Fwd: Re: kelp effectiveness?

For thoses of you who have thought about using kelp on your pumpkins here is an interesting short paper on the subject.  John Mc

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  • Subject: Re: kelp effectiveness?
  • From: Keith Addison k*@JOURNEYTOFOREVER.ORG
  • Date: Sun, 11 Aug 2002 03:15:09 +0900
  • Content-length: 8462
As promised, if somewhat belatedly - sorry!

Keith


Chapter 7, Seaweed in Agriculture and Horticulture, by W.A.
Stephenson, Faber & Faber, 1968

Seaweed and Plant Growth

Seaweed contains all major and minor plant nutrients, and all trace
elements; alginic acid; vitamins; auxins; at least two gibberellins;
and antibiotics.

Of the seaweed contents listed after nutrients and trace elements,
the first, alginic acid, is a soil conditioner; the remainder, if the
word may be forgiven in this context, are plant conditioners. All are
found in fresh seaweed, dried seaweed meal and liquid seaweed extract
-- with the one exception of vitamins: these, while present in both
fresh seaweed and dried seaweed meal, are absent from the extract.

We will deal first with alginic acid as a soil conditioner. It is a
matter of common experience that seaweed, and seaweed products,
improve the water-holding characteristics of soil and help the
formation of crumb structure. They do this because the alginic acid
in the seaweed combines with metallic radicals in the soil to form a
polymer with greatly increased molecular weight, of the type known as
cross-linked. One might describe the process more simply, if less
accurately, by saying that the salts formed by alginic acid with soil
metals swell when wet and retain moisture tenaciously, so helping the
soil to form a crumb structure.

These brief notes cover two examples: one of the way in which seaweed
helps to produce a crumb structure in the soil, another of the way in
which it helps soil to retain moisture.

We have a market gardener customer at Sittingbourne in Kent who tells
us that before he used seaweed meal, heavy rain used to run down his
sloping plots and carry all his seedlings and fertilizers into the
ditch. Since his introduction of seaweed, the structure of his silty,
sandy soil has so improved that soil, seedlings and nutrients are no
longer of being washed away, even in the heaviest rain.

As to water-retaining characteristics, Miss Constance MacFarlane of
the Nova Scotia Research Foundation told members of the Fourth
Seaweed Symposium at Biarritz, in 1961: 'In the spring of 1956 I was
greatly impressed with fields in the island of Jersey. This was not
in any way a scientific experiment, but the results were most
obvious. The year 1955 had been exceedingly dry. The only fields
suitable for a second crop of hay were those which had been
fertilized with seaweed. All the others had dried out, and had to be
ploughed up for other crops.'

Research confirms this observation: two workers at the Agricultural
Research Council's unit of soil metabolism (now disbanded) reported
in 1947 that 0.1 of a gram of sodium alginate added to 100 grams of
soil increased its water-holding power by 11 per cent. This is the
first way in which seaweed and seaweed products condition the soil:
by increasing its water-holding capacity, and encouraging its crumb
structure. This in turn leads to better aeration and capillary
action, and these stimulate the root systems of plants to further
growth, and so stimulate the soil bacteria to greater activity.

As far as soil-conditioning is concerned -- and that is all we are to
consider for the moment -- bacterial activity in the presence of
seaweed has two results: first the secretion of substances which
further help to condition the soil; and second, an effect on the
nitrogen content of the soil. We will deal with these in turn.

The substances secreted by soil bacteria in the presence of seaweed
include organic chemicals known as polyuronides. Polyuronides are
chemically similar to the soil conditioner alginic acid, whose direct
effect on the soil we have already noticed, and themselves have
soil-stabilizing properties. This means that to the soil-conditioning
agent which the soil derives from undecomposed seaweed -- alginic
acid -- other conditioning agents are later added: the polyuronides,
which result from the decomposition of seaweed.

The second effect of adding seaweed, or seaweed meal, to a soil well
populated with bacteria, has already been mentioned briefly. It is a
more complex matter, and requires consideration in some detail.
Basically, the addition of seaweed leads to a temporary diminution of
nitrogen available for crops, then a considerable augmentation of the
nitrogen total.

