Subject: Re: Was: an experiment w/ pH, Now: an experiment w/ elemental sulphur

From: Oz <[email-masked]>
Date: Sat, 3 May 1997 06:59:16 +0100

In article <[email-masked]>, Stuart
Brown <[email-masked]> writes
>
>I recently asked a fertiliser salesperson about the risk of sulphate leaching 
>from applying elemental sulphur just proir to the winter (a normally wet 
>time of the year here). He told me that as soil temperature falls below 
>about 8 deg Celicus (about 46 F) elemental S stops being oxidised 
>(converted to soluble S). He said this was because bacteria are involved 
>in the conversion process and their activity is reduced with low 
>temperatures. He said you can chuck a handful in a bucket of cold water 
>and it won't dissolve. Any comments ?

This is an interesting area. Quite a lot of work has been done on it but
I have never been able to locate any papers on the Net. If anyone has
any real data on the oxidisation rates of elemental sulphur wrt particle
size, temperature and soil water content I would be very grateful indeed
for the location and/or a copy of any relevent papers.

As I understand it there has been significant work done in New Zealand
(Aukland U.?) and at Newcastle U. in the UK. Doubtless work has also
been done elsewhere. Some at least is confidential, having been paid for
by sulphur suppliers.

I have been able to glean the following:

1) Elemental sulphur is indeed very insoluble in water.

2) Particle size is critical. Small particles break down very much
faster than large ones. For realistic rates of oxidation we are talking
micron sized particles. Large lumps are essentially inert.

3) I believe that it's breakdown is essentially a 'slow burn' and is not
mediated by bacterial activity.

4) Rates of oxidation at low temperatures and in waterlogged (ie low
oxygen levels) soils are very slow, even for small particles. This is
unsurprising as one would expect the rate of oxidation to be dependant
on temperature and oxygen concentration.

5) Plants can, and do, absorb very significant amounts of sulphur as
sulphur dioxide directly from the air, through their stomata, in the
same way they absorb CO2. Some experiments have indicated 80% of
requirement can be taken up in this way.

Elemental sulpur is probably the cheapest source of sulphur for plants
and it should be possible to select particle sizes so that an
application could be made in the autumn that would supply sulphur
throughout the following growing year. The problem is in spreading the
very fine dust, and some sort of pellet that will break down liberating
the powder is required. Alternatively an aqueous slurry could be sprayed
on.

Sulphur is positively hazardous if it were to be stored close to
ammonium nitrate and there is a significant risk of fire and/or
explosion.

Sprayed as a foliar spray in water, finely divided sulphur is a useful
(if not very effective) fungicide as well as providing sulphur for
plants. Presumably the low level of SO2 produced is the active
ingredient.

The reduction in sulphur emissions from industrial and domestic sources
is such that in the UK, and probably elsewhere, plants are becoming
deficient in sulphur and there is now a requirement to apply it as a
fertiliser for optimum plant growth. The quantities that will be
required worldwide are truly huge.

-- 
'Oz     "Is it better to seem ignorant and learn,
         - or seem wise and stay ignorant?"

---

From: [email-masked] (Stuart Brown)
Date: Fri, 02 May 1997 08:48:00 +1200

[email-masked] (Allyn Weaks) writes:

>In article <[email-masked]>, [email-masked] wrote:
>
>As for the pH test, it's not telling you what you hope it does.  Using
>straight dolomite in water doesn't provide the same conditions as dolomite
>plus soil.  Dolomite raises the pH by breaking down and releasing Ca++,

Cheers,
Stuart.
--

---

From: [email-masked] (Stuart Brown)
Date: Sun, 04 May 1997 08:32:00 +1200

>for the location and/or a copy of any relevent papers.

Reading from a NZ fertiliser newsletter (Quinphos) : To be effective,
elemental sulphur must be less than 1mm in size. It must also contain good
proportions  of very fine sulphur ie below 0.15mm (150 microns). The 
proportion in this fine size range depends to which it's being put.

They recommend for genral maintenence in the North Is of NZ 20-30% of the 
sulphur should be in this fine (<.15mm) fraction.

