The Red Soils of China

Approximately 22% of the World’s population lives in China and is fed largely by the efforts of indigenous agricultural production. However, these efforts are concentrated on only 7% of the World’s cultivable land and in China this land is shrinking year-by-year due to soil erosion and urbanization. At the same time, the Chinese population continues to increase, albeit at a slower rate, and it is evident that if China is to maintain her relative self-sufficiency in food then the challenge must be to increase food production from current soil resources. This can only be done by increasing agricultural production from currently cultivable land and/or by bringing more uncultivated land into production, at the same time taking measures to stabilize population growth.

Red soils are highly leached soils of the humid tropics having a high content of sesquioxides. In the current system of U. S. Soil Taxonomy, red soils are usually designated under the orders of Oxisols, Ultisols, and occasionally Alfisols, Mollisols and even Inceptisols. Red soils are predominantly found in South America, Central Africa, South and Southeast Asia, China, India, Japan and Australia. In general, these soils have good physical conditions for plant growth although they often have very low water-holding capacity. Low natural fertility is the main limiting factor for good crop production on these soils and they are frequently acidic and deficient in all essential nutrients, especially N, P, K, Ca, Mg, S, Zn, B, and Cu. Adequate applications of lime and fertilizers are important strategies for replenishing soil fertility and improving crop yields on these soils. In addition, cultural practices such as appropriate crop rotation, improvement of organic matter content, use of nutrient efficient or acid tolerant plant species or cultivars, and control of soil erosion can optimize nutrient use efficiency and improve crop yields on these soils. In China, utilization of red soils for crop production by farmers depends not only upon the employment of such practices but also upon socio-economic factors and the availability of adequate incentives.

Red soils in China include latosols, lateritic red earths, red earths, and yellow earths and are mainly equivalent to Oxisols, Ultisols, and some Alfisols in the US Taxonomy. They cover an area of 102 million ha and are mainly distributed in the tropical and subtropical regions of China, including Hainan, Guangdong, Yunnan, Taiwan, Fujian, Guangxi, Jiangxi, Hunan, Sichuan, Guizhou, Zhejiang, and Anhui. Having been subjected to intensive weathering, these soils are usually dominated by variable charge minerals such as kaolinite and Fe and Al oxides. Most red soils in China are acidic, nutrient-deficient and low in organic matter and cation exchange capacity, partly because of soil erosion and intensive use.

The mineral composition of the different size fractions of red soils from southern China was investigated using X-ray diffraction (XRD), infrared spectroscopy analysis (IR), transmission electron microscopy (TEM) and chemical methods. Surface charge and phosphate adsorption characteristics of the soils were also determined. The results showed that kaolinite and/or halloysite are the most common clay minerals in the soils. However, the abundance and mineral composition of the soils varied with latitude, elevation, parent materials, and topographic position. Types of kaolin mineral in the soils changed with soil types, the relative proportion of kaolinite increasing with weathering degree. Under current subtropical climates, a transformation process of mica to vermiculite also occurs in these soils. Goethite and hematite are the only two crystalline Fe oxides occurring in significant quantity in these soils. The goethite/(goethite+hematite) ratios ranged from 0 to 1, being the highest in yellow soils, and the lowest in soils derived from purple sandstone where only hematite was present. Substitution of Al in goethite ranged from 6.6 to 29.9 mole % with a mean value of 16.7 mole %Al, while substitution of Al in hematite ranged from 0 to 12.1 mole %. The values of Al substitution of hematite were closely related to the corresponding values of the coexisting goethite. Phosphorus (P) adsorption of all the soils studied was well described by the Freundlich and Langmuir equations. The maximum buffering capacity (MBC) of P ranged from 66.5 to 9880 mg kg^-1 in the increasing order of red-purple sandstone soil < purple sandstone soil < red sandstone soil < red soil < lateritic red soil < yellow soil < latosol. The zero point of charge (ZPC) values obtained by salt titration-potential titration varied from 3.03 to 5.49, the highest value being found in the latosol derived from basalt and the lowest in purple sandstone soil. Correlation analysis indicates that the main minerals responsible for phosphate adsorption in the soils were gibbsite, amorphous iron oxides and kaolin, whereas the PZC was mainly controlled by kaolin, gibbsite and oxides.

