NITRATE/AMMONIUM RATIOS AFFECT RYEGRASS GROWTH AND NITROGEN ACCUMULATION IN A HYDROPONIC SYSTEM

Ryegrass has increasingly been used in constructed wetlands for treatment of eutrophic wastewater. To properly match plant species with the characteristics of wastewater being treated, it is important to know the performance of plant species under different nitrate/ammonium (NO3 −/NH4 +) ratios. We investigated ryegrass (Lolium perenne L.) dry matter (DM) production and N accumulation under five NO3 −/NH4 + ratios (100/0, 75/25, 50/50, 25/75, 0/100) in a hydroponic system. The results showed that ryegrass total DM, shoot DM, root DM and nitrogen (N) accumulation were greater under NO3 −/NH4 + ratios of 50/50 and 75/25 than under other NO3 −/NH4 + ratios, indicating that ryegrass can be best used in constructed wetlands for treating wastewater with such NO3 −/NH4 + ratios to achieve high biomass production and efficient removal of N. On the other hand, for treating wastewater with either NO3 − or NH4 + dominate the inorganic N, other plant species that are more adapted to such conditions should be explored.