need to include management of complex production systems like agroforestry, polycultural, and silvo-pastoral systems.
     There are many methods for estimating the costs and benefits of educational policies; the cost-benefit analysis (CBA) is possibly one of the most used. The results of many CBA studies for developing countries in Africa, Asia and Latin America between 1960 and 1985 have been compiled and summarized (Hough, 1993). Major conclusions from this study included the following: (1) private Rate-of-Re-turns3 (ROR) are always higher (27%) than social RORs4 (19%); (2) RORs are always highest (32%) at the lowest level of education, but vary across regions; (3) social RORs to higher education are always lower (14%) than those to secondary education (16.7%), but the converse was true with private rates (24.3% and 21.3% for higher and secondary education, respectively); (4) public subsidies are particularly high in the cases of both primary and higher education, and in general, the poorer the country, the more subsidized is its education, particularly higher education, and (5) where time series data on earnings exist, there appears to be a decline in RORs over time (Psacharopoulos and Patrinos, 2004). Finally, some types of education that exhibit higher rates-of-return are general education for women and lowest per-capita income sector, and vocational education.

4.3.5.2 Culture
Culture has had a profound influence on the creation of new agricultural systems, as well as on the continued improve­ment of existing ones and will continue to do so in the fu­ture. However, as with education—cultural factors are often difficult to capture in scenarios.
     One factor where culture plays a role is in diets. On an aggregated level changes in diet seem to mostly follow closely changes in income, independent of cultural factors or geographical location (FAO, 2002b). However, at equiva­lent incomes, cultural differences become conspicuous driv­ers of food quality and type (FAO, 2002b) (e.g., low pork consumption rates in some regions and low beef consump­tion rates in others). These factors are generally taken into account in the projections of existing assessments (see also 4.4.1).
     Organic agriculture has been increasing in the past, and further expansion seems likely—certainly if the actual costs of agricultural commodity and food production were reflected in both domestic and international agricultural prices. It is, however, unlikely that organic farming will become a real substitute for industrial agricultural production systems, even if organic farming yield were similar to conventional yield (see e.g., Badgley et al., 2007). Production costs would likely be higher because it is a more labor-intensive activity and it might have additional standardization costs (OECD, 2002; Cáceres, 2005). Organic farming therefore does not play a very important role in the scenarios of existing as­sessments though it could have an impact on poverty and hunger alleviation in, for instance, least developed countries
3 These RRs take into account the costs borne by the students and/ or their families in regard to net (post-tax) incomes. 4 These RRs relate all the costs to society to gross (before deduc­tion of income tax) incomes.

with large rural populations, mostly of small-scale farmers living from subsistence traditional agriculture. This trend may be explored in new scenarios.
     Another factor that might be considered is that tradi­tional and indigenous cultures may be sources of agricul­tural knowledge useful for devising sustainable production systems. However, the future of that knowledge is likely to be grim in a globalized world if those who retain this knowl­edge do not receive assistance to pursue their futures in a manner acceptable to their value system (Groenfeldt, 2003). The practical knowledge stored in traditional and indige­nous agriculture could be conserved if it were the subject of interdisciplinary inquiry by research organizations and uni­versities (Thaman, 2002; Rist and Dahdouh-Guebas, 2006) with the aim of adapting otherwise unsustainable produc­tion systems to the likely incoming environmental shocks, such as the changing climate caused by global warming (cf. Borron, 2006), natural resource depletion (e.g., irrigation water), and pollution.

4.3.5.3 Ethics
The use of biotechnology (see 4.3.4) may have consider­able benefits for society, but will likely raise ethical con­cerns about food and environmental safety (FAO, 2002b). The adaptation of these technologies in different scenarios should therefore be related to assumptions on ethical fac­tors. In the next decade, development of biotechnological products will be faster for issues that relate to challenges recognized by the general public (e.g., herbicide-tolerant plants) than for other areas.

4.3.6 Changes in biogeophysical environment
Over the last 50 years, the use of fertilizers, primarily N fertilizers, has increased rapidly (FAO, 2003; IFA, 2006; Figure 4-12). In the same period, the quantity of nutrients supplied in the form of manure has increased as well (Bouw-man et al., 2005). Increased use made a major increase in crop production possible. However, only a portion of the supplied nutrients are taken up by crops, with the remain­der lost in different forms to the environment. These losses cause progressively serious environmental problems (Gal­loway et al., 2002; MA, 2005a), some of which can directly affect agriculture through a reduction in water quality and through climate change, and can indirectly affect agricul­ture through increased pressure for agricultural systems to minimize off-site environmental impacts.
     To produce more food and feed in the future, the fertil­izer demand is projected to increase from 135 million tonnes in 2000 to 175 million tonnes in 2015 and to almost 190 million tonnes in 2030 (Bruinsma, 2003). These projections are based on assumed crop yield increases. In a "Constant Nitrogen Efficiency scenario" the use of nitrogen fertilizers is projected to grow from 82 million tonnes in 2000 to around 110 million tonnes in 2020 and 120-140 million tonnes in 2050 (Wood et al., 2004). In an "Improved Nutrient Use Efficiency scenario" the use increases to around 100 million tonnes in 2020 and 110-120 million tonnes in 2050. These nitrogen fertilizer projections are based on the crop yields projected by AT 2030 (FAO, 2003) and they have been used for the Millennium Ecosystem Assessment (MA, 2005a). As the number of livestock is projected to increase as well, the