Environmental Engineering Reference
In-Depth Information
slowly, but if very slow release is desired, coarse grades should be
applied. Several other types of nitrogen sources are the subjects of on-
going research. Fertilizer manufacturers continually discover improved
sources and bring them to market. Modern turf-grass management with
complex fertilization programmes often uses a combination of several
nitrogen sources. Manufacturers serve the needs of the turf industry by
providing fertilizers that contain various nutrients in both quick-release
and slow-release forms.
Phosphorus carriers
Far fewer sources of phosphorus than of nitrogen are used in turf-grass
situations. Phosphorus is usually applied to the soil as superphosphate
(20% P 2 O 5 ) or triple superphosphate (46% P 2 O 5 ). Two other water-sol-
uble ammonium phosphate sources, known as MAP (monoammonium
phosphate 12-61-0) and DAP (diammonium phosphate 18-46-0), supply
both nitrogen and phosphorus. In addition to easily soluble forms of
phosphorus, sulphur-coated or polymer-coated fertilizers are available
in some countries, but their importance is marginal.
Potassium carriers
Two sources of potassium are especially popular, potassium chloride
(60% K 2 O) and potassium sulphate (50% K 2 O). Potassium sulphate is
usually a little more expensive but is less likely to burn foliage. A third
popular source is potassium nitrate (13-0-44), which supplies both potas-
sium and nitrogen. Slow-release potassium is available in the form of
sulphur- or polymer-coated products.
Iron carriers
Several sources of iron are applied to the soil or to foliage. On acidic soils
(pH below 6.5), ferrous sulphate (20% Fe) or ferrous ammonium sulphate
(14% Fe) are used most often. These forms are insoluble at higher pH and
under those conditions should be replaced with a so-called chelated form
of iron. A chelator is a large organic molecule that holds iron bound to
its carbon ring structure. Chemical binding forces are relatively weak
but strong enough to prevent iron from rapidly changing into forms that
are unavailable to plants. Fertilizers made up of iron chelate contain
7-10% Fe.
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