ROOFTOP FARMING WITH SWEET POTATO FOR REDUCING URBAN HEAT ISLAND EFFECTS AND PRODUCING FOOD AND FUEL MATERIALS

The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, Japan
ROOFTOP FARMING WITH SWEET POTATO FOR REDUCING URBAN HEAT
ISLAND EFFECTS AND PRODUCING FOOD AND FUEL MATERIALS
Yoshiaki Kitaya, Masashi Yamamoto, Hiroaki Hirai and Toshio Shibuya
Osaka Prefecture University, Sakai, Osaka, Japan
Abstract
Sweet potato was cultured with a lightweight hydroponic system on a rooftop as a cooling equipment for reducing
urban heat island effects and also as urban agriculture in a summer season in Osaka, Japan. In the result, The
difference in surface temperatures between concrete plates exposed to sun light and under the vegetation
coverage were increased with increasing solar radiation flux and reached 13oC. The tuberous roots yield was 3,2
kg m-2 in this method. Sweet potato culture in rooftop farming will be a promising practice for environmental
conservation in urban areas.
Key words: hydroponics, rooftop farming, sweet potato, urban agriculture, urban heat island
1. INTRODUCTION
A rooftop farming system was developed as a cooling equipment for reducing urban heat island effects and
also as urban agriculture that wil be practice of crop production and thus supply of food and fuel materials such
as bioethanol. Sweet potato can grow under a stressful condition even on rooftops and has relatively high abilities
of transpiratory latent heat loss and photosynthetic carbon fixation compared with other plant species. In this
study, sweet potato was cultured with a lightweight hydroponic system on a rooftop and performances of the
plants to reduce excess temperature rise and to yield tuberous roots were examined in a summer season in
Osaka, Japan. Sweet potato was cultured hydroponically on a roof in this study. Hydroponic techniques for sweet
potato production have been developed by Uewada (1990), Mortley et al. (1991), Uewada et al. (1992) and Hill et
al. (1992). We have been developing a new hydroponic method for culturing sweet potato with a fibrous rooting
substrate in order to ensure high yield with a simple system compared with previous studies.
In this study, sweet potato plants were cultured in a newly developed hydroponic system. Cooling
performance of the sweet potato vegetation and the yield and growth performance of plants were investigated.
2. MATERIALS AND METHODS
Culture containers containing rooting substrates were used to culture sweetpotato (Ipomoea batatas (L.)
Lam. Var. Kokei-14) hydroponically (Fig. 1a). The rooting substrates made with rockwool slabs were inclined in
the container and absorbed nutrient solution from the lower end by capillary action (Fig. 1b). Sweetpotato were
planted using stem cuttings, which were inserted into the rooting substrate. Cuttings were 0.25-0.28 m long and
had 9-11 nodes with 7-9 leaves each. Tuberous roots of sweetpotato were developed in the aerial space between
the rockwool slab and the nutrient solution filled at the bottom of the culture container. The nutrient solution used
was modified Hoagland solution.
Water depth was kept at 0.05 m
Sh
S adi
a ng
n
Roc
Ro kwo
k olo
throughout the experimental period.
film
sl
s ab
a
16 plants were cultured at a planting
1.9 m
9
density of 2 plants m-2 on a rooftop for
?????
???
150 days from June to November as
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0. ??
5
??? 5
5 m
??
5
??
shown in Fig. 2.
Thermal images of the surfaces
of the vegetation canopy and concrete
0.25
.2
5 m
plates were captured using infrared
thermography (TH9100, NEC-San-ei
Co., Japan). Air temperature and solar
(a)
(a
(b)
0.05
05 m
radiation flux were also measured.
Cul
C t
ul ure
r co
c n
o taianer
Mean daily integrated solar radiation
was 13.2 MJ m-2 during the culture
period.
Fig. 1. A
A phot
ph ograp
ogr h o
h f
o the cu
c ltur
u e
r co
c nt
n aine
n r (a) and
and a diagr
a am sh
s owing
owing a
a
cros
r s sse
s ctcion
o of the
h
e hydr
y o
dr poni
pon c csy
s stsem with
h the
h
e incl
inc ine
n d
d rookw
ok o
w ol slabs (b)
3. RESULTS AND DISCUSSION
used
s
ed in the
h exp
ex eri
e ment
e .
nt
Lower temperatures were observed at the sweet potato vegetation canopy than at concrete plates in the
thermal image (Fig. 3). Temperatures at the concrete surface under the vegetation coverage were mostly the
same as the temperature at the vegetation canopy surface (Fig. 4). The difference between the air temperature
and the surface temperature of the concrete plates exposed to sunlight was increased with increasing solar

