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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

3. Classification scheme for the 1:1,000,000 map of China's land resources

Shi Yulin
Commission for Integrated Survey of Natural Resources, Chinese Academy of Sciences, Beijing

Abstract

China's land resources are being mapped at the scale of 1: 1, 000, 000 in order to compile and present land-survey data and the results of research undertaken since 1949, to estimate the quantity and quality of the nation's land resources, and to indicate their current uses and future potential. On the basis of their suitability and limitations and potential for development for primary use, the land resources of China are classified into a number of orders (regions), classes, sub classes, groups and types.

One of the important projects outlined in the national "Survey of Agricultural Natural Resources and Agricultural Regionalization Programme, " specified by the Scientific and Technological Development Plan of the People's Republic of China (1978-1985), was the mapping of China's land resources at the scale of 1 : 1,000,000. The aim of the mapping project is systematically to compile and present data showing the achievements of land surveys and research undertaken since the establishment, in 1949, of the People's Republic of China, to map and briefly estimate the quantity and quality of all types of land resources in China, and to show the conditions under which they are used at present, as well as their potential for farming, forestry and animal husbandry. Such a project is necessary to provide basic data for the effective development and use of land resources, for agricultural regionalization, which can lead to better farming performance, and for the long-range planning and development of agriculture.

Experimental mapping at a scale of 1:1,000,000 has been conducted on the land resources of the Harbin, Qiqihar and Shenyang areas in China's North-east Region. The classification scheme discussed in this chapter was designed while the maps of those three areas were being compiled. This scheme has been used in mapping parts of South China. Owing to China's size and given that the project is still in its initial stage of development, among
other complications, the classification scheme described here is preliminary and future revisions are anticipated.

The classification of land resources is an essential prerequisite to their mapping and to land evaluation. Land resources were classified on the basis of current land-use patterns together with the productivity of the land. Since the chief purpose of compiling 1:1,000,000 maps is to facilitate the development of primary resources, the main considerations used in devising the classification scheme were:
1. The natural productivity of the land and whether this corresponds to actual production performance.
2. The degree of land suitability for particular primary uses and whether present land-use patterns best fit the quality of the land.
3. The limitations of the land on the development of primary resources and whether the measures taken, or that should be taken, to transform, conserve and improve productivity are justified.
4. Whether the productivity of the land is consonant with production costs.

Based on Chinese conditions and foreign experiences, a multiple grade scheme of orders (regions), classes, subclasses, groups and types was adopted for the classification of China's land resources. The sub-classes supplement classes, so four grades are actually used in the scheme. Each is discussed below.

Land Orders (Regions)

This is the highest unit in the classification. Orders are differentiated on the basis of moisture and thermal conditions, and reflect inter-regional differences in productivity. The orders may be used to assess interregional productive potentials. Within an order, land use is relatively homogeneous. Based on agroclimatic characteristics, 14 regions can be distinguished in China (see the Preface to this volume) (table 3. 1), which correspond with the orders of land resources.

TABLE 3.1. Criteria Used to Distinguish Land Orders (Regions) in China

Land order (region) Accumulated
Temperature
>= 10°C
Average annual
precipitation
(mm)
Aridity
index
a
1. Humid cool temperate <1,700 400-500 <1.0
2. Humid moderate temperate 1,700-3,200 400-800 <1.0
3. Subhumid moderate temperate 1,700-3,200 400-600 1.0-1.5
4. Semi-arid moderate temperate 1,700-3,200 200-500 1.5 2.0
5. Arid moderate temperate 1,700-3,500 (or 4,000) <200 (300) >2.0
6. Humid warm temperate 3,200 4,500 600-900 <1.0
7. Subhumid warm temperate 3,500-4,500 400-700 1.0 1.5
8. Semi-arid warm temperate 3,500-4,500 300-500 1.5-2.0
9. Arid warm temperate 3,500-4,500 (or 5.000) <200 >2.0
10. Humid cool sub-tropical 4,000(4,500)-5.000 (5,500) 700-1,200 <1.0
11. Humid moderate subtropical 5,000 (5,500)-6,000 (6,500) 1,000-1,800 <1.0
12. Humid warm subtropical 6,000(6,500)-7,500(8,000) 1,600-2,000 <1.0
13. Humid and subhumid tropical >7,500 (8,000) 1,400-2,000 <1.0
14. Alpine - Arctic <1,000 - -

a. Aridity index



where
E = average annual potential evapotranspiration
r = average annual precipitation

Land Classes and Sub-classes

The second category is land classes, which reflect the suitability and potential productivity of the land. Land classes form the core of the assessment of land resources. Within a class the suitability and potential productivity of the land should be virtually homogeneous. Suitability of the land is divided into five categories: (1) farming, forestry and animal husbandry; (2) forestry and animal husbandry; (3) animal husbandry; (4) forestry; and (5) temporarily unsuitable for any primary resource use. Land suitability may be further divided into three subclasses; very suitable, generally suitable and marginally suitable. To reduce the number of possible combinations and also to emphasize land for cultivation, land suitable for primary-resource use has been divided into three subcategories in terms of degree of suitability for farming: good-quality land with no limitations for farming; mediumquality land generally suitable for farming, but with some limitations; and poorquality land with many or severe limitations and only marginally suitable for farming. Thus at the land-class level, seven degrees of land suitability and potential productivity may be distinguished (fig.3.1).

