Geographical Review of Japan Vol. 62 (Ser. B), No. 2, 170-178, 1990

On the Relationship between Climate and Soil in Hainan Island, China

Shizuo NAGATSUKA* and Kazuko URUSHIBARA-YOSHINO**

Abstract

The geographical distribution pattern of zonal soils in Hainan Island, China is rather complicated, because the island is located in the transitional zone from subtropics to tropics and humidity decreases from the east to the west. In order to elucidate the taxonomical position of the zonal soils of the island, three representative soil profiles of Latosol, Lateritic red earth and Ferric latosol were select ed to analyze general chemical properties, clay-mineralogical composition and the mode of existence of iron compounds. Based on these properties correlation with the categories in the U. S. Soil Tax onomy, FAO/Unesco sytem and the ecological soil classification system of France was made. The results obtained are as follows: 1) The Latosol under subtropicl or tropical monsoon forest climate with 5 months of dry season is correlated with Oxic Rhodustalf (USA), Chromic Lixisols (FAO/Unesco) and Typical Tropial fer ruginous soils (France). 2) The Lateritic red earth under subtropical monsoon forest climate with 4 months of dry season is correlated with Oxic Haplustults (USA), Haplic Alisols (FAO/Unesco) and Tropical ferruginous soils with low base saturation (France). 3) The Ferric latosol under subtropical or tropical rain forest climate is correlated with Tropeptic Haplorthox (USA), Rhodic Ferralsols (FAO/Unesco) and Ferrisols (France). Consequently, the so-called Latosol and Lateritic red earth of Hainan Island do not belong to the category of true Latosols, viz. Oxisols or Ferralsols; only the Ferric latosol is barely considered to belong to true Latosols.

Key words: Hainan Island, Lateritic red earth, Latosol.

part, the climate is warm throughout the year, I. INTRODUCTION i.e., the mean temperature in January is higher than 18•Ž and the average extreme minimum Hainan Island is located on the northern mar temperature is over 8•Ž. The amount of annual

gin of the tropics between 18•K10' and 20•K10' N, precipitation is the highest in the eastern part, and between 108•K37' and 110•K03' E, occupying which is frequently visited by typhoons, and

a total area of about 34,000km2, which makes gradually decreases westward until it attains less it the second largest island of China. Annual than 1,000mm in the western coastal region

mean air temperature and annual precipitation (HE, and ZHANG, 1986). of the whole island range from 22.5°C to 25.5°C Soil-geographically, Hainan Island is divided and from 993 mm to 2,447mm, respectively into the following four soil regions (Zou et al.,

(Xu, 1988). Bio-climatic conditions in the is 1981) (Fig. 1): land, however, vary considerably from north to 1)The northeastern region mainly consists of south and from east to west. The northern part Latosol(博 紅 壌,zhuanhongrang)and Ferric of the island, where cold frontal zones can reach latosol(鉄 質 樽 紅 壌, tiezhizhuanhongrang). and settle on the windward-side of Mt. Wuzhi, 2)The eastern coastal region mainly consists has relatively cold and gloomy weather in winter of Yellow latosol(黄 色 薄 紅 壌, huangsezhan- and spring. On the contrary, in the southern hongrang).

* Institute of Applied Biochemistry , University of Tsukuba, Tsukuba, Ibaraki 305 ** Department of Natural Sciences , Komazawa University, Setagaya-ku, Tokyo Climate and Soil in Hainan Island 171

Figure 1. Soil Map of Hainan Island (modified after Zou, G. et al. 1981)

