Effects of agri-environmental and organic rice farming on yield and macrophyte community in Mediterranean paddy fields

Abstract

The Ebro Delta (Catalonia, Spain) is one of the largest wetland areas in the Mediterranean with 65% of its area occupied by rice fields. Because of the crucial role of rice fields in biodiversity and the regional economy, it is essential to find an optimum equilibrium between wetland conservation and rice productivity. The environmental and agronomic effects of three cropping systems with different degrees of farming intensity (organic, agri-environmental scheme and conventional) were assessed. The three cropping systems mainly differed in the use of agrochemicals, type of fertilizer and winter flooding. A 3-year field study was conducted in which agronomic performance and diversity and dynamics of macrophyte community in rice fields were assessed. Agri-environmental system yielded the same as the conventional one, whereas organic system significantly reduced grain yield. Biomass of weeds and macrophytes was the main contributor to yield decline. Both organic and agri-environmental systems, through winter flooding, promote the ecological succession and temporal heterogeneity of the macrophyte community in rice fields, whereas less impact on macrophyte diversity was observed. Filamentous algae were the most abundant group irrespective of the cropping system, followed by Chara vulgaris, Najas minor and Lemna minor in conventional, organic and agri-environmental systems, respectively. The environmental and agronomic benefits of winter flooding are discussed along with the current limitations of organic farming and suggested measures to make it agronomically feasible. This discussion is done under an integrative approach in which the agri-environmental legislation for the last 20 years is examined.