Evaluation of nitrogen and phosphorus nutritional needs of halophytes for saline aquaponics

Abstract

To evaluate the nitrogen and phosphorus requirements of Salicornia neei, Apium graveolens and Paspalum vaginatum for use in saline aquaponics, plants were hydroponically cultivated with distinct concentrations of sole and mixed nitrogen forms, under low and high phosphorus concentrations. The low nitrogen concentration (0.2 mg L− 1) caused inhibition of many growth parameters. All species can take up both nitrogen forms, but S. neei and A. graveolens prefer nitrate. The high ammonium concentration as the sole nitrogen form (10 mg L− 1) negatively affected S. neei and A. graveolens, and the toxicity may be explained by rhizosphere acidification, since the negative effect was relieved by increasing the nutrient solution pH. Paspalum vaginatum was not sensitive to the high ammonium concentration. Mixed nitrogen forms resulted in plentiful growth of all species, which increased markedly towards the nitrate rich treatment. High ammonium might be applied once the nitrate concentration is ≥ 10 mg L− 1. Phosphorus was not an issue but may limit S. neei and A. graveolens production under a highly nitrifying condition in the water, a common feature of intensive aquaculture systems.