Ground elemental sulphur sells in NZ for around $NZ375/ton ($US260), this 
is 100% S. Of course no one will transport it in this form as sulphur dust
is explosive. My understanding is that a phosphate based product is safe 
at levels up to about 18% S. I understand phosphate helps as it is 
electrically conductive.

Another fertiliser manufacturer in NZ (Ravensdown) produces a product 
they call Maxi Sulphur Super. This is made by spraying molten sulphur 
onto super phosphate granules. This achicves a fine particle size (indeed 
the opposition claim it's too fine). Maxi sulphur super has an NPKS of 
0-5-0-50. It retails for about $NZ180/ton ($US125).

>(Aukland U.?) and at Newcastle U. in the UK. Doubtless work has also

I couldn't see any references. I should think a trip to an agricultural 
university library should yield some info.

>mediated by bacterial activity.

Both Ravensdown and Quinphos claim it is significantly affected by 
bacterial activity.

Cheers,
Stuart.
--

---

From: Oz <[email-masked]>
Date: Sun, 4 May 1997 08:03:44 +0100

In article <[email-masked]>, Stuart
Brown <[email-masked]> writes

>Reading from a NZ fertiliser newsletter (Quinphos) : 

Forgive me for being a bit cautious on material produced by fertiliser
manufacturers. Unless one of the major names, and even then they can be
selective about which trials they use, I would want independent work to
back them up.

>To be effective,
>elemental sulphur must be less than 1mm in size. 

Do you have lifetimes in soil for sulphur at the 1mm size? I would be a
bit suspicious of sizes this large. They may well be effective, but for
decades. Nothing wrong with this as such, so long as you know.

>It must also contain good

Could you illustrate some uses and proportions?

>sulphur should be in this fine (<.15mm) fraction.

OK. How much is typically applied as a maintenance dressing, how much
for the initial dose, and on which crops. I presume mostly clover-rich
grassland.

>is 100% S. 

Similar to the UK. Other forms of sulphur are significantly more
expensive (in general), but very much easier to buy and spread.

>the opposition claim it's too fine). 

Why *too* fine?

>university library should yield some info.

Not so easy for a rural peasant.

>Both Ravensdown and Quinphos claim it is significantly affected by 

I find it difficult to see a mechanism due to the aqueous insolubility
of elemental sulphur. On top of that it is known that S (presumably due
to the SO2 produced) is rather toxic to micro-organisms. On reflection I
suppose that S can be dissolved in various organic solvents and
microbial activity in the soil will produce some of these, albeit at low
level. OK, it's possible.

I presume that elemental sulphur is used in NZ mainly because it's high
concentration makes spreading bt plane that bit cheaper.

---

From: "David B. Hedrick" <[email-masked]>
Date: Sun, 04 May 1997 04:30:00 -0400

Oz: 

	I've got a bit of info to add to your growing pile. 

Oz wrote:
> 
> Stuart Brown writes
> >
> >He told me that as soil temperature falls below
> >temperatures. 

> micron sized particles. Large lumps are essentially inert.

Since S has such a low solubility, the oxidation can only happen at the
surface.  Smaller particles, more surface area.  

> mediated by bacterial activity.

S does not appreciably oxidize in air.  It is bacterially mediated, and
that is probably the source of the temperature dependence.  

-- 
		~DBH

Technical writing, literature search, and data analysis at the interface
of chemistry and biology. 

	[email-masked]

	David B. Hedrick
	P.O. Box 16082
	Knoxville, TN 37996

---

From: Oz <[email-masked]>
Date: Sun, 4 May 1997 12:46:42 +0100

In article <[email-masked]>, "David B. Hedrick"
<[email-masked]> writes
>       I've got a bit of info to add to your growing pile. 

Great, keep it coming.

>surface.  Smaller particles, more surface area.  

Agreed. So if, say, it takes ten years for a 1mm sized piece of sulphur
to oxidise at room temperature then it will only take one year for a
0.1mm sized particle and 1/10 year for a 10 micron particle. (Number of
particles up as the cube, area per particle decreases as the square).