Red soils, consisting of Ultisols and partly of Alfisols under the Soil Taxonomy system of the USA, are important land resources in China. A good understanding of the physical and chemical properties of these soils is essential for their improved management and utilization. In this study, typical profile samples of red soils were collected from Zhejiang Province, and their physical and chemical properties, nutrient concentrations and water-stable aggregate distributions were studied. The red soils had low cation exchange capacity, high exchangeable acidity, and low pH. The textures of the red soils vary greatly, from clayey to sandy loam, and are mainly influenced by parent material. Amounts of organic matter, total nitrogen (N), total phosphorus (P) and total potassium (K) varied with parent materials, elevations and land use patterns. About 60% of the red soils had total N < 1.5 g kg⁻¹,and Olsen-P < 5 g kg⁻¹, and 32% of the soils were deficient in available K (< 80 g kg⁻¹). Deficiencies of available B, Mo and Zn were common, whereas available Fe, Mn and Cu were abundant in the red soils. Organic matter plays a key role in the formation of water-stable soil aggregates. The larger the soil aggregate size, the greater the impact of organic matter on the water stability of the aggregates. Small water-stable aggregates (0.50–0.25 mm) in the red soils were chiefly cemented by Fe and Al oxides. Land use patterns and parent materials had a significant influence on the formation and water-stability of aggregates in the red soils.

The distribution of rare earth elements (REEs) in red soil profiles in southern China was studied in detail. Much higher total REE contents were observed in red soils than in the bedrocks. The highest total REE contents were found in gneiss-, limestone- and granite- derived red soils and the lowest in quartzitic sediments. There were no significant differences in total REE contents between the red soil horizons although soluble REEs accumulated in the lower horizons of the profiles. Amounts varied greatly with parent materials. There was a significant exponential relationship between the total REEs and soluble REEs in red soils. Soluble REEs were also positively correlated to a chemical index of alteration (CIA) values and clay contents, but were negatively correlated with organic matter, pH values and Al₂O₃/Fe₂O₃ mole ratios. These results imply that soluble REE contents could be a useful indicator of red soil development. Total REE contents were negatively correlated with SiO₂/Al₂O₃, Al₂O₃/Fe₂O₃ mole ratios, but were positively correlated with the R₂O₃/SiO₂ mole ratio, reflecting the fact that REEs are mainly inherited from parent rocks. It was concluded that soluble REEs tended to be leached out from the red soils at an early stage of soil development and that residual forms became enriched at a later stage. The main form of REEs in red soils is as a residual phase associated with primary minerals inherited from the parent rocks, while the non-residual forms are closely related to the laterization process.

The most widespread chemical constraints on crop production from Chinese red soils include soil acidity, toxicity of Al, Mn and Fe, and deficiencies of the major nutrients N, P and K, as well as some minor nutrients such as B, Mo and Zn. Other nutrients which can be deficient include Mg, S and Si. Particular attention was paid to the N and P incorporated into the microbial biomass. The results indicate that this is an important pool of available N and P in the red soils and may have use as a biological index of nutrient availability.

A review of the climate of southern China combined with data from an experimental site in Yunnan Province reveals a number of climatic constraints to crop production in the area dominated by red soils. In addition to the well-known effects of late summer drought and high summer evaporation, other factors include variability of the onset date of the summer monsoon as well as the intensity and damaging effects of the monsoon. Other climatic constraints identified are the occurrence of cold conditions and frost during the winter monsoon and local microclimatic variability due to topographic factors.

