Effect of nitrogen,potassium fertilizer enrichment and light intensity on photosynthetic characteristics and yield of different lettuce cultivars

In a pot experiment,the effects of nitrogen,potassium fertilizer enrichment and light intensity on photosyn- thetic characteristics and yield of different lettuce cuhivars were studied.The results indicated that net photosynthetic rate (Pn)of lettuces was increased by adding nitrogen and potassium fertilizer and light intensity.The higher Pn was observed inDabaijiaandGuasihong,and the lowest was inDouble tip.There was little effect of nitrogen and potassium fertilizer on photosynthetic characteristics ofDouble tip.The higher photosynthetic characteristics ofGuasihongwas obtained in+N treatment under low light,in+K treatment under middle and high light,but forDabaijiathe effect was opposite.The yield of lettuce was in the order ofGuasihongDabaijiaDouble tipand increased with light intensity and application of nitrogen and potassium fertilizer.Under high light,the highest and lowest yield increase effi- ciency of N and K was acquired inDouble tipandDabaijia,respectively.Dabaijiahad the highest efficiency un- der middle light,andGuasihonghad the lowest efficiency under low light.The yield increase efficiency of N was higher than K under low light,but the latter was higher than the former inDabaijiaandGuasihong,and the former was high- er than the latter inDouble tipunder middle and high light intensity.It was important to control nitrogen application lev- el and increase potassium fertilizer level under low light to achieve high yield and better quality of lettuce,but the measure was contrary to that under middle and high light intensity.The correlation analysis showed photosynthetic characteristics and yield of lettuce were significantly correlated and the relationship between Pn,Chl a and Ci with yield were better.