Table 2. Elemental content of rockwool,
perlite, coir, pinebark and peat moss
determined by Mehlich No. 3 Extraction
Element
Rockwool
Perlite
Coir
Pinebark Peatmoss
lbs/a
Phosphorus (P)
54 (S)*
0.17 (D)
76 (S)
58 (S)
60 (S)
Potassium
(K)
284 (S)
4.4 (D)
2,340 (E)
420 (H)
190 (S)
Calcium
(Ca)
2,828 (S)
30.0 (D)
1,430 (S)
1,084 (S)
1,314 (S)
Magnesium
(Mg)
774 (H)
7.6 (D)
866 (H)
200 (S)
738 (H)
Sulfur (S)
480 (H)
18.0 (D)
40 (S)
4 (D)
236 (S)
Boron (B)
2.0 (H)
0.90 (D)
4.0 (E)
3.9 (H)
0.1 (S)
Copper (Cu)
0.12 (S)
0.20 (S)
0.18 (S)
3.6 (H)
0.1 (S)
2,220.0 (E)
3.80 (S)
114.0 (E)
64.0 (H)
14.0 (H)
Manganese
(Mn)
64.0 (E)
0.24 (S)
20.0 (H)
46.0 (E)
2.0 (H)
Zinc (Zn)
1.6 (S)
0.20 (S)
4.8 (H)
1.2 (S)
6.6 (E)
Iron (Fe)
*(D) = deficient, (L) = low, (S) = sufficient, (H) = high, (E) = excessive
These results do not necessarily verify what
portion of the element content of the rooting
medium is indeed “available” for root absorption,
but it does provide as basis for comparison among
rooting medium. The assay results would suggest
that all but perlite could be considered a “fertile
soil.” It might also suggest that one needs to match
a fertilizer or nutrient solution formulation with
the available elemental contents of the plant rooting
media. In addition, these results would suggest
that when using these rooting medium, including
the micronutrients would not be necessary in the
selected fertilizer or nutrient solution formulation.
The next issue when it comes to rooting media is,
“What occurs when a nutrient solution is brought
into contact with a rooting medium and allowed
to come to equilibrium?” To answer this question,
a nutrient solution was added in an equal volume
to rockwool, perlite and coir. The mixtures were
stirred intermittently for 30 minutes, and then the
liquid phase removed by filtration and the filtrate
assayed for its elemental content by
ICP spectrometry.
There are three possible outcomes: there is no
change in elemental content from that in the initial
nutrient solution, there is an adsorption that results
in a decrease in concentration or there is an increase
in the elemental content of the recovered nutrient
solution as result to a release.
Maximum Yield USA | September 2012
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