(average) fertilizer use, many fields have a negative soil nu­trient balance. Although the fertilizer use projections show an increased use for sub-Saharan Africa, application rates remain too low to compensate losses and crop yields will therefore remain low. Some believe that land degradation will not be a major issue in food security for the future gen­erations (Crosson, 1994; Rosegrant and Sombilla, 1997); others argue that it will be a major constraining factor for food production in the future (Brown and Kane, 1994; Hin-richsen, 1998)
.      Crops are highly depended on an adequate supply of nutrients, notably N, P and potassium (K). The use of min­eral fertilizer has increased significantly over the last 50 years, from 30 million tonnes in 1960, to 70 million tonnes in 1970 to 154 million tonnes in 2005 (IFA, 2006). This in­creased use is one of the drivers behind the increase in crop yield over the last 50 years. About two thirds of the global N fertilizer is currently used in cereal production (Cassman et al., 2003). Fertilizer use is expected to increase by 188 million tonnes by 2030 (FAO, 2004a). The projections for 2030 indicate that approximately 70% of the increase in total crop production will stem from higher yields per ha and about 30% from expansion of harvested areas. The in­creased (and more efficient) use of fertilizers is one of the key drivers to attain these higher crop yields.
     The use of mineral and organic fertilizers is very diverse between countries and regions (Palm et al., 2004; Bouw-man et al., 2005; IFA, 2006). Nitrogen input varies from virtually nil to over 500 kg N per ha; with these differences likely to continue (Daberkow et al., 2000; Bruinsma, 2003; Bouwman et al., 2005). The use of fertilizers is expected to increase further in South and East Asia; in sub-Saharan Af­rica the present low application rates are projected to persist and seriously hamper crop production. Low application is caused by a range of factors, which without targeted policies and interventions are likely to persist. These factors include a weak crop response to fertilizers (e.g., limited water avail­ability, poor soil conditions), unfavorable price relations be­tween input and output, and low net returns (Kelly, 2006).
     The increase in consumption of animal products is, next to population growth, one of the major causes of the in­crease of global fertilizer use. World meat consumption (and production) is expected to grow by 70% in the period 2000-2030 and 120% in the period 2000-2050 (FAO, 2006b). The production and consumption of pig and poultry meat is expected to grow at a much higher speed than of bovine and ovine meat. Over the last years there has been a major expansion in large scale, vertically integrated industrial live­stock systems, and this development is expected to continue over the coming decades (Bruinsma, 2003). These systems can lead to concentration of manure; although manure is a valuable source of nutrients, concentrated spreading of ma­nure leads to significant emissions, to air, soil and water.

4.4.3 Land use and land cover change
Growing demand for food, feed, fiber and fuel, as well as increasing competition for land with other sectors (e.g., human settlement, infrastructure, conservation, and recre­ation), drive the need for change in the use of land already dedicated to agricultural production, and often for addi­tional land to be brought into production. The significance

of the cumulative historical growth in demand for agricul­tural products and services is reflected in the fact that agri­culture now occupies about 40% of the global land surface. There is also clear evidence that this enormous change in land use and land cover has brought about, and continues to bring significant impacts on local, regional and global environmental conditions, as well as on economic and so­cial welfare. In turn, such impacts spur demand for specific types of improvements in agriculture. AKST can help miti­gate negative outcomes and enhance positive ones.
     In this context, AKST can be seen as playing a dual role in both shaping and responding to a dynamic balance of land use and land cover conditions that deliver specific mixes of agricultural and other goods and services. As hu­man well-being needs and preferences evolve in different societies, so too will the goals and priorities for the devel­opment of new AKST. The relative scarcities of land in Ja­pan and labor in the USA shaped their agricultural research priorities (Hayami and Ruttan, 1985). Global experience with rampant land degradation caused by inappropriate production practices that gave rise to degradation of land cover, migration and often further expansion of the agri­cultural frontier has driven the search for new knowledge on sustainable farming technologies and land management practices. Land use/cover change is a complex process with multiple factors and drivers acting synergistically. In the tropics, deforestation was frequently driven by an interplay of economic, institutional, technological, cultural, and de­mographic factors (Geist and Lambin, 2004) (Figure 4-19). There are numerous other studies that link environmental land cover change to socioeconomic factors (e.g., Hietel et al., 2005; Xie et al., 2005).

4.4.3.1 Global land cover and land use change
Current drivers. Globally, there are a small number of recur­rent drivers of land use and land use change (Figure 4-19): demographic; economic; technological; policy; and cultural. Yet, some factors play a decisive role in determining land use and thus land use change. For example, globally 78% of the increase in crop production between 1961 and 1999 was attributable to yield increases and 22% to expansion of harvested area (Bruinsma, 2003). While the pattern of yield increases outpacing increases in harvested area was true for most regions, the proportions varied. For example, 80% of total output growth was derived from yield increases in South Asia, compared to only 34% in sub-Saharan Africa. In industrial countries, where the amount of cultivated land has been stable or declining, increased output was derived predominantly through the development and adoption of AKST that served to increase yields and cropping intensi­ties. Thus, the role of land use change and (adoption of) AKST has varied greatly between regions. Particularly in Latin America, land abundance has slowed the introduction of new technologies.

Projected global land cover and land use changes.  Few global studies have produced long-term land cover and land use projections. The most comprehensive studies, in terms of land type coverage, are the Land Use and Cover Change Synthesis book (Alcamo et al., 2005), IPCC Special Report on Emissions Scenarios (SRES) (IPCC, 2000), the