Nitrogen nutrition, yield and quality of spinach.

When grown in solution culture spinach plants confirmed the preference toward NO; 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)