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close this bookLand Resources of the People's Republic of China (UNU, 1983, 84 pages)
close this folderI. Land-use evaluation and classification
View the document1. Major land-type categories of China
View the document2. Land classification and mapping in China
View the document3. Classification scheme for the 1:1,000,000 map of China's land resources
View the document4. Supplement to the preliminary standard classification system for land evaluation in China
View the document5. Land use on the Lake Taihu Plain
View the document6. Salt-marsh resources of China

4. Supplement to the preliminary standard classification system for land evaluation in China

Li Xiaofang
Commission for Integrated Survey of Natural Resources.
Chinese Academy of Sciences. Beijing

Abstract

An effort was made in 1979 to rank, classify and map China's land resources. For this purpose 11 agroecological zones were delimited nationwide, each of which was classified into eight land-use classes. This preliminary system of land evaluation is deemed too complex and a new approach based on land suitability orders, sub-orders, types and ranks. together with the factors limiting land uses. is suggested in this chapter.

Since 1978, there has been a clear need in China for maps of land evaluation for use in planning rural development and land use. A classification system for land evaluation was also required for use in compiling maps. This chapter describes briefly the preliminary standards used to evaluate China's land resources and presents a system of land evaluation that may be used to supplement the existing one.



Fig. 4.1. Agro-ecological Regions of China

TABLE 4.1. Criteria for Agro-ecological Recionalization of China

Agro-ecological regions Criteria
  Accumulated annual temperature and number of days of > 10°C Aridity index Cropping system Frost-free days
I. Tropical 7,500°C
320
0.5-1.0 Three crops of rice Entire year
II. Southern subtropical 6,500-7,500°C
280-320
0.5-1.0 Two crops of rice or one crop of wheat plus sweet potatoes About 330
III Centralsubtropical 5,000-6,500°C
225-280
0.5-1.0 Same as above 260 330
IV. Northern subtropical 4,500 5,000°C
180-225
0.5-1.0 One crop of rice and one crop of wheat 230-260
V. Warm temperate 3,200-4,800°C
150-210
0.7-1.5 Two or three crops in two years 150-230
VI. Sub-humid warm temperate 3,200-3,600°C
150-170
1.5-2.0 Three cropsin two years 145-195
VII. Temperate <3,200°C
<150
0.5-1.2 One crop <145
VIII. Arid temperate 3,200-4,500°C
About 180
Over 4 One to three cropsin two years 210
IX. Semi-arid temperate 2,000 3,200°C
90-160
1.2-2 One crop <180
X. Sub-humid and semi-arid temperate 2,700-3,500°C
135-170
2 4 One crop <180
XI. Qinghai-Xizang(Tibetan)Plateau 2,000°C
<130
0.5 2+ One crop <120

 

TABLE 4.2. Standard Classes of Land Resources Used in Compiling Land Resources Map of China

Class I Superior quality land with no limitations and suitable for agriculture, animal husbandry and forestry.
Class II Good quality land with only minor limitations. Crop yield slightly lower than class I, but well-suited to animal husbandry.
Class III Land of medium quality. Limited by low soil nutrient levels, imperfect drainage and salinity. Easily improved.
Wide suitability.
Class IV Poor quality land. Limitations include steep slopes, soil erosion, thin soils, salinity, or unavailability of water.
Marginally suitable for crops but suitable for animal husbandry and forestry.
Class V Land of very poor quality owing to severe biological and/or physical limitations. Difficult to improve.
Unsuitable for crops but marginally suitable for animal husbandry and forestry.
Class VI Land at high altitudes, with steep slopes and bare rocks. Marginally suitable for animal husbandry.
Class VII Land on rocky mountains or gravel and sandy deserts with thin pasture. Marginally suitable for animal husbandry.
Class VIII Land of sandy and gravel deserts, permanent snowfields or tundra.

Preliminary Criteria for Compiling Land Evaluation Maps of China

One of the first steps involved in compiling maps of land evaluation is to establish the agro-ecological zones. The zonation used here is based on: (1 ) the accumulated annual temperature of more than or equal to 10°C; 12) the number of days per year with temperatures of more than or equal to 10°C; (3) the aridity index; (4) the cropping system; and (5) the number of frost-free days per year.

Eleven broad agro-ecological zones were delimited (fig. 4.1 and table 4.1). In the tropical region, where the temperature is high throughout the year and the aridity index is 0.5-1.0, triple cropping of rice is possible. Three zones are located in the sub-tropical region, where the annual accumulated temperature of >=1 0°C is 4,5007,500°C, the number of days with temperatures of >=1 0°C is 180-320, and there are 260-330 frost-free, days, and two crops of rice or one crop of rice plus one crop of wheat are grown. The other six zones are distributed in the temperature belt where the values of such diagnostic criteria are below those of the first four zones. The last zone lies in the Qinghai-Xizang (Tibet) Plateau, which is characterized by a low agricultural productivity.

