Soil microbial communities associated with the rhizosphere of cucumber under different summer cover crops and residue management: A 4-year field experiment

Continuous cropping has led to the predominant decline of soil productivity and crop yields in Chinese vegetable production systems. Recently, the use of summer cover crops to restore degraded soil during vegetable production has attracted attention in China. A 4-year field experiment on a greenhouse cucumber double-cropping system was therefore conducted to understand how different summer cover crops affect soil microbial communities associated with the crop rhizosphere. The treatments included sweet corn with residue removal after harvest (SR), sweet corn with residue incorporation after harvest (SI), common bean with residue removal after harvest (CR), common bean with residue incorporation after harvest (CI), Garland chrysanthemum and edible amaranth as summer cover crops (GR), and bare fallow during the summer period (Control). Soil microbial communities were evaluated with a combination of sole-carbon-source utilization capacities, the population of microorganisms and enzymes. Generally, sole-carbon utilization capabilities and enzyme activities were higher in the summer cover crop-related soils compared to control soil in each cropping season. Multivariate analysis indicated that microbial communities differed among the cropping seasons, and significantly separated summer cover crop treatments from the control. Treatments SR, SI and GR with relatively high cucumber productivity generally showed relatively high urease activity and relatively low Fusarium oxysporum population. We concluded that summer cover crops generally had a greater effect on soil microbial communities associated with crop rhizosphere compared to the traditional bare fallow. Soil microorganisms associated with crop rhizosphere played an important role during the phytoremediation processes of summer cover crops.

► Summer cover crop (SCC) can be used to improve the degraded cucumber soil.
► Microbial communities significantly separated SCC treatments from the control.
► Carbon utilization capacities by microbes were enhanced by the planting of SCC.
► Treatments with high productivity generally showed high urease activity.
► Treatments with low productivity generally showed high Fusarium oxysporum.