This document summarizes an experimental archaeological project investigating ancient paddy fields in Japan. The project involved cultivating rice under different planting densities and conditions at an experimental paddy field to understand rice farming practices in the past. Key findings include that dense planting of 121 plants/m2 reduced weeds and increased yields compared to normal densities of 18 plants/m2, and crop yields in ancient Yayoi period fields could be estimated at 100-110 kg/10a for normal densities and 144-212 kg/10a for dense planting. Phytolith analysis found rice phytolith densities varied among surface samples from the same fields, making it difficult to detect short fallow periods less than 2 years.

1. Experimental archaeological
project investigating ancient
paddy fields
Yukiko Kikuchi 1
Masashi Mori 1
Hiroo Nasu 2
Makoto Kikuchi 3
Takuma Yogo 4
1 Paleo Labo Co. Ltd., Japan
2 The graduated university for advanced studies
3 Kobe University
4 Waseda University

2. • Investigation of paddy soils and rice at a
restored paddy field
1. Information about aspects that no longer exist
ex) crop yields of rice, cultivation methods
2. Information to interpret analysis results
ex) phytolith analysis, pollen analysis, seed
identification …
Introduction

3. • Criterion for judging whether it is a paddy soil
or not （Fujiwara and Sugiyama 1984）
5,000 rice phytoliths (from motor cells) per gram
→ case 1 : very few rice phytoliths from some paddy fields
case 2 : more than 5,000 rice phytoliths /g from other
remains (not paddy fields)
• Some cases : multiple samples (horizontal or
vertical) analyzed from one same paddy field
Phytolith analysis of ancient
paddy fields in Japan

4. • Clarify the real situation of rice farming in the
past by comparing the data collected from
carefully controlled experiments at our paddy
field and the data from archaeological sites
• Yield survey
Phytolith analysis
Goal of our project

5. Location Iruma city, Saitama Prefecture
☆
Sayama Hills

6. • Paddy fields at valley
bottom
• East : Copse
West : Tea garden
Experimental paddy field
Location
Nishikubo Wetlands

7. • Plant 2 types of red rice
• Different densities (18/m2, 30/m2, 121/m2)
• No agricultural chemicals
• No fertilizers, no manures
• Cultivated, Planted, cut, all by human power
-no machines
• 18th year of cultivation since 1998
Cultivation condition

8. Planting Density
7cm
・Density of the tracks of stubbles
121 stubbles/m2 (8cm between stubbles)
Present paddy fields : 18 plants/m2 (25cm between
plants)
Archaeological site of Hyakkenngawa-Haraojima
Late Yayoi period
(0-250 AD)

9. • Tsutsu
・From Tsutsu, Tsushima
(Nagasaki prefecture)
・Black chaff
• Kitakami
・Obtained from a farmer in
Tohoku region
・Yellow chaff
* These are expedient names
Planted red rice
Tsutsu Kitakami

10. Planted sections
6 Jul
Normal plant density
(18 plants/m2
)
High plant density
(121 plants/m2
)
Broadcast seeding
(2014)
Broadcast seeding

11. Yield calculation
• Investigate 4 yield components
1 Panicle number per 1m2
2 Grain number per panicle
3 Percentage of ripened grains
4 1,000–grain weight (dehulled)
・1 & 2 : Investigate 20 average sized plants in each section
・3 & 4 : Investigate 10 average sized plants in each section
• Crop yields per 1m2
= Product of 4 yield components

12. 0
50
100
150
200
250
300
350
2005 2006 2007 2008 2009 2010 2011
kg/10a
Tsutsu
Broadcast seeding
Tsutsu
18 plants/㎡
Tsutsu
30 plants/㎡
Tsutsu
121 plants/㎡
Kitakami
Broadcast seeding
Kitakami
18 plants/㎡
Kitakami
30 plants/㎡
Kitakami
121 plants/㎡0
50
100
150
200
250
300
350
2005 2006 2007 2008 2009 2010 2011
kg/10a
Tsutsu
Broadcast seeding
Tsutsu
18 plants/㎡
Tsutsu
30 plants/㎡
Tsutsu
121 plants/㎡
Kitakami
Broadcast seeding
Kitakami
18 plants/㎡
Kitakami
30 plants/㎡
Kitakami
121 plants/㎡0
50
100
150
200
250
300
350
2005 2006 2007 2008 2009 2010 2011
kg/10a
Tsutsu
Broadcast seeding
Tsutsu
18 plants/㎡
Tsutsu
30 plants/㎡
Tsutsu
121 plants/㎡
Kitakami
Broadcast seeding
Kitakami
18 plants/㎡
Kitakami
30 plants/㎡
Kitakami
121 plants/㎡
The difference of crop yields by density

13. 0
50
100
150
200
250
300
350
kg/10a
Nara-Heian period
(710-1185)
Historical record
Conventional
estimates
Results of
the experiment
Estimating crop yields in Yayoi period

14. Normal plant density
(18 plants/m2
)
High plant density
(121 plants/m2
)
Japanese name Scientific name
Number of
individuals
Cover
degree (%)
Number of
individuals
Cover
degree (%)
Konagi Monochoria vaginalis 40 20 8 5
Kikashigusa Rotala indica 248 15 29 1
America-azena Lindernia dubia subsp. major 10 1 33 1
Kikumo Limnophila sessiliflora 7 1 4 1
Total 305 37 74 8
Monochoria vaginalis Rotala indica Limnophila sessiliflora
(3 Aug 2014)
Lindernia dubia subsp.
major
Normal plant density (18 plants/m2
) High plant density (121 plants/m2
)
The difference in the appearance of
weeds by plant density

15. Phytolith analysis sampling

16. Horizontal distribution of the
density of rice phytoliths
Fallow Field
2014
Fallow Field Kitakami 18/m2Kitakami 18/m2
0 - 5,000
- 10,000
- 15,000
- 20,000
- 25,000
- 30,000
30,100-
( /g)
/g a b c d e g i j l m
2012 3 45,300 17,700 - 20,900 20,000 21,700 13,300 8,700 22,700 19,300
2012 4 7,600 12,500 16,000 18,000 - 7,700 21,700 16,700 14,400 27,000
2014 3 - 22,200 - 19,600 - 17,200 - 11,800 8,400 -
2014 4 - 21,500 - 16,800 - 4,400 - 27,500 2,600 -
3 34 4
2012

17. Changes of the amount
3
Fallow Field
( /g)
4
Normal
Plant Density
/g)
2012 Spring 18,340 13,860
2014 Spring 15,840 14,560
P-value
(α = 0.05) 0.497 0.874

18. Vertical distribution of rice phytoliths

19. • Dense planting seen at Hyakkengawa-Haraojima site (121
stubbles/m2) was a possible cultivation method in late
Yayoi period.
• Crop yield per unit area will be higher when densely
planted.
• Dense planting (121 plants/m2) reduces weed growth to
25% of normal density planting.
• Crop yields of rice in Yayoi period can possibly be estimated
up to 100-110 kg/10a from normal planting (18 plants/m2),
and 144-212 kg/10a from dense planting (121 plants/m2).
• The density of rice phytoliths varies greatly among surface
samples from same rice fields.
• It is difficult to get evidence of a short term fallow less than
2 years using phytoliths analysis.
Summary