In this study we investigated autotoxicity in lettuce under successive cultivation and applied alternating current electro-degradation (ED) to non-renewed nutrient solution to degrade the accumulated allelochemicals and consequently to improve the retarded yield and quality of lettuce. In our first experiment, lettuce was grown in renewed, non-renewed and non-renewed + ED solution. Every two weeks interval nutrient solution was changed in the renewed treatment while non-renewed solution was unchanged throughout the growing period but major minerals were adjusted bi-weekly. ED was also applied bi-weekly for 24 h. Compared to renewed solution, shoot fresh weight was decreased to 24% (301.8 g plant−1) in non-renewed solution. But when ED was applied, non-renewed + ED solution produced shoot fresh weight statistically similar to renewed solution plants. In the second experiment, lettuce was grown in renewed nutrient solution, one culture non-renewed (non-renewed 1C), two culture non-renewed (non-renewed 2C) and non-renewed 2C + ED solutions. In non-renewed 1C, the starting solution was fresh nutrient solution while in non-renewed 2C it was once used. Lettuce grown in non-renewed 2C solution produced shoot fresh yield (258.8 g plant−1), about 35% lower compared to renewed solution. When ED was applied to non-renewed 2C solution produced shoot fresh weight 383.3 g plant-1 which was statistically similar to renewed solution. Calcium and iron concentration in lettuce followed the similar trend. Therefore, it was evident that yield and quality of lettuce could be improved through ED in non-renewed solution in two successive cultivations using same nutrient solution. In the following study, we tried to determine the proper ED interval in the third experiment. Results showed that ED to non-renewed solution both weekly and bi-weekly equally improved growth, yield and mineral concentration in lettuce. Hence, ED at two weeks interval was sufficient.
Faculty of Life and Environmental Science