3) The western coastal region mainly consists (DUCHAUFOUR, 1976) was made for three of Brown latosol(褐 色 博 紅 壌, hesezhuanhong- representative soil profiles of Lateritic red earth, rang ,)and Dry red earth(燥 紅 土, zaohongtu). Latosol and Ferric latosol, based on the analyses 4) The central mountain region mainly consists of general chemical properties, clay of Lateritic red earth赤 紅 壌,chihongrang)and mineralogical composition and the mode of ex Yellow earth(黄 壌, huangrang). istence of iron compounds. Locations where the In the mountainous region the verticl zonality soil profiles were investigated are shown in Fig. of soil distribution is as follows: Mountain yel 1. low earth above 700m a. s. l., Mountain lateritic red earth between 400 m and 700m a. s. l., Moun II. CLIMATIC CONDITION OF tain latosol between 200m and 400m a. s. l., THE STUDY AREA latosol below 200m a. s. l. and Dry red earth be tween 80m and 100m a. s. l. (Guangzhou Insti Climatic diagrams of the study area are shown tute of Geography, 1985). in Fig. 2. The climatic data of Lingao, which In order to elucidate the taxonomical position represent the climatic condition of the north of these soils in the worldwide soil classification western Latosol region show that mean annual system, correlation with the categories in Soil air temperature is 23.4•Ž and annual precipita Taxonomy (Soil Survey Staff, 1975), the World tion is 1,447 mm with 5 months of dry season Soil Map Legend (FAO/Unesco, 1974) and the from December to April. This means that the French System of Soil Classification region belongs to a subtropical or tropical mon 172 S. NAGATSUKA and K. URUSHIBARA-YOSHINO

Figure 2. Climatic Diagrams of the Study Area

soon forest climate. The climatic data of Qion Topography: Altitude 130m a. s. l., gentle mar

ghai, which represent the climate of the eastern ginal slope on plateau with gradient 16•K facing Ferric latosol region, show that mean annual air to the east. temperature is 24.0°C and annual precipitation Vegetation: Orchard of lizhi trees (Litchi is 2,070mm with no dry season. This implies that chinensis) and jack-fruit trees (Artocarpus het this region belongs to a subtropical or tropical erohylla). The ground surface is covered with rain forest climate. The climatic data of Tong weeds. zha, which represent the southern mountainous Parent material: weathering crust of granite Lateritic red earth region show that mean annu covered with quartzitic gravel. al air temperature is 22.4•Ž and annual precipi Morphology: tation is 1,689mm with 4months of dry season L: Very thin litter of broad-leaves. from December to March. This means that the All: 0-5cm. Dark brown (7.5YR3/3) grav region also belongs to a subtropical or tropical elly clay loam when dry, no color change when monsoon forest climate, but the duration of the wet; moderate fine granular and fine subangu dry season is shorter than that of the north lar blocky structures, hardness 10, abundant fine eastern Latosol region. roots, dry, smooth clear boundary. A12: 5-10cm. Dark reddish brown (5YR3/3)

III. DESCRIPTION OF SOIL PROFILES gravelly light clay when dry, dark brown (7.5YR4/3) when wet; moderate fine to medium 1) Pedon 1. Latosol on granitic plateau (H-1) subangular blocky structure, hardness 16, com Location: Baodao Xincun, Danxian Country, mon fine roots and a few meidum roots, dry, Hainan. Experimental field of South China wavy gradual boundary. Academy of Tropical Crops (Huaguoshan). Bl: 10-35cm. Reddish brown (2. SYR4/4) Climate and Soil in Hainan Island 173

when wet, moderate fine to medium subangular gravelly light clay when dry, red (2.5YR4/6) when wet, strong fine nutty structure, hardness blocky structure, large pores present, hardness 18, common fine roots and a few medium roots, 25, a few medium roots, very dry, wavy gradual dry, smooth diffuse boundary. boundary. B1: 10-35cm. Yellowish brown (10YR5/8) B21: 35-80cm. Red (2.5YR4/8) gravelly heavy clay when dry, no color change when wet, sandy clay when dry, dark yellowish brown strong very fine subangular blocky structure, (10YR4/6) when wet, strong fine to medium common fine pores, hardness 25, few fine roots, subangular blocky structure, fine to medium dry, smooth diffuse boundary. pores present, hardness 27, a few meidum roots, B22: 80-115cm. Red (2.5YR4/6) gravelly dry, smooth diffuse boundary. sandy clay with strong very fine subangular B2t: 35-70cm. Yellowish red (5YR5/8) heavy blocky structure, abundant fine pores, hardness clay when dry, strong brown (7.5YR5/8) when 30, few fine and meidum roots, dry, smooth wet, strong medium subangular blocky structure, diffuse boundary. clay cutan on peds clearly recognized, fine pores 11B2: 115 -160cm. Red (10R4/6) fine gravel present, vertical cracks are common, hardness ly light clay, moderate meidum to coarse suban 28, a few medium roots, dry, smooth diffuse boundary. gular blocky structure with weak coarse prismatic structure composed of fine subangular blocky B3: 70-100cm. Strong brown (7.5YR5/8) light clay when dry, yellowish brown (10YR5/8) peds, abundant fine pores, hardness 27, few fine and meidum roots, somewhat moist, smooth when wet, moderate fine subangular blocky diffuse boundary. structure with some cracks, fine pores present, I IB3: 160-190cm. Red (2.5YR4/8) clay loam clay cutan on peds clear, hardness 30, no roots, with highly weathered pebbles of granite, mas dry, smooth diffuse boundary. sive structure, no roots, somewhat moist, wavy C1g: 100-130cm+ . Strong brown

