The usual method of making liquid or dry soluble humates is
to extract in an alkaline solution which does not solubilize silica
to the silisic acid form required by plants . However, in
our technology it turns in amorphous silica into sodium
and potassium salts of monosilicon acids. These connections, as
has appeared, play major role in stimulation of development of
plants especially such as rice and cotton. We add addtional silicicacid
to our process making Humisolve-ION14 our high soluble silica
humic acids product.
See information on the importance of silicon below:
H. F. Birch' found that, for a group of East African soils, the
most efficient method of predicting the response of wheat to a
phosphatic fertiliser was to determine the amount of water-soluble
silica in the soil, or better still, the amount of silica soluble
in I per cent citric acid; for the response decreased linearly
with increases in the amount of silica extracted, up to certain
level, after which there was no response to phosphate. This result
does not have universal application, and is probably restricted
to soils which contain their phosphate associated with sesquioxide
films.
Crops differ considerably in the amount of silicon they take up,
but little systematic work has been done on the normal level of
silicon in different plants. Grasses and cereals normally have
over I per cent of SiO, in their dry matter, and most dicotyledons
under I per cent. H. W. Dougal' has deter-
mined the silicon content of several hundred samples of grass
and foliage of bushes and trees belonging to forty-seven families
and growing in the drier areas of Kenya, and found that the silica
content of grasses varied from I to over 10 per cent of the dry
matter, with contents of between 2 and 5 per cent being common,
while most other plants had silica contents below I per cent and
many below 0-2 per cent. Coming to British crops, Table 2-1 on
p. 24 shows that cereal straw commonly contains between 10 and
15 kg of silicon per ton while clover, beans and root crops remove
only a few kilo-
grams per hectare.
Plant roots take up their silica as silicic acid. It is possible
that the amount taken up by most gramineous crops is equal to
the amount of silicic acid present in the water the roots absorb,
so that the greater the amount of water transpired, the greater
their uptake of silica.' Dicotyledonous crops on the other hand
take up much less silica than is present in the water their roots
take up, often only about 5 per cent, and L. H. P. Jones and K.
A. Handreck 4 consider that crimson clover (T. incarnatum), the
plant they studied, trans-
located a constant proportion of the silica that reached the roots
to the tops, so again, the greater the transpiration the greater
the silica content of their tops.
But the validity of these generalisations is uncertain for uptake
both by the gramineous crops and the dicots appears to be a metabolic
process since enzyme inhibitors, such as sodium azide and
dinitrophenol,
will cause a reduction in silica uptake without causing a corresponding
reduction in ranspiration.' Many varieties of rice 2 and barley
will also take up more silica than is carried to the roots by
mass flow and dicots, which take up much less silica than comes
to the roots by this process, may have a concentration of silica
in their xylem sap that is appreciably greater than in the soil
solution. Thus, Barber and Shone found that broad beans (Viciafaba)
had a silica concentration in their sap five times greater than
in the solution bathing their roots.
Grasses and cereals have much of their silica content present
as a continuous film, either of a hydrated opal or of some
silica-organic
complex beween the walls of contiguous cells, and if the organic
matter of the cell wall is oxidised away carefully the opal films
show up the fine structure of the fibrils forming the wall very
clearly.' Grasses and cereals also often possess small cells which
are filled with opal. These silica structures break down when
dead grass leaves or cereal straw decompose in the soil or are
burnt to g' ive the opal phytoliths which are a characteristic
feature of grassland soils.
An adequate supply of silica is essential if grasses and cereals
are to give a good yield, for it increases the strength and rigidity
of their cells. Thus it helps rice leaves to have a more upright
habit under conditions of high nitrogen manuring, which may increase
the rate of photosynthesis per un' it area of land.' It increases
the oxidising power at the surface of rice roots, probably by
increasing the rigidity of the walls of the aerenchyma or gas
channels within the plant. It is also essential for a good seed
set in some varieties of rice, but its mode of action is still
unknown .5 It has the same type of action in some dicots, for
stinging nettles (Urtica dioica) lose their power of stinging
if grown in a silica-free medium, presumably because silica is
necessary for hardening their stinging hairs .6 Silica also increases
the tolerance of some crops to high levels of available soil manganese
for reasons that are not fully understood, but it prevents the
manganese in the leaf becoming concen-
trated in a number of spots, which then become necrotic;' and
in the case of padi rice allows a greater oxygen supply to the
root surface, ensuring a more rapid oxidation of manganese within
or just outside the root.
