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2 Characterisation and importance of agro- ecological zones in South Asia

Introduction

In an earlier assessment of the role of livestock in mixed farming systems in the AEZs of South-East Asia, the report dealt exclusively with rainfed agriculture (Devendra et al 1997). In this evaluation, although priority is given to rainfed AEZs, some discussion of irrigated systems relevant for livestock, particularly in countries such as Bangladesh, India, Pakistan and Sri Lanka, is included.

In Asia and the Pacific, the area under rainfed agriculture amounts to 223 million hectares, which represents some 67% of the total arable land (ADB 1989). Within this rainfed area, approximately 52% of the land is found in the six countries of South Asia, amounting to some 116 million hectares (Table 3). The proportion of arable land under rainfed agriculture varies from 26.7% for Pakistan to 84% for Nepal. Only in Pakistan (73.3%) and Sri Lanka (50.6%) does the proportion of irrigated land exceed that in the rainfed areas. However, in absolute terms, the largest amount of irrigated land, 43.8 million hectares, is located in India.

Table 3. Importance of rainfed agriculture in South Asia.

Country

Total rainfed area (x 106 ha)

Rainfed area as proportion of total arable land (%)

Rainfed production as proportion of agricultural GDP (%)

Population dependent on rainfed agriculture (%)

Bangladesh

7.70

81.6

40.5

41.0

Bhutan

0.07

81.0

28.9

93.0

India

100.00

69.5

25.7

42.2

Nepal

2.63

84.0

40.9

74.8

Pakistan

5.43

26.7

4.6

11.5

Sri Lanka

0.53

49.4

20.1

29.1

Source: ADB (1989).

Rainfed production accounts for 4.6–40.9% of agricultural GDP. From 11.5% to 93.0% of the human population in the six countries depend on rainfed agriculture for its livelihood. Most of the resource-poor farmers engaged in rainfed agriculture are smallholders with farm sizes averaging 1.5 ha. Alexandratos (1995) estimated that rainfed land suitable for cropping in South Asia, and currently not utilised, approximates 37 million hectares. The potential for the production of crop residues and agro-industrial by-products (AIBP), for use as animal feeds, would be enormous if only a fraction of this land was cultivated.

Characterisation of the agro-ecological zones

Definition of AEZs

For consistency with definitions used by the CGIAR, the classification of AEZs has been adopted from the Technical Advisory Committee (TAC) of the CGIAR (TAC 1994). In this system, the original AEZ 1 (warm arid and semi-arid tropics) and AEZ 5 (warm arid and semi-arid tropics with summer rainfall) are consolidated to cover the arid/semi-arid zones; AEZ 2 (warm subhumid tropics) and AEZ 6 (warm/cool subhumid subtropics with summer rainfall) are combined to cover the subhumid zones; AEZ 3 (warm humid tropics) and AEZ 7 (warm/cool humid subtropics with summer rainfall) are aggregated to cover the humid zones; and AEZ 4 (cool tropics) and AEZ 8 (cool subtropics with summer rainfall) are consolidated to cover the cool tropical zones with summer rainfall (Fischer 1995). A fifth zone encompasses the cool subtropics with winter rainfall. In this study, priority is given to the first three AEZs. The cool tropics/subtropics with winter/summer rainfall predominate outside the South Asia subregion, in China and adjoining border areas and in West Asia. Small areas that may occur in South Asia are in the northern Himalayan region and are more associated with Alpine grassland-based systems.

Humid AEZs are characterised by a length of growing period (LGP) in excess of 270 days; subhumid AEZs have a LGP ranging from 180 to 270 days; and arid/semi-arid zones have LGPs varying from 0 to 74 days (arid) and 75–179 days (semi-arid). South Asia is dominated by climates that range from arid to subhumid. Only Bangladesh, small parts of north-west, eastern and southern India and south-west Sri Lanka are characterised by humid conditions. India has by far the largest human population living in the semi-arid tropics; more than 400 million people or 55% of the total for the semi-arid tropics globally. Total rainfall in South Asia ranges from less than 75 mm in western India, the northern Himalayan regions of Bhutan and Nepal and parts of Pakistan to over 3000 mm in Bangladesh and Sri Lanka. Rainfall varies from year to year and is erratic and unreliable in the drier zones. In the wet season in these drier areas, dry spells can occur which may result in the complete loss of a crop. In Bangladesh, some 93% of arable land is found in regions with a 4–5 month wet season. In Nepal and Sri Lanka comparable values are 88% and 63%, respectively. However, in India, only 26% of arable land is found in zones with a 3–4 months wet season. The extent of the major AEZs in South Asia is shown in Figure 1. A classification of farming systems in which livestock occur is given by Sére et al (1995) for the major AEZs.

