Effects Of Different Irrigation Quantity Treatments On The Growth And Quality Of Lettuce

Shortage of water has been a problem which has a strongly inhibitory effect on agriculture sustainable development and entironment improvement, and is also a key point to improve production of vegetable. So investgation on water-use-rule of vegetables and effects of water on vegetables physiology is one of the hotpots of physiology and bionomy reserach all the time. There were many investgations on vegetable irrigation, but they almost focused on fruit vegetables, like cucumber, tomato and so on, while few of them were about leaf vegetables. Lettuce is a kind of representative leaf vegetables, but there were few reports about the relationship between letttce and irrigation till now. In this study effects of different irrigation treatments on the growth, quality of two lettuce cultivars (cv. Hongnong and Lvling) were investigated. The study was made up of three parts: different irrigation quantity treatment, different irrigation maximums treatment and different irrigation minimums treatment.1. The effects of different irrigation quantity(100ml, 75ml, 50ml and 25ml per plant)on the growth and photosynthesis of two lettuce cultivars(cv. Hongnong and Lvling) were investigated. The results showed that shoot fresh weight, leaf area, leaf number and water content decreased significantly with diminish of irrigation quantity. Leaf chlorophyll content, photosynthetic rate, transpiration rate and stomata conductance decreased with the decrease of irrigation quantity. Fv/Fm, Fv/Fo and qP decreased whereas qN increased with decreasing of irrigation quantity. The mineral content decreased as irrigation quantity, N,P,K content decreased significantly.2. The effects of different irrigation maximums (60%-100%,60%-90%,60%-80%, 60%-70%) on the growth, quality and physiological characteristics of two lettuce cultivars were investigated. The results showed that the greatest shoot fresh and dry weight, leaf area and leaf number were obtained in 90% irrigation maximum treatment, soluble sugar, soluble protein of lettuces gradually increased with the decrease of irrigation maximums, the vitamin C contents of lettuces under 80% and 70% irrigation maximums were significantly higher than those of other treatments. The highest contents of MDA, SOD, CAT and Pro were obtained in 70% irrigation maximum treatment. The results also showed that the highest yield was obtained in 90% irrigation maximum treatment. But as a whole 80% irrigation maximum treatment was the most proper irrigation treatment. 3.The effects of different irrigation minimums (70%-90%,60%-90%,50%-90%,40%-90%) on the growth, quality and physiological characteristics of two lettuce cultivars were investigated. The results showed that the greatest shoot fresh and dry weight, leaf area and leaf number were obtained in 70% irrigation minimum treatment. soluble sugar, soluble protein of lettuces gradually increased with the decrease of irrigation minimums, the vitamin C, content of lettuces in 50% irrigation minimums were significantly higher than that in other minimums treatments. The contents of MDA, SOD, CAT and Pro increased with the decline of irrigation maximum, whereas chlorophyll fluorescence parameters showed that Fv/Fm,Fv/Fo,qP gradually decreased with the decline of irrigation minimums, but qN was the opposite. Taking the quantity and quality into consideration, in 60% irrigation minimum treatment, lettuces could gain a better quality but a slightly decrease in quantity. So 60% irrigation minimum treatment was suitable for lettuce.