Soil Modification in pre- contact Māori kūmara gardening: Use of charcoal ? Mike Burtenshaw Senior Lecturer Natural Resource Centre The Open Polytechnic.

Soil Modification in pre-contact Māori kūmara gardening: Use of charcoal ?

Mike BurtenshawSenior LecturerNatural Resource CentreThe Open Polytechnic of New ZealandKuratini 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 Bio-Protection 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

Extent of Māori kūmara gardening In Aotearoa/ New Zealand with key plaggen soil locations1. Waikato Basin2. Waimea West3. Makara Beach4. Palliser Bay5. Papamoa.

1

2

5

34

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 49-

86%) 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

ConclusionMāori 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 papersMcFadgen, 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.