The effects of different parent materials and land use on water holding and supplying capacities of some typical red soils were evaluated. Results show that (1) parent material and land use had considerable effect on maximum available water content in the red soils. The difference between different soil types is greater than that among land utilizations for the same soil; (2) land use changed distribution ratios of soil pore size and volume. (3) After red soils were transformed into irrigated paddy fields, soil water holding and supplying characteristics were greatly changed, with improved effective soil water retention and supply abilities.

China experiences severe soil erosion problems, as a result of population pressure and a lack of land suitable for cultivation. In the south-west province of Yunnan, heavy monsoonal rains, combined with the fact that 95% of the province is mountainous, create erosion problems. This is exacerbated by the common practice of cultivating steep slopes due to lack of flat land. The best way to minimise soil erosion in these circumstances is to devise cultivation practices that conserve soil loss without reducing crop productivity. Work was carried out to consider the effectiveness of contour cultivation (CC) and contour cultivation plus straw mulch (CC+SM), in relation to their effects on soil erosion and maize productivity. Results were compared to the traditional practice of downslope cultivation (D) on 3 slope classes 3, 10 and 27°. In a wet year CC significantly reduced soil loss on the 3° and 10° slopes and adding straw mulch gave no extra protection. On the 27° slope, CC was not effective, but CC+SM reduced soil loss by almost 100%. In 1999, a drier year, no significant treatment effects were found on the 3° slope, but CC significantly reduced soil loss on the 10 and 27° slopes. The addition of straw mulch gave no extra reduction on either of the steeper slope in 1999. There was a tendency for yields to be higher under CC+SM and in 1999 this difference was significant on the 10° slope.

Seven field locations were selected in a hilly region of red soils to monitor surface runoff and soil erosion. These locations correspond to typical land use patterns in this region: mixed forest, broad-leaf forest, grass land, citrus orchard, tea bush, sparse coniferous forest, and bare soil. From in situ observations, the effect of different land use patterns on soil erosion and related soil properties was evaluated. Eroded soil amounted to greater than 5,000 ton km⁻² yr⁻¹ from bare land. Under stable cultivation conditions soil erosion significantly decreased, and the amount of erosion could be controlled to under 300 ton km⁻² yr⁻¹. The differences in runoff and eroded soil under different land use patterns were mainly determined by vegetation coverage and plant characteristics. Soil fertility degradation became more and more severe with increasing erosion in the following order of land use patterns: sparse coniferous forest < tea bush<citrus orchard< grass land< deciduous forest< mixed forest. Soil structure destruction, soil organic matter and nutrient losses, and soil microbial deterioration occurred even in the soils with slight erosion. Soil fertility degradation under different land use patterns follows the same sequence in other hilly red soil regions of China.

Utilization of red soils in China can be divided into four periods: (1) Minimal use in agriculture before the 1950s; (2) Development of upland red soils for crop production; (3) Conversion of upland red soils to paddy cultivation; and (4) Integrated use and comprehensive exploitation of red soils. Intensive use of red soils for upland crops caused severe soil degradation through erosion and nutrient loss. Conversion from upland crops to rice paddy soils improves soil fertility by reducing soil erosion, especially through the increasing inputs of organic matter. An integrated system of land use on red soils enables their comprehensive exploitation and is the most promising approach for improving their resilience and increasing the economic value of the land. Future studies need to address soil and water issues in the red soil region.

