CULTIVATION OF DUCKWEEDS IN SEPTAGE-LOADED EARTHEN PONDS

A series of three experiments was conducted on the cultivation of duckweeds (Spirodela polyrrhiza, Lemna perpusilla, and Wolffia arrhiza) in 200 m2 septage-fed earthen ponds. Mean short- and long-term (27 and 182 days) extrapolated yields of Spirodela were 21.4 and 9.2 t dry wt/ha/year in Experiments 1 and 2, respectively. In the 90 days of Experiment 3, extrapolated yields of Spirodela and Lemna were 20.4 and 10.9 t dry wt/ha/year, respectively. Growth of Lemna continued for 160 days, but it was contaminated with Wolffia which reduced the yield. Mean crude protein contents of Spirodela and Lemna were 24.1 and 28.0% dry matter, respectively. Duckweed nitrogen and phosphorus contents increased significantly with an increase in nitrogen and phosphorus concentrations of pond water. Algal blooms, insect infestation, wind, low temperature, and loss of pigments and decay of duckweeds had noticeable effects on the growth and productivity of duckweeds.