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Wisconsin Cranberry School 2006 proceedings

DeMoranville, Carolyn
Fertilizers: types, reactions, and responses,   pp. 44-48

Page 44

Carolyn DeMoranville
UMass Amherst Cranberry Station
East Wareham, MA
Fertilizer types
Fertilizer can be categorized in several ways based on physical and chemical
properties. Fertilizers may also be broken up into two broad groups -- soil applied or
foliar applied. As the terms imply, these categories define the target of the application:
either the material is meant to be placed on and incorporated into the soil or it is applied
to the plant surface. The nutrients in soil applied fertilizers are intended for uptake by the
plant roots while those in foliar applications enter the plant primarily through the leaves,
although some material may wash onto the soil and be taken up by the roots. Generally
we think of soil applied fertilizers as solids or granular materials. However, liquids may
also be used in soil applications. A good example of this is fish hydrolysate fertilizer
which is applied at relatively high rates (gallons per acre) and is intended to be washed
onto and into the soil and eventually taken up by plant roots.
Soil applied fertilizers are most commonly granular materials. The predominant
granulars used in cranberry production are soluble inorganic materials. These
manufactured materials may be ammoniated (chemically produced materials in which
each particle contains all of the fertilizer minerals and the nitrogen is in the ammonium
form) or blended (combinations of particles any one of which may contain only some of
the mineral content). Both types may have a variety of sizes of particles. This is not an
issue for the ammoniated fertilizer, since each particle is minerally complete. However,
in a blended fertilizer, as the particles sort by weight during application and are
distributed unequally, the various minerals in those particles are also unequally
distributed. Additionally, some blended fertilizers contain filler materials, often lime.
Many growers prefer ammoniated fertilizers since this assures the ammonium form of
nitrogen (preferred by cranberry plants), no carrier materials, and equal distribution of the
fertilizer mineral components. But, cost and availability are increasingly an issue for
ammoniated fertilizer.
In addition to untreated granular materials, the soil fertilizer category includes
organic fertilizers, liquids, and slow release materials. A primary difference among these
materials is the timeline from application until the mineral elements are available for
uptake by the roots. The minerals in soluble inorganic fertilizers are immediately
available if applied in a liquid formulation and quickly available if applied as granulars
(as soon as they dissolve into the soil water). The mineral elements in organic forms only
become available as the fertilizer breaks down in the soil, a process that is often mediated
by soil microorganisms. Slow release fertilizers are intentionally designed to be slowly
available. Depending on the product, the minerals are relcased to the soil water over a
period of one to several months. The release may depend on soil temperature, moisture
content, pH, coating thickness, and/or microbial activity. The mineral elements in all of
these products are used similarly by the plant once the minerals dissolve or are digested
and move into the soil solution. Mycorrhizal associations may also mediate direct uptake
on small organic molecules containing nitrogen (for example, amino acids).

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