Controlled-Release Fertilizers

Coated fertilizers - [CONTROLLED RELEASE TECHNOLOGY - AGRICULTURAL] (Vol 7)... 

Calcium nitrate fertilizer, controlled-release Oxamide fertilizer, soluble Potassium phosphate fertilizer, specialty Potassium tripolyphosphate fertilizer, trace element Cobalt fiber... 

Slow-Release Fertilizers. Products containing urea—formaldehyde are used to manufacture slow-release fertilisers. These products can be either soHds, Hquid concentrates, orHquid solutions. This market consumes almost 6% of the formaldehyde produced (115) (see Controlled release TECHNOLOGY, AGRICULTURAL). 

Fig. 1. United States agricultural crop markets for manufactured controlled release fertilizers, 1990. (a) Total percentage ( 14 million) of market value by crop and (b) total percentage (6,800 t) of consumption by product type. IBDU is isobutyUdene diurea PCF, polymer-coated fertilizer UF,...

Numerous technologies have been developed with varying degrees of success to maximize the various benefits of controlled release. Heightened attention to environmental concerns has prompted increased activities worldwide in the development and commercialization of controlled release fertilizers. 

Coated fertilizers achieve controlled release by coating a soluble fertilizer core (substrate) with a water-insoluble barrier which limits the access of water to the fertilizer and thus limits its dissolution rate. 

Urea—Formaldehyde Reaction Products. Urea—formaldehyde (UF) reaction products represent one of the older controlled release nitrogen technologies. An early disclosure of the reaction products of urea [57-13-6] and formaldehyde [50-00-0] was made in 1936 (1) (Amino resins and plastics). In 1948, the USDA reported that urea (qv) and formaldehyde (qv) could react to produce a controlled release fertilizer at urea to formaldehyde mole ratios (UF ratio) greater than one (2). 

Oxamide is produced commercially by Ube Industries, Ltd. (Japan) and a pilot process is being operated by Enichem (Italy). It is not produced domestically as a commercial fertilizer, although it was the subject of much research and development activity by the Tennessee Valley Authority s (TVA) National Fertilizer Research and Development Center. It is made in small quantities for industrial use by AUied Chemical, Hummel Chemical Co., and United Guardian, Inc. Oxamide has appHcation as a controlled release nitrogen source for the turf and specialty agricultural markets. 

Cyclopentadiene oligomers have been formed by vapor deposition of CPD on kaolin to afford a sorbant for removal of oil from water (71). They are also employed as coatings for controlling release rates of fertilizers (72). Thermal addition of sulfur to a mixture of DCPD and CPD oligomers has led to a number of beneficial appHcations such as waste water oil adsorbant powdery foams (73), plasticized backing for carpets and artificial turfs (74), and in modified sulfur cements for encapsulating low-level radioactive wastes (75). 

R. A., Comparative evaluation of the safety and contraceptive effectiveness of 65 mg and 100 mg of 90-day norethindrone microspheres for controlled release steroid contraception Phase II study, Fertil. Steril., 51. 803, 1989. 

H.B. Croxatto, S. Diaz, R. Vera, M. Etchart and P. Atria, Fertility Control in Women with a Progestagen Released in Microquantities from Subcutaneous Capsules, Am. J. Obstet. Gynecol. 105, 1135 (1969). 

Polymers are becoming increasingly important in the area of controlled release, for drugs, flavors, fragrances, fertilizers, and pesticides, to name a few. Often the drug is suspended in a biodegradable polymer that is slowly degraded and metabolized (in other words, is a renewable resource). 

Controlled-Release Phosphate Fertilizers. Several controlled-release phosphates have been produced commercially. Important among them are ground phosphate rock, basic slag, and fused calcium magnesium phosphate. These products have been discussed earlier. 

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