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 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, N-containing 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 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 25o C? 100 grams CRN in 71 grams out Stir 100 - 71 = 29 grams (29%) CWSN and 71 grams (71%) CWIN

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

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%

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

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

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%

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

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

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?

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

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

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

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

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

Sulfur Coatings Break Down Solid Urea H2O Solid Urea H2O + S 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