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The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, Japan
radiation flux. Differences between the air temperature and surface temperatures of the vegetation canopy and
the concrete plates under the vegetation coverage were decreased with increasing solar radiation flux. The
difference in surface temperatures between concrete plates exposed to sun light and under the vegetation
coverage were, therefore, increased with increasing solar radiation flux and reached 13oC.
The final harvest produced large yields of
tuberous roots in the hydroponic system (Fig. 5).
The yield of tuberous roots of sweet potato
cultured for 150 days was 1.6 kg/plant (Table 1)
and 3.2 kg m-2, showing 1.4 times greater yield
than the average yield of this variety in the
conventional soil culture.
In conclusion, sweet potato production was
performed successful y in the hydroponic system
on the rooftop. It was confirmed that sweet
potato vegetation showed a suitable
performance for cooling. Although the rockwool
substrate was used for several times, reuse of
the rockwool material is restricted because of its
fragile property. In order to reuse the substrate
for numerous cycles, we need to develop stable
substrates or culture methods without solid
substrates for rooting, which can keep water and
air optimum in the same manner as the rockwool
substrate. Sweet potato culture in rooftop
farming will be a promising practice for Fi
F g.
g. 2.2 A photo
pho gr
to aph
gr

aph of the
th
e vege
e ta
ge ti
ta on
o
n of sw
s e
w e
e t
e pot
po ato c
to uluture
ur d
e d
environmental conservation in urban areas.
in a ahy
h dr
y o
dr p
o on
o ic sys
y tem
e on
o nthe
the ro
r ofotop.
top. (26 6Septe
e m
pte ber,
ber 2005
20 )
05
(a)
12
o C) 8
4
Te
T mp
(oC)
0
(b)
(b
-4
p
e
r
a
t
u
r
e

d
i
f
e
r
e
n
c
e
s

(
T
e
m -80 200 400 600 800
Sola
ol r rrad
r iation (W m-2
m )
-2
Fi
F g.
g 4. Ef
E ectcs of solar
ar radiation on temp
m era
er ture
r
dif
di eren
e ces bet
e we
w en the air temperature
ur and surf
ur ace
temp
em er
e ature
ur s sof the concre
r te pla
pl tes exposed to su
s n
Fig. 3.
3 Visisble (a)
a and
a ther
the m
r ala
light ( ( ),) the swe
w et
e potato vegetation ca
c nopy y( ( ),
(b)
b images
m

ages inc
n luding
di the
h sweet
w
and the
e co
c n
o crcete pla
pl tes under the vegetation
po
p tat
a o
o ve
v g
e e
g t
e at
a ion
o
n ca
c n
a o
n p
o y
p y an
a d
n
d
cov
o era
r g
a e
e ( ( ).)
the conc
o rete
e plat
a es wi
w thout the
vegetati
e
on c
on o
c v
o era
e g
ra e.
e
10
0
Fig. 5. T
g.
u
5. T be
b ro
r us r
s oot
r s
oot of
o swe
w e
e t potato
po
va
v rirety
e ‘
ty Kok
K e
ok i-14’
culutur
u ed
e for 15
for 0 da
15
ys
y i
s n
i the h
e ydr
y opo
dr
ni
opo c
ni sys
y tem
te .

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The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, Japan
Tab
a le 1.
1 Sh
S oot and t
d uber
e ous
u r
s oot w
o e
t w ights
h ,
ts sh
s o
h ot le
l n
e gtgh and dleaf ar
f a ea aindex
e (
x LA
L I) of sw
s e
w et po
p tato
ta
pla
pl nt
a s scultured
ur
ed for 150 da
d ys
y in nthe
he hyd
hy r
d opon
op ic csy
s s
y tsem.
Fresh
s we
w ight
h (g/gplant)
n
Dry yweigh
ig t (g/gplantn)
Ma
M in stsem
em length
ng
LAI
(m/plan
a t)
(m2
(m m-2
m )
-2
Sh
S oo
o t tube
b rou
o s srootos Tot
T al
Sho
h ot tuberou
ber s sroots Totala
1311±
11 63
±
1591±
91 1
± 96
9 29
2 22±
2 2
± 4
2 7
262±
2 1
± 4
1 445±
45 56
±
73
7 7±
7 69
6
2.
2 6±
6 0.4
±
2.
2 8
Mean
M
ean + stsandar
nda d derror (n=5
n= )
References
Hill, W.A., Mortley, D.G., Mackowiak, C.L., Loretan, P.A., Tibbits, T.W., Wheeler, R.M., Bonsi, C.K., Morris, C.E.,
1992. Growing root, tuber and nut crops hydroponically for CELSS. Advances in Space Research, 12(5), 125-131.
Mortley, D.G., Bonsi, C.K., Loretan, P.A., Morris, C.E., Hill, W.A., Ogbuehi, C.R., 1991. Evaluation of sweetpotato
genotypes for adaptability to hydroponic system. Crop Sci. 31, 845 – 847.
Uewada, T., 1990. The solution culture of sweetpotatoes. Environ. Control in Biol. 28, 135 – 140. (in Japanese
with English summary)
Uewada, T., Kiyota, M., Kitaya, Y., Aiga, I., 1992. Hydroponic cultivation of sweetpotato. In "Sweetpotato
Technology for the 21st Century." (ed. by Hil , W.A., Bonsi, C.K., Loretan, P.A.) Tuskegee University, Tuskegee,
AL 36088, USA. pp 120-125.

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