gradual boundary. (7.5YR5/8) light clay when dry, yellowish brown TIC: 190-250cm+. Weathered granite, (10YR5/8) when wet, massive, filmy iron strong brown (7.5YR5/6) sandy loam with mas mottlings are common, hardness 25, slightly sive structure, no roots, somewhat moist, mica moist. 3) Pedon 3. Ferric latosol on basalt plateau grains are abundant. Clay cutan on ped is not clear throughout the (H-6) Location: Road cut near Nanhai State Farm, profile. 2) Pedon 2. Lateritic red earth in hilly regoin Huangzhu, Dingan County, Hainan. Topography: Altitude 160m a. s. l., flat land (H-2) Location: North of Tongzha, near Hongshan. on basalt plateau. Topography: Altitude 300m a. s. l., hill slope Vegetation: A windbreak of evergreen trees. with gradient 20•K facing to the south. Parent rock: Basalt. Vegetation: Secondary bush of evergreen trees. Morphology:

Ground surface is covered with Pueraria A1: 0-20cm. Dark reddish brown (2.5YR3/3) heavy clay with weak fine granular and fine phaseoloides and Eupatorium odoratum. Parent material: Colluvial slope deposit of subangular blocky sructures, hardness 4, com weathered granite, no gravel. mon fine and medium roots, pebbles of meta Morphology: morphic rock present, slightly moist, smooth All: 0-5cm. Grayish brown (10YR5/2) san diffuse boundary.

dy loam when dry, dark brown (10YR3/3) when B1: 20-60cm. Dark reddish brown wet, moderate fine granular and weak fine (2.5YR3/4) heavy clay with moderate fine granu

subangular blocky structures, hardness 18, large, lar and fine subangular blocky structures, hard medium and fine roots are common, very dry, ness 8, common fine and medium roots, pebbles

slightly wavy clear boundary. of metamorphic rock present, slightly moist, A12: 5-10cm. Brown (10YR3/4) sandy clay smooth diffuse boundary. loam when dry, yellowish brown (10YR5/4) B21: 60-130cm. Dark reddish brown 174 S. NAGATSUKA and K. URUSHIBARA-YOSHINO

(5YR3/6) heavy clay with moderate fine to me (Pedon 1), total organic carbon content to the dium subangular blocky structure, hardness 20, depth of 10cm ranges from 6 to 3%, and it common medium roots and a few fine roots, no decreases to less than 1% below 10cm. gravel, dry, smooth diffuse boundary. pH(H20) and pH(KC1) range from 5.6 to 5.3 B22: 130-200cm. Dark reddish brown and from 4.8 to 4.3, respectively, showing acid (2.5YR3/4) heavy clay with strong fine to me ic soil reaction throughout the profile. The ca dium subangular blocky structure, hardness 25, tion exchange capacity (CEC) of the humic a few fine and medium roots, no gravel, dry, A-horizons shows relatively higher figures of 23 smooth diffuse boundary. to 12meq/100g, while it suddenly decreases to B3: 200-230cm+. Dark reddish brown 6 to 4meq/100g below B1-horizon. The total (5YR3/6) heavy clay with moderate very fine to of exchangeable cations amounts to 18-9 fine subangular blocky structure, hardness 22, meq/100g in A-horizons, but it also decreases a few large, medium and fine roots, stone and to 41meq/100g below B 1-horizon. It is highly weathered pebbles of basalt present, dry. characteristic of this profile that the degree of Clay cutan on ped is not observed throughout base satuation is high (77-50%) except for B22 the profile. and IIC horizons. In Lateritic red earth (Pedon 2), the topmost IV. PHYSICO-CHEMICAL PROPERTIES All-horizon contains 2.34% of organic carbon OF THE SOILS and 6.2meq/100g of total exchangeable cations, showing a relatively high degree of base satura 1. General chemical propertis tion (72%) and weak acid reaction. Below 5cm Table 1 shows general chemical properties of of depth, however, the organic carbon content the three representative soil profiles. In Latosol suddenly decreases to less than 1%, and the to

