Nitrogen concentration and nitrate/ammonium ratio affect yield and change the oxalic acid concentration and fatty acid profile of purslane (Portulaca oleracea L.) grown in a soilless culture system

Purslane is an excellent source of omega‐3 fatty acids, amino acids and vitamins. The aim of this research was to study the effect of different nitrogen levels and NO 3 − ‐N/NH 4 + ‐N ratios in the nutrient solution on the yield and on the oxalic acid content and fatty acid profile in purslane grown in a soilless culture system. Two experiments were carried out to test different levels of nitrogen: (1) 8–12–16 mmol L −1 and (2) 0–12–24–36 mmol L −1 . A third experiment was carried out maintaining the N level fixed (12 mmol L −1 ) but varying the NO 3 − ‐N/NH 4 + ‐N ratio: 60:40, 40:60, 0:100. The results indicated that plants grew with increasing nitrogen level up to 36 mmol L −1 . Nitrogen supplied in both NO 3 − and NH 4 + forms produced bigger plants than N supplied in NH 4 + form only. Nitrogen did not significantly influence the polyunsaturated fatty acid content in the canopy. Significant trends were found for α‐linolenic acid (LNA; 18:3 n ‐3) and linoleic acid (LA; 18:2 n ‐6), indicating a favorable accumulation of omega‐3 fatty acids with increasing N; palmitic acid decreased by increasing N and by switching the NO 3 − /NH 4 + ratio towards the NH 4 + level in the nutrient solution, but using 0:100 NO 3 − /NH 4 + , decreased plant quality. Increasing N lowered oxalic acid production and palmitic acid content, enhancing purslane nutritional quality. Keeping a high N level in the nutrient solution with a 40:60 NO 3 − /NH 4 + ratio would give the best results in terms of yield, oxalic acid concentration and fatty acid profile.