OR1-3
低土圧条件下におけるサツマイモの塊根肥大
Tuberous root enlargement of sweet potato under low
soil presser conditions
工藤航平 1, 佐藤直人 1, 登尾浩助 1,Kohei KUDO1, Naoto SATO1 and Kosuke NOBORIO1
1

明治大学農学部，School of Agriculture, Meiji university

1. Introduction
To realize long-term manned space exploration, we must overcome many challenges, such as securing water,
oxygen, and food, regenerative circulation of materials, transportation cost of supplies, and ensuring a richliving environment for astronauts1)2). These challenges may be solved through space agriculture inducingmicrogravity, which reduces earth pressure because the volumetric force of gravity does not act3). Root
diameter increases, whereas root elongation is hindered as mechanical impedance from soil particlesincreases4). Therefore, low gravity makes low earth pressure, i.e., low mechanical impedance, which may
impede the enlargement of sweet potatoes, an optimal crop for space agriculture5). We investigated the effectof reduced earth pressure on the tuberous root enlargement of sweet potatoes.
2.

Materials and methods
Polystyrene foam microbeads with 1 mm diameter (Refillable Beads, Kinshi) were used as the growing

medium to produce low earth pressure. The bottom of a plastic growing container (42.5 cm long, 65.5 cm wide,and 39 cm high) was covered with granular rockwool (R110, Taiheiyo Materials), and the microbeads werefilled on it. The bulk density of microbeads filled in the container was 0.024 g/cm3. We prepared a low earthpressure treatment in which no load was applied to the microbeads and a high earth pressure treatment inwhich weights were applied to the top surface of the foam microbeads (Fig. 1). We planted sweet potato shoots(Ipomoea batatas Lam., Koke 14 go). We grew until their roots have grown to 30 – 40 cm long. The root tips wereallowed to touch the rockwool on the bottom. The plant bodies were fixed with strings to prevent them fromsinking into the microbeads. The containers were covered with black mulching film to reduce evaporationfrom the surface. We supplied nutrient solution (Tank mix A and B, OAT Agrio) using a peristaltic pump for
20 minutes every hour. The experiment was conducted in a natural-light gas-exposed chamber (S-2003A, KoitoIndustries) at Ikuta Campus, Meiji University, Kawasaki, Japan. The room temperature inside the chamber
was 27 °C, and the relative humidity was over 80%. We harvested the whole plants forty days after
transplanting and measured total fresh weight, stem and leaf fresh weights, root fresh weight, tuber freshweight, stem and leaf lengths, and root length. We assumed roots more than 5 mm in diameter as tuberous
roots.
1 of 3

Figure 1. Cross-sectional view of experimental apparatuses: (a) high earth pressure, and (b) low earthpressure.

3. Results and Discussion
Figure 2 shows the fresh weight difference between high and low earth pressure treatments. The shootand root weights of low-pressure treatment were larger than those of high-pressure. Root tubers wereheavier in the high-pressure treatment than in the low-pressure treatment (Fig. 3). These results suggestthat the tuber roots grew faster under the high-pressure treatment than the low-pressure treatment,
although the growth of the whole plant was slower. The weight of roots at the high-pressure treatment
was smaller than at the low-pressure treatment, whereas the weight of root tuber at the high-pressure
treatment was larger than at the low-pressure treatment. This suggests that the amount of fine roots (<5mm in diameter) might decrease in high pressure. Tuberous root formation was observed even under
low earth pressure conditions, indicating that tuberous root enlargement is possible even at earthpressures lower than the usual field earth pressure. It was also confirmed that increasing the earthpressure could accelerate tuberous root enlargement.
100ighowFresh weight (g)806040200Shoot

Root

Root tuber

Figure 2. Growth of sweet potatoes in high (black) and low (gray) earth pressure treatments.

Figure 3. Effect of earth pressure on root tuber length: (a) high earth pressure, and (b) low earth pressure.

References

2 of 31)

2)
3)
4)
5)

G.D. Massa, N.F. Dufour, J.A. Carver, M.E. Hummerick, R.M. Wheeler, R.C. Morrow, T. M. Smith: VEG01: Veggie
Hardware Validation Testing on the International Space Station. Open Agriculture, 2 (2017) 33, DOI:
https://doi.org/10.1515/opag-2017-0003.
M. Yamashita and Space Agriculture Saloon: Development of the Space Agriculture Concept. Space Utiliz. Res., 23(2007) 396.
Y. Kitaya: The Interface between Space Exploration and Agricultural Science: Construction of a Closed EcologicalLife Support System. Academic Trends, 21 (2016) 87, DOI: https://doi.org/10.5363/tits.21.2_87. (in Japanese)
R.S. Russell: Plant root Systems: Their function and interaction with the soil (N. Tanaka, Trans.). Rural Culture
Association (1981). (Original work published 1979)
Lunar Farming Concept Study Working Group: Report of Lunar Farming Concept Study Working Group 1st, JAXASpecial Publication, JAXA-SP-19-001 (2019)© 2023 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

3 of 3