Fertilisers, controlled release

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). 

A goal of controlled release fertiliser research since the 1940s has been the development of a product that deUvers its nutrients at a rate matching the demand rate of the plant to which it is appHed. Such a fertiliser would represent the ultimate in use efficiency agronomic performance, ie, crop yield, quahty, and appearance agronomic safety and labor savings, ie, reduced appHcation frequency. It also would minimise potential losses to the environment. 

J. T. Hays, "Controlled Release Nitrogen Fertilisers," ManualFert. Proc. (1987). 

S. P. Landels, M. M. Smart,. Bakker, and. Shimosato, "Controlled Release Fertilisers and Nitrification Inhibitors," Chemical Economics Handbook, SRI International, Menlo Park, Calif., 1989. 

Photo-biodegradable polyethylene using the above system was developed commercially for use in agriculture by D. Gilead of Plastopil Hazorea in Israel in collaboration with the author and is now widely used as Plastor in mulching films in Europe and Plastigone in the USA. It is also used in polypropylene baler twines as Cleanfields by AMBRACO in the USA, and in controlled release fertilisers as Nutri-cote by Chisso-Asahi Fertilizer Company in Japan. The biodegradation mechanism will be discussed below. 

Degradable materials also offer new perspectives in agriculture (e.g., the controlled release of fertilisers, insecticides and herbicides)... 

Trenkel ME (1997) Improving Fertiliser Use Efficiency -Controlled Release Stabilized Fertilisers in Agriculture. Paris IFA. 

Controlled-release fertilisers can be made by coating the granules with paraffin wax or urea formaldehyde. This limits the access of water and reduces the rate of solubilisation [34]. Slow-release fertilisers based on mixed cation polyphosphates have been patented [35]. 

P. PoweU, Controlled Release Fertilisers, Noyes Data Corp., NJ, 1968. 

Besides mulch films, other potential agricultural applications for biodegradable polymers include devices for the controlled release of agrochemicals (such as fertilisers, soil applied active ingredients, insect pheromones and so on), disposable articles such as plant pots, composting containers and bags, envelopes of ensilage, seed trays and so on. 

Matrix for controlled release systems (slow release of fertilisers, agrochemical, pharmaceuticals, food additives)... 

An important development in Japan is the use of biodegradable polyolefins in controlled release of fertilisers by encapsulation [30]. This results in controlled release in leaching environments over an extended period of time compared with direct application. This in turn effectively reduces the pollution of streams and the eutrophication of lakes and watercourses. Controlled release of pesticides by encapsulation has also considerable potential by matching the application time to the life cycle of the pest [11]. 

Controlled release systems for fertilisers, pesticides and seed sowing... 

Edible films/coatings Matrix for controlled release systems Super-absorbents Films, non woven tissues, etc. Barrier internal layers, surface coatings, active superficial layers Soluble sachets for instant dry/soft agrochemicals or additives formulations, etc. Slow release of fertilisers, agrochemicals, additives, etc. Material for plant planting in desert, etc. 

The large amount of fluorine values released from phosphate rock in the manufacture of fertilisers (qv) gives a strong impetus to develop fluorine chemicals production from this source (see Phosphoric acid and the phosphates). Additional incentive comes from the need to control the emission of fluorine-containing gases. Most of the fluorine values are scmbbed out as fluorosiUcic acid, H2SiPg, which has limited useflilness. A procedure to convert fluorosihcic acid to calcium fluoride is available (61). 

---