Transcript Why Use Slow Release Fertilizers?

Slow Release = Controlled
Release
eg CRN = Controlled Release
Nitrogen
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

Uncoated Slow Release
Fertilizers
Urea formaldehyde (UF)
 Methylene urea (MU)
 Isobutylidene diurea (IBDU)
 Natural organics

Ureaform and Methylene Urea

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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
Products
Formolene 30-0-2
 FLUF 18-0-0
 Nitro 26 CRN 26-0-0
 Nitroform (Powder Blue, Blue Chip)
38-0-0
 CoRoN 28-0-0 (25% of total N is urea)

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
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
Mineralization
The decomposition of complex, Ncontaining organic molecules
and the resulting release of NH4
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.
N Release from UF, MU
Determined by Solubility Test
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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
How Much Dissolves at
o
25
100 grams
CRN in
C?
71 grams
out
Stir
100 - 71 = 29 grams (29%) CWSN
and 71 grams (71%) CWIN
How Much Dissolves at
71 grams
CRN in
o
100
C?
22 grams
out
Stir
Thus, in 100 g of CRN, there are 22 g HWIN
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
X 100%
CWIN
 Fertilizers with a higher AI have
increased N solubility, better slow-N
release characteristics.
 UF should have an AI of > 40%
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Summary
CWSN - 29%
 CWIN - 71%
 HWIN - 22%
 Activity Index = CWIN - HWIN
X 100%
CWIN
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= 71% - 22%
X 100% = 69%
71%
CRN Sources* Vary
Which Will Give Longer Response?
36%
HWIN
Formolene
38-0-0
71%
HWIN
18%
CWIN
11% urea
Nutralene
40-0-0
51%
CWIN
13% urea
*Both from
Agrevo
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
18-4.5=13.5% of the N is WSN.
What % of the N is WIN? 4.5/18=25%
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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
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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
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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?
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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
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Coated Slow Release Fertilizers
SCU, sulfur coated urea
 Polymer coated urea
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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
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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
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Polymer Coatings Remain Intact
Water
Solid
Urea*
Dissolved
Urea
Water
Dissolved
Urea
Dissolved
Urea
Complete
Release
*Or other nutrient
Sulfur Coatings Break Down
Sulfur
Coating
H2O
Solid
Urea
H2O
H2O
+S
Solid
Urea
H2O
Solid
Urea
H2O
Dissolved
Urea
SCU Contains Intact and Breached
Particles, Thin and Thick Coatings
IBDU Releases N Based on Solubility
H2O
Urea
Urease
NH4
Root
Release Depends on Granule Size
Small Granules Release Faster,
Shorter