In a message dated 8/22/2003 7:29:39 AM Pacific Daylight Time,
hjalti.andrason@... writes:
Substrate and Fertilization Introduction
By Robert Paul H
Plants need a balance of macro nutrients, (those they use the most
of), and minor or trace nutrients, (which they use to a lesser
degree).
Macronutrients
Nutrients used by plants in relatively large amounts. They are
nitrogen (N), phosphorus (P), sulfur (S), calcium (Ca), magnesium
(Mg) and potassium (K).
Micronutrients
Nutrients used by plants in small amounts. They are iron (Fe),
manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), cobalt (Co),
and boron (B).
The Substrate is the growing medium that the plants are rooted in. It
is important to add a source of these nutrients to the substrate,
particularly in a new aquarium that has no mulm or fish waste settled
in it yet.
It is also advisable to use a medium such as porous gravel that will
provide a good CEC and not compact together. CEC, (cation exchange
capacity) is the ability of the medium to absorb cation ions,
(minerals from fertilizers) and hold them making them accessible to
the plants when the plants need them. Sand and coated gravel do not
provide a good CEC. Good CEC mediums include porous gravel, clay
litter, and clay soils.
Macro nutrients include nitrogen, oxygen, CO2, potassium, phosphorus,
calcium. Minor elements include iron, Boron, zinc, manganese, and
other trace minerals. Iron is an important element for many plants
and is often added to the substrate with other minerals.
Laterite is a sediment soil that is formed in nature by decaying
rocks which are high in iron and aluminum. There are a few aquarium
products made of laterite, such as Duplarit, and First Layer. Other
sources of iron are soils, clay litter, red pottery clay, and
sphagnum peat.
Various substrate methods
Layered substrate with "sub" soil (soil low in organics), sphagnum
peat, gravel, and trace element mix, as outlined by Steve Pushak
Pottery clay balls enhanced with fritted trace elements, as outlined
by Steve Pushak, or commercial additives made for the aquarium
Clay gravel
Granular laterite, sphagnum peat, and gravel, my mix of choice.
Fail-safe beginner substrates:
Commercial products, laterite, clay gravel, clay based additives made
for the aquarium
NPK What are those three numbers?
Nitrogen supplied by the fish, phosphates by the water supply and
uneaten food, and potassium to a lesser degree in the water supply.
NPK fertilizers should only be added if you have low or unreadable
levels already. RO, distilled, and some bottled spring water will be
low in NPK and mineral elements. Most tap water will have sufficient
levels of P. Even some aquarium products contain NPK. An NPK
fertilizer high in potassium, but low or 0 in nitrate and phosphate
is has the least affect on algae. Check the numbers. Single digits
are low, double digits are high. In a heavily planted tank with fast
growing plants, and a small number of fish, it is possible to have
consistent 0 readings of nitrate and phosphate creating a nitrogen
and phosphate deficiency for the plants.
Target nutrient ranges
Nitrate (N03) 5 to 10ppm Phosphate (PO4) 0.2ppm to 0.5ppm
Iron (Fe) 0.2 to 0.7ppm Potassium (K) 20-30ppm
Types of fertilizers
tablets spikes
balls liquid
Sources of trace elements
Sphagnum Peat: Iron (Fe) High CEC
Soils: Iron (Fe) other trace elements High CEC
Pottery clay: Iron, (Fe) High CEC
Clay litter: Iron, (Fe) High CEC
Vermiculite: trace amounts Iron, Potassium, Magnesium Very High CEC
Drawbacks of Soil substrates
When plants are removed, replanted, the soil mixture can come up with
the plants and pollute the water. You are better off using a clay
gravel if you anticipate moving and transplanting plants often.
The Following information is taken from "Something to Grow on",
Cornell University. It is not written specifically for aquariums, but
the information is very useful. I particularly like the information
on CEC.
Ions Cation exchange capacity
(CEC) Quantifies the ability of media to provide a nutrient reserve
for plant uptake. It is the sum of exchangeable cations, or
positively charged ions, media can adsorb per unit weight or volume.
It is usually measured in milligram equivalents per 100 g or 100 cm3
(meq/100 g or meq/100 cm3, respectively). A high CEC value
characterizes media with a high nutrient-holding capacity that can
retain nutrients for plant uptake between applications of fertilizer.