Table 1. General chemical properties of the soils Climate and Soil in Hainan Island 175 tal of exchangeable cations to less than 1 nized at B2t-horizon, whereas in Ferric latosol, meq/100g, showing a very low degree of base clay content is rather homogeneously distribut satuation (12-19%) and strong acid reaction. ed throughout the profile, showing no clay ac The value of CEC shows also low figures from cumulation. 6 to 11meq/100g. The general chemical properties of Ferric latosol (Pedon 3) are relatively homogeneous throughout the profile. About 2% of organic carbon is contained to the depth of 60cm. pH(H20) and pH(KC1) range from 4.9 to 5.8 and from 4.5 to 5.6, respectively, showing strong acid reaction. The value of CEC is slightly higher than those of the other soils (8.2-9.5meq/100g), but the total of exchangeable cations is very low (3.1-1.4meq/100g), showing a low degree of base satuation (35-18%).

2. Granulometric analysis

Fig. 3 shows distribution patterns of coarse sand (2-0.2mm), fine sand (0.2-0.02mm), silt (0.02-0.002mm) and clay (<0.002mm) frac tions through the soil profile. In Latosol (Pedon 1), an increase of clay content is observed at the part from B1 to B21-horizon and at 11B2-horizon. In Lateritic red earth (Pedon 2), Figure 3. Profile Distribution of the Particle Size increase of clay content is more clearly recog Fractions

Figure 4. Profile Distribution of Total Iron and Free Iron Oxides 176 S. NAGATSUKA and K. URUSHIBARA-YOSHINO

3. Distribution of iron compounds in soil profile V. X-RAY ANALYSIS OF Distribution patterns of oxalate-soluble iron CLAY FRACTION (Feo), dithionite-citra te-bicarbonate-soluble iron (Fed) and total iron (Fe) are shown in Fig. Fig. 5 shows an X-ray diffractogram of the clay 4. The content of Fed and Fet increases at the fraction (<2ƒÊm). Strong and sharp diffraction part from B22 to 11B3-horizon in Latosol and peaks at 7.24A and 3.58A are observed in all the at B-horizons in Lateritic red earth. On the other clay specimens, showing predominance of hand, the content of Fed and Fet in Ferric kaolinite. Diffraction peaks at 10.1A and 5.00A latosol is evenly distributed to the depth of 2m. due to illite and those at 3.35A due to quartz are These tendencies in the distribution pattern of also clearly observed in the specimens of Latosol Fed and F; are parallel with those of clay dis (H-1) and Lateritic red earth (H-2), though the tribution, which suggests the presence of clay diffraction intensities of illite and quartz are very migration in Latosol and Lateritic red earth and weak as compared with those of kaolinite. On absence of clay migration in Ferric latosol. the other hand, in the specimens of Ferric latosol

. (H-6), weak but sharp diffraction peak at 14.3A

0 due to 2:1-type of clay mineal and those at 4.87A

0 and 4.39A due to gibbsite are clearly observed. The weak diffraction at 4.84A observed in All and B22 horizons of Latosol may indicate the presence of small amount of gibbsite.

VI. DISCUSSION AND CONCLUSION

From the foregoing, the following conclusions are made of the characteristics of the zonal soils of Hainan Island: 1) Latosol under subtropicl or tropical mon soon forest climate with 5 months of dry season contains a large amount of kaolinite (1: 1-type of clay mineral) as well as a small amount of gibb site and quartz; however, it still contains a small amount of illite (2:1-type of clay mineral). There fore, this Latosol cannot be considered as true latosol, namely Oxisol (Soil Survey Staff, 1975) or Ferralsol (FAO-Unesco, 1974). This soil is characterized with an argillic horizon with in distinct clay cutan on peds, an apparent cation exchange capacity of the fine-earth fraction of 16meq or less per 100g clay by NH4OAc (8-16meq), and a relatively higher degree of base satuation (77-50%). From these charac teristics it is considered that this soil corresponds to Oxic Rhodustalfs in the U. S. Soil Taxonomy or Chromic Lixisols in FAO/Unesco system which have recently been separated from Lu visols as soils with an argillic B-horizon, high

