When considering all crop types modeled in Global AEZ (excluding silage maize, forage legumes and grasses) and mixing all three input levels (see Box), we estimate that a little more than one quarter of the global land surface (excluding Antarctica) can be regarded as suitable for crop cultivation. In developed countries about one-fifth comprises of land with rain-fed cultivation potential. In developing countries it amounts to about 30 percent. This estimate of land with cultivation potential is more than twice the area that was actually in use for cultivation during 1994-96 (according to FAOSTAT). Despite this optimistic aggregate picture, there are several regions where the rain-fed cultivation potential is nearly fully exhausted or has already been exceeded.
| Gross extents with rain-fed cultivation potential - maximizing technology mix. |
Note that the extents in this table are termed 'gross' since no land was subtracted as is required for non-agricultural uses, such as infrastructure and settlements, nor legally protected areas. In reality, some 10 to 30 percent of gross suitable areas may not be available for cultivation even with full exploitation of suitable potentials for cropping.
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Various ways are available for estimating the extent of land with cultivation potential for rain-fed crops. Any quantification depends on a variety of assumptions: the range of crop types considered, the definition of what minimum level of output qualifies as acceptable, the social acceptance of land-cover conversions (in particular forests), and the assumptions on what land constraints may be alleviated with modern inputs and investment. The results presented in this section are based on the following calculation procedures for each grid-cell:
The total extents obtained in this way for each grid-cell, referred to as mixed level of inputs, were calculated for rain-fed and rain-fed plus irrigated conditions. The results have been aggregated to various levels (e.g., climatic zones, country, and region). |
 | Land with rain-fed cultivation potential - maximizing technology mix. |
By looking at all crop types, without consideration of the actual demand for different products, we may well overestimate the useful extents of land with cultivation potential. Therefore, results were also compiled by restricting the considered crop types to the three major cereals, namely wheat, rice, and grain maize, and accounting for housing and infrastructure land requirements. Under these assumptions, a net[1] estimate of about 2.4 thousand million ha of land with rain-fed cultivation potential (VS+S+MS) was obtained. Of these, 1.5 thousand million ha were found in less developed countries and 0.9 thousand million ha in developed countries.
| Extents of land in use for crop cultivation (1994 -1996) and gross extents of land with potential for rain-fed wheat, grain maize or rice cultivation. |
To take yet another look at the Global AEZ crop suitability results, we have compared per capita land currently (i.e., average of 1994-96) in use for cultivation and per capita net rain-fed land with cultivation potential for populations in 1995 and projected populations in 2050. In the calculations the population projections of the United Nations medium variant were used (United Nations, 1998). With very few exceptions (notably Australia, Russia, and North America), most regions were characterized by a use of some 0.1 to 0.4 ha arable land per person in the mid-1990s, the world average in 1995 being about 0.26 ha/person for a world population of almost 5.7 thousand million people.
| Per capita land in use for cultivation and net rain-fed cultivation potential for cereals, populations of 1995 and projected populations of 2050. |
The results suggest a considerable availability of resources suitable for agricultural uses. However, we do not hesitate to state that such increased use of cultivated land is neither likely (because of improvements in input use and technology leading to higher average per hectare output, and because of competition with other non-agricultural uses) nor desirable (because of obvious implications for bio-diversity and the carbon cycle).
[1]
Net rain-fed land with cultivation potential excludes land requirements for
infrastructure and settlement. In order to estimate land requirements for
housing and infrastructure, we used a gridded population dataset of the year
1995, available from the World Data Center for Human Interaction in the Environment
at the Center for International Earth Science Information Network (CIESIN,
2000). The data provides population counts and population density (people
per square kilometer) for grid-cells of 5 minutes latitude/longitude. Housing
and infrastructure requirements population density. They amount to 0.1 ha
per person in areas with very low population density, and are estimated at
0.05 ha per person when population density is 35 persons per square kilometer,
and they decline monotonously to 0.01 ha per person when the density reaches
3000 persons per square kilometer.
