Optimization of Nitrogen Supply Concentration in Nutrient Solution for Hydroponics Lettuce

Lettuce was chosen in this study and five treatments of nitrogen levels were set，i.e.0.9，3.5，7，14 and 28 mmol/L，denoted as T1，T2，T3，T4，T5，respectively.Response of growth and quality of hydroponic lettuce to concentration of nitrogen in nutrient solution was analyzed.Test results showed that there was no significant difference for lettuce stem diameter among five treatments.The lettuce leaf number for treatment T1 was less than that for T2，T3，T4 and T5.Lettuce leaf SPAD value for T3 was significantly higher than that for treatment T1.The highest yield of lettuce for T3 treatment was obtained，and higher of 482.11%，53.53%，14.48%，32.49%，compared to T1，T2，T4，T5 treatments，respectively.Increasing the nitrogen concentration of nutrient solution was beneficial to soluble sugar content of lettuce was improved by increasing nitrogen concentration of nutrient solution.The content of Vc and nitrate in lettuce showed a similar trend of firstly increasing and then decreasing with increasing of nutrient solution nitrogen concentration.The suitable nitrogen supplying concentration for hydroponic was optimal as 9.69 mmol/L using relationship between lettuce yield and nutrient solution nitrogen concentration.Therefore，the higher yield was achieved under this situation.