Nitrogen nutrition, yield and quality of spinach

When grown in solution culture spinach plants confirmed the preference toward NO3− nutrition and showed heavy toxicity to NH4+. In open field condition the highest yield was achieved with the ammonium sulphate in Bari (autumn–winter cycle—110 days) and with calcium nitrate in Policoro (winter–spring cycle—64 days). By increasing N level, yield, nitrates and oxalates leaf content increased. Oxalate content was not affected by nitrogen form. Remarkable differences were observed between leaf petiole and blade in nitrate (4062 vs 925 mg kg−1 of fresh mass) and oxalate (1051 vs 6999 mg kg−1 of fresh mass).