Straw amendment can improve soil properties and is an effective strategy to control soil-borne diseases. However, gramineous straw application to vegetable fields has rarely been studied. In this study, rice straw was added to the field of Chinese cabbage for one or two years (repeated), and Chinese cabbage plant growth, disease occurrence and changes in soil chemical properties were measured. In addition, the bacterial community composition of Chinese cabbage was analyzed using Illumina MiSeq sequencing. Results showed that rice straw application increased the content of available nutrients, pH and electrical conductivity, but decreased the diversity and richness of the bacterial community. The relative abundances of Acidobacteria and Chloroflexi were increased after repeated rice straw application, which were associated with the available potassium and pH in the soil. Network analysis revealed that rice straw amendment differentially affected the key bacterial genera. These results suggest that repeated application of rice straw changed the soil chemical properties and altered the bacterial community composition to suppress the clubroot disease incidence in Chinese cabbage.

Straw incorporation is known as an environmentally friendly agricultural practice that can effectively enhance soil nutrient contents and crop yields; its potential to suppress soil-borne disease has also been reported in recent years. Here, we perform a field experiment for two consecutive years (2017–2018) to evaluate the effectiveness of maize (Zea mays), rice (Oryzae sativa L.) and wheat (Triticum aestivum L.) straws incorporation in alleviating Chinese cabbage (Brassica rapa L. ssp. pekinensis) clubroot disease caused by Plasmodiophora brassicae Woronin. Microbial composition in Chinese cabbage rhizosphere and soil P. brassicae abundance were estimated by high-throughput amplicon sequencing and quantitative polymerase chain reaction (qPCR). Results showed that, during the two-year field experimental cycle, all three straw amendments promoted Chinese cabbage plant growth, inhibited clubroot disease and increased the alpha diversity of the bacterial community in Chinese cabbage rhizosphere. Rice and wheat straws also increased the alpha diversity of the fungal community. These straws diversified the composition of the Chinese cabbage rhizosphere microbial community. All three straws promoted Cryptococcus carnescens; both rice and wheat straws stimulated Lysobacter sp.; maize straw boosted Sphingomonas sp. and wheat straw increased Talaromyces sp. These microbial taxa are either considered to have positive influences on plant growth or potential biocontrol effects. In addition, straw amendments also increased soil pH, electrical conductivity, available nitrogen and available potassium contents in both years of the field experiment. Taken together, we concluded that these three gramineous straw amendments ameliorated Chinese cabbage rhizosphere microorganisms, inhibited clubroot disease and promoted the growth of Chinese cabbage, and that rice straw worked best amongst the three. This study could potentially provide a new tactic of massive grain crop straw utilization and a direction in dealing with clubroot disease.