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| Compound fertilizers contain several nutrients in each granule |
Production
Compound fertilizers are made using basic fertilizer materials, such as
NH3, ammonium
phosphate, urea, S, and K salts. There are many methods used for making these
fertilizers, with the specific manufacturing processes determined by the
available basic components and the desired nutrient content of the finished
product. Here are four brief examples.
Compaction methods
(agglomeration) involve binding small fertilizer particles together using
compaction, a cementing agent, or a chemical bond. Various nutrient ratios can
be combined using undersized particles that may not be suitable for other
applications.
Accretion-based fertilizers are
made by repeatedly adding a thin film of nutrient slurry which is continually
dried, building up multiple layers until the desired granule size is reached.
Pipe-cross reactors are used to
chemically melt NH3, acids containing
S or P, and other nutrients—such as K sources and micronutrients—into a solid
fertilizer with the desired nutrient content.
The nitrophosphate process involves reacting
phosphate rock with nitric acid to form a mixture of compounds containing N and
P. If a K source is added during the process, a solid fertilizer with N, P, and
K will result.
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| Three different techniques for making compound fertilizers (l) Compaction, (c) accretion, (r) pipe-cross reactor |
Compound fertilizer contains multiple nutrients in each individual
granule. This differs from a blend of fertilizers mixed together to achieve a
desired average nutrient composition. This difference allows compound
fertilizer to be spread so that each granule delivers a mixture of nutrients as
it dissolves in the soil and eliminates the potential for segregation of
nutrient sources during transport or application. A uniform distribution of
micronutrients throughout the rootzone can be achieved when included in
compound fertilizers.
These fertilizers are especially effective for applying an initial
nutrient dose in advance of planting. There are certain ratios of nutrients
available from a fertilizer dealer for specific soil and crop conditions. This
approach offers advantages of simplicity in making complex fertilizer
decisions, but does not allow the flexibility to blend fertilizers to meet
specific crop requirements. Turf managers and homeowners often find compound
fertilizers desirable.
Management
Practices
Compound fertilizers are sometimes more expensive than a physical
combination or blend of the primary nutrient sources since they require
additional processing. However, when a consideration is made of all the factors
involved with nutrient handling and use, compound fertilizers may offer
considerable advantages.
Nitrogen is the nutrient that most commonly needs to be carefully
managed and reapplied during the growing season. It may not be feasible to
supply sufficient N in advance of planting to meet the entire demand (using
only compound fertilizer) without overapplying some of the other nutrients. It
may be advisable to use a compound fertilizer early in the growing season and
then later apply only N fertilizer as needed.
Compound fertilizers are usually produced regionally
to meet local crop needs. There is a wide range of chemical and physical
properties that can be adjusted to meet these needs. For example, a desire to
minimize P in urban stormwater runoff has led some communities to restrict the
addition of P to compound fertilizers sold for turf and ornamental purposes.
Soils of a region that are typically low in a specific nutrient may have this
element boosted in the compound fertilizer.
A pdf version of this post can be found at the IPNI website here:
A pdf version of this post can be found at the IPNI website here:
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