[Terrapreta] Soil ph

[Randy Black]

Rich, There are ways to reduce ph including sulphur. One way I am
looking at is using pine needle biochar. I do not have any field results
as of yet but the idea is:

 

 

The ph of Pine Needle Biochar by Randy Black 

 

Note: This experiment was done in my kitchen using a blender, small
measuring cup, and litmus paper. Do not confuse this with a real
laboratory science experiment or a real science journal article. I tried
to be as exact as I could but the variability of the pine needle
biochar, the charring process, and my measuring and material processing
make the results a measure of generalized trends not specific facts. I
encourage others to try this or other Terra Preta science experiments
and report the results as there are huge areas of Terra Preta applied
technology that we are only now experimenting with and understanding.

 

Introduction and Experimental Procedures

Pine needles are an acidic material and pine needle mulch has been used
to lower the ph in soil. This investigation looks at the ph effects of
pine needle biochar on water with ph levels of 7, 8, and 9. It also
looks at pine needle char from across the combustion continuum of
partial char to char and compares them with uncharred pine needles and
an oil/water material collected from condensed pine needle smoke.
Charcoal has the affect of increasing the ph in soil and this experiment
investigates the ability of pine needle biochar to decrease the ph in
soil. 

 

The pine needles were charred in a small metal kiln at a low temperature
for 6 hours. There was a high variability in the temperature as the heat
source from burning wood in the bottom of the kiln was closer to the
some of the pine needle material than other parts of the sample. The
pine needles were separated by larger wood pieces from the burning pine
wood (heat source), but were exposed to smoke from this source. It has
been noted in previous burnings that this smoke leaves a thin coat of
volatile oil on the sides of the kiln and material at the top of the
kiln so it is presumed that the partial char pine needles also were
coated with this oil and a small part of the ph results may be due to
this oil.

 

The pine needles were collected from the forest floor and were a
combination of last years needles which were tan (70%), and previous
year's needles which were tan to grey (30%). The needles maintained
their structural integrity and were dry to the touch. One thing noted in
this and in previous experiments with charring pine needles is that the
smoke given off is much thicker than regular pine wood being charred and
there is noticeably higher moisture content. This was evident by the
condensation on the top of the kiln lid which was collected and is the
"bio-oil" in this investigation. One interesting fact when charring pine
needles is that when the oxygen is restricted to stop the burn unlike
regular charcoal loads the mix continues to smolder at a low level until
put out by water. This implies that the gases from the heated pine
needles provide enough oxygen to continue the charring process. The pine
needles in this study continued to smolder in these conditions for an
additional 9 hours.

 

When the mass of needles was removed from the kiln it was layered with
partial char on top to charred pine needles on the bottom. The samples
in these ph experiments are from these two layers and have the following
characteristics. The partial char is a golden brown color, maintains the
original pine needle structure, and is sticky wet to the touch due to
the condensate from the pine needle pitch and burning wood. The pine
needle char still looks like pine needles but is dry and can be easily
crumbled into small pieces and powder. The variability of the pine
needles across the combustion continuum and variability of the charring
process temperatures and conditions makes the data of this study highly
subjective and the results should be looked at as generalized trends not
specific data points.

 

All of the ratios in the following results are by volume not weight and
further studies using weight ratios will need to be done to calibrate
the ph reduction capacity of pine needle biochar. The processing of the
material (dry unburnt pine needles, partial char, char, and bio-oil),
and its effective surface area lends further uncertainty to these
results and again these results are generalized trends not specific
facts.

 

The pine needle material was tested with distilled water (ph 7), tap
water (ph 8), and water that had been soaking in pine charcoal (ph 9).
The testing was done with litmus paper and read visually so the data is
not exact figures but approximations of the ph affects of pine needle
biochar.

 

Results

Experiment 1

The four types of pine needle material are dry unburnt needles, partial
pine needle biochar, charred pine needles, and bio-oil made from
condensed pine needle smoke. In the first set of experiments each
material was mixed with an equal volume of water stirred for 30 seconds
and measured in the next 30 seconds. Data is given in ph of water
followed by ph of the change.

1.      Dry unburnt pine needles with ph 7 water - 6.9 to 7 ph; ph 8
water - 7 ph; ph 9 water - 8 ph.

2.      Partial pine needle char with ph 7 water - 6.4 ph; ph 8 water -
6.5 ph; ph 9 water - 6.5 ph.

3.      Charred pine needles with ph 7 water - 7 ph; ph 8 water - 7.5
ph; ph 9 water - 8.1 ph.

4.      Pine needle bio-oil with ph 7 water - 6 ph; ph 8 water - 6 ph;
ph 9 water 6 ph.

 

Experiment 2

The following results are from charred pine needles in both ph 8 and ph
9 water with readings taken at 1, 5, 10, and 20 minutes.