The world population is increasing rapidly and will likely to reach 10 billion by the year 2050 of which half will probably be living in the regions dominated by acid soils. The limited availability of additional arable land and the degradation of soil quality make food security a major challenge in the 21^st century. Elemental toxicities and deficiencies are the major constraints limiting crop production in acid soils. Plant genotypes are known to differ greatly in their tolerance to elemental toxicity or deficiency in soils. In this paper, physiological and genetic mechanisms of crop plant adaptation to stresses of selected elements in acid soils are reviewed. Plant tolerance to toxicity stresses such as aluminum (Al) and manganese (Mn), and deficiency stresses of nitrogen (N), phosphorus (P), potassium (K), boron (B) and zinc (Zn) are closely related to the physiological processes of ion uptake, transport and re-distribution in the plant. In the last decade, considerable knowledge in the mechanisms of Al resistance or tolerance has been gained. The resistance of many plant species to Al toxicity is associated with increased root excretion of organic acids and with the involvement of specific anion transporters in the plasma membrane, whereas. Mnanganese tolerance seems to be mainly related to its distribution and compartmentalization in plant cells. The mechanisms of N, P, K, B, and Zn use efficiency in crop plants are not fully understood even although in recent years research on these elements has been increased considerably. The definition and expression of nutrient use efficiency (NUE) of the selected elements (N, P, K, B, and Zn) in crop plants and the physiological and genetic traits associated with the NUE are addressed in this context. To achieve sustainable crop production in acid soils, it is essential to increase crop plant tolerance to element stresses through genetic improvement and to further optimize soil nutrient availability and pest management so that adaptive and efficient farming systems an be established.

The water balance in crop growth field for wheat, rice, corn and soybean was analyzed using the crop growth and soil water balance model MACROS (L1D, L2C, and L2SS), in combination with the local soil, crop, and weather data in a hilly red soil region of southern China. Water saving irrigation approaches are developed and discussed according to the requirements of each different crop. Intermittent irrigation for rice showed that the total water requirement for early and late rice production could be decreased by more than 60% and 80%, respectively, as compared with the conventional flooding irrigation.. For the winter wheat in the region, the major problem for water management was waterlogging during the spring and early summer. For spring corn, measures should be taken to avoid the drought season starting from the middle of July. The yield of autumn corn and soybean in the red hilly soil region is closely related to irrigation conditions.

Pot experiments were conducted to study the acid tolerance of six perennial forage species and the effects of phosphate (P), potassium(K), and magnesium(Mg) fertilizer applications on the growth of forage crops in acid red soils. The results showed that the sequence of acid tolerance among the six species were as follows: Shcep’s Festuca, Paspalum dilatatum >Lolium perene.L., Trifolium repens L.>Meadow Festuca, Trifolium.pratens L. There were no obvious differences in aluminum and phosphorous concentrations among the acid tolerant forages at different pH. At low pH, acid-sensitive forage crop species contain significantly higher aluminum concentrations. The yields of the -P, -K or -Mg treatments were 11–17%, 87–93%, and 77–90%, respectively of the control (with complete fertilizers). These results suggest that phosphorous deficiency was the key factor for limiting forage crop yields. Phosphorous and potassium concentrations of plants with the treatment of -P decreased significantly, whereas nitrogen concentrations of the plants increased, as compared to those of the control.

Pot experiments were conducted to investigate the effects of P fertilizer and lime on ryegrass growth on highly acid and P deficient soils. The results showed that application of P fertilizers could considerably increase dry matter yields of annual ryegrass grown on these soils. The requirement for phosphate fertilizer was relatively higher for a Quaternary red clay soil than for a red sandstone soil. A close correlation was found between phosphate application rates and Olsen P as well as with the dry matter yield of ryegrass. Critical Olsen P was higher for the red sandstone soil than for the Quaternary red clay soil. The effect of liming on ryegrass yield was less obvious. The increase in yield due to lime varied with phosphate fertilizer application rates. The yields increased with increasing lime at low P application rates. When soil pH was lower than 5.5, the effect of high liming rates on yield was much reduced at higher phosphate application rates. The results demonstrated that P is a more important factor than liming for ryegrass growth on acid red soil.