Figure 5. X-ray Diffractogram of the Clay Fraction base saturation but low clay activity (FAO,

(<2ƒÊm) 1985). The Latosol is also very similar to typical Climate and Soil in Hainan Island 177

Tropical ferruginous soils in the ecological soil Soil Taxonomy or Rhodic Ferralsol in the classification system in France (DUCHAUFOUR, FAO/Unesco system, and to Ferrisol in the eco 1976). logical classification system. 2) Lateritic red earth under a slightly humid The conclusions mentioned above are summa subtropical monsoon forest climate with 4 rized in Table 2. months of dry season contains a large amount of kaolinite as well as a small amount of illite Acknowledgements and quartz, and is characterized with an argillic horizon with clear clay cutan on peds, an appar This study was carried out as a part of a joint research ent CEC ranging from 18 to 22meq per 100g work between Japan and China financially supported by the Ministry of Education, Science and Culture, Japan clay and a very low degree of base saturation (Leader: Professor M. YOsHINo, No. 62043011). The (12-19%) except the topmost horizon. From authors are grateful to Prof. Z. HUANG (Director), Prof. these characteristics this soil is considered to be Y. HAO and many other staff members of the South long to Oxic Haplustults in the U. S. Soil Tax China Academy of Tropical Crops, Hainan, who kindly onomy or Haplic Alisols in the FAO/Unesco took the trouble to arrange the research itinerary. The authors also wish to express their gratitude to Prof. Ch. system which have also separated from Acrisols XI and Prof. Z. GONG of the Institute of Soil Science, as soils with an argillic B-horizon, low base satu Academia Sinica, Nanjing, for the courtesy of undertak ration and high clay activity (FAO, 1985). The ing soil chemical analyses. Lateritic red earth corresponds to Tropical fer (Received Oct. 14, 1989) ruginous soils with low base saturation in the (Accepted Jan. 15, 1990) ecological soil classification system. 3) Ferric latosol under subtropical or tropical rain forest climate contains a large amount of References kaolinite as well as small amount of 14A-mineral and gibbsite. This soil has no argillic B-horizon DUCHAUFOUR,Ph. (1976): Atlas Ecologique des Sols du and the apparent CEC ranges from 18-20 meq Monde. Masson, Paris, 178p. FAO-Unesco (1974): Soil map of the world 1:5000000, per 100g clay at the depth of 0-130cm, while Volume I, Legend. Unesco, Paris, 59 p. it is about 15meq per 100g clay at the depth FAO (1985): FAO/Unesco Soil map of the world, 1:5 of 130-200cm which is considered to be an oxic 000000, Revised Legend (Third Draft). FAO, Rome, horizon. From these data this soil is considered 115 p. to belong to Tropeptic Haplorthox in the U. S. Guangzhou Institute of Geography (ed.) (1985): Maps

Table 2. Taxonomical characteristics of Latosol, Lateritic red earth and Ferric latosol 178 S. NAGATSUKA and K. URUSHIBARA-YOSHINO

of Tropicl Natural Resources of Hainan Islands. XU, S. (ed.) (1988): Hainan Province. Shangwuyin Science Pub., Beijing, 47 p. (in Chinese) shuguan, Beijing, 420 p. (in Chinese) HE, D. and S. ZHANG (1986): The climatic regionaliza Zou, G. et al. (1981): Soil regionalization of Hainan Is tion of Hainan Island. Climatological Notes, 35, land. Reports on Agricultural Regionalization of Hai 89-96. nan Island, Guangzhou Institute of Pedology, Soil Survey Staff (1975): Soil Taxonomy. U. S. Depart 9-1-9-51: (in Chinese) ment of Agriculture, Washington DC, 754 p.

中 国,海 南 島 の 気 候 と 土 壌 の 関 係

永 塚 鎮 男*,漆 原 和 子**

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気 候 下 の ラ トソル は オ キ シ ッ ク ロ ドァス タ ル フ(USA), ろうじて真のラトソルに属すものと見なされる。

* 〒305茨 城 県 つ くば市 ,筑 波 大 学 応 用 生 物 化 学 系 ** 〒154東 京 都 世 田谷 区駒 沢 ,駒 沢 大 学 自然 科 学 教 室