Azolla filiculoides as a biofertiliser of wheat under dry-land soil conditions

The invasive aquatic fern Azolla filiculoides can be put to potentially good use as a biofertiliser. This study reports on the response of wheat to soil fertilisation with varying proportions of A. filiculoides subjected to three pre-treatments. In a preliminary study, treated Azolla was mixed with acid-washed sand at three application rates. Results demonstrated that pre-heated A. filiculoides added at 80% (v/v) resulted in the highest wheat above-ground biomass, but that the use of dried Azolla had a similar effect. In order to differentiate between the effects of fertilising nutrient-poor soils versus effects that could be expected from the fertilisation of field soils a second study was conducted applying dried A. filiculoides in various proportions to acid-washed sand and topsoil. Wheat performance in response to fertilisation was assessed by monitoring yield of grain, leaf areas and above-ground biomass. Wheat grown in acid-washed sand and fertilised with 80% (v/v) air-dried A. filiculoides significantly out performed other treatments. When added to topsoil, 20% and 80% (v/v) A. filiculoides, and the N, P and K-fertiliser treatments resulted in higher wheat yields than the control treatments. The potential contamination of water-bodies with A. filiculoides spores was also tested. It was found that A. filiculoides spores germinated from mixtures of air-dried A. filiculoides after a period of four months. A. filiculoides, an invasive water-weed, can thus be put to agricultural use under dry-land conditions, but may be a potential source of contaminating spores, perpetuating it as an invasive.