When seaweed, or indeed any undecomposed organic matter, is put into
the soil, it is attacked by bacteria which break the material down
into simpler units -- in a word, decompose it. To do this effectively
the bacteria need nitrogen, and this they take from the first
available source, the soil. This means that after seaweed has been
added to the soil, there is a period during which the amount of soil
nitrogen available to plants is reduced. During this period seed
germination, and the feeding and growth of plants, can be inhibited
to greater or lesser degree. This temporary nitrogen deficiency is
brought about when any undecomposed vegetable matter is added to the
soil. In the case of straw, for example, which is ploughed in after
harvest, bacteria use up soil nitrogen in breaking down its
cellulose, so that a 'latent' period follows. Farmers burn stubble
after harvest to avoid this latent period, and the short-term loss of
available nitrogen which causes it. But such stubble-burning is done
at the cost of soil structure, soil fertility, and long-term supplies
of nitrogen which ultimately would have been released from the
decomposed straw.

It has been said by one authority that the latent period following
the application of seaweed to the soil is one of fifteen weeks. But
during this period, while there is a temporary shortage of available
nitrogen, total nitrogen in the soil is being increased. This
increase makes itself felt after the seaweed is completely broken
down. Total nitrogen then becomes available to the plant, and there
is a corresponding upsurge in plant growth.

It is therefore clear that while seaweed, in common with all organic
matter, is beneficial to soil and plant, it has to be broken down, or
decomposed, before its benefits are available. (I have already
pointed out, but repeat it here, that liquid seaweed extract is not
subject to this latent period. The nutrients and other substances it
contains are available to the plant at once.)

This period of decomposition -- or composting, as gardeners know it
-- usually extends over months. It can, however, be reduced by the
use of dried blood and loam according to the technique invented by
Mr. L. C. Chilcott, Brent Parks Manager. Only fourteen days of
heating up are required before the mixture is used, and no latent
period follows. This technique is described in detail on page 182.

So much for the soil conditioning effects of seaweed. Now a word
about what I have called its plant-conditioning contents, beginning
with vitamins.

Brown seaweeds, which are the ones used in agriculture and
horticulture, not only contain vitamins common to land plants, but
also vitamins which may owe their origin to bacteria which attach
themselves to sea plants, in particular vitamin B12. There is still
some doubt about this -- B12 may be contained in the seaweed,
although in some cases it is in associated bacteria. Vitamins known
to be present in the brown seaweeds include vitamin C (ascorbic
acid), which appears in as high a proportion as in lucerne. Vitamin A
is not present, but its precursor, beta-carotene, is, as well as
fucoxanthin, which may also be the precursor of Vitamin A. B group
vitamins present are B1 (thiamine), B2 (riboflavin), B12, as well as
pantothenic acid, folic acid and folinic acid. Also found in brown
seaweeds are vitamin E (tocopherol), vitamin K, and other
growth-promoting substances. The unusual nature of the vitamin E in
seaweed should be stressed. It has valuable characteristics (put
technically, a complete set of isomers) found only in such seed oils
as wheat germ oil.

Auxins in seaweed include indolyl-acetic acid, discovered in seaweed
in 1933 for the first time. Two new auxins, as yet unidentified, but
unlike any of the known indolyl-acetic acid types, were also
discovered in 1958 in the Laminaria and Ascophyllum seaweeds used for
processing into dried seaweed meal and liquid extract. These auxins
have been found to encourage the growth of more cells -- in which
they differ from more familiar types of auxin which simply enlarge
the cells without increasing their number. One of the auxins also
stimulates growth in both stems and roots of plants, and in this
differs from indolyl-acetic acid and its derivatives, which cause
cells to elongate but not to divide. The balanced action of this
seaweed auxin has not been found in any other auxin.

