Can organic rice crops help conserve aquatic plants in southern Brazil wetlands?




Are organic rice crops better than convention crops for aquatic plant conservation? We tested three hypotheses: (1) richness, diversity and biomass of aquatic macrophytes are higher in organic rice fields than in conventional ones; (2) aquatic macrophyte species composition in organic rice fields is more similar to that of natural wetlands than to conventional rice fields; and (3) aquatic macrophyte richness, diversity, biomass and species composition in natural wetlands will differ from those of organic and conventional rice fields.


Coastal plain of southern Brazil.


We sampled macrophytes at four conventional crops, four organic crops and four natural intermittent wetlands. We sampled at six different times at each site throughout the rice cultivation cycle.


A total of 55 species was recorded in natural wetlands and 36 species in rice fields, with 23 found in conventional crops and 27 found in organic crops. The richness, biomass and species composition of macrophytes was similar in the two rice production systems and lower than that of natural wetlands over the cultivation cycle studied. Species composition of natural wetlands differed from that of rice crops mainly through the presence of hydrophytes and rushes.


Some macrophyte species used rice crops as a complementary habitat, but diversity was lower and composition was different from that of natural wetlands. Both conventional and organic systems negatively impacted macrophyte biodiversity. However, the similar richness and biomass of plants in organic and conventional crops indicated that natural techniques with less impact could be efficient in reducing undesirable plant diversity in agricultural systems.