Effects of annual three-cropping system on soil physicochemical properties and microbial community structure of tobacco-growing soil in the Jinsha River Basin

Objectives This study aims to investigate how planting two-season crops after tobacco in winter idle lands in the Jinsha River Basin impacts the microbial community structure of tobacco-planting soil.

Methods A field experiment was conducted in Qiaojia tobacco-growing area, Yunnan, with five treatments: local conventional planting mode with only flue-cured tobacco throughout the year as control (CK), and flue-cured tobacco-corn-broad bean (B1), flue-cured tobacco-corn-green manure (B2), flue-cured tobacco-corn-rapeseed (B3), and flue-cured tobacco-corn-pea (B4). Soil physicochemical properties, enzyme activities and soil microbial community were measured after the harvest of third crop for two consecutive years.

Results Compared with CK treatment, the three-cropping treatments significantly increased urease activity in B1 and B2, and significantly increased sucrase activity in B1 to B4 after harvest. The Shannon index of bacteria in the three-cropping treatments B1−B4 and the Simpson index in B1−B3 were significantly higher than CK, with B2 significantly increasing by 5.03% and 0.30%, respectively. The Shannon index of fungi in the three-cropping treatments B1, B3, B4 was significantly higher than CK, with B4 significantly increasing by 10.03%; however, fungal Simpson indices showed no significant difference. At the genus level, the relative abundance of beneficial bacteria such as Candidatus_Udaeobacter, Sphingomonas, Bryobacter and Mortierella in three cropping treatment increased to varying degrees, while the pathogenic genera such as Fusarium and Alternaria decreased to a certain extent, and B3 treatment showed better performance. RDA showed that soil pH and hydrolyzed nitrogen were the main driving factors affecting soil bacterial community structure, and available potassium and organic matter were the main driving factors affecting soil fungal community structure.

Conclusions The annual three-cropping system in the Jinsha River basin improved soil quality. The flue-cured tobacco-corn-green manure treatment had the best positive effects on soil nutrients, enzyme activities and soil microbial diversity. The flue-cured tobacco-corn-rapeseed treatment increased beneficial microbial genera and reduced pathogenic genera, thereby optimizing the soil microbial community structure.