Alleviating effect of strong reduction and flooding treatment on continuous cropping obstacles in Rehmannia glutinosa

Rehmannia glutinosa is a popular medicinal herb in China. During R. glutinosa cultivation, serious consecutive monoculture problems are often encountered and have not yet to be effectively resolved. Preliminary studies found that an imbalance in the microbial communities in the rhizosphere soils is the main reason for consecutive monoculture problems; the abundance of pathogenic microorganisms significantly increased, whereas the beneficial microorganisms were inhibited. Therefore, it is important to control and alleviate the consecutive monoculture problem by inhibiting and balancing pathogenic microbes. This study sought to develop critical technology for alleviating the consecutive monoculture problems of R. glutinosa with strong reducing and flooding measures that may effectively inhibit the proliferation of pathogenic microbes. The key indices of treated R. glutinosa were analyzed, including plant growth and development, the physical and chemical properties of continuous cropping soil, the bacterial community structure, and its biological functions. The results indicated that the strong reducing and flooding treatments significantly increased the relative abundance of anaerobic heterotrophic bacteria, including Ruminococcus and Enterococcus, in the continuous cropping soils. This enhanced soil denitrification, creating special soil environments rich in Fe²⁺ and organic acids that inhibited pathogenic bacteria. Compared with the control soils, in the soils treated with strong reducing, the Fe²⁺ and organic acid levels increased by 4.73 times and 3.54 times, respectively, and in the soils treated with flooding, the same values increased by 1.65-fold and 1.12-fold, respectively. Concurrently, the beneficial bacteria community, such as Pseudomonas, was rapidly rebuilt in the treated soils; these bacteria have important roles that inhibit the proliferation of pathogens. The two methods, reducing and flooding, have different effects on the soil physical and chemical properties and the bacterial community structure of the consecutive cropping soils. Thus, the two methods have different efficiencies for alleviating the consecutive monoculture problem of R. glutinosa. Due to addition of straws, the strong reducing method increased contents of organic matter, available nitrogen, available phosphorus and available potassium of the consecutive cropping soils, while the flooding method did not show these effects. The Shannon index and Chao1 index under flooding decreased, while Shannon index decreased and Chao 1 index increased under the strong reduction. Both methods effectively increased the survival rate and yield of replanted R. glutinosa. The survival rate and yield of continuous cropping R. glutinosa treated with strong reducing increased by 1.94 times and 4.04 times, respectively, compared with those of the control plants. In contrast, the strong reducing treatment has more optimized effects that alleviate the consecutive monoculture problems of R. glutinosa. Both treatments alleviate the consecutive monoculture problem and improve the survival rate and yield of replanted R. glutinosa via improvements in the physical and chemical properties of the continuous cropping soils and their microbial communities. This study provides an important theoretical basis and technical reference for future studies of the strategies used to alleviate the consecutive monoculture problem during R. glutinosa production.