Lemna minor L. as Unconventional Fertilizer for Lettuce (Lactuca sativa L.)

Recycling plant waste as nutrients source for crops represents a circular approach to enhancing the sustainability of intensive horticultural production systems. Lemna minor L. is an invasive aquatic species which can proliferate on the nutrient solution in hydroponic systems requiring removal operations from the cultivation tanks. This study evaluated the possibility of using the biomass of this weed as an organic fertilizer for lettuce. The following fertilization treatments were applied: Control (0 kg N ha-1), Lemna (60, 120, and 180 kg N ha-1), Urea (60 kg N ha-1), commercial organic fertilizer (60 kg N ha-1). Fertilization with Lemna showed similar or better results than control and both inorganic and organic fertilization treatments. No differences in yield and quality were observed between the three doses of Lemna but L60 resulted to be the treatment with the best performance in terms of N productivity. These results suggest that Lemna biomass may be a proper source of nutrients for lettuce with advantage for yield and no effect on quality. Therefore, its use as an organic fertilizer can allow farmers to profitability exploit a waste product and, at the same time, reduce the costs of purchasing commercial fertilizers, thus achieving environmental and economic benefits.