An adequate supply of silica to the cereals will thicken those
cell walls on which it is deposited, and this may have a number
of desirable consequences. An adequate silica supply reduces the
tendency of a cereal to wilt during the initial stages of drought,
probably because of the reduced permeability to water or water
vapour of the walls of the leaf epidermal cells. There is also
evidence that plants adequately supplied with silica have increased
resistance to some pests and diseases. Thus, an adequate silica
content may increase the resistance of some cereals to powdery
mildew (Erysiphe graminiv) 1 and of rice to blast (Pyricularica
oryzae),' and to some stem borers, such as Chilo suppressalis,'
of sorghums to central shoot fly (A theraqone indica)' and wheat
to hessian fly (Mayetiola destructor).'
The use of silica fertilisers, in the form of either soluble silicates,
or of calcium silicate slags is still very restricted. Slags are
used on some padi rice soils low in soluble silica, which in addition
to increasing the pH of the soil are also said to increase the
silicic acid concentration in the soil solution. Silicates also
increase the yield and sugar content in the juice of sugar-cane
growing on soils low in soluble silica.' Silicate fertilisers
can, however, increase crop yields for quite other reasons, for
they increase the availability of soil phosphate to the crop,
presumably by displacing phosphate absorbed on sesquioxide surfaces.
This is illustrated in Table 24.1 1 for barley on Hoos-
field at Rothamsted, which shows that a dressing of 450 kg/ha
of sodium silicate annually is still increasing the yield of the
no-phosphate plots after a century of use. The effect is unlikely
to be due to the sodium in the silicate as the source of nitrogen
is sodium nitrate, and the plots receiving potash also receive
I 10 kg/ha of sodium sulphate. It is probably another example
showing that the concentration of water-soluble silicic acid and
of phosphate are not two independent quantities in soils, but
are closely linked since their solubilities are controlled by
the sesquioxide and, in particular, the aluminium hydroxide surfaces.
| IH. F. Birch, J. agric. Sci., 1953, 43, 229, 329; P. K. Garberg, E. Afr. Agric. For. J., 1970, 35, 396. |
| 2 With V. M. Drysdale and P. E. Glover, E. Afr. Wildlij@ J., 1964, 2, 86. |
| 3 L. H. P. Jones and K. A. Handreck, Pi. Soil, 1965, 23, 79. |
| 4 Aust. J. biol. Res., 1967, 20, 483. Silicon 637I |
| D. A. Barber and M. G. T. Shone, J. exp. Bot., 1966, 17, 569. |
| I E. Lowig, Pflanzenbau, 1937, 13, 362. F. Wagner, Phytopath, 1940, 12, 427. |
| 2R. J. Volk, R. P. Kahn and R. L. Weintraub, Phvtopath., 1958, 48, 179. |
| 3A. Djamin and M. D. Pathak, J. econ. Entoni., 1967, 60, 347. |
| 4B. W. X. Ponnaiya, J. Madras Univ., 1951, 21 B, 203. |
| 5B. S. Miller, R. J. Rcbinson et al., J. Econ. Ent., 1960, 53, 995. |
| 6A. S. Ayres, Soil Sci., 1966,101, 216. Y. W. Y. Cheong and P. Halais, Exp. Agric., 1970,6,99 |
| 7R. A. Fisher, J. @qric. Sci., 1929,19,
132. 0. Lemmermann, Ztsch.,Pflanz. Du@q., 1929,13A, 28. |
| 2A. Okuda and E. Takahashi,
The mineral Nutrition o Rice, International Rice Research Institute, 1965, ch. 10. |
| 3For some excellent photographs of these films see L. H. P. Jones, A. A. Milne and S. M. Wadham, PI. Soil, 1963, 18, 358. |
| 4S. Yoshida et al., Pi. Soil, 1969, 31, 48. |
| 7J. Vlamis and D. E. Williams, PI. Soil, 1967, 27, 13 1; PI. Physiol., 1957, 32, 404. |