| Abstract | Three experiments were conducted in an outdoor system of fifteen
circular concrete tanks each of 2.07m~ area, to investigate the effects of
light intensity, urea- N and triple super phosphate- P, and water depth on the
production and nutrient uptake of Lemna perpusilla. Experiment 1 involved a
fertilization rate of 0.25g N/m3 /day and a water depth of 1.0m at 301., 401.,
651., 80/. and 100/. ambient light; Experiment 2 involved a 30/. ambient light in
O. lg, 0.2g, 0.3g, 0.4g and 0.5g N/m3 /day (N:P ratio 2:1) in a depth of 1.0m;
and Experiment 3 involved a fertilization rate of 0.25g N/m3 /day and with 30/.
ambient light, and 0.2m, 0.4m, 0.6m, O.Bm and 1.0m water depths of tanks.
The highest extrapolated net yields in the three experiment were, 3.486
tonnes/ha/yr in Experiment 1 with 0.25g N/m3 / day in 1.0m depth and with a 30/.
ambient 1 ight when photosynthetic active radiation was 3 to 11 Umol/m-2/s-.1.;
and with a fertilization rate of 0.25g N/m3 /d and with 30/.light, in a depth of
0.4m it was 3.515 tonnes/ha/yr, and in Experiment 2 with a varying rates of
fertilization and 30/. light, the yield was 3.78 tonnes/ha/yr in the lowest
concentration rate of O.lg N/m3 /day .
Nitrogen contents in Lemna were not significantly different (p>0.05),
but phosphorus contents were significantly different (p<0.05) in the first two
experiments. The experiment with depth showed significance differences in
nitrogen and phosphorus contents in Lemna (p<0.05). Nitrogen and phosphorus
contents increased with nutrient loading rate.
Most of the nitrogen added remained in the water in all experiments,
except in the experiment with a fertilization rate of O.lg N/m3 /day, with 30/.
ambient light; and 0.4m tank in an experiment with 0.25g N/m3/day and 30/.
light, where the largest amounts, 55.79/. and 52.8/. respectively, were taken up
by Lemna. On the other hand, phosphorus always showed the highest accumulation
in the sediments in all experiments, except for the nutrient loading rate and
depth mentioned above, where Lemna contained the largest amoL1nt of added
nitrogen, 39.12/. and 42.21., respectively. |