Soil conservation on the highland red soils of Southern China is essential for sustainable agroenvironmental development. The effectiveness of soil conservation treatments developed in runoff plots was investigated in farmer-managed plots on a natural catchment. This was achieved by the development and scientific evaluation of modified and novel cropping practices in a representative highland catchment in Yunnan Province, China. Wang Jia Catchment covers 40.1 hectares near Kedu, in Xundian County, northeast Yunnan (25°28' N, 102°53' E). The initial project consisted of an evaluation of the effects of modified cropping practices on maize productivity and soil properties. This programme was extended to investigate ways of increasing the productivity of maize, wheat and soybean on fragile slopes in a sustainable and environmentally-friendly way. The approach incorporates modified and novel agronomic and soil conservation measures, with the evaluation of their agricultural, environmental and socio-economic impacts using multidisciplinary approaches. This European Union funded project involved an international research team from Belgium, China, Ireland, Thailand and the U.K. Five co-ordinated work packages were implemented. Involving:

Land use patterns have a significant effect upon the chemical and physical properties of the red soils in the hilly regions of Zhejiang Province. The organic matter content of the red soils under forest is significantly higher than for similar soils under other land uses. However, available K and P tended to be higher in the red soils under upland crops as well as when used for growing tea bushes or fruit trees. For upland crops and orchards too, the percent base saturation of the red soils was very much higher than under forest. There was also a noticeable effect of land use for available microelements. On the other hand, the content of water stable aggregates in the red soils tended to increase in the order; orchard > tea garden > wasteland > upland crops > forestland. This order reflected the organic matter content under the different land uses and emphasizes the importance of increasing the organic matter content as a means of improving the structure of the red soils and hence making them less susceptible to erosion.

The influence of fertilization with urea and ryegrass on nitrogen utilization and transformation in a typical red clayey soil has been investigated. When urea or ryegrass were applied alone, the percentage of N uptake by ryegrass from labeled urea was 3 times that from labeled ryegrass. However, the ratio declined to 1.7 when urea and ryegrass were applied in combination. Combining application of ryegrass and urea reduced uptake of urea N and increased uptake of ryegrass N by the ryegrass plants, but the percentage of residual N in the soil increased for urea and decreased for ryegrass. When urea and ryegrass were applied alone, the percentage of N remaining in the soil from labeled ryegrass was more than 69% while that from labeled urea was less than 25%, and much more ryegrass N was incorporated into humus than urea N.

Either ³²P-labeled KH₂PO₄ with or without unlabeled ryegrass or ³²P-labeled ryegrass with unlabeled KH₂PO₄ was applied to red clayey and red sandy soils belonging to the Ultisol order. Ryegrass was grown in the fertilized soil and harvested one month after sowing. The radioactivity and total P content in the ryegrass samples were measured. The results showed that application of organic matter to the red soils significantly enhanced the uptake of P by ryegrass seedlings from the inorganic P applied to the soil, and that the utilization of P from inorganic source was 5.3 times that from the organic source under the same conditions. Moreover, at the same application level of phosphorus, a larger proportion of the phosphorus derived from ³²P-labeled inorganic phosphate was distributed in shoots than that from the ³²P-labeled ryegrass.

The transformation dynamics of phosphorus from ³²P-labeled ryegrass in the two red soils were also investigated under laboratory incubation conditions. The results showed that a rapid increase in ³²P flush related to microbial biomass P (Pmij was accompanied by a decrease in extractable ³²P during the first 3d after incubation in both red sandy and clayey soils. Between 3~20 days after incubation, flush ³²P fluctuated greatly in the red sandy soil, but was about the same in the red clayey soil. At the later stage of incubation, the increase in extractable ³²P was accompanied by a decrease in flush ³²P. The opposing changes in content of extractable ³²P and flush ³²P suggested that transformation of ryegrass P was closely related to its utilization and subsequent release from microorganisms in the red soils. It can be concluded that application of organic matter accelerated the release of soil native P according to the changes in the extractable soil P during incubation.

