Agriculture Reference
In-Depth Information
Seufert et al. (2012) reviewed 66 studies representing 62 study sites that reported
316 organic-to-conventional yield comparisons on 34 different crop species. Their
analysis was restricted to (1) organic systems defined as those with certified organic
management or noncertified organic management, following the standards of
organic certification bodies; (2) studies with comparable spatial and temporal scales
for both organic and conventional systems; and (3) studies reporting sample size
and error or information where these could be estimated. Seufert et al. (2012) stated
that, overall, organic yields are typically lower than conventional yields, but the dif-
ferences were highly contextual, depending on system and site characteristics, and
range from 5% lower organic yields (rain-fed legumes and perennials on weak-acidic
to weak alkaline soils), 13% lower yields (when best organic practices are used),
to 34% lower yields (when the conventional and organic systems are most compa-
rable). Under conditions with good management practices, however, they found that
organic systems can nearly match conventional yields for particular crop types. For
example, organic fruits and oilseed crops showed slightly lower, but not statistically
significant, yields of 3% and 11%, respectively, when compared to conventional crop
yields. In contrast, organic cereals and vegetables had significantly lower yields of
26% and 33%, respectively. Seufert et al. (2012) stated that part of the yield response
could be explained by differences in the amount of N input received by the systems.
Most of the N in organic materials is only slowly available and often over multiple
crops, whereas N fertilizer is readily available. Therefore, Seufert et al. (2012) stated
that organic systems appear to be N limited, whereas conventional systems are not.
de Ponti et al. (2012) conducted a similar study to that of Seufert et al. (2012) in
that they compiled and analyzed 362 published organic-conventional comparative
crop yields. They began their review with the hypothesis that the yield gap between
organic and conventional agriculture increases as conventional yields increase. The
stated rationale behind the hypothesis of de Ponti et al. (2012) was that when con-
ventional yields are high and relatively close to the potential or water-limited level,
nutrient stress, as per definition of the potential or water-limited yield levels, must
be low, and pests and diseases well controlled, which are conditions more difficult
to attain in organic agriculture. They showed that organic yields of individual crops
are on average 80% of conventional yields, but variation was substantial having a
standard deviation of 21%. They further stated that relative yields differed between
crops with soybean, some other pulses, rice, and corn scoring higher than 80% and
wheat, barley, and potato scoring lower than 80%. Most regions had relative yields
fairly close to the overall average, but Asia and Central Europe had comparatively
higher relative yields and Northern Europe had lower relative yields. In Denmark
and The Netherlands, countries with very intensive agricultural systems, they found
the gap between organic and conventional yields somewhat larger. de Ponti et al.
(2012) concluded that the findings gave some support to their hypothesis that the
organic-conventional yield gap is higher when conventional yields are high, but that
the relationship and hence the evidence underpinning were not strong.
Although studies that compare yields of organic and conventional systems are of
interest, it is clear that high yields are dependent on high inputs and the inputs must
be available to the crop. From a theoretical viewpoint, there is every reason to believe
that a well-managed organic crop can yield as much as a conventional crop as long
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