1. Characteristics of the humic substances in sugarcane cultivated soils of Minami daito and Kita daito islands in Japan.
INTRODUCTION
●Sugarcane yields in Minami daito and Kita daito islands in Japan showed a declining tendency in recent years. 10
Minami daito island
Kita daito island 8
●The cause of the decline in sugarcane yields may be low content of humic substances. 6
Yields(t/10a) 4
●A study was conducted to examine the characteristics of the humic substances, which are being considered of having close relationship with the properties of sugarcane cultivated soils. 2
1995
1997
1999
2001
2003
(Year)
Yields of sugarcane in Minami and Kita daito islands, Japan.
Sampling sites
Methods
●Soil chemical and mineralogical properties were determined.
131°20′N
K-6
K-7
K-5
●Humic substances were extracted and quantified according to the method described by Kumada (1977).
K-4
K-8
K-3
K-1
<Kita daito island>
K-2
K-9
<Kumada method>
M-11
Soil sample
M-14
M-8
0.1M NaOH+
0.1M Na4P2O7
M-12
M-10
M-9
<Minami daito island>
Precipitation
(insoluble fraction
; humin)
M-4
M-7
Supernatant
25°50′E
M-6
0.1M H2SO4
M-1
M-13 km
M-3
M-5
M-2
Humic acid
(precipitation)
Fulvic acid
(Supernatant)
●Sugarcane cultivated soils in two islands is classified into calcareous soil.
*Humic acid, fulvic acid and humin were determined by back titration using the potassium permanganate solution.
●Sugarcane cultivated soils were collected from 9 fields in Kita daito island and 14 fields in Minami daito island, respectively.
●Collected surface soils were utilized characterize the humic substances.
*The degree of humification was determined by calculating ΔlogK(logK400nm-logK600nm) and RF({K600nm×1,000} / {0.1N KMnO4 consumption(mL) / 30mL of humic acid solution)

2. ●Kazutoshi Kinjo1, Koichi Yoshida2, Yoshihiro Tokashiki1, Makoto Kitou1, Yasushi Gima3, Shigeru Kameya3 and Naoko Miyamaru3
1). Faculty of Agriculture, University of the Ryukyus,Okinawa, Japan, 2). Okinawa Agricultural Technology & Dvelopment Office, 3). Okinawa Prefectural Agricultural Research Center
Results & Discussions
⇒Soil pH and EC of the soils from both islands were in the range of about and S/cm, respectively. The results of XRD indicated that kaolinite and illite were the most predominant mineral in all soils. Soil texture was almost heavy clay in all soils.
<Humification of humic acids of sugarcane surface soils>
⇒The degree of humification of humic acids in sugaracane soils showed a low degree(Rp type). Rp B A P
160
⇒The percentage of humin, fulvic acids and humic acids contents in Total humic substances were 42%, 37% and 20%, respectively.
Content of humic and fulvic acids and humin (g/kg)
3.0
120
2.0 80
⇒The low degree of humification is classified into degradation-resistant categories of which the materials are lignin, tannin and melanoiding. RF
1.0 40
0.0
Humic acid (HA)
Fulvic acid (FA)
1.1
0.9
0.7
0.5
Humin
⊿log K
Significant correlation coeficients (Kita daito and Minami daito islands,n=23, **1%, *5%)
Coarse sand
Fine sand
pH(KCl)
Humin
T-HS Na Ca Mg
Silt
Clay
pH(H2O)
0.994**
0.471*
0.837**
0.693**
0.421*
-0.410*
pH(KCl)
0.471*
0.854**
0.651**
0.424*
-0.414* EC
0.590** HA
0.524** FA
0.419*
-0.601**
-0.483*
Humin
0.619**
0.626**
⊿logK
-0.406* Na
0.429* K
-0.575**
-0.568** Ca
0.458*
0.514*
-0.445*
Fine sand
0.761**
-0.515*
●Soil organic matter(humin) accumulation in the sugarcane soils has been enhanced by the presence of exchangeable calcium.
●It was suggested that liming materials, which are having high concentrations of calcium, can be effectively utilized to enhance the soil organic matter(humin) accumulation to improve the soil properties.