沙漠研究 22-1, 29 -32 (2012 )"ICAL 1 / DT X"

Journal of Arid Land Studies－Refereed Paper－

Creation of Soils by Humic Substances and CO2 for Space Agriculture
Yuuki YAZAWA*1), Shojiro ASAMI1), Kouhei YAMAGUCHI1), Yui ITO1) and Hiroshi TAKEDA1)
Abstract: In the present research, we investigated that soil created from Ca-plagioclase (source from Crystal Bay) by geochemical
weathering with non-living natural humic substances (humic acid extracted by Canadian peat moss) and nano-bubble aqueous solutionof CO2 gas. The CO2 bubble solution was adjusted to pH 3.4 (calculated concentration: 320 mmol-CO2/L) with nano-size bubble.
Production of soils were accomplished by the addition of 0.1 g of Ca-plagioclase, 0.0~0.2 g of humic acid and 20 mL of CO2 bubble
water in the 25 mL of high-pressure Teflon reactor under 293 or 473 K (autogenous pressure 0.02 or 1.62 MPa). After reaction, these
metal elements released from Ca-plagioclase were useful in assessment of soil formation. As the result, four metal ions composed inCa-plagioclase were slightly soluble by the addition of humic acid but freely soluble by the addition of humic acid and CO2 gas incombination. In addition, the increasing reaction temperature was characterized by a marked difference in this dissolution tendencyof Ca-plagioclase. Consequently, terrestrial humic materials including fulvic acid can not only accelerate to dissolute elements andsynthesize clay form from Lunar and Martian regolith with chemical weathering but also control to buffer for nutrient, toxic elementand CO2 gas. And the derived water-soluble humic materials with CO2 and its complex with metals bring the expected results toaccelerate for physiological activities of root growth in higher plants and chlorophyll production in phytoplankton for space agriculture.
Key Words: Chemical weathering, CO2 nano-bubble, Humic substances, Soil, Space agriculture

1. Introduction
Scope for manned space activities is widely discussed
among space faring nations as one of the important features inpost-International Space Station era. There seems to be aconsensus that human presence is necessary to expedite Moonand explore to Mars for purpose of clarifying the birth andorigin of life. The goal of space agriculture is to create andmaintain optimum living environment on extraterrestrial planet
for human and other living organisms, including animal, plantand microorganism to live comfortably. Although newphilosophy suggests that the hyperthermophilic aerobic
composting bacterial ecology utilize to create soil from humanand animal waste and inedible biomass, an exploration ofastrobiology may be complicated in case living bacteria
administer irresponsibility. But then the global climatechange of our living earth is accelerating by human activities
involving land-use management. Despite great progress inoverall agricultural productivity in recent decades, landdegradation has reduced the productive capacity of soils onnearly 40% of the world’s agricultural land. On oneself,
today’s people lost readily soil resource created fortuitously byancient microbes. Consequently, we may be difficult tosustainedly control the chemical and biochemical reaction inbiosphere before creating “good soil” on the Earth and Moon.
We investigated that soil created from Ca-plagioclase bygeochemical weathering with non-living natural humic* Corresponding Author: yuuki.yazawa@it-chiba.ac.jp
2-17-1 Tsudanuma, Narashino, Chiba 275-0016, JAPAN1) Department of Life and Environmental Sciences, Faculty of Engineering, Chiba Institute of Technology

substances and nano-bubble aqueous solution of CO2 gas.
The concept of our research suggested not only an application
for space agriculture by terrestrial desert technologies but also a
feedback to clarify the origin of desertification on the earth.

2. Experimental Methods
2.1. Soil materials
We employed Ca-plagioclase from Crystal bay, Minnesota,
with An76 (Ca0.78Na0.23Al1.73Si2.23O8), which is in betweenlunar mineral regolithes and Martian ones. After smash, thepowdered Ca-plagioclase through a sieve less than 75 µm in
diameter, and its relative surface area was 1.75 m2/g. The
used humic acid in this experiment was extracted from
Canadian peat moss in accordance with the standard method ofInternational Humic Substance Society. This humic material
had average molecular weight of 60,000 g/mol, andC2450H3000N86O1650 as chemical formula. The nano-bubble
aqueous solution of CO2 gas was prepared by nano/micro
bubble generator with pressure type (Aura Tec Co., Japan).
The formed solution was pH 3.4, which is equivalent to 320
mmol-CO2/L, with void ratio of 0.15% and bubble diameter of340 nm.
2.2. Hydrothermal reaction and analysis
The 0.1 g of Ca-plagioclase and 20 mL of water
with/without CO2 bubble added into high-pressure gas vessel
with 25 mL. The each 0.0, 0.1, and 0.2 g of humic acid

WaterHumic catalyst(g/20 mL)

CO2 water

0.00.1
0.2

150

1500

T=473 K

T=473 K

100

CDOC (mg/dm3)

1000

50CSi (mg/dm3)

added to those reaction systems, and reacted at 293 or 473 Kfor 24 h. Each self-begotten pressures in vessel werecomparable to 0.02 or 1.62 MPa.
After predetermined time, these reaction solutions wererefreshed immediately to 293 K and separated into solid-liquidby centrifuge. Each supernatant liquids were measured forpH, metal ions (Na, Ca, Al, and Si) by atomic absorption
spectrophotometer, and dissolved organic C (DOC) by totalorganic carbon analyzer.

