Table 3. Summary of findings.

Performance indicator or ecosystem service Size of effect Significance of effect Strength of evidence § Selected key references | Explanatory notes
Biodiversity
Abundance Large+ * Strong Meta-analyses:
Bengtsson et al. 2005,
Batáry et al. 2011.
Quantitative synthesis:
Anand et al. 2010.
Local factors (e.g., organic vs. conventional) and landscape factors (e.g., complexity) influenced biodiversity outcomes in temperate and tropical regions.
 
Richness Medium+ * Strong

Soil quality
Soil organic matter Small to Medium+ * Strong Long-term study:
Drinkwater et al. 1998.
Meta-analysis:
Marriott and Wander 2006.
Soil
Physical properties Small to Large+ * Strong Long-term study:
Mäder et al. 2002.
Biological properties Medium to Large+ * Strong Long-term studies:
Mäder et al. 2002,
Reganold et al. 2010.
Erosion Large+ * Strong Long-term study:
Reganold et al. 1987.
Nutrient management
Intercropping Studies:
Knudsen et al. 2004,
Li et al. 2007.
No meta-analyses or quantitative syntheses exist for intercropping, but several well-developed studies show how intercropping enhances nutrient-use efficiency. In their meta-analysis, Gardner et al. (2009) show how agroecological practices of crop rotation and organic fertilizers enhance retention of N in the system, promoting N uptake into crops and reducing losses to air and water. While Mondelaers et al.'s (2009) comparison of organic vs. conventional agriculture (meta-analysis) does not provide convincing evidence of organic-resolving nutrient leakage issues, the quantitative study of Zhang et al. (2010) unequivocally demonstrates how riparian buffers, another diversified farming system feature, can mitigate N and P runoff into waterways.
 
Crop rotation Small to Medium+ * Strong Meta-analysis:
Gardner et al. 2009.
Organic fertilizer source Medium+ * Strong Meta-analysis:
Gardner et al. 2009.
Nitrogen leaching
Organic–conventional Small+ * Weak Meta-analysis:
Mondelaers et al. 2009.
Riparian buffer Large+ * Strong Quantitative synthesis:
Zhang et al. 2010.

Phosphorus leaching
Organic–conventional Small+ n.s. Equivocal Meta-analysis:
Mondelaers et al. 2009.
Riparian buffer Large+ * Strong Quantitative synthesis:
Zhang et al. 2010.

Water-holding capacity
Medium+ * Strong Long-term study:
Reganold et al. 1997.
Lotter et al. (2003): under drought conditions, water percolation doubled on organic vs. conventional fields.
Mäder et al. (2002): reported 20 to 40% higher water-holding capacity in organic vs. conventionally managed soils in a 21-year long-term study.
 
Small to Large+ * Strong Long-term study:
Lotter et al. 2003.
Small to Medium+ * Weak to Strong Long-term study:
Mäder et al. 2002.
Control of weeds Moderate to Strong+ Vote count review:
Liebman and Dyck 1992.
 

Control of plant pathogens
Aerial Large+ * Strong Study:
Zhu et al. 2000.
Hiddink et al. (2010): while 74.5% of studies found a significant effect of crop diversification in reducing soilborne diseases, yields were still reduced substantially in some systems due to soil pathogens.
 
Soil Weak to Moderate+ Vote count review:
Hiddink et al. 2010.
Control of arthropod pests
Local scale Small+ * Weak Meta-analysis:
Letourneau et al. 2011.
Here, we considered effects on yield as the most direct measure of the ecosystem service of pest control. Few studies on pest control are available at the landscape scale. See text for information on other indicators of pest-control services.
 
Landscape scale None to Large+ n.s. to * Equivocal Meta-analysis:
Chaplin-Kramer et al. 2011.
Multiregional study:
Meehan et al. 2011.
Pollination services
Small+ * Weak Quantitative synthesis:
Garibaldi et al. 2011.
Here, we considered effects on yield as the most direct measure of the ecosystem service of pollination. The contribution of wild pollinators to crop yield may be masked in part by the ubiquitous presence of managed honey bees. See text for information on other indicators of pollination services.
 
Carbon sequestration
30-cm soil depth Small+ * Weak Long-term study:
Syswerda et al. 2011.
In general, too few measurements deeper in soil profiles have been taken to determine effects of agricultural practices on soil C stocks (Dolan et al. 2006, Kravchencko and Roberts 2011). In the long-term study of Syswerda et al. (2011), significantly higher C sequestration was found in the upper soil profiles for organic or no-till agriculture vs. conventional row-crops, but no significant difference considering the profile to 1 m, possibly due to much higher variability in the lower soil profile layers in C sequestration. There are many other diversified farming system practices that can influence soil C storage (i.e., crop rotations, composting, manuring/green manuring, crop residue retention, etc.) but we lack information on how they affect soil C storage through the soil profile, either alone or in combination.
 
1-m soil depth n.s. Equivocal Long-term studies:
Syswerda et al. 2011,
Dolan et al. 2006.
Energy-use efficiency Strong+ Vote count review:
Lynch et al. 2011.
Most studies showed energy-efficiency gains that surpassed the authors’ threshold of a 20% differential needed for policy action.
 
Global-warming potential Equivocal Vote count review:
Lynch et al. 2011.
Uncertainty in measurements of NO2 from soils and manure contributed to high variability. Also, for some production systems, greenhouse gas emissions were higher per unit of product for organic production.
 
Resiliency to environmental disturbances
Drought Medium to Large+ * Strong Long-term study:
Lotter et al. 2003.
Hurricanes and heavy rainfall Small to Large+ * Strong Study:
Holt-Giménez et al. 2002.

Productivity/yield
All countries
Organic-conventional Small− * Weak Meta-analyses:
Seufert et al. 2012;
L. Ponisio and C. Kremen 2012,
personal observation.
Quantitative synthesis:
de Ponti et al. 2012.
Two meta-analyses and a quantitative synthesis found a similar yield gap between organic and conventional, i.e., 20 to 25%. The majority of acceptable studies were from developed countries. For the subset of studies from developing countries, results conflicted among studies (see text). The Seufert et al. (2012) meta-analysis found a much larger yield gap in studies from developing countries, likely due to the conventional yields being larger than local averages. However, the L. Ponisio and C. Kremen (2012, personal observation) re-analysis of the Seufert et al. (2012) dataset (which took into account pseudo-replication) found no significant difference. The de Ponti et al. (2012) quantitative study found no significant difference between yield gaps for developing and developed countries. The Badgley et al. (2007) quantitative study found a large yield gain, but they compared resource-conserving agroecological techniques to subsistence or low-input conventional systems. Many of the studies were “ before and after” studies but did not have a control. We therefore rated this evidence as weak.
Developing countries
Organic–conventional Small to Medium− n.s to * Equivocal Meta-analyses:
L. Ponisio and C. Kremen 2012,
personal observation;
Seufert et al. 2012.
Quantitative syntheses:
Badgley et al. 2007,
de Ponti et al. 2012.

Resource-conserving to subsistence
Large+ N.A. Weak Quantitative synthesis:
Badgley et al. 2007.