Influence of different nitrogen levels on biomass, nitrate and oxalate accumulation in spinach

An experiment of soluble culture was carried out to determine the effects of different solution N levels (4,8,12,16,20 mmol/L) on biomass, nitrate and oxalate content of spinach (Spinacia oleracea ). Results showed that spinach biomass was drastically increased by increasing N level from 4 to 8 mmol/L and was not obviously different at higher N level. Vitamin C content of leaf increased up to 8 mmol/L N and then decreased as N level further increased, while Vitamin C content in petiole decreased obviously as N rate increased. Nitrate content in leaf increased with increasing N rate, whereas nitrate content of petiole decreased when nitrogen level was increased from 4 to 8mmol/L then increased at the range of 8 ~ 20 mmol/L N. Soluble oxalate in leaf decreased slightly from 4 to 8 mmol/L N and then increased with further increasing N level, while soluble oxalate in petiole and total oxalate in leaf and petiole of spinach were increased up to 12 mmol/L N and then decreased at over 12 mmol/L. It follows that spinach has higher biomass and Vc content, lower nitrate and oxalate content as 8 mmol/L N was supplied in solution. This shows that spinach has high yield and high quality under proper nitrogen level.