It has been proved at the Marine Laboratory at Aberdeen that
indolyl-acetic acid and the other newly discovered seaweed auxins are
extracted in increased quantities by the process of alkaline
hydrolysis. We believe that much of the value of our hydrolized
seaweed extract is due to this auxin content; but since the amount of
auxin in the extract is scarcely enough to promote the increased
growth which follows its use as a foliar spray, we think plants so
treated are themselves stimulated to produce more vitamins and growth
hormones than would otherwise be the case.

At least two gibberellins (hormones which simply encourage growth,
and have not, like auxins, growth-controlling properties too) have
been identified in seaweed. They behave like those gibberellins which
research workers have numbered A3 and A7 -- although they may in fact
be vitamins A1 and A4.

We now come to trace elements, some of the most important and most
complex of all seaweed constituents. Two things must be said at once.
The first is, that the more one studies the effect of trace elements
on plants and animals, the more difficult and involved the subject
becomes. Even those who devote their whole working life to the
subject are far from having a complete grasp of it. The second point
to make here is that while one can hope, at first, to treat trace
elements separately for plants and animals, there comes a time when
the two become hopelessly mixed. I shall try, in this chapter, to
deal with the effect of trace elements on plants only; but some
mention of their effect on animals will be inevitable, if only
because animals eat plants and the trace elements they contain.

We have seen that seaweed contains all known trace elements. This is
important. But it is also important that these elements are present
in a form acceptable to plants. We have seen that trace elements can
be made available to plants by chelating -- that is, by combining the
mineral atom with organic molecules. This overcomes the difficulty
that many trace elements, and iron in particular, cannot be absorbed
by plants and animals in their commonest forms. This is because they
are thrown out of solution by the calcium carbonate in limy soils, so
that fruit trees growing in these soils can suffer from a form of
iron deficiency known as chlorosis. It is for this reason that plants
such as rhododendrons and azaleas, which are particularly sensitive
to iron deficiency, can grow only in acid soils. In these soils, iron
does not combine with other elements to form insoluble salts which
the plant cannot absorb, and it is therefore more freely available.

It is true that an iron salt such as iron sulphate can be dissolved
in water and the solution poured on the soil, injected into an
animal, or put into its feed. But iron has such a tendency to become
bound up with other elements that it is not available to plants or
animals when introduced in this way. If, on the other hand, iron in
the form of iron oxide is dissolved in an organic compound, there
will be no fusion with other chemicals in the soil, and it will be
available to the plants which need it. This is the technique of
chelating which makes possible the absorption of iron by living
matter.

Such chelating properties are possessed by the starches, sugars and
carbohydrates in seaweed and seaweed products. As a result, these
constituents are in natural combination with the iron, cobalt,
copper, manganese, zinc and other trace elements found naturally in
seaweed. That is why these trace elements in seaweed and seaweed
products do not settle out, even in alkaline soils, but remain
available to plants which need them.

Hydrolized seaweed extract also 'carries' trace elements in this way,
in spite of the fact that the liquid is alkaline, having a pH of nine
-- in the ordinary way so alkaline a solution would automatically
precipitate trace elements. This precipitation does not take place in
seaweed extract because the trace elements already form part of
stronger, organic, associations.

With liquid extract, this ability to chelate can be taken a stage
further than happens naturally with seaweed and seaweed meal.
Chelation can also be used, artificially, to cause extract to carry
more trace elements than are found in fresh seaweed, in seaweed meal,
or in ordinary hydrolized extract.

We have ourselves exploited these chelating properties of liquid
seaweed extract by manufacturing three special types, one containing
added iron, one added magnesium, and one containing the three trace
elements of iron, magnesium and manganese. We have also made
experimental batches with copper and boron. Most metals could be
chelated in this way.

It will be remembered that liquid seaweed extract differs from
seaweed meal in that it can be used directly on the plant in the form
of a spray. We know that the minerals in seaweed spray are absorbed
through the skin of the leaf into the sap of the plant -- and not
only minerals, but the other plant nutrients, auxins and so on,
listed earlier. Experience further suggests that plants' needs for
trace elements can be satisfied at lower concentrations if those
elements are offered to the leaves in the form of a spray, rather
than being offered through the soil to the roots.

