Agricultural Lands

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Agricultural lands consist of three main types: (1) arable land (including cropland and fallows), (2) land under permanent crops, and (3) pastures and hayfields. The total area of agricultural lands in the world is 4973.4 million ha. They cover 33.3% of terrestrial surface (2003), including 10.3% of arable land and land under permanent crops and 23% of pastures and hayfields. The largest areas of agricultural lands are found in Asia (33.8% of the world value) and in Africa (23.0%); in Europe, the Americas, and Oceania, they occupy 9-12% of the world value (Table 2).

In the aggregate structure of agricultural lands, pastures and hayfields comprise 69.0% of the total agricultural area; arable lands, 28.2%; and lands under permanent crops, only 2.8%. But this structure is different in different regions: Oceania, Africa, and South America have the maximum portion of pastures and hayfields (80-88%) and minimum portion of arable land (10-18%). In Europe and North America, the portion of pastures and hayfields decreases to

Table 1 Production and effectiveness of different types of agriculture

Collecting

Long-fallow

Three-field

High-input

Hothouse

Systems of crop farming

Production (109 J ha-1 yr-1)

0.8

25

40

145

>400

Effectiveness (output/input) (J/J)

20

10

8

1.5

0.003

On natural

On artificial

At farms

Hunting

pastures

pastures

Systems of animal husbandry

Production (109J Jha-1 yr-1)

<0.8

17-34

50-59

92-110

Effectiveness (output/input) (J/J)

10.0

2.0-1.5

1.0-0.2

0.1-0.05

Systems of poultry farming

Production (109Jha-1 yr-1)

<0.04

67-75

92-126

Effectiveness (output/input) (J/J)

10.0

2.0-1.0

0.5-0.1

Table 2 The area of agricultural lands (million ha)

Africa

Asia

Europe

N. America

S. America

Oceania

World

Agricultural lands

1146.1

1681.4

483.6

618.9

584.3

459.1

49l3.4

%

23.G

33.8

9.l

12.4

11.l

9.2

1GG.G

Arable lands

199.4

5G6.9

284.1

255.2

1G1.1

49.l

14G2.3

Permanent crops

25.9

64.G

16.l

14.8

13.6

3.3

138.3

Pastures, hayfields

92G.8

111G.5

182.9

348.9

463.5

4G6.2

3432.8

Table 3 The structure of agricultural lands (%)

Table 3 The structure of agricultural lands (%)

Africa Asia Europe N. America S. America Oceania World

Pastures and hayfields 80.3 66.0 37.8 56.4 79.3 88.5 69.0

38-56%, whereas the portion of arable land gains its maximum (41-59%). In Asia, the structure of agricultural land resembles that in the whole world (Table 3).

Throughout history, the area of agricultural lands has been continuously expanding in all parts of the world, except for short periods of wars, epidemics, crises, etc. At present, the total agricultural area continues to rise (Figure 1), but the rate of this process has been decreasing since 1985.

Moreover, from the middle of the twentieth century, the dynamics of agricultural lands have been different in different regions (Figure 2). Their areas have increased in Asia and South America (by 30% from 1960 to 2003) and Africa (by 6%), but they have decreased in Europe (by 14%), North and Central America (by 4%), and Oceania (by 9% since 1981). Arable lands have similar dynamics: they have increased in South America (by 85%), Africa (by 33%), and Asia (by 15%), and they have decreased in Europe (by 15%). In North and Central America, the area of arable land was increasing up to year 1981 (by 5% since 1960) and then began to decrease (by 5%). Therefore, at present, the dynamics of agricultural areas have dissimilar trends in different parts of the world.

Agricultural activity is the main process altering the plant canopy on Earth. As a result of agricultural development, areas of steppe and savannah biomes have decreased by 7-10 times and the areas of forest biomes, by one-third (Figure 3). Australia, USA, China, Brasilia, India, and Russia have the largest areas of natural ecosystems replaced by agricultural lands.

Agricultural lands, as well as other ecosystems with plant canopy, are able to produce phytomass. The net primary productivity of arable lands and lands under permanent crops lies in the range of 1-40 tha-1 yr-1, with an average value of 6.5 tha-1 yr-1. This is close to the average net primary productivity of terrestrial ecosystems (7.81 ha- yr- ). The primary productivity of pastures and hayfields is near to that of corresponding grasslands, or somewhat lower, if the grazing pressure exceeds the critical level. As agricultural lands replace natural ecosystems with the highest primary productivity (first of all, forests, savannas, and meadows), the global biosphere production decreases by 12-15% under the impact of agricultural development. Moreover, agricultural activity leads to serious changes in landscapes and affects the global carbon (C) cycle. Cultivated soils have lost up to 30% of C (in the tropical zone, up to 70%); at present, the carbon emission from agricultural lands is estimated at 2.5GtCyr-1 (the emission related to combustion of fossil fuels reaches 5.8 GtC yr-1).

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