0T=293 K

500

0T=293 K

1000

100

3. Results and Discussion
500500006121824606121824t (h)(b) DOCt (h)(a) Si
T=473 K

4Log {(a Ca+a2 Na) / a2 H}

3.1. Dissolution reaction of Ca-plagioclase by humic acidand CO2 bubble
The concentration changes of Si and DOC with reaction
time under 293 and 473 K show in Figure 1 (a) and (b),respectively.
As estimation of process of Si concentration in reaction
solution, the carbonated bubble water was accelerated todissolute Ca-plagioclase under 293 K in comparison with water(reaction route ① in Fig. 2). Moreover it was confirmed todissolute Ca-plagioclase by H+ ion dissociated from humic acid(route ②). With raise in temperature, dissolution rates of all
reaction system were accelerated, the combinational effect ofhumic acid and carbonated bubble water became prominent(route ④). The process of DOC concentration in Figure 1(b) leads to a further understanding of this advantageous effect,
humic acid was slightly soluble under 293 K but freely soluble
to 1/4 ~ 1/3 of DOC in initial added humic acid under 473 K.
So, it has a guess that water-solubilization of humic acid wasaccelerated by hydrothermal decomposition and carboxylation
with CO2 gas and metal cation (M+) eluviated fromCa-plagioclase (route ③). As mentioned above, the H+ ion
was sequentially generated in reaction system with exchanging
between H+ in acidic functional groups of water-soluble humic
acid and M+, and the chemical weathering made further progress
to create soil (organo-clay complex, aggregation, route ⑤).
At a carboxylic concentration of 0.01 mol-COOH/L in acidsolution under 293 K, the relative effectiveness of these ligands
on promoting dissolution rate of Ca-plagioclase was humic
acid (2.0 nmol/m2/s) with the standard of Si element. Thisvalue was only little lower than oxalic (14 nmol/m2/s), lactic(9.0), garlic (7.8) and fulvic (5.7) acid however dramaticallyincreased to 10.5 by a combination of humic acid andcarbonate bubble solution. The strengths of organic acids topromote dissolution is related to the initial pKa 2.58 (oxalic),3.52 (lactic), 4.37 (garlic) and 4.16 (fulvic or water-solublehumic), respectively, but it is related to strength of Ca-ligand
complex formed in solution (formation of secondary mineral;clay) or on the mineral surface (development of soil20-2T=293 K
420-2-4.0-3.5-3.0-2.5

Log a Si(OH)4(c) Stability-2.0

Fig. 1. Time dependence of Si dissolved from Ca-plagioclase andDOC by humic acid and carbonated bubble water under 293
or 473 K. Estimation of stability in mineral solutes on a basis ofdissolution equilibrium with acid.

aggregation). Formation of clay minerals is expected after
adjusting condition of pH and Al/Si ratios to bring them in thestability field of clay minerals.
As estimation about temperature dependence of dissolution
rate of Ca-plagioclase by the Arrhenius equation, the additionof humic acid caused frequency factor and activation energy toincrease. In contrast, the carbonate bubble solution wassubstantially reduced activation energy of reaction between
Ca-plagioclase and humic acid, therefore acted as catalyst forthis reaction.
3.2 Estimation of stability in mineral solutes on a basis ofdissolution equilibrium with acid
The stability of secondary mineral from mineral solutes as
the mentioned in 3.1 organized on the Ca-plagioclase, Camontmorillonite, kaolinite, and gibbsite of dissolution

Carbonated water
CO2 + 2H+

CO2 + 2H+

①H+M+

④Plagioclase ②
CO2 + 2M+

⑤H+Soil (Organo-clay)

COO-H+Humic acid

COO- M+
COO- M+③orM+ - OOC
COO- M+
Water-soluble humate

Fig. 2. Reaction mechanism of Ca-plagioclase, humic acid, and carbonate bubble water to soil.

equilibrium with acid. This means the generation of gibbsite
has an advantage in the event that Log aSi(OH)4 value lower, andthe generation of clay with layer silicate (i.e. montmorillonite,kaolinite) in the event that both values of Log aSi(OH)4 andLog {(aCa+a2Na)/a2H} higher. From the result in Figure 1 (c),the addition of humic acid significantly increased Log aSi(OH)4value but decreased Log {(aCa+a2Na)/a2H} value.
Incomparison with 293 K, both values were increased by acombination of humic acid and carbonate bubble solution
under 473 K, especially the stabilization of clay formation wasexpected.

