The effect of N forms and NO-3-N/NH+4-N ratio on iron nutrition in hydroponicallygrown lettuce were investigated.It was found that suitable NO-3-N/NH+4-N ratio(9:3,6:6me/L) in nutrient solution can significantly promote plant growth, raise chlorophyll content,improve plant iron utilization efficiency , and reduces nitrate accumulation in leaves,and the costof nutrient solution was thus reduced. The role of iron in N metabolism was also analysed. Withthe increase of iron supplemented to the nutrient solution...