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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 Yields(t/10a) 8 ●The cause of the decline in sugarcane yields may be low content of humic substances. 6 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 0 1995 1997 1999 (Year) 2001 2003 Yields of sugarcane in Minami and Kita daito islands, Japan. Sampling sites Methods 131°20′N K-6 K-7 K-5 K-4 K-3 K-8 K-1 <Kita daito island> K-2 K-9 ●Soil chemical and mineralogical properties were determined. ●Humic substances were extracted and quantified according to the method described by Kumada (1977). <Kumada method> M-11 M-14 Soil sample M-8 M-12 M-9 <Minami daito island> M-7 25°50′E M-10 M-4 M-6 0.1M NaOH+ 0.1M Na4P2O7 Supernatant 0.1M H2SO4 M-1 M-13 M-3 M-2 M-5 0 5km ●Sugarcane cultivated soils in two islands is classified into calcareous soil. ●Sugarcane cultivated soils were collected from 9 fields in Kita daito island and 14 fields in Minami daito island, respectively. Precipitation (insoluble fraction ; humin) ●Collected surface soils were utilized characterize the humic substances. Humic acid (precipitation) Fulvic acid (Supernatant) *Humic acid, fulvic acid and humin were determined by back titration using the potassium permanganate solution. *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) ●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 4.0-8.0 and 0.08-0.36 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). 160 120 A 3.0 ⇒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) 2.0 RF 80 B 40 P Rp 0 1.1 0.9 0.7 ⊿log K 0.5 ⇒The low degree of humification is classified into 1.0 degradationresistant categories of which the materials are lignin, 0.0 tannin and melanoiding. Humic acid (HA) Fulvic acid (FA) Humin Significant correlation coeficients (Kita daito and Minami daito islands,n=23, **1%, *5%) pH(H2O) pH(KCl) EC HA FA Humin ⊿logK Na K Ca Fine sand Ca Mg Coarse sand 0.471* 0.837** 0.693** 0.421* -0.410* 0.471* 0.854** 0.651** 0.424* -0.414* pH(KCl) Humin 0.994** T-HS Na Fine sand Silt Clay 0.590** 0.524** 0.419* -0.601** 0.619** -0.483* 0.626** -0.406* 0.429* -0.575** 0.458* -0.568** 0.514* 0.761** -0.445* -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.