4. Point of Soil Creation by Humic Substances forSpace Agriculture
Wada et al. (2009) examined the possibility of space
agriculture, for which air, water and regolith are brought into apressurized dome at the first stage. At the second stage, theyplan to revitalize air and water, in addition to supplying
ordinary agricultural products such as foods, fibers and timber.
Recycled use of materials is a major function of agriculture on
Moon and Mars. Space agriculture is also characterized bylimited species in the ecosystem, contained inside a small dome.
Because the main target of lunar and Martian exploration isastrobiology research to search for extraterrestrial life or biotic
substances, Wada et al. (2008) pointed out that physicalisolation barriers or a minimum distance should be secured
between the site of scientific exploration and the dwelling site.
Since it is important to keep microorganisms within a small
space in the dome, we should not use microorganisms to makeagricultural soils in the dome. Organic matter contributes tomany important functions of the soil, to form and maintainsuitable aggregate sizes in the fine regolith, and to store
nutrients (bio-elements), especially Wada et al. (2009) pointed
out that storage of the nutrients in organic matter can beachieved by applying compost and excreta of animals.
The important functions of microorganisms inhabiting thesoil on the earth, are decomposition of various organic waste,release of nutrients stored in the organic matter, nitrification,and N-fixation. Wada et al. (2009) proposed to use peat mosswith the desired microorganisms to endow the soils with thesefunctions, but it is to be avoided to rely upon microorganisms
by the above reasons. Desalinization and neutralization arerequired to grow plants in lunar and Martian soil. These soils
usually contain water-soluble salts. Removal of thewater-soluble salts can be achieved by leaching the salt-rich soil
with non-saline water. Common plants are damaged by soil
with too low or too high pH. The pH of the soil should be
adjusted for both too acidic and too alkaline soils. Improvementof physical properties of soil is also difficult if we do not know
where we are going to live on Moon and Mars.
There seems to be a consensus that human presence isnecessary to explore Moon and Mars for the purpose ofclarifying the origin of life. Microorganisms should not be
used for this goal. The goal of space agriculture is to create
and maintain optimum living environment on extraterrestrial
planet for human life. Although some scientists promoting anidea to utilize ecological system of the hyperthermophilic
aerobic composting bacteria for producing soil from humanand animal waste and inedible biomass, astrobiological
exploration of Moon and Mars may encounter problems for
detecting signs of life on Moon and Mars if living terrestrial
bacteria were introduced to Moon and Mars. Yazawa et al.
(2009) are also trying to introduce vegetables to support our lifeon Moon and Mars, which have been evolved on soils andatmosphere of the earth for billions of years. We have toproduce soils from Martian rocks for terrestrial vegetables
keeping microorganisms as small as possible.
This section has been designed to determine if it is possible
to grow plants that will provide a significant portion of the(A)(B)
Untreated control

Fulvic acid treatment

Fig. 3. Influence of fulvic acid or its iron complex on physiological activities of rice plant (A) and sea phytoplankton (B) under solar energy (Yazawaet al., 2009).

NASA-defined human nutritional requirements utilizing lunar
and Martian regolith as the growing medium. Photosyntheticplants require N, P, K, Ca, Mg and S in considerable quantities
and Fe, Mn, Zn, Cu, B and Mo in trace quantities. The lunar
and Martian regolith contains P, Ca, Mg, S, Fe, Zn, Cu and Mo
in sufficient quantities.
Other elements provide special concern due to the specificnature of the lunar and Martian regolith. Aluminum is present
in a smaller concentration than is common in earth soils, but
due to the acidic conditions on Moon and Mars, it may be a
toxic level for plants. In soil solution culture experiments,
Yazawa et al. (2000) found that addition of humified naturalorganic matter reduced the amount of monomeric Al present insolution and alleviated the toxic effect of Al on root growth ofwheat under acidic condition. Consequently, terrestrial humic
matters including fulvic acid can not only control to buffer for
nutrient and toxic element but also accelerate to dissolute
elements and synthesize clay from Martian regolith withchemical weathering.
Fulvic acid and its complex with iron had a strong
accelerative for physiological activities of root growth in riceand chlorophyll production in phytoplankton (Fig. 3).
Confirmation of dissolution of the main rock-forming silicatesby fulvic acid will give us better understanding of the basic
process of weathering in nature on the earth, as well as ofapplication for lunar and Martian agriculture (Yazawa andTakeda, 2008).

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