Effects of pH change on microbial biomass-C and -P were examined using three red soils under citrus production but with different cultivation periods. Microbial biomass C and P were significantly affected by soil pH. The changes of C_mic and P_mic as a function of soil pH appeared to follow a normal distribution pattern with the original pH value as its center. Microbial biomass C or P was the greatest at the original soil pH and declined when the pH shifted to either acid or alkaline side. Moreover, there was a critical pH value at both the sides, beyond which the microbial biomass C or P abruptly decreased. The critical pH values were approximately 3.0 at the acid side and 8.0 to 8.5 at the alkaline side. The effect of pH on microbial biomass C and P was related to the original soil pH. The higher the original soil pH was, the less the microbial biomass C and P were affected by pH change. It is explained that soil microorganisms that grow in the soil environment with nearly neutral soil pH range (pH 5.5–7.5) may have greater tolerance to pH changes than those grow in the acid or alkaline soil pH conditions.

Eleven red soils varying in land use and fertility status were used to examine the effect of land use on microbial biomass carbon (C_mic), nitrogen (N_mic) and phosphorus (P_mic). Microbial biomass-C in the red soils ranged from 68.3 to 224.9 mg C kg⁻¹, which is generally lower than that reported from other types of soil, probably because of low organic matter and high acidity in the red soils. Land use had considerable effects on the amounts of soil C_mic. The C_mic was the lowest in the eroded fallow land, followed by the woodland, tea-garden, citrus-grove and grassland, and the highest in vegetable and paddy fields. There was a significant correlation between C_mic and organic matter content, suggesting that the influence of land use on C_mic is mainly related to the input and accumulation of organic matter. Microbial biomass-N in the soils ranged from12.1 to 31.7 mg N/kg and was also affected by land use. The change of N_mic with land use was similar to that of C_mic. The microbial biomass C/N ratio ranged from 5.2 to 9.9 and averaged 7.6. The Nmic was significantly related with soil total N (r=0.787**) and available N (r=0.794**). Microbial biomass-P in the soils ranged from 4.5 to 52.3 mg P kg⁻¹. The microbial biomass C/P ratio was in the range of 4–23. The P_mic was relatively less affected by land use due to difference in fertilization practices for various land use systems.

A laboratory experiment was conducted to evaluate the effect of different land uses, soil fertility and environmental quality on substrate utilization patterns. Multivariate analysis of Biolog sole carbon source utilization tests demonstrated that land use history and plant cover type had a significant impact on microbial community structure. However, there was no systematic change in microbial community structure associated with increased organic matter or microbial biomass. Microorganisms were sensitive to environmental change. Addition of Cu to three red soils (short-term cultivated red sandy soil, mid-term cultivated red clayey soil, and long-term cultivated red clayey soil) at a rate of 500mg kg⁻¹ resulted in a lower utilization rate for 21 carbon sources. In addition, microbial community structure in the long-term cultivated red clayey soil was significantly altered by Cu addition at the rate of 500 mg kg⁻¹.

This study investigated the soil acidification caused by continuous planting of tea bushes and its influence on the population distribution and community structure of microorganisms, soil basal respiration and activities of 3 soil enzymes (urease, invertase, acid phosphomonoesterase) and related ecological factors in the rhizosphere of 10-, 40- and 90- year old tea bushes, respectively, in Hangzhou, China. Soil pH decreased significantly by 0.57 of a pH unit with the tea bushes’ age, from 10- to 90-year old. Total exchangeable acidity of the soil also increased, ranging from 1119 to 1436 mmol (1/3 Al ³⁺ + H⁺) kg⁻¹ oven-dried soil. However, the dominant component of soil total exchangeable acidity shifted from exchangeable H⁺ to exchangeable Al³⁺ with increasing cultivation age of the tea bushes. The soil organic carbon and total nitrogen contents, as well as the C/N ratio and soluble phenol content were significantly negatively correlated with soil pH, suggesting an accumulation of organic matter in the root-layer of the tea bush soils caused by the soil acidification. The bio-characteristics of these soils varied with the increasing age of the tea bushes and with soil acidification. Bacteria dominated the microbial community of the root-layer soils and soil microorganisms were not generally affected by soil pH. However, oligotrophic bacteria were obviously inhibited by soil acidification. Soil microbial biomass carbon and daily basal respiration were stimulated by soil acidification and the reverse was true for the metabolic quotient (qCO₂). Decline of soil pH enhanced only the activity of soil acid phosphomonoesterase but not the activities of urease and invertase. The numbers of bacteria and actinomycetes in the soils of the 40- and 90-year old tea bushes were only half those in the 10-year old tea bush soil; however, the amount of soil microbial biomass carbon and the potential of daily basal respiration showed a two-fold increase for the 40- and 90-year old tea bush soil, compared with the 10-year old tea bush soil. The metabolic quotient (qCO₂) declined as the cultivation age increased. Activities of urease and especially invertase in the root-layer soils declined with increasing tea bush age but, on the contrary, the activity of acid phosphomonoesterase increased.