Hang on, we ought to be able to get an estimate from the micronised
sulphur used as a foliar spray. I'll look it up. Ahh, it has a particle
size of 6-10 microns. Probable lifetime at 15C, a few months? This would
suggest an oxidation rate of about 1.5 micron per month (from both
sides). At that rate a 100micron (0.1mm) would take about three years, a
1mm particle about thirty years and a 1cm cube about 300 years

>S does not appreciably oxidize in air.  

See above. It depends what you mean by 'appreciably'.

>It is bacterially mediated, and

It may be bacterially mediated. However temperature dependence is not
solely a bacterial phenomena. Certainly oxidation rates are temperature
dependent also, if you don't believe me, light some sulphur! Typically
reactions change by a factor of 2 or 3 for a 10C temp change round room
temperature. As a result I would expect temperature dependence even if
the reaction was entirely one of inorganic chemistry. Of course in a wet
cold soil, with oxygen supply to the sulphur particles slowed by a water
layer, the reaction rates could be very significantly lower.

---

From: [email-masked] (Wayne Richardson)
Date: Sun, 04 May 1997 15:22:50 GMT

>particles up as the cube, area per particle decreases as the square).

If you are assuming dissolution rate is rigorously proportional to
surface area - 10 years dissolution time for a 1mm diameter ((0.524
mm3 per particle) is equivalent to only 0.01 year for the 0.1 mm
diameter particle (0.000524 mm3). - The surface area is a cubic
function of the particle size.

More realistically, the rates of reaction are probably first order,
dependent on the amount of surface remaining at any given time. 

>sides). At that rate a 100micron (0.1mm) would take about three years, a

1,500 - 2,000 times longer using the SA approximation only

>1mm particle about thirty years and a 1cm cube about 300 years

1,500,000 - 2,000,000 times longer than the 6 - 10 micron particle

I believe that - on this scale - other factors may become quite
significant. See, e.g. Stumm and Morgan.  Solubility increases as a
function of SA but so does sublimation in the case of sulfur.
<snip>

Regards,
Wayne Richardson

---

From: Oz <[email-masked]>
Date: Sun, 4 May 1997 22:11:31 +0100

In article <[email-masked]>, Wayne Richardson
<[email-masked]> writes
>function of the particle size.

Oh? Take a cube 10mm on a side, each side has an area of 10x10=100mm^2,
to give a total surface area is 800mm^2. Cut it into cubes 1mm on a
side. You have 1000 of them. Each cubelet has a surface area of 8mm^2 so
a total surface of 8000mm^2. You have increased the area by a factor of
ten, not 1000. The surface area is proportional to the particle size for
any given quantity. Sorry about this as it validates my original figures
and invalidates yours.

>dependent on the amount of surface remaining at any given time. 

True. However we are actually more interested in how long it takes for
all the sulphur to be oxidised. This is likely to be most easily
expressed as a surface reaction rate expressed as mm per year (or
microns or whatever) which should be approximately constant. The amount
liberated as oxidised sulphur will not be linear of course, I haven't
bothered to work out the shape of the curve but for any given quantity
it will start high (lots of material, big surface area) and fall as the
particles become smaller and the surface area reduces. The rate of
change of volume will start small and grow bigger of course.

>function of SA but so does sublimation in the case of sulfur.

I would expect sublimated sulphur to have a rather short life in an
oxygen rich environment, wouldn't you? Soon converted to SO2? This
explains it's fungicidal activity of course since SO2 is known to have
fungicidal (and bactericidal) effects. In high doses it is not very good
for plants either.

---

From: [email-masked] (Allyn Weaks)
Date: Sun, 04 May 1997 02:02:13 -0700

In article <[email-masked]>, [email-masked]
wrote:

[snip]
> I have never been able to locate any papers on the Net. 

Unfortunately, getting full text for most journals, especially anything
older than a year or so, pretty much means going on a hunt for paper.  Even
for recent things, you generally have to either pay for a subscription, or
be at an organization or university that pays for a site subscription.

