The efficiency of agricultural subsidy programmes for preserving biodiversity and
improving the environment has been questioned in recent years. Organic farming operates
without pesticides, herbicides and inorganic fertilizers, and usually with a more diverse
crop rotation. It has been suggested that this system enhances biodiversity in agricultural
landscapes. We analysed the effects of organic farming on species richness and
abundance using meta-analysis of literature published before December 2002.
2.
Organic farming usually increases species richness, having on average 30% higher
species richness than conventional farming systems. However, the results were variable
among studies, and 16% of them actually showed a negative effect of organic farming on
species richness. We therefore divided the data into different organism groups and
according to the spatial scale of the study