assovarieties in countries such as India can be attributed to increased fertilizer use (Bruinsma, 2003). However, there is also evidence of declining efficiency of nitrogen applications in cropping systems (Figure 3-3).

Tractors and other sources of mechanization are increasingly important to agriculture in developing countries, but many systems remain dependent on traditional forms of human and animal power.

In developing countries, human, draft animal, and tractor power are used in approximately equivalent proportions in terms of total land under cultivation. There are, however, significant differences between and within countries and between regions and different types of agricultural systems. In SSA, about two-thirds of all agricultural land is cultivated by hand, whereas in LAC approximately 50% of the land is mechanically cultivated (Bruinsma, 2003). Although it is difficult to directly establish cause and effect relationships between single classes of assets and human welfare, it is generally recognized that households with animal or mechanical power tend to have better crop yields, more opportunities to pursue off-farm employment, and greater food security (Bishop-Sambrook, 2004).

Pesticide use is increasing on a global scale, but increases are not universally observed; several of the most hazardous materials are being phased out in well-regulated markets.

In constant dollars, global expenditures on agricultural pesticide imports has increased more than 1000% since 1960 (Tilman et al., 2001) with some estimates placing recent growth rates for pesticide use at between 4.0 and 5.4% per annum (Yudelman et al., 1998). There are exceptions to these trends, particularly in OECD countries. For example, in the US, agricultural pesticide use declined significantly after peaking in the late 1970s and has remained relatively constant since the 1990s (Aspelin, 2003). Moreover, regulatory and technological advances have, in some cases, resulted in the phase-out of particularly toxic organic compounds and the introduction of pesticides with lower non-target toxicity, which are less persistent in the environment and can be applied at lower rates (Aspelin, 2003; MA, 2005).

Total factor productivity has increased worldwide, with some regional variation.

Total Factor Productivity (TFP), i.e., the efficiency with which all the factors of agricultural production (land, water, fertilizer, labor, etc.) are utilized, has improved over the last fifty years (Coelli and Rao, 2003). The index of TFP for world agriculture has increased from 100 in 1980 to 180 in 2000. The average increase in TFP was 2.1% per year, with

efficiency change contributing 0.9% and technical change 1.2% (Coelli and Rao, 2003). The highest growth was observed in Asia (e.g., China 6%) and North America and the lowest in South America followed by Europe and Africa. However, a positive trend does not necessarily imply a sustainable system since rapid productivity gains from new technologies may mask the effects of serious resource degradation caused by technology-led intensification, at least in the short to medium-term (Ali and Byerlee, 2002).

3.2.1.1.2 Agriculture has impacts on natural capital and resource quality

In regions with the highest rates of rural poverty and undernourishment, depletion of soil nutrients is a pervasive and serious constraint to sustaining agricultural productivity.

To sustain long-term agricultural production, nutrients exported from the agroecosystem by harvest and through environmental pathways (e.g., leaching, erosion) must be sufficiently balanced by nutrient inputs (e.g., fertilizer, compost, atmospheric deposition, in situ biological nitrogen fixation). In the tropical countries where shifting agriculture is the traditional approach to regenerating soil fertility, increasing population pressure has resulted in shorter periods of fallow and often severe reductions in soil stocks of organic carbon and nutrients (Palm et al., 2005a). Nutrient depletion is particularly acute in many of the continuous cereal production systems on the Indian sub-Continent, Southeast Asia, and sub-Saharan Africa, especially since many of the soils in these regions have low native fertility (Cassman et al., 2005). With reduced land availability for fallows, low use of fertilizer amendments, and (in some circumstances) high rates of erosion, many soils in sub-Saharan Africa are highly degraded with respect to nutrient supply capacity (Lal, 2006; Vanlauwe and Giller, 2006). It has been estimated that 85% of the arable land in Africa (ca. 185 million ha) has net depletion rates of nitrogen, phosphorous and potassium (NPK) that exceed 30 kg ha-1 yr -1 (Henao and Baanante, 2006) with 21 countries having NPK depletion rates in excess of 60 kg ha-1 yr-1.

In high-yielding agriculture, the application of modern production technologies is often associated with environmental damage. In some cases, this damage is most attributed to inappropriate policies and management practices rather than to the technologies per se.

The adoption of MVs and yield enhancing technologies like inorganic fertilizer use and irrigation have been linked to a loss of biodiversity, reduced soil fertility, increased vulnerability to pests/diseases, declining water tables and increased salinity, increased water pollution, and damage to fragile lands through expansion of cropping into unsuitable areas. A detailed assessment of the environmental impacts assovarieties