Most of my information below is from Ken Killham's _Soil Ecology_, a fairly
short overview, considering the complexity of the whole thing, but pretty
recent (1994).  He has about 10 pages on the sulfur cycle, and gives
references--primarily to books rather than papers, but the books he
references look like they'll probably point to papers. 

> 1) Elemental sulphur is indeed very insoluble in water.

Yup.  It's considered completely insoluble in both cold and hot water. 
It's slightly soluble in some organic solvents such as toluene, alcohol,
and ether.
 
> mediated by bacterial activity.

Quoting from Killham: "Elemental sulfur, sulphides, and several other
inorganic S-compounds can be oxidized in soil by purely chemical processes,
but these are generally less important than microbial S-oxidation."

> on temperature and oxygen concentration.

Maybe, if no bacteria are involved...but once you let them in, the rules
aren't so simple.  "In most soils, oxidation is dominated by the
thiobacilli(*) [...] Of the 9 species of thiobacilli, five have been
studied extensively and their substrate-specificity found to vary greatly. 
Oxidation of soil sulphur by thiobacilli can therefore be seen as involving
a community of species, many of which are dependent for substrate on the
product of others"  So it could be that the waterlogged soils are deficient
in one or more thibacillus species, or the temperature may not be in the
range they need to be active, or the soil porosity could be wrong for the
bacteria to physically get to the sulfur, or... 

*  Thiobacilli are bacteria that get their energy by oxidizing sulfur
(thio) compounds.  They tend to be the most acid tolerant species, which is
good, since they tend to produce sulfuric acid as a waste product :-)

'Substrate' above is the sulfur compound eaten by the bacteria.  There are
several possible pathways to get from S to SO4++; from Killham's figures,
it looks like it takes a minimum of 2 steps, i.e. 2 species.  The simplest
goes from  S  ->  SO3--  ->  SO4--.  A more complex path is:

   S  ->  S2O3--  ->  S4O6--  ->  S3O6--  ->  SO3--  ->  SO4--

Just to complicate things further, some fungi and other types of bacteria
can also get into parts of the act.  As for the rate at which S becomes
available to the plants:  "With very few exceptions, the rate of supply of
plant-available sulphate in soils is not limited by the rate of
S-oxidation, but by the rate at which organic sulfur is mineralized into
the inorganic S-pool."

> throughout the following growing year.

In practice, I don't think particle size matters all that much (aside from
gigantic lumps, perhaps).  Certainly, gardeners have been using straight
flowers of sulfur (admittedly fairly finely divided, but I'm pretty sure
it's a good bit bigger than micron sized) successfully for years to lower
pH and add sulfur.  How much you need to use, and how fast it oxidizes into
something the plants can use is going to be soil dependent even if bacteria
weren't involved (pH, moisture and other factors would make a difference). 
In an empirical system, you usually get the best rong-term results by good
note taking from year to year.

> The problem is in spreading the

But you need to be careful about when you apply it to foliage.  It's
phytotoxic above about 80F, isn't it?

> ammonium nitrate and there is a significant risk of fire and/or

Yes.  Very little sulfur is needed to set off ammonium nitrate.  But it's
more that ammonium nitrate can be very touchy.  Sulfur is a notorious
sensitizer for it, but not the only one.  There's a longish list of
compounds that OSHA rules don't allow you to store in the same cabinet with
a.n., for good reason!  Sulfur on it's own is pretty safe stuff, though as
with any dust, avoid breathing it.

>From  Killham again, in addition to the reduction of SO2 in air, the
reduction of available sulfur in some soils is due to modern fertilizers
not containing significant sulfur content, unlike the old-style ones (not
just compost, but early formulations of synthetics) combined with a
tendency to grow more crops that demand lots of sulfur.  He says that the
most common agricultural addition of sulfur now is from pesticides!  I
doubt that sulfur deficiency is really a crisis though.  It's quite a
common element, and obviously easy enough to add to soils in a way that
keeps the soil ecology healthy, unlike pesticides and the fortunately
diminishing air pollution.
-- 
Allyn Weaks  [email-masked]
PNW Native Wildlife Gardening:  http://chemwww.chem.washington.edu/natives/
Any advertisements sent to any of my email accounts will be billed $25 per
message, $1 per character, including all header lines.  No exceptions. 
Sending such mail constitutes agreement to these terms.