Each agro-ecological zone was sub-divided into eight classes, based on certain diagnostic criteria that were used to evaluate the suitability of the land for different purposes and to rate the factors limiting land use (table 4.2). The classes are numbered consecutively by Roman numerals in descending order of potential and in ascending order of the limiting factors (cf. chapter 3 of this volume).

A Supplement to the Preliminary System of Land Evaluation

The land-evaluation procedures mentioned above in the preliminary standard classification system are too complex and the system has recently been revised at the provincial and county levels. In addition, the approach to land evaluation in the comprehensive surveys of land resources has changed. During the last 30 years, land evaluation was restricted to the physical aspects of the land only, but it was realized recently that land evaluation also requires a cost-benefit analysis of different types of land use. It would be useful to develop a dual approach for land evaluation, one being concerned primarily with physical factors and the other with social and economic factors. These two aspects have been studied simultaneously during multidisciplinary integrated surveys of natural resources in China. There follows a description of this approach, based on the concept of land suitability.

Geographers generally use the term "land evaluation" synonymously with "land suitability" and "land capability." Here "land suitability" is considered appropriate, since it refers to land fit for a given type of use. The process of classifying land suitability involves an appraisal of the degree of suitability for particular uses within a defined area. This process can also be used to distinguish a type of land with limitations from one without limiting factors. It also rates the limiting factors.

TABLE 4.3. Land Suitability Classification

Order Suborder Type Rank
Suitable (S) Suitable for agriculture
(SA)
Rainfed farming (SAr) 1 No limitations
Irrigated farming (SAi) Example: SAr1
Paddy rice (SAp) 2. Some limitations
Sugar-cane and sugar-beet (SAs) Example: n1d1
Fruits (SAf) 3. Major limitations
Mulberry and oak trees (SAm) Example: n2d1
Tea (SAt) 4. Severe limitations
  Example: n2d3
Suitable for forestry (SF) Timber (SF:)  
Water conservation (SFc)
Economic forest (SFe)
Fuelwood (SFw)
Shelterbelts and soil protection (SFp)
Suitable for pastoral
production (SP)
Natural pasture (SPp)
Improved pasture (SPi)

Four categories of land suitability are recognized: orders, suborders, types, and ranks (table 4.3).

1. Land Surtability Orders

Three orders, which indicate whether an area is assessed as suitable (S),unsuitable (N), or conditionally suitable (Sc) for productive use, have been established. Order S means that land is suitable for various kinds of sustained use. Depending on both physical and socio-economic factors, the land is expected to yield benefits without unacceptable risks of damage to the land resources, and inputs are easily justified. Land designated as N is unsuitable for sustained use and anticipated benefits would not justify the expected costs of inputs required. Land defined as Sc means that it may be suitable for a given type of use if certain conditions are fulfilled, after which suitability might increase significantly. Usually, a conditionally suitable land area is small and generally results from such localized phenomena as poor drainage, soil salinity, and the like. Poor choice of crops in relation to market values may also make a piece of land conditionally unsuitable. Such a land area requires physical modification and/or improved management.

2. Land Suitability Sub-orders

Three sub-orders of suitability are recognized: agricultural use (SA). pastoral production (SP). and forestry (SF).

Sub-order SA: Depending on both physical and socioeconomic factors, the land is suitable for sustained cultivation, under which it will not deteriorate. This highly productive type of land is characterized by fertile soils and sufficient water. (Additional categories within a sub-order may be created for special cash crops.)

Sub-order SP: Denotes land suitable for pastoral production, on which, with normal management, degradation would not be expected. Suitability depends mainly on physical factors, but sometimes socioeconomic factors must be considered. Land in pasture is usually inferior in quality SA land.

Sub-order SF: SF land is suitable for forestry, where anticipated benefits justify inputs. Suitability depends mainly on physical factors although socio-economic considerations may be important.

3. Land Suitability Types

Different types of suitability are distinguished within the suborders. Seven types are distinguished under SA five under SF, and two types under SP.

SAr: Rain-fed farming is widespread on the flood-plains in north China and in limited roiling or hilly areas in the centre and south of the country. Water supply is generally limited in the north, where occasional droughts may occur during part of the growing season. In some areas occasional flooding may also occur.

SAi: Irrigated farmland occurs nationwide. This type of land is usually level or gently rolling, with a high soil nutrient content and a thick solum. Cereals have long been grown on this type of land. In general, irrigated land is highly productive, but the tracts are small.

SAp: Paddy rice is widely grown in subtropical and tropical China, but only in a small area of the north. Commonly it is grown on flood plains with a high or medium level of soil nutrients. Recently, waterlogging owing to poor drainage has occurred in subtropical China.

SAs: This type of land is suitable for both sugar-cane, in south China, and sugar-beet, in the north. It occurs usually on flood plains with a high soil-nutrient content and where water is plentiful.

