Azolla-Anabaena as a Biofertilizer for Rice Paddy Fields in the Po Valley, a Temperate Rice Area in Northern Italy

Azolla is a floating pteridophyte, which contains as endosymbiont the nitrogen-fixing cyanobacterium Anabaena azollae (Nostocaceae family). Widely cultivated in the Asian regions, Azolla is either incorporated into the soil before rice transplanting or grown as a dual crop along with rice. To examine the feasibility of its use in flooded rice fields sited in the Temperate European Areas, we carried out a series of experiments in PVC tanks during 2000–2002 in Po Valley (northern Italy) conditions, to study the growth-development dynamics and the resistance/tolerance to low temperatures and to commonly used herbicides of several different Azolla strains. Three out of five strains tested survived the winter, with an increase in biomass from March to May producing approximately 30–40？kg？ of nitrogen. One of these strains, named “Milan”, emerged as the most resistant to herbicide and the most productive. Of the herbicides tested, Propanil permitted the survival of growing Azolla. 1. Introduction Azolla is a heterosporous pteridophyte, with seven species. It contains, as endosymbiont, Anabaena azollae Strasburger, a nitrogen fixing cyanobacterium (Nostocaceae family). Available bibliographical data on its environmental development are principally related to experiments carried out in Asian countries [1–3]. However, the wide ranges of temperature, humidity, and solar radiation in which the fern flourishes suggest the possibility of using Azolla outside these regions [4]. At 3 million tonnes per year, the EU ranks 17th (0.5%) amongst world rice producers, but in terms of consumption, with 3.5 million tonnes, the EU ranks only 19th. Rice is produced in specific areas of France, Greece, Italy, Portugal, and Spain. The main areas of cultivation are in the western part of the Po valley in Northern Italy and in the river delta areas, Ebro and Guadalquivir, in Spain. Together these represent 84% of the total European cultivated area of about 400,000？ha of rice. Cultivation centers such as Vercelli or Lomellina (Italy), Camargue (France), Ebro and Guadalquivir (Spain) tend to possess distinct “rice-related” characteristics: agronomic (specialization, simplification), landscape (“rice landscape”), natural resources (intensification of the resource use), economy and culture. Furthermore, these rice districts are located in reclaimed, marshy areas/wetlands of high environmental value which are also highly vulnerable, creating a need for sustainable and environmentally sound management techniques. Rice yields decline with time, as noted by Ladha et al. [5] in long-term