Media characterized by a high CEC retains nutrients from leaching
during irrigation. In addition, a high CEC provides a buffer from
abrupt fluctuations in media salinity and pH. Important cations in
the cation exchange complex in order of adsorption strength include
calcium (Ca2+) > magnesium (Mg2+) > potassium (K+) > ammonium (NH4+),
and sodium (Na+). Micronutrients which also are adsorbed to media
particles include iron (Fe2+ and Fe3+), manganese (Mn2+), zinc
(Zn2+), and copper (Cu2+). The cations bind loosely to negatively
charged sites on media particles until they are released into the
liquid phase of the media. Once they are released into the media
solution, cations are absorbed by plant roots or exchanged for other
cations held on the media particles. Anion exchange capacity Some
media retains small quantities of anions, negatively charged ions, in
addition to cations. However, anion exchange capacities are usually
negligible, allowing anions such as nitrate (NO3-), chloride (Cl-),
sulphate (SO4-), and phosphate (H2PO4-) to leach from the media.
Cation Exchange Capacities for various growing media amendments and
selected media.
Material Cation Exchange Capacity meq/100g
Perlite 1.5 - 3.5
Silt 3.0 - 7.0
Clays 22.0 - 63.0
Pine Bark 53.0
Vermiculite 82.0 - 150.0
Sphagnum Peat 100.0 - 180.0
Humus 200.0
Peat moss : vermiculite 1:1 141.0
Peat moss : sand 1:1 8.0
Peat moss : perlite 1:3 11.0
Peat moss : perlite 2:1 24.0
Sources: see Bunt, A.C. 1988, and Landis, T. D. 1990.
Sphagnum peat moss
Sphagnum peat moss, derived from the genus Sphagnum, contains at
least 90% organic matter on a dry weight basis. In addition, this
peat moss contains a minimum of 75% Sphagnum fiber, consisting of
recognizable cells of leaves and stems. Approximately 25 species of
Sphagnum exist in Alberta, Canada and 335 species are present
throughout the world. Sphagnum fuscum is an important species bearing
many desirable traits. Sphagnum grows in northern cool regions and is
also located in peat bogs found in Washington, Maine, Minnesota, and
Michigan. Many pores are present in the leaves of sphagnum; when used
as growing media, as much as 93% of the water occupying this internal
pore space is available for plant uptake (Peck, 1984). After
draining, sphagnum peat can hold 59% water and 25% air by volume.
Sphagnum is usually characterized by an acidic pH, low soluble salts
content, structural integrity, and the ability to serve as a nutrient
reserve (Landis, 1990). Although peat mosses are classified into four
different groups, variation may exist within any one type of peat
moss. Peats of the same classification often differ notably in
quality, and even peats from the same bog taken from separate layers
can possess different chemical and physical properties.
Sphagnum peat moss is classified as light or dark peat, based on its
color. Light peats are characterized by a large amount of internal
pore space, 15-40% of the pore space comprises aeration porosity Dark
sphagnum peat does not display the elasticity of light peat and is
usually not as long lasting.. Dark sphagnum peat moss maintains twice
the cation exchange capacity of light peats, yet does not possess as
much total or aeration porosity. An associated table lists general
characteristics of sphagnum peat moss.
Inorganic media
Materials such as vermiculite, perlite, and sand represent the
inorganic fraction often used in container media formulations. These
materials generally increase the aeration porosity and drainage yet
decrease the water-holding porosity of media. Inorganic components
are usually inert materials characterized by a low cation exchange
capacity.
Vermiculite
Vermiculite is a commonly used inorganic media component which is
mined in the U.S. and Africa. This mineral, comprised of an
aluminum/iron/magnesium/silicate mixture, is excavated as a material
composed of thin layers. Processing includes heating the vermiculite
to temperatures upwards of 1000Æ'C, which converts water trapped
between the layers of the material into steam. The production of
steam results in a pressure that expands the material, increasing the
volume of the pieces 15 to 20 times their original size. Vermiculite
is sterile because of these high heating temperatures used during
processing. Vermiculite is characterized by a high water-holding
capacity as a result of its large surface area: volume ratio, a low
bulk density, nearly neutral pH, and a high cation exchange capacity
attributed to its platy structure. Because it compacts readily when
combined with heavier materials, vermiculite is sometimes recommended
more for propagating material than container media.
Vermiculite gradually releases nutrients for plant absorption; on
average it contains 5-8% available potassium and 9-12% magnesium.
This inorganic media component can adsorb phosphate--some of which
remains in an available form for plant uptake--but cannot adsorb
nitrate, chloride, or sulfate. Vermiculite can fix ammonium into a
form that is not readily available for plant absorption. This fixed
nitrogen is gradually transformed to nitrate by microorganisms,
making it available for plant uptake.
Vermiculite is manufactured in four different grades, differentiated
by particle size. Insulation grade vermiculite and that which is
marketed for poultry litter (which has not been treated with water
repellents) has been used with some success. Vermiculite which has
been treated with water repellent, such as block fill should not be
used as growing media. Because vermiculite tends to compact over
time, it should be incorporated with other materials such as peat or
perlite to maintain sufficient porosity. It should not be used in
conjunction with sand or as the sole media component, because as the
internal structure of vermiculite deteriorates, air porosity and
drainage decreases (Landis, 1990).
