Interpreting nutrient analysis
How to read nutrient label analyses (i.e. “Guaranteed Analysis”)
With the common exception of potassium and phosphorus, most nutrient
labels state the concentration of nutrient species in their elemental form
– as per the “Element” column in Chart 1.
K2O and P2O5:
By convention, many labels represent potassium (K) as dipotassium oxide
(K2O). To convert K2O to K, multiply the K2O figure by 0.83. Similarly,
phosphorus (P) is often represented as phosphorus pentoxide (P2O5). To
convert P2O5 to P, multiply the P2O5 figure by 0.44.
Concentration:
The concentration of elements are represented in percentage (%).
Specifically this is %m/v (i.e. percentage mass per unit of volume).
Multiplying this figure by 10 derives the concentration in grams per litre
e.g. 3.0% equals 30g/L. Alternatively, multiplication by 10,000 derives
the concentration in ppm or mg/L e.g. 3.0% equals 30,000ppm.
How to compare
nutrient label analyses of 1, 2 & 3-part labels
Label analysis figures
for 2 & 3-part nutrients are usually based upon the concentration of
nutrients in the individual packs. Therefore, for example, in order to
make a meaningful comparison between a 2-part and 1-part nutrient, it is
necessary to first double the figures quoted on the 1-part. This ensures
we are comparing the contents of equal volumes e.g. 2 x 1L bottles of the
1-part with 2 x 1L bottles (’A’ and ‘B’) of the 2-part.
Obviously, to compare a
1-part with a 3-part, we would firstly ‘triple’ the 1-part figures. Further, to compare a
2-part with a 3-part, we must first halve the 2-part figures before
multiplying them by 3.
Using this
information we are able to compare analyses. For instance, in
Graph 3.1 we
are able to make a meaningful comparison between a 1, 2 and 3-part
nutrient.
Concentration of specific nutrient elements yielded by a given dose
To determine this,
the individual analysis specification should first be converted into ppm
(or mg/L), then multiplied by the dose rate (per litre). For example, if
part ‘B’ of a 2-part, contains 3.0% phosphate as P2O5, then when this part
is used at 4ml per litre, it will yield 53ppm phosphorus as P. That is:
Step 1. “3.0% P2O5”
= 30,000ppm as P2O5 (i.e. 3.0% x 10,000).
Step 2. Convert this
figure to P: 30,000ppm as P2O5 = 13,200ppm as P (30,000ppm x 0.44).
Step 3. 4ml per
litre yields 53ppm P (i.e. 13,200ppm x 4ml /1,000ml).
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