---

From: Oz <[email-masked]>
Date: Sun, 4 May 1997 22:19:15 +0100

In article <[email-masked]>,
Allyn Weaks <[email-masked]> writes
>inorganic S-compounds can be oxidized in soil by purely chemical processes,

I would not disagree about S-**COMPOUNDS*, particularly where they are
soluble, or at least partly so. I probably wouldn't disagree if we were
talking about those strange species that live in sulphurous pools,
although most of these do seem to use H2S as a food source rather than
elemental S.

>but these are generally less important than microbial S-oxidation."

OK. I suppose I have to bow to the evidence. I would be more convinced
if I saw some experimental evidence of this, though.

>good, since they tend to produce sulfuric acid as a waste product :-)

I wonder how well they would survive in a soil with pH 8? Typically acid
tolerant species are highly INtolerant of alkaline conditions. Put
another way, they die. Despite this elemental sulphur sprays carry no
warning about their use on alkaline soils.

>it looks like it takes a minimum of 2 steps, i.e. 2 species.  

Whilst I would not disagree that many other soil microflora would get
into the act once the sulphur has been transferred to anything other
than elemental sulphur, I would not agree that each bacteria can only do
one step. Typically bacteria can do several steps though some might be
better than others at any particular step. Also bear in mind that
bacteria excrete the active chemicals since their rigid cell wall does
not allow them to ingest particles. They thus exist in a soup of enzymes
and other products produced by themselves and any other species that may
exist nearby. 

>As for the rate at which S becomes

Ah. So now we are getting into soil anaysis. This IS a valid point since
work done in the UK has had serious problems associating sulphur
deficiency in soils with sulphur deficiency in crops. As far as I can
see this could be due to at least three things. 

1) As is documented, sulphur dioxide can be absorbed directly into
plants from the air which is not of course affected by soil anaysis.

2) Availability from the organic sulphur compounds in the soil may vary
widely from season to season, and indeed during a season.

3) Deep sulphur from older atmospheric deposition mat be accesses by
deeper rooting plants. People tend to forget that wheat roots get 2M
deep by harvest.

>pH and add sulfur.  

Hah! Unless you are going to apply tens (at least) of tonnes a year on
my soil you aren't going to get anywhere as far a pH is concerned.
Sulphates are capable of blocking the absorbtion of some essential trace
elements so I would suggest caution. I was always under the impression
that flowers of sulphur was mainly used in gardens as a fungicide, for
various rose diseases for example.

>phytotoxic above about 80F, isn't it?

Odd statement to be made for an element that is 'almost completely
insoluble' and 'does not react directly with oxygen at normal
temperatures'? On the other hand I would expect sulphur dioxide to be
distinctly phytotoxic at high levels.  :-)

>not containing significant sulfur content,

Correct. Single superphosphate contained significant sulphur (12%, I
forget). However the phosphate content was very much lower and the price
was the same. Given the costs of haulage, I doubt this will change much
which makes it an expensive fertiliser. The same with sulphate of potash
and ammonia.

>He says that the
>most common agricultural addition of sulfur now is from pesticides!  

I think rather tongue in cheek. Until very recently (in the UK at least)
NO sulphur was applied, except elemental sulphur as a fungicide.

>I
>keeps the soil ecology healthy, 

Better to have it for free.   :-)
I suppose sooner or later the power station sulphur cleaning waste will
be processed (lots of heavy metals in them I understand) and sold back
to farmers to put on the land. Not remotely as efficient as the old way
that gave agricultural sulphur for free, and no sulphur processing
charge for your electricity. OK, somewhat in jest I admit but I doubt
anyone included the cost of having to use sulphur as a fertiliser when
they did the cost-benefit analysis.

>unlike pesticides and the fortunately

The soil, in my part of the world, was not affected by acid rain. Quite
the contrary. It's pretty much neat chalk chippings.