It is also possible that seaweed sprays stimulate metabolic processes
in the leaf and so help the plant to exploit leaf-locked nutrients --
for it is known that trace elements won from the soil, and delivered
by the plant to the leaf tissue, can become immobilized there. And
if, as has been suggested by E. I. Rabinowitch in a standard work on
photosynthesis, a 'considerable proportion' of photosynthesis is
carried out by bacteria at the leaf surface, spraying with seaweed
extract at this point may feed and stimulate them, and thus increase
the rate of photosynthesis.

We now come to the debatable matter of antibiotics in seaweed --
debatable, not because there is any doubt that seaweed contains
therapeutic substances, but because the precise nature of those
substances is unknown. We call them antibiotics for convenience.

It is known that plants treated with seaweed products develop a
resistance to pests and diseases, not only to sap-seeking insects
such as red spider mite and aphides, but also to scab, mildew and
fungi. Such a possibility may seem novel, but it is in keeping with
the results of research in related fields. The control of plant
disease by compounds which reduce or nullify the effect of a pathogen
after it has entered the plant is an accepted technique. It is in
this way that streptomycin given as a foliar spray combats fireblight
in apples and pears, and antimycin and malonic acid combat mosaic
virus in tobacco. The subject of controlling plant disease by
introducing substances into the plant itself is known as
chemotherapy, and is dealt with in a useful round-up article in the
Annual Review of Plant Physiology, 1959, by A. E. Dimond and James G.
Horsfall of the Connecticut Agricultural Experiment Station, New
Haven, United States.

As far as chemotherapy through seaweed is concerned, the annual
report for 1963 of the Institute of Seaweed Research stated that
trials in which soil-borne diseases of plants were reduced by adding
seaweed products to the soil were the first recorded instance of the
control of disease by organic manure. 'Hitherto', the report ran,
'the majority of agricultural scientists believed that the value of
organic manures was restricted to their nitrogen-phosphorus-potassium
content, with perhaps some additional value as soil conditioner. This
new discovery challenges this over-simplified view of the value of
organic manures, and has initiated a new appraisal of this very
complex problem.'

The reason why seaweed and seaweed products should exert some form of
biological control over a number of common plant diseases is unknown.
Soil fungi and bacteria are known to produce natural antibiotics
which hold down the population of plant pathogens, and when these
antibiotics are produced in sufficient quantities they enter the
plant and help it to resist disease. The production of such
antibiotics is increased in soil high in organic matter, and it may
be that seaweed still further encourages this process.

I am aware that the claims made here, and elsewhere in this book, for
the control of diseases by seaweed products, are supported more by
the practical experience of growers than by the result of trials at
research institutions. We have reported such trials as have taken
place, but they are few in number. I cannot accept that the testimony
of hard-headed farmers and horticulturists is any less reliable than
that of academic researchers. But the reader might think that my
attitude has been coloured by my interest, and for this reason I
would say a word or two about the evidence on which these statements
are based.

I have said elsewhere in this book that the evidence of the
disease-controlling qualities of seaweed came to us as a complete
surprise. It was those who used seaweed extract as a foliar nutrient,
or seaweed meal as fertilizer, who first discovered these
characteristics, and described them to us. We make no other claims
than these, only record what users say, and it would be a poor
service to truth to censor this evidence of the value of seaweed
because it has not been confirmed in all respects by trials at
research stations. Where these trials have taken place they are later
reported. Trials in this country [UK] have been few, for a variety of
reasons which need not concern us. We might regret that
state-supported stations noted for a high standard of scientific
integrity are also conservative in outlook, and little disposed to
test that which is unusual. It is not for us to criticize their
choice of subjects for research, but our own information is so
striking that we should wholeheartedly welcome testing of seaweed and
seaweed products by those with complete facilities for doing so. The
evidence we have collected would then be respectably 'scientific' --
and we do not doubt that the findings would corroborate our claims to
the full.
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