Yields in organic agriculture are typically 10-30% lower than those with conventional management, but in many cases organic systems are economically competitive.

Yield reductions are commonly associated with adoption of organic practices in intensive production systems (Mäder et al., 2002; Badgley et al., 2007). While yields may be 10-30% lower, profits are, on average, comparable to those on conventional farms. Pest and fertility problems are particularly common during transitions to organic production. As with all production systems, the yield penalty associated with organic agriculture depends on farmer expertise with organic production methods and with factors such as inherent soil fertility (Bruinsma, 2003). In contrast to the reduced productivity responses observed in many high-yielding systems, traditional systems converted to organic agriculture, yields typically do not fall and may increase (ETC/KIOF, 1998).

Organic agriculture greatly reduces or eliminates the use of synthetic agents for pest control.

The use of synthetic agrochemicals, the foundation of modern agriculture, has been linked to negative impacts such as ground and surface water contamination (Barbash et al., 1999; USGS, 2006), harm to wildlife (Hayes et al., 2002), and acute poisoning of agricultural workers, particularly in the developing world where protection standards and safety equipment are often inadequate (Repetto and Baliga, 1996). Organic systems greatly reduce or eliminate synthetic pesticide use (Mäder et al., 2002), thereby diminishing these concerns. However, a small minority of the pest control substances allowed under organic standards (e.g., copper for downy mildew control in viticulture) also pose human and environmental health risks. Also, the lower efficacy of some organic pest control methods contributes to the yield penalty associated with organic systems. In the longer term, increased biodiversity and an increase in predator species can contribute to a more balanced agroecosystem.

Enhanced use of organic fertility sources can improve soil quality and sustain production, but in some situations supplies of these sources can be inadequate for sustaining high-yielding organic production.

Adequate soil organic matter are vital for maintaining soil quality; it is a source of macro and micronutrients for plant nutrition, enhances cation exchange capacity and nutrient retention, and facilitates aggregation and good soil structure. However, shortages of organic soil amendments are common in many developing regions (e.g., Mowo et al., 2006; Vanlauwe and Giller, 2006), especially where high population density and cropping intensity preclude rotations with N-fixing legumes or improved fallows and there are competing uses for animal manures (e.g., for cooking fuel). When population pressure is high or environments

are degraded, some of the most common organic resources available to farmers (e.g., cereal stovers) are of poor quality, with low nutrient concentrations and macronutrient ratios not commensurate with plant needs. Modern best practice guidelines for conventional production systems advise the full use of all indigenous fertility sources (composts, crop residues, and animal manures), with mineral fertilizers employed to bridge deficits between crop needs and indigenous supplies (e.g., http://www.knowledgebank.irri.org/ssnm/)

Some facets of organic agriculture have clear benefits for environmental sustainability; evidence for others is mixed, neutral, or inconclusive.

Since organic agriculture is more clearly defined by what it prohibits (e.g., synthetics) than what it requires, the environmental benefits that accrue from organic production are difficult to generalize. Some evidence suggests that above and below-ground biodiversity is higher in organic systems (Bengtsson et al., 2005; Mäder et al., 2006), but neutral outcomes are also reported from long-term experiments (e.g., Franke-Snyder et al., 2001); species richness sometimes increases among a few organisms groups while others are unaffected (Bengtsson et al., 2005). Biodiversity impacts from organic agriculture are influenced by factors such as crop rotation and tillage practices, quantity and quality of organic amendments applied to the soil, and the characteristics of the surrounding landscape. Although some studies demonstrate reduced environmental losses of nitrate N in organic systems (e.g., Kramer et al., 2006), most evidence suggests that nitrate losses are not reduced in high-yielding organic systems when contrasted to conventional production system (Kirchmann and Bergstroem, 2001; DeNeve et al., 2003; Torstensson et al., 2006). While fossil energy consumption can be substantially reduced in organic systems, energy savings must be balanced against productivity reductions (Dalgaard et al., 2001). For organic systems with substantially lower yields than conventional alternatives, total enterprise energy efficiency (energy output per unit energy input) can be lower than the efficiency of conventional systems (Loges et al., 2006).

Organic markets are mostly in industrialized countries but organic markets, with a comparative advantage are emerging in developing countries.

Although the highest market growth for organic produce is in North America, the highest reported domestic market growth (approx. 30%) is in China; organic is also increasing in Indonesia. The range of marketing approaches is diverse and includes organic bazaars, small retail shops, supermarkets, multilevel direct selling schemes, community supported agriculture and internet marketing (FAO/ITC/CTA, 2001; IFOAM, 2006; Willer and Yussefi, 2006). The low external input production systems found in many developing countries are more easily converted to certified organic systems than to high external intensive production systems. Organic