1.      In ph 8 water - 7.5 ph at 1 minute; 7.1 ph at 5, 10, and 15
minutes.

2.      In ph 9 water - 8.1 ph at 1 minute; 7.8 ph at 5 minutes, 7.5 ph
at both 10 and 20 minutes.

 

Experiment 3

The following experiment uses ph 8 water and charred pine needles in
increasing ratios of  water to charred pine needles with readings taken
at 1, 2, 5, and 10 minutes.

1.	Ratio 4 to 1; ph 7.4 at 1 minute; ph 7.1 at 2 minutes; ph 7 at
both 5 and 10 minutes.
2.	Ratio 8 to 1; ph 7.6 at 1 minute; ph 7.3 at 2 minutes; ph 7.2 at
both 5 and 10 minutes.
3.	Ratio 16 to 1; ph 7.9 at 1 and 2 minutes; ph 7.8 at both 5 and
10 minutes.

 

Experiment 4

The following experiment used ph 9 water and bio-oil in increasing
ratios of water to bio-oil. Measurements were taken at 1 minute.

1.	Ratio 4 to 1 ph 6
2.	Ratio 8 to 1 ph 6
3.	Ratio 16 to 1 ph 6
4.	Ratio 32 to1 ph 6.5
5.	Ratio 64  to 1 ph 7.1

 

Discussion

The results in Experiment 1 show that the acidic effects of pine needles
rest mainly in the volatile oil/acids contained in pine needles as seen
in the partial char and bio-oil results bringing the ph levels down to
below 7. However pine needle char will bring the ph level of water down
to towards the neutral level of ph 7 as seen in Experiments 2 and 3 with
longer exposure. The difference between the ph affects of bio-oil and
charred pine needle may be due to a chemical process versus and
physical-chemical process as low temperature biochar does contain some
of the parent materials properties as impurities with the char. More
investigations are needed to identify what affects the high surface
area, adsorption properties, and impurities in low temperature pine
needle biochar have on modifying ph. Dry ground uncharred pine needles
also lower the ph of water but take much more processing time and energy
and do not have the adsorption properties or increased cation exchange
capacity of char.

 

The results of Experiment 4 show that a small amount of pine needle
bio-oil can significantly reduce the ph of large amounts of water. At a
ratio of 16 parts ph 9 water to 1 part bio-oil the ph was still reduced
to 6 within one minute. At a large ratio of 64 to 1 the bio-oil still
reduced the ph to 7.1. It is clear that the condensed pine needle smoke
concentrated the acids in pine needles. Field investigations should also
look into this bio-oil being applied back to pine char before use and if
the adsorption properties and recalcitrance of char might make this a
long term ph modifying soil amendment. 

 

 

What affects partial char, char, and bio-oil would have on high ph soils
would need to be field tested with a variety of soil under various
condition and with differing percentages of pine needle biochar/bio-oil.
Reducing the ph of water and reducing the ph of soils are two different
processes and long term field testing is needed. Most likely the
acidifying affects of the bio-oil and partial pine needle biochar would
be temporary but due to the recalcitrance of charcoal, its high surface
area, and adsorption properties, charred pine needles may be able to
maintain soil at a ph level of 7 for much longer. 

 

Summary

The implications of pine needle biochar for Terra Preta research and
charcoal enhanced soils are tremendous. First, we now have the ability
to add char to soil that will reduce the ph level instead of increase it
but still contribute the benefits of charcoal in soil using a common
readily available material. This has implications for alkaline soils and
to create soils for crops that need acidic conditions. Second, this
demonstrates that we can tailor one of the chemical properties of
biochar to match soil conditions based on the chemistry of the parent
material. This means that Terra Preta science can be applied to a wide
variety of soils and has the potential to be individualized to match
soil ph conditions and crop ph ranges. Third, if we can do this with ph
levels can Terra Preta science be applied to doing this with trace
minerals for crop nutrients or for a chemical/mineral balance that may
be selective in establishing a desirable specific microbial community.
The physics and chemistry of pine needle biochar's ph affects are
entirely different from what would be needed to add specific
minerals/chemicals to soil but demonstrates that Terra Preta technology
is much more than just adding charcoal to the soil and could
revolutionize our ideas on soil and crop management.

 

 

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