Combination of Bacillus and Low Fertigation Input Promoted the Growth and Productivity of Chinese Cabbage and Enriched Beneficial Rhizosphere Bacteria Lechevalieria

SIMPLE SUMMARY: Chinese cabbage is often threatened by soft rot disease caused by Pectobacterium spp., which becomes severe due to overirrigation or heavy rainfall. An improved application technique of biocontrol Bacillus agents with low fertigation input is suggested as an environment-friendly strategy to control soft rot disease and improve the cabbage yield. In this study, the effect of Bacillus velezensis B006 on cabbage growth under normal and low fertigation conditions was firstly evaluated, and then the relationships of the plant growth with the cabbage rhizosphere microbial communities and the production of endogenous hormones in cabbage roots were studied. Our results highlighted that B006 application combined with low fertigation input promoted cabbage growth and increased root vitality which were positively related to enrichment of Lechevalieria in the cabbage rhizosphere and the production of indole-3-acetic acid and salicylic acid in cabbage roots. In conclusion, we provide supporting evidence on the improvement of Bacillus application in fields to promote the healthy growth and productivity of cabbage. ABSTRACT: Long-term overfertilization increases soil salinity and disease occurrence and reduces crop yield. Integrated application of microbial agents with low fertigation input might be a sustainable and cost-effective strategy. Herein, the promoting effects of Bacillus velezensis B006 on the growth of Chinese cabbage under different fertigation conditions in field trials were studied and the underlying mechanisms were revealed. In comparison with normal fertigation (water potential of −30 kPa and soluble N, P, K of 29.75, 8.26, 21.48 Kg hm(−2)) without B006 application, the combination of B. velezensis B006 and reduced fertigation input (−50 kPa and N, P, K of 11.75, 3.26, 6.48 Kg hm(−2)) promoted cabbage growth and root development, restrained the occurrence of soft rot disease, and improved the yield. High-performance liquid chromatography (HPLC) analyses indicated that B006 application promoted the production of indole-3-acetic acid and salicylic acid in cabbage roots, which are closely related to plant growth. Rhizosphere microbiota analyses indicated that the combination of low fertigation input and B006 application promoted the enrichment of Streptomyces, Lechevalieria, Promicromonospora, and Aeromicrobium and the abundance of Lechevalieria was positively correlated with the root length and vitality. This suggested that the integrated application of reduced fertigation and Bacillus is highly efficient to improve soil ecology and productivity and will benefit the sustainable development of crop cultivation in a cost-effective way.