SAf: In general, this type of land is devoted to fruit cultivation. It is either level or gently sloping with high soil fertility and good drainage of both water and air. The water supply is good and there is no flood hazard.

SAm: Land of this type is used for mulberry and oak, the leaves of which feed silkworms. It occurs on floodplains or in hilly areas with gentle slopes. The soils are fertile, water is plentiful, there is no flood risk, and occasional, minor limiting factors neither reduce productivity nor require additional inputs. Such land usually occurs in small pieces, scattered among rice paddies or in other level and rolling areas.

SAt: Such land is suitable for tea bushes and is found in subtropical China. It occurs in gently rolling and hilly areas where the solum is thick, acidic soils are fertile, and the drainage good.

SFt: This land is suitable for timber and occurs throughout China, except for arid and permanent snow areas. Most such land is in upland areas with steep or moderately steep slopes, and stony soils.

SFc: Such land is suitable for water conservation forests and occurs in mountainous areas or in the vicinity of newly built reservoirs, where soils are thin and the slopes steep. Soil erosion is problematical.

SFe: This type of land is fit for forests or for, largescale plantation of crops with a high economic value, such as oil palm, camphor tree, Camellia oleosa, roses, rubber, and the like. It occurs in the subtropical and tropical regions, and only a limited part of the temperate zone is suitable for economic forests. This type of land is characterized by high quality soils and abundant water.

SFw: This is hilly land around rural settlements usually suitable for growing fuelwood. Such land has poor quality soils with a thin solum and is low in nutrients. Soils may have been eroded. Since wood accounts for 80 per cent of the fuel used in Chinese villages, land suitable for its production is urgently needed.

SFp: This type is suitable for windbreak forests and those established to protect against soil erosion. It occurs in several parts of China, especially on the periphery of oases in arid regions, in the Loess Plateau area, and in subtropical areas where the soil has been eroded and the bedrock deeply weathered. Such land has a number of limiting factors and is inferior to any other type of land adapted to forests.

SPp: This land is suitable for natural pasture and occurs in steppe, dry steppe, desert steppe, and mountainous steppe areas. Available water is enough for livestock but cannot support agriculture.

SPi: Such land is suitable for improved pasture, and occurs in both north and south China. It requires fertile soil, a thick solum, and enough water.

4. Land Suitability Rank

Ten factors limiting land use are rated by the degrees of limitation (table 4.4). Four classes of limitation are recognized for each of the ten factors, ranging from zero, or no limitation, to 3, meaning severe limitations. Thus a land type with a low level of soil nutrients is coded n2, whereas an area without drought risk is designated simply as i. The total value of the numerical subscripts accompanying the letters determines the rank of a land type. Land is ranked 1 when there are no limiting factors or when the sum of the numerical subscripts is zero or less than, but including, 1, e.g.. S. and do, which together have a combined numerical value of 1 + 0 = 1. In rank 2, there is usually one dominant limiting factor, and rarely two. A land type is ranked 2 when the combined numerical value is between 1 and 2, e.g. n1d1 (medium soil nutrient with a solum of between 60-100 cm). Rank 3 has a numerical value of between 2 and 3 whereas that for rank 4 is greater than 3 (such as n2d3).

TABLE 4.4. Preliminary Ratings of the Intensities of Limiting Factors Used to Rank Land Suitability

Factor Rating
0 1 2 3
Slope steepness (s) 15 15-25 25-35 35
Solum depth (cm) (d) 100 60 100 30-60 30
Soil nutrient (n) High Medium Low Very low
Soil erosion (e) None Slight(sheet) Moderate(rill) Strong (gully)
Surface rocks and/or
stones (%) (r)
5 5-25 25-35 35
Drought risk (i) None Possible drying of upper
horizon for short period
Drought during part of
growing season
Profile dries for indefinite
period
pH 4-6 6-7.5 6 7.5  
Flood hazard (f) None Occasional flooding Occasional heavy
flooding
Frequent of irregular
devastating flooding
Drainage status (g) Well-
Drained
Imperfectly drained
easily improved
Poorly drained but
drained;
Poorly to very poorly
difficult to improve
Water supply (w) Plenty Medium Low Very low

The relationship between ranks and the values of the limiting factors is summarized as follows:

Land-suitability
rank
Numerical values of
limiting factors
Rank 1 0-1
Rank 2 1-2
Rank 3 2-3
Rank 4 3 +

The four ranks represent different qualities of land assessed. The first rank indicates the most productive land in a given land type, and it may differ significantly from other ranks in the same land type in management requirements or in the potential for improvement owing to different limiting factors. In the present system, the number of limiting factors has been kept to a minimum, and usually only one dominant factor is emphasized. However, if two factors are equally important, then both are used. Ranks may be employed as a fundamental tool for mapping land suitability at the county, provincial or national levels, and such rank symbols as SAr1 or SAr2n2 are easily depicted on maps.

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