Land Class I: This is high-quality land with no or little limitations for farming. It is also suitable for forestry and animal husbandry. Class l land is characterized by low relief, high fertility, and good conditions for mechanization. It is the main farm land with high and stable yields, or land that can easily become basic farmland. The uncultivated land of this class needs little or no improvement and after cultivation it easily becomes basic farmland. Land in this class does not deteriorate with use.

Land Class II: Land in this category has certain limitations for farming and its quality is moderate. Generally, class Il land is suitable for primary resource exploitation. Among its limitations for farming are thermal and/or moisture deficiencies, poor relief, alkaline and/or saline soils, swampiness and soil erosion. Certain improvement measures must be taken before the land can be cultivated or changed into basic farmland. Conservation measures are needed to prevent deterioration.

Land Class III: This class has limitations for farming. It is poor quality land, only marginally suitable for farming. Among its major limitations are the uncertainty of obtaining even one crop a year owing to moisture and water deficiencies, unstable yield of dry farming, steep slopes, thin soils, serious soil alkalinity or salinity, swampiness and severe soil erosion. Class Ill land requires major rehabilitation before it can be cultivated and converted to basic farmland, but it can be used for forestry and animal husbandry. Stringent conservation measures must be enforced to avoid further deterioration.

Land Class IV: Such land has very severe limitations for farming but has few if any for forestry or animal husbandry. Under exceptional conditions and with vigorous rehabilitation measures, some land in this category could be used for farming, for improved pasture, or for specialized agricultural uses.



Fig. 3.1. Relationship between Land Suitability and Land Potential



Fig. 3 2. Land Resources of the Anda Area, Heilongjiang Province

TABLE 3.2. Criteria for Rating Factors that Limit Land Use

Limiting factor Rating Land use
    Farming Forestry Animal husbandry
Slope <3°(po) I A a
3-7°(p1) II A a
7-15°/25°(P2) III A a
15-35°/25°(P3) None B b
>35°(P4) None C c
Erosion (percentage of area occupied by gullies) None (e0) I A a
Slight<10%(e1) II A a
Moderate10 30%(e2) III B b
Strong 30-50%(e3) None C c
Severe>50%(e4) None C None
Soil texture Homogeneous loam (m0) I A a
Homogeneous clay (m1) II A a
Interlayer (m2) I-II A a
Sandy (m3) None B b
Gravelly (m4) None C c
Soil depth (cm) (¡ = developed on rock or consolidated bedrock; s = developed on soft bedrock) Very deep (l0) - ¡ 100; s 50 I A -
Deep (I1) -¡ 100 50; s 50-30 II A -
Moderatelydeep(12)-¡50-30; s30-10 III B -
Shallow (13) - ¡ 30-10; s < 10 None B  
Very shallow (14) - Y <10 None C -
Hydrological and drainage conditions No-occasional flooding. Well-drained (w1) I A a
Seasonal flooding. Poorly drained (w2) II B b
Extended flooding. Poor prospect III C None
for improved drainage (W3)      
Severely extended flooding None None None
Improvement very difficult (W4)      
Soil salinization None/slight (s1) I A a
Moderate/strong (s2) II B b
Strong (s3) III C b
Severe (s4) None None b
Lime hardpan (depth from surface in cm thickness >20 cm) <40 (h1) I B -
  40-30 (h2) II C -
30-20 (h3) III None -
>20 (h4) None None -
pH 6 7(a1) I A -
6-4 5 (a2) II B -
4 5 (a3) III B/C -

Land Class V: Land in this class suffers severe limitations for farming and forestry, but few or none for animal husbandry. Under exceptional conditions and with major rehabilitation measures some areas could be made suitable for farming, forestry, or improved pasture.

Land Class Vl: Such land has very severe limitations for farming and animal husbandry, but is suitable for forestry. In exceptional cases small areas could be used for animal husbandry, and major improvements are required before any could be used for special agricultural activities.

Land Class Vll: This refers to land unsuitable for farming, forestry and animal husbandry owing to its present dedicated use or particular natural characteristics. Among the different types of land in this class are shifting sand dunes, gobi, land with rare and endangered biota, glaciers, protected sources of water, tourist areas, areas producing industrial raw materials, mines, and urban land.

Within a class, sub-classes reflecting suitability of forestry and natural pasture may be used as supplementary units. The capital letters "A", "B" and "C" denote suitability for forestry, and minuscules "a", "b" and "c" refer to animal husbandry.