This paper reports on the socio-economic outcome of a study of innovative, integrated, agricultural management practices in a catchment near Kelang village in Yunnan Province in south-west China. The focus of these practices, which included biological and engineering measures, was enhanced productivity in maize production and soil conservation on the Kelang uplands. Although these measures did enhance productivity and reduced soil erosion, there is strong evidence that the farmers are unlikely to implement these practices without significant support on the part of the authorities. In particular, investment measures, which have a medium to long-term payback period, will not be implemented without significant assistance from the public authorities. These outcomes follow from the fact that maize production is relatively marginal to the total integrated earning activities of the farm household, where 45% of income comes from off-farm activities, while rice, and particularly tobacco, give a much higher return per labour unit. The critical factor is the “opportunity cost” of labour. If significant off-farm employment exists at a wage above what can be earned from maize production with the new management practices, then the consequence will be that these new practices will not be embraced. The Kelang catchment area is dominated by red soils and has many of the erosion problems associated with these soils which occur extensively across southern China. However, because of their derivation from limestone, the Kelang soils are inherently more fertile. Nevertheless, the results from Kelang have implications concerning the utilization of Chinese red soils in general, particularly the likelihood of uptake by the Chinese farmer of novel and integrated management approaches on these soils based on scientific experimentation.

Red soils, broadly equivalent to Ultisols in the US taxonomy system, could be a very important soil resource in southern China. However, due to extensive use and severe degradation, these soils require to be carefully managed and utilised if they are to be put into production. An Integrated Soil Resource Information System (ISRIS) based on remote sensing and A geographic information system (GIS) could play an important role in the survey, evaluation, utilization and management of the red soil resource. An ISRIS of Zhejiang Province (1:500,000), Quzhou City (1:250,000), and Longyou County (1:50,000) was compiled and integrated into a running system using ARC/INFO and Mapobject software. This paper introduces the system design, database creation and system functions and it focuses particularly on the development of applied models, such as red soil resource classification and mapping, suitability evaluation, erosion risk evaluation, p1ant utilization zones etc. The problems of ISRIS study and its developing strategy are also discussed.

Proper agricultural regionalization, that is the division of agricultural lands into uniform regions for agriculture development, is of crucial importance to farmers, researchers, and decision-makers in the context of utilizing and managing the red soil resource (Ultisols) of China. This paper shows how a soil information system (SIS) can be integrated using an optimal tree cluster approach so as to study agricultural regionalization. Taking Longyou County, Zhejiang Province as a case study, an SIS created in ARC/INFO was used to provide data acquisition, systematic model parameter assignment, and the visual display of analytic results. The topography, temperature, soil component (e.g. organic matter, pH), and the type of agricultural production were selected as parameters for the optimal tree cluster, in which Prim’s algorithm was adopted to calculate the minimal spanning tree. The effectiveness of this integration and recommendations are discussed for future research.