Influence of nitrogen supply rates on growth and nutrient storage by water hyacinth (Eichhornia crassipes) plants

The effect of nitrogen (N) levels of the culture medium (0.5-50.5 mg N l^-1 or 38-3820 mg N m^-2 day^-1) on net productivity and nutrient (N, phosphorus (P) and potassium (K)) storage by water hyacinth (Eichhornia crassipes (Mart.) Solms) plants was investigated using outdoor tanks. Net productivity increased with N supply rate of up to 5.5 mg N l^-1 (or 416 mg N m^-2 day^-1); higher concentrations did not significantly increase the yield. The net productivity increased until plant tissue N content reached 16 mg N g^-1 dry weight, but additional increase in tissue N content did not improve yield. However, N storage in the plant tissue increased in response to N supply rate with maximum N storage (80 g N m^-2) measured in plants cultured at 50.5 mg N l^-1. Plant density affected N storage in the tissue; when water hyacinths were cultured in N-limited water, plant tissue-N decreased by 75% within 4 weeks of growth. The storage of P and K in the plant tissue was increased up to 5.5 mg N l^-1 and 2.5 mg N l^-1 in the culture medium, respectively.