Characteristics of the humic substances in sugarcane cultivated

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/10 a) 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 M-13 M-2 M-5 0 Supernatant 0. 1 M H 2 SO 4 5 km ●Sugarcane cultivated soils in two islands is classified into calcareous soil. ●Sugarcane cultivated soils were collected from 9 fields in Kita daito island 14 fields in Minami daito island, respectively. 0. 1 M Na. OH+ 0. 1 M Na 4 P 2 O 7 ●Collected surface soils were utilized characterize the humic substances. Humic acid (precipitation) Precipitation (insoluble fraction ; humin) 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 Δlog. K(log. K 400 nm-log. K 600 nm) and RF({K 600 nm× 1, 000} / {0. 1 N KMn. O 4 consumption(m. L) / 30 m. L of humic acid solution)

1 Kinjo , 2 Yoshida , ●Kazutoshi Koichi Kameya 3 and Naoko Miyamaru 3 Yoshihiro 1 Tokashiki , Makoto 1 Kitou , Yasushi 3 Gima , Shigeru 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 p. H 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 RF 80 B 40 P Rp 0 1. 1 0. 9 0. 7 ⊿log K 0. 5 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 ⇒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%) p. H(H 2 O) p. H(KCl) EC HA FA Humin ⊿log. K 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* p. H(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.