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 photosynthetic characteristics and yield of different lettuce cultivars 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 in Dabajia and Guasihong, and the lowest was in Doubletip. There was little effect of nitrogen and potassium fertilizer on photosynthetic characteristics of Doubletip. The higher photosynthetic characteristics of Guasihong was obtained in +N treatment under low light, in +K treatment under middle and high light, but for Dabaijia the effect was opposite. The yield of lettuce was in the order of Guasihong ＞Dabajia＞Doubletip and increased with light intensity and application of nitrogen and potassium fertilizer. Under high light, the highest and lowest yield increase efficiency of N and K was acquired in Doubletip and Dabajia, respectively. Dabajia had the highest efficiency under middle light, and Guasihong had 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 in Dabajia and Guasihong, and the former was higher than the latter in Doubletip under middle and high light intensity. It was important to control nitrogen application level 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，Chla and Ci with yield were better.