EQUUS - - Special Report -

A fer­til­izer is any ma­te­rial ap­plied to the soil that sup­plies nu­tri­ents nec­es­sary to plant growth. In ad­di­tion, some fer­til­iz­ers are ap­plied di­rectly to plants. Th­ese prod­ucts fall into two gen­eral cat­e­gories: syn­thetic and or­ganic.

Syn­thetic fer­til­iz­ers are gen­er­ally in­or­ganic (mean­ing they do not con­tain car­bon) and are de­rived from min­eral salts and other syn­thetic chem­i­cals. The three most im­por­tant in­gre­di­ents they pro­vide, called macronu­tri­ents, are ni­tro­gen (N), phos­pho­rus (P) and potas­sium (K).

All syn­thetic fer­til­iz­ers are la­beled with three num­bers, called the fer­til­izer grade, which in­di­cate the rel­a­tive per­cent­age of each macronu­tri­ent. For ex­am­ple, a bag la­beled as “12-12-12” con­tains 12 per­cent of each macronu­tri­ent, in the form of ni­tro­gen com­pounds, phos­phate (P O ) and potash (K O). Fer­til­iz­ers are for­mu­lated in dif­fer­ent bal­ances for spe­cific us­ages: Ni­tro­gen pro­motes leaf growth and is rec­om­mended for green lawns; phos­pho­rus pro­motes the growth of roots, flow­ers, seeds and fruit; potas­sium pro­motes the growth of strong stems as well as flow­ers and fruits. Syn­thetic fer­til­iz­ers may also con­tain sec­ondary nu­tri­ents, such as cal­cium, mag­ne­sium and sul­fur, as well as other trace min­er­als.

The chem­i­cal com­pounds in syn­thetic fer­til­iz­ers are wa­ter sol­u­ble, which means they break down eas­ily into their com­po­nent el­e­ments and can be ab­sorbed into the roots of the plant al­most im­me­di­ately. Yet only a frac­tion of ni­tro­gen-based fer­til­izer is used by the plant—the down­side of syn­thetic fer­til­izer is that the chem­i­cals not drawn im­me­di­ately into the plant are read­ily washed away in runoff. High con­cen­tra­tions of ni­tro­gen, phos­pho­rus and potas­sium in runoff col­lects in wa­ter­ways with ad­verse ef­fects. For ex­am­ple, el­e­vated phos­phate lev­els en­cour­age the growth of cyanobac­te­ria in streams and lakes. Th­ese or­gan­isms can pro­duce harm­ful tox­ins that can en­ter the food chain, even­tu­ally af­fect­ing the an­i­mals and peo­ple who con­sume them. Ni­tro­gen runoff de­pletes oxy­gen in the oceans and creates “dead zones” at the mouths of rivers.

Or­ganic fer­til­iz­ers (which con­tain car­bon) are de­rived from plant or an­i­mal sources, such as peat, ma­nures and com­posted wastes. Th­ese prod­ucts con­tain all the same macro-, mi­cro- and trace nu­tri­ents as the syn­thetic fer­til­iz­ers, but the el­e­ments are bound into more com­plex or­ganic com­pounds that do not dis­solve as read­ily. This means that it takes longer for the nu­tri­ents to be ab­sorbed into the plant roots, but it also means that more of the nutri­tion re­mains in the soil with less runoff into the wa­ter­ways, and the ef­fects of one ap­pli­ca­tion last longer. Or­ganic fer­til­iz­ers

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