Agriculture Reference
In-Depth Information
Organic sources of nutrients include the different
types of bulky organic matter that release nutrients
many of which are better known as '
manures
'.
Organic fertilizers
are normally considered to
be the materials with concentrated sources of
nutrients derived from organisms, such as hoof and
horn, bone meal, blood meal (see Table 14.2). Urea
presents an anomaly in so far as when originating
from urine it is clearly 'organic', but the same
chemical when synthesized is not in an 'organic
gardening' sense.
i.e., the nutrients in bulky organic matter are more
diluted (or non-existent).
Besides the major nutrient content, fertilizer
regulations require that details of trace elements,
pesticide content and phosphorus solubility should
appear on the packaging. For
organic gardening
it is
necessary to look at specific requirements including
the limitations on fertilizer use.
There are many different types of fertilizers in terms
of their
X
content (straight/compound)
X
formulation (granules/powders, quick/slow/
controlled release)
X
the ways they are used (base/top dressing, liquid
feed, foliar feed).
Straight fertilizers
are those that supply only one of
the major nutrients: nitrogen, phosphorus, potassium
or magnesium such as ammonium sulphate
(supplying N), triple superphosphate (P), potassium
chloride (K).
Compound fertilizers
are those that supply two
or more of the nutrients nitrogen, phosphorus
and potassium, such as Growmore. The accepted
convention for describing the fertilizer content of
compounds is to label the content in the order N P K
so Growmore is described as 7:7:7, that is, 7% N: 7%
P
2
O
5
: 7% K
2
O. Most of the proprietary fertilizers
for gardeners are compounds including those
specifically for tomatoes, roses, orchids and cacti (see
Figure 14.7).
Quick release or soluble fertilizers
are those
that dissolve immediately in water before or after
application to soil - for example, ammonium sulphate
and urea both of which yield nitrogen that can be
taken up by plants within days of application. The
Fertilizers
Organic fertilizers
include those derived from organic
sources such as bone meal; hoof and horn; dried
blood; fish, blood and bone; comfrey feed; or nettle
tea.
Inorganic fertilizers
are those commonly
referred to as 'synthetic', 'artificial' or 'bag'
fertilizer such as ammonium sulphate, triple
superphosphate, potassium chloride and National
Growmore. Some are mined/quarried materials such
as rock phosphate.
The quantity of nutrient supplied by a fertilizer is
expressed in terms of a percentage of the contents.
X
Nitrogen fertilizers are given terms of percentage
of the element nitrogen in the fertilizer, i.e. %N.
X
Phosphate fertilizers provide the element
phosphorus and given as %P and more usually
in Britain and Ireland described in terms of the
'equivalent amount of phosphoric oxide', i.e.
%P
2
O
5
.
X
Potash fertilizers provide the element potassium
and given as % K; the 'old' name for potassium
is 'Kalium'; and more usually in Britain and Ireland
described in terms of 'equivalent amount of
potassium oxide', i.e. %K
2
O.
X
Magnesium fertilizers are described in terms of
%Mg.
The percentage figures show the quantities of
nutrient in each 100 kg of fertilizer - for example,
ammonium sulphate is 20% N so there is 20 kg of the
element nitrogen in every 100 kg of the fertilizer so by
proportion there is 5 kg in a 25 kg bag or 1 kg in a 5 kg
bag.
Fertilizers are a concentrated source of nutrients as
illustrated by the following materials that supply the
element nitrogen (N) - for example:
1kg N is supplied in a 5kg bag of ammonium sulphate.
1kg N is supplied in 2-5 tonnes of fresh farmyard
manure.
Figure 14.7
Range of fertilizers. Some are sold
as straights or general compounds, but many for
gardeners are compounds formulated for specifi c
plants
