Several meta-analyses have been published showing that the yield gap between organic and mainstream (often labelled conventional) crop yields is 20-25% on average, with a lot of variation across crops, sites and conditions. Such results at crop level are increasingly used in European or global studies, to indicate whether an organic agriculture can be an alternative to conventional types of agriculture. The 20-25% difference is valid at individual crop level, but at the cropping or farming system level it is not. Organically grown crops depend on nitrogen (and other nutrients) produced on additional land (e.g. green manure crops) or through manure which also requires land (e.g. grassland or land to produce feed). Livestock does not produce nutrients, but only recycles nutrients with inherent losses. A real comparison between organic and mainstream types of agriculture requires an analysis at systems level, also accounting for the land needed to collect the nutrients. This subject can be studied with a combination of experiments and (simple) quantitative models. There is also a possibility to participate in an experiment in the north of the Netherlands (Kollumerwaard), the so-called Planty Organic experiment, in which all nitrogen of a 6-years crop rotation is produced on-farm.
Louis Bolk institute and SPNA Kollumerwaard
A solid background in crop and farming systems and quantitative analysis of (large) datasets will be important for this study
Wageningen and possibly Friesland (experimental farm SPNA Kollumerwaard)
Martin van Ittersum 0317-482382 email@example.com
Gerrie van de Ven 0317-482140 firstname.lastname@example.org
Bert Rijk 0317-480402 email@example.com