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Yield variability in organic versus conventional systems : a meta-analysis for horticultural systems. PS-8.1-02

Malézieux E., Lesur-Dumoulin C., Ben-Ari T., Langlais C., Makowski D.. 2018. In : Book of abstracts of the XV European Society for Agronomy Congress : "Innovative cropping and farming systems for high quality food production systems". Genève : Agroscope, p. 52-52. European Society for Agronomy Congress (ESA 2018). 15, 2018-08-27/2018-08-31, Genève (Suisse).

Organic agriculture has the potential to reduce the impacts of agriculture on humans and ecosystems but its productivity compared to conventional agriculture remains a contentious issue. Previous meta-analyses have shown that yields in organic systems are 10 to 25 % lower compared with conventional systems. However, those metaanalysis estimated the average yield gap of organic versus conventional farming systems but did not consider yields spatio-temporal variability. Although it is a major concern for farmers and food chains, only few studies analysed the relative variability of organic systems compared to conventional ones. Two contrary hypotheses exist in the literature. On the one hand, because of its reliance on biological and ecological processes, organic production can be assumed to be more vulnerable to pests and diseases outbreaks. On the other hand, organic farming systems are known to have a greater structural diversity and to optimize nutrient cycling and biological pest regulation, which may hence induce a higher resilience of the system and yields. Here we focus on horticulture crops (fruits and vegetables) and make progress by estimating the variability of organic to conventional yield ratio across experiments and across years for a series of horticultural species from a meta-analysis of published field experiments. We define horticulture as production systems based on vegetables and/or fruit production, both in fields, market gardens or orchards. We analyse a dataset including the results of 52 papers reporting yield data for 37 horticultural species in 17 countries. We find that yields in organic horticulture are on average 10 to 32 % lower than those in conventional horticulture. The variance of yields was not significantly different between organic and conventional systems, hence we find no evidence of a larger inter annual variability in organic versus conventional horticulture. However, the coefficient of variation is significantly higher for organic yields vs. conventional ones reflecting the yield gap between these systems. We find no significant effect on yield ratios of type of crop, type of product nor type of climate. However, data on tropical zones were scarce. As a conclusion, despite lower yields, productivity of organic systems is not more instable that productivity of conventional ones, an important result for farmers and future development of organic horticulture.

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