Turf and Landscape - Slow Release Fertilizers: IBDU

This is the sixth in a series on slow release fertilizers for turf and landscapes. This post contains information on IBDU.

Isobutylidene Diurea (IBDU). Unlike the condensation of urea and formaldehyde, which forms a distribution of different UF polymer chain lengths, the reaction of urea with isobutyraldehyde forms a single oligomer. Although similar in chemical structure to methylene diurea (MDU), its physical properties are quite different.

Isobutylidene diurea (IBDU) is a non-hygroscopic white crystalline solid available in fine (0.5-1.0mm), coarse (.7-2.5mm) and chunk (2.0-3.0mm) particle sizes. The product contains a minimum of 30% N with 90% of the N in water-insoluble form. The typical commercialized product contains 31% N.

Nitrogen from IBDU becomes available to plants through hydrolysis. In the presence of water, the compound will hydrolyze to urea and isobutyraldehyde. The rate of hydrolysis is accelerated by low pH and high temperature. Unlike UF polymers that rely on soil microbialpopulations to make the N available, IBDU is primarily dependent on water as the critical element in N availability. Its low water solubility controls the transport of the product into the soil solution. Once in the soil solution, the rate of hydrolysis is affected by both soil pH and temperature. The rate of dissolution is affected by particle size and amount of water available. The powder form is mineralized much more rapidly than large particles under the same field conditions. Because the release is not microbe-dependent, N can become available at low temperatures; thus IBDU is one of the preferred products for cool-season application. This attribute and the dependency on moisture are the distinguishing characteristics of IBDU.

IBDU is used on turfgrasses, in commercial nurseries, and in landscaping, forestry, and speciality agriculture. Although some fine-size IBDU (31-0-0) is used for direct application to golf course greens, most of the turfgrass use is in the form of blended fertilizers, often in combination with other types of controlled release fertilizers.

Reprinted from Selected Fertilizers Used in Turfgrass Fertilization by J. B. Sartain and J. K. Kruse, University of Florida Extension.

Turf and Landscape - Slow Release Fertilizers: Ureaformaldehyde Reaction Products

This is the fifth in a series on slow release fertilizers for turf and landscapes. This post contains information on ureaformaldehyde reaction products.

Ureaformaldehyde Reaction Products, also known as Nitroform, Ureaform, UF, Methylene Urea, Blue Chip, Nutralene or Methex, represent one of the oldest controlled-release nitrogen technologies, having been first produced in 1936 and commercialized in 1955.

Ureaform is the oldest class of UF reaction products. Ureaform is sparingly soluble. It contains at least 35% total nitrogen with at least 60% of the total nitrogen as cold water-insoluble nitrogen (CWIN). Further, it must have an Activity Index (AI), i.e., the percent of CWIN that is soluble in hot (100°C) water, of not less than 40%. Ureaform is composed largely of longer-chained UF polymers, primarily tetramethylene pentaurea (TMPU) and longer. Unreacted urea nitrogen content is usually less than 15% of the total nitrogen. This product is commonly marketed under the following names: Nitroform, UF, Blue Chip, Powder Blue or Methex.

Methylene Ureas are a class of sparingly soluble products which evolved during the 1960s and 1970s. These products contain predominantly intermediate chain-length polymers, primarily trimethylene tetraurea (TMTU) and tetramethylene pentaurea (TMPU). The total nitrogen content of these polymers is 39 to 40%, with between 25 and 60% of the nitrogen present as CWIN. The unreacted urea content generally is in the range of 15 to 30% of the total nitrogen. This product is typically marketed under the trade name Nutralene.

UF solutions are clear water solutions. They contain only very low molecular-weight, water soluble UF reaction products plus unreacted urea. Various combinations of the UF solutions are produced. They contain a maximum of 55% unreacted urea with the remainder as one or more of methylolureas, methylolurea ethers, MDU, DMTU, or triazone. One of the commercial names under which this product is currently marketed as CoRon.

Agronomic Properties and Nutrient Release Mechanism of UF Products:

The conversion of UF reaction products to plant available N is a multistep process, involving dissolution and microbial decompositon. Once in the soil solution, UF reaction products are converted to plant available N through either microbial decomposition or hydrolysis. Microbial decomposition is the primary mechanism of N release with the carbon in the methylene urea polymers providing the site for microbial activity. Environmental factors such as soil temperature, moisture, pH and aeration affect the rate of N release.

The rate of N release from UF reaction products is directly affected by polymer chain length. The longer the methylene urea polymer, the longer it takes for the N to become available. For ureaform and methylene urea products, the rate of mineralization is reflected by the cold water insoluble N (CWIN) content and its Activity Index. It is questionable if the very long methylene urea polymers are effectively used by the plant.

Reprinted from Selected Fertilizers Used in Turfgrass Fertilization by J. B. Sartain and J. K. Kruse, University of Florida Extension.