Soils

The soil classification systems suffer from considerable confusion and a lack of consistency between countries. Therefore, presenting a standardised classification is not easy. There are 16 major soil groups in South Asia with different textural characteristics and fertility profiles. The four largest soil groups are the Lithosols, Luvisols, Cambisols and Vertisols in that order. The Yermosols, Arenosols, Acrisols, Nitosols, Fluvisols and Xerosols follow these again in order of importance. The remaining soil groups occupy relatively small areas of land regionally. The three major soil groups, in descending order of area covered, are given in Table 4.

Table 4. The most important soil groups in the six countries of South Asia.

Bangladesh

Bhutan

India

Nepal

Pakistan

Sri Lanka

Gleysols

Acrisols

Luvisols

Cambisols

Lithosols

Luvisols

Cambisols

Lithosols

Vertisols

Lithosols

Yermosols

Acrisols

Fluvisols

Cambisols

Cambisols

Fluvisols

Arenosols

Fluvisols

In Bangladesh, 78.5% of arable land is under Gleysols; in India, 27.4% of arable land is under Luvisols and 22.4% under Vertisols; and in Sri Lanka, 69% of arable land is under Luvisols and 25.6% under Acrisols (ADB 1989).

Figure 1. Agro-ecological zones of South Asia

Rainfed farming systems

Background information for Asia on the priority AEZs is presented in Table 5. Currently, data limited to the AEZs in South Asia are not available, so the statistics shown include South-East Asia. However, most of the arid/semi-arid lands and a significant proportion of the subhumid zone occur in South Asia. The humid areas of South Asia are relatively small, and occur mostly in Bangladesh, parts of India and Sri Lanka. The largest areas of both rainfed and irrigated arable land occur in the arid/semi-arid zones. These zones, together with the subhumid zone, produce nearly 50% of the food crops and some 60% of the cash crops grown in Asia.

Mixed farming systems that include crops and animals are found in all the AEZs. Major crops include rice, wheat, maize, sorghum, pearl millet, pulses, oilseeds, sugar-cane, jute and cotton. Ruminants (cattle, buffalo, sheep and goats) and non-ruminants (pigs and poultry) are integrated into both rainfed and irrigated systems. In the cool tropics/subtropics, which is not a priority zone in this study, species such as yak (Poephagus gruniens) and mithun (Bos frontalis) are found. However, these animals are associated predominantly with Alpine grassland-based systems.

Table 5. Human populations, food demand and land use in the priority AEZs of Asia.

Parameters

Arid/semi-arid zones

Subhumid zone

Humid zone

% of Asia2 in AEZ

 

Amount/ number

% of Asia

Amount/ number

% of Asia

Amount/ number

% of Asia

 

Human populations in 2010 (×106)

1311.4

35.7

588.8

16.0

1264.5

34.4

86.1

Food demand in 2020 (×106 t GE)1

358.6

33.4

175.5

16.3

383.9

35.8

85.5

Production of food crops (×106 t GE)

230.9

31.5

123.6

16.9

262.7

35.9

84.3

Production of cash crops (×106 t GE)

79.6

33.6

62.8

26.5

89.7

37.9

98.0

Land area (×106 ha)

327.6

16.1

237.7

11.7

534.1

26.2

54.0

Arable land (×106 ha)

191.9

41.5

73.0

15.8

123.4

26.7

84.0

Rainfed arable land (×106 ha)

126.8

38.8

55.2

16.9

86.1

26.3

82.0

Irrigated arable land (×106 ha)

65.2

48.0

17.8

13.1

37.3

27.5

88.6

1. TGE = tonnes of grain equivalent.
2. Excludes cool tropics.
Source: TAC (1992).

Conclusions

This chapter classifies the AEZs in South Asia. The priority AEZs are the arid/semi-arid, and subhumid/humid zones.

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