Soil Modification in precontact Māori kūmara
gardening: Use of
charcoal ?
Mike Burtenshaw
Senior Lecturer
Natural Resource Centre
The Open Polytechnic of New Zealand
Kuratini Tuwhera
Introduction
“There is one way we could save ourselves [from global
heating] and that is through the massive burial of
charcoal” - James Lovelock.
Carbonscape. New Zealand Company was judges top
choice in 2009 Financial Times Climate Challenge
Award. This company has perfected a method of
producing charcoal or biochar using mobile commercial
microwave oven.
Terra preta soils in central Amazon Basin an example of
where people amended soils to increase productive
capacity.
Māori commonly amended soils by adding sand and
gravel but did they deliberately use charcoal as a
addition?
Table 1
5454
New Zealand Biochar Research Centre and BioProtection Research Centre are two New Zealand
organisations researching the use of biochar.
Method - evidence of the use of charcoal in ‘Maori
Plaggen soils’
• A review of key literature on Māori gardens and soils
was undertaken (Colenso 1880, Best 1976, Rick and
Bruce 1923, McFadgen 1980, Leach 19197)
• Personnel communication with archaeologists (Gumbley,
Leach, Davidson) who are currently or have in the past
undertaken archaeological investigation of Māori garden
sites
Māori garden soil modification
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Kumara garden puke (Whatarangi)
Māori soils
1
2
3
4
5
Extent of Māori
kūmara
gardening In
Aotearoa/ New
Zealand with key
plaggen soil
locations
1. Waikato Basin
2. Waimea West
3. Makara Beach
4. Palliser Bay
5. Papamoa.
Manure was tapu
• Deeply held beliefs concerning and sacred and profane
meant the use of animal dung as manure was totally
abhorrent
• Various tapus (taboos) played and important part in the
agricultural life of Māori
• Food must not be contaminated by unsanctioned contact
with manure including human waste
Soil modification with sand and sandy
gravel common
• Colenso (1880) described the transportation and addition
of sand to garden soils as an annual task.
• McFadgen classified Māori plaggen soils as varying
between two types. One where sediments are thickly
spread 20cm-30cm deep but poorly mixed with base soil
and one where transported sediments are well mixed with
the base soil.
• Gumbley believes sand was added at the position of
individual puke (mounds) and the excavated soil
dispatched by sand was used to form the planting mound
Gumbley’s interpretation of sand
additions to puke
Grades of sand from Gumbley et. al.
Particle sizes sampled
• > 2mm = gravel
• 0.5 – 2mm = coarse sand
• 0.25 -0.5mm = medium sand
Results
• One site had 67% added sand and gravel (range 4986%) equivalent to 2 litres of added sand per litre of soil.
• The second site had 47%( range 31-87%)
• 70% added sand is roughly equivalent to adding 2 litres
of sand per litre of soil
Grades of sand used from McFadgen
Coarse sand additions common practice
but not on all Māori garden areas
• Added sand ensured adequate drainage of kūmara puke,
helped with early warming of the puke and aeration is
also essential for the initiation of tuber roots on sweet
potato plants. Māori had an established practice of
adding coarse sand.
What about charcoal?
• Did we have the equivalent of terra preta soils Māori
garden areas?
• What is the evidence?
Addition of ash and charcoal
according to Best
Elsdon Best describes a treatment for some soils
• Manuka brush or second growth is cut and spread over
the field and left lying there until planting time is near
• Then set fire to so a layer of charcoal and ash covers the
earth
• Residue of burned brush called “kota”
• Cover again with mānuka to prevent wind blowing away
the kota before mound forming and planting
• No deliberate effort to create a slow burning environment
that would result in more charcoal
Rigg and Bruce (1923) on charcoal
Reporting on Waimea West these authors describe
• Māori gravel soil is so dark when wet to appear black in
contrast to natural brown of parent soils
• They conclude dark appearance results from the
presence of charcoal introduced during preparation of the
land
• No recent analysis of these soils found but it requires
further investigation.
Gumbley, Higham & Low (2004)on charcoal
additions
Reporting on Māori soils in mid-Waikato Basin
• Charcoal present was from original podocarp/broadleaf
forest rather than pioneer seral species and was
deposited from original burn off.
• However they do comment that mānuka charcoal was
present in other sites.
McFadgen on charcoal
Archaeological evidence
Conclusion
Māori have an extensive knowledge of different soil types with
many linguistic terms for soil types.
The use of sand and gravel to modify soil in kūmara gardens
was common and well embedded in traditional agricultural
knowledge. Further experimental work is need to investigate
the effects.
Reports of burning wood to create ashes for soil modification
relate to specific sites or types of soil.
There is no evidence pointing to the deliberate production of
charcoal as a soil additive in pre-contact Māori kūmara
gardening with the exception of Waimea West
The occurrence of elevated levels of charcoal in some soils
result from the original forest burning where a reduced
oxygen or slow burning event occurred.
Acknowledgements
• Plant and Food Research Ltd for continued funding of our
experimental kūmara gardens
• Warren Gumbley, Foss Leach and Janet Davidson for
personnel communications on this topic
• Key research papers
McFadgen, B. G. (1980)> Maori Plaggen Soils in New Zealand, Their
Origin and properties. Journal of the Royal Society of New Zealand,
10: 1. 3-19.
Gumbley, W., Higham, T.F.G., Low, D.J. (2004) Prehistoric Horticultural
Adaption of Soils in the Middle Waikato Basin: review and Evidence
from S14/201 and S14/185, Hamilton. New Zealand Journal of
Archaeology, 24: 5-30.
Rigg, T. & Bruce, J. A. (1923) The Maori Gravel Soil of Waimea West,
Nelson New Zealand. Journal of the Polynesian Society. 32: 84-93.