"A" refers to land most suited to forestry. It has a good climate, fertile soils and appropriate slope. The land is suitable for many species, especially those with economic value, forest productivity is high and timber quality good. " B" is land generally suitable for forestry, but has certain limitations for some species. Development of economic forests and valuable species is limited by topography and soils, and forest productivity is not high. " C " refers to land marginally suitable for forestry, but severely limited in the number of species, especially high grade species, that can be grown. Such land may need improvement before forestry use. C-grade land may be suitable for watershed protection forests, windbreak plantations, trees grown to fix drifting sand, and the like.

TABLE 3.3. Micro-relief as a Factor Limiting Land Use

  Sparse and small
hillocks (g
1)
Moderate hillocks (g2) Higher
hillocks (g
3)
High
hillocks (g
4)
   
<1 m <30% Dense and
small hillocks
<1 m >30%
Sparse but
large hillocks
1-2 m <30%
1-2 m 30-50% >2 m 1-2 m
>30% >50%
Farming I II III None

TABLE 3.4. Temperature as a Factor Limiting Land Use

  Adapted to one
cool-season
crop per year.
Unstable yield(t
1)
Adapted to
cool-season crop.
Cannot mature
(t
2)
Forest will
not grow
(t
3)
Livestock
will not
live
(t
4)
Farming III None - -
Forestry - - None -
Animal husbandry - - - None

TABLE 3.5. Moisture as a Factor Limiting Land Use

  Adequate
moisture
for dry
farming
Irrigation water
supply guaranteed
on arid and
semi-arid lands
Irrigation
water supply
not guaranteed
on arid and
semi-arid lands
Non-irrigation
water supply
not guaranteed
on arid and
semi-arid lands
Insufficient
water supply.
Cannot be used
for dry farming
(r0) (r1) (r2) (r3) (r1)
Farming I II III III None

In terms of pasture lands, "a" refers to land of good quality and very suitable for animal husbandry. It is characterized by thick. good quality and highly nutritious grasses palatable to livestock. Such land has high yields and is suitable for many kinds of animals. Pasture land "b" is of moderate quality and generally suitable for animal husbandry. The grasses grow moderately well, but their high quality is off-set by low yield, or vice versa. The nutritional values, especially the N content, are relatively low. The kind of livestock that may be raised on this type of land may be limited. The letter "c" refers to grassland of poor quality, only marginally suitable for animal husbandry. Both the quality and the productivity of the grasses are poor. The grassland is degenerated with a low carrying capacity, and needs improvement. The number and kinds of livestock that can be raised on this category of land is severely limited.

Sub-classes can be combined into as many as are needed. The cultivated fields of classes I and II are not evaluated for animal husbandry and forestry.

Land Groups

Land groups follow land classes and sub-classes and are differentiated on the basis of limiting factors and the corresponding measures needed for their amelioration. There are similar limiting factors within groups, and similar ameliorative measures are needed. In compiling the map of land resources of the Anda area, in Heilongjiang Province (fig. 3.2), at a scale of 1:1,000,000, primary consideration was given to the main limiting factors that fluctuate little and which play different roles in different groups. Eleven limiting factors and one non-limiting factor have been used on the map. These 12 factors are: erosion (e), slope (p), soil texture (m), soil depth (I), hardpan (h), hydrological and drainage conditions (w), soil salinization (s), soil acidity (a), microrelief (9), temperature (t), moisture (r). and no limitations (0).

TABLE 3.6. Criteria for Rating Pasture

Yield
(fresh pasture)
Quality of pasture
Good
>60%
Moderate
>60%
Poor
>60%
>300 kg/ha a b c
100-300 kg/ha a b c
<100kg/ha b b c

These limiting factors are arranged according to their degree of stability. The factors of erosion and slope are stable whereas acidity and micro-relief factors are relatively more liable to change. Although the temperature and precipitation factors are fairly stable, they do have regional significance, as has been reflected in the classification of orders (regions). At the group level moisture and temperature are significant only in exceptional cases. In addition, each limiting factor is further rated in terms of severity. For example, in evaluating erosion (e), five subgroups (e0, e1, e2, e3, e4, e5) are recognized. Examples of some factor ratings are given in tables 3.2, 3.3, 3.4, 3.5, and 3.6.

Two or more limiting factors often appear simultaneously in dividing the groups. Owing to the constraint of the small map scale, the main limiting factor is clearly indicated under such circumstances. The relative importance of the factors may be indicated by the rating codes. If necessary, two factors can be given at the same time, but the main factor must be identified first.

Types of Land Resources

Below groups, land-resource types are differentiated. They are the smallest unit in the classification and constitute the foundation of land-resource evaluation. The characteristics of the land in a type should be relatively uniform, including landform, soils, vegetation and the present use status. In addition, within a type, the measures needed to up-grade the productivity and the landmanagement methods should also be similar. There is no limit to the number of land-resource types in a given area, the number being flexible to fit local conditions. The names given to landresource types may include compound terms, such as flood plain - meadow swampy soils - Deyeuxia angustifolia-Carex meadow, but local terminology may also be used.