The particle size of vermiculite influences the water-holding and
aeration porosity of the material. Although grade classification is
based upon particle size, each grade is represented by a range of
particle sizes. Note that grades consisting of larger particle sizes
have a higher aeration porosity and lower water-holding porosity than
grades consisting of a smaller range of particle sizes. Properties of
the four vermiculite grades are shown in an associated table.
Perlite
A mineral of volcanic derivation, perlite is a second inorganic
component which may be used in formulating container mixes. This
chemically inert material is extracted in New Zealand, the U.S., and
other countries and is usually mined by scraping the earth's surface.
The processing method includes a grinding and heat treatment (up to
1000â°C) which results in very lightweight, white sterile
fragments.
As the ore is heated, internal water escapes as steam, resulting in
the expansion of the material.
Perlite has a very low cation exchange capacity, low water-holding
capacity (19%), and neutral pH. The closed-cell composition of
perlite contributes to its compaction resistance, enhances media
drainage, and heightens the aeration porosity of peat-based media
(Bilderback 1982). Because perlite contains only minute amounts of
plant nutrients, liquid feeding is a practical mode of fertilization.
Be aware of possible aluminum toxicity in acidic media (pH < 5).
The very low levels of fluoride perlite contains is not likely to
pose plant health problems. Any soluble fluoride present in a media
characterized by 6.0 < pH < 6.5 will precipitate out of the media
with excess calcium from sources such as gypsum, limestone, or
calcium nitrate.
Although perlite has several positive attributes, it also has
drawbacks. Perlite consists of many fine fragments which, when dry,
can lead to lung or eye irritation. In addition, because water clings
to the surface of perlite, it may tend to float in the presence of
water (Landis, 1990).
Perlite contains, on average, 47.5% oxygen, 33.8% silicon, 7.2%
aluminum, 3.5% potassium, 3.4% sodium, 3.0% bound water, 0.6% iron
and calcium, and 0.2% magnesium and trace elements (Perlite
Institute, 1983). Although a uniform categorization of perlite does
not exist, individual producers of this inorganic component assign
grade levels. Perlite classifications for horticultural use are
listed in an associated table. This inorganic media amendment is
sometimes recommended for use only in propagation media because of
its low bulk density and tendency to compact.
In comparison with sand, polystyrene, or pumice, perlite has the
greatest inner total porosity. Coarse perlite is characterized by
approximately 70% total porosity, 60% of which is aeration porosity.
Perlite can retain two to four times its dry weight in water, which
is much greater than that of sand and polystyrene, yet much less than
the water-holding capacity of peat and vermiculite (Moore, 1987).
Sand
Sand has been used as an inorganic media component to add ballast to
containers. Some sands contain calcium carbonate which may raise
media pH undesirably. A rise in pH may lead to nutrient deficiencies,
particularly of minor elements such as iron and boron. A few drops of
dilute hydrochloric acid or strong vinegar may be added to sand to
test for carbonates; if bubbling and fizzing result, carbonate is
present as a result of carbon dioxide production. Sand used for
container media should have a 6 < pH < 7. Sand maintains good
drainage, a low water-holding capacity, and a high bulk density when
used independently of other materials. Because of its shape and size,
sand can obstruct pore spaces, decreasing drainage and aeration,
instead of improving porosity. Various sand particle sizes have been
recommended for container media use, including ranges of 2-3 mm or
0.05 - 0.5 mm (fine sand) in size (Landis, 1990). In addition,
another recommendation suggests that 60% of the particles be within
0.25-1.0 mm range, and 97% be greater than 0.1 mm and less than 2 mm
(Swanson, 1989). Uniformity coefficients assigned to sand mixtures
signify the amount of sand which is within a certain size range; a
coefficient < 4 is evidence of a homogeneous sand mixture (Swanson,
1989). If the correct grade of sand is used, the wet ability of the
media is enhanced.
Calcined clays
When fired at high temperatures, some clays, fuel ash, and shales
form stable compounds that possess low bulk densities and internal
porosities of 40-50%. Though calcined clays alter the physical
attributes of media in a positive way, they also decrease the level
of water-soluble phosphorus in the mix. Because calcined clays are
characterized by a high cation exchange capacity, fertilizer
application rates may need to be modified if calcined aggregates are
incorporated into the media mixes (Bunt, 1988).
Pumice
Pumice is produced as volcanic lava cools; escaping steam and gas
contribute to its porous nature. This alumino-silicate material
contains potassium, sodium, magnesium, calcium, and slight amounts of
iron. Pumice can absorb K, Mg, P, and Ca from the soil solution and
render it available for plant absorption later (Bunt, 1988).
