Optimization of EM water-retention agent application in flue-cured tobacco

Flue-cured tobacco is an important economic crop in China, with the highest planting area and yield in the world. With a huge capacity to improve financial revenue, flue-cured tobacco production in China’s southwest provinces (e.g., Yunnan, Guizhou, Sichuan) is critical for the national economy. But periodic droughts in tobacco planting zones affect the production of flue-cured tobacco and the normal maturity process. Enhancing studies on drought resistance, water-saving techniques and reasonable regulation of field water supply in flue-cured tobacco production is necessary to guarantee high quality and yield production in arid regions. In this study, MP3005KM water-retention agent, straw, EM activated calcium and EM rejuvenation were used to determine the effect of EM water-retention agent on tobacco growth, yield and quality. The study also used entropy weight coefficient evaluation model and system evaluation indexes to select the optimal application schemes with the most comprehensive benefits. The results showed that different treatments all increased tobacco leaf area of a single plant, especially, straw treatments (T1 and T2) more significantly increased leaf area of a single plant at later growth stage of flue-cured tobacco. The crop growth model simulating the dynamics of LAI showed that T2 (40 gplant^-1 EM activated calcium + 300 gplant^-1 straw) and T6 (40 gplant^-1 EM activated calcium + 6 gplant^-1 MP3005KM) obtained more larger increasing range. EM water-retention agent treatments increased net photosynthetic rate (P_n) and decreased transpiration rate (T_r), which regulated photosynthetic effects of tobacco leaves at vigorous stages (including maturity stage). Principle component analysis showed that EM water-retention application significantly increased the overall quality of tobacco leaves compared with no EM water-retention agent. Straw treatments had better quality improvement effects, with comprehensive quality indexes 3.25 and 2.76, respectively, for T1 and T2. In terms of high yield, good quality, water-saving potential and fertilizer use efficiency, the 40 gplant1 of EM-calcium combined with 4 500 kg.hm^-2 of straw system was recommended as the application scheme of EM water-retention agent for flue-cured tobacco. Under this scheme, flue-cured tobacco yield, irrigation water use efficiency and nitrogen use efficiency were 2 433.5 kg.hm^-2, 0.608 kgm^-3 and 27.04 kgkg^-1, respectively.