25-35% are typical figures

23. Polymer Coated Urea
Solid urea or other nutrient core, coated with various polymers (“plastics”)
Coatings are tough, resist damage, thin
Coating chemistry affects membrane properties, release rate
Release is due to controlled diffusion, which is fairly constant over time
Release depends on coat thickness, chemistry, temperature, moisture

24. Polymer Coatings Remain Intact
Water
Solid
Urea*
Dissolved
Urea
Water
Dissolved
Urea
Complete
Release
Dissolved
Urea
*Or other nutrient

25. Sulfur Coatings Break Down
Solid
Urea
H2O
Solid
Urea
H2O
+ S
Solid
Urea
H2O
Dissolved
Urea

26. SCU Contains Intact and Breached Particles, Thin and Thick Coatings

27. IBDU Releases N Based on Solubility
H2O
Urea
Urease
NH4
Root

28. Release Depends on Granule Size

29. Small Granules Release Faster, Shorter