Comprehensive test of rhizobacteria as biostimulant, vesicular arbuscular mycorhizza (VAM) and graded dose of NPK fertilizer on the growth of bok choy (Brassica rapa L.)

Collaboration test of rhizobacteria as biostimulant, vesicular arbuscular mycorhizza (VAM) and graded dose of NPK fertilizer was a preliminary experiment to re-fertilize marginal soils. The objective of this experiment was to obtain the suitable collaboration of rhizobacteria as biostimulant, VAM and NPK dose that effectively supports the productivity of the growth media (zeolite) and the growth of bok choy plants. The experiments design was RCD factorial with 2 treatments which were NPK dose (0 %, 25 %, 50 %, 75 %, and 100 %) and microbial biostimulant. Rhizobacteria acting as biostimulant used were nitrogen fixing bacteria (NFB) (Azospirillum sp., Azotobacter sp., Rhizobium radiobacter InaCCB835), phosphate solubilization bacteria (PSB) (Serratia sp., Klebsiella variicola InaCC B827, Mangrovibacter plantisponsor InaCC B841, Tolumonas osonensis InaCCB831) and VAM. Each treatment, including control, was repeated 3 times. Bok choy seeds from each treatment were planted individually on zeolite media and grown in a greenhouse for 40 days. The results showed that the treatment of MIXN1 (NFB + PSB + VAM + NPK 25%) and MIXN2 (NFB + PSB + VAM + NPK 50%) were effective collaborations of biostimulating rhizobacteria, VAM and NPK dose on supporting the fertility of growth media with the number of rhizobacteria of 10⁷ cfu g^-1 zeolite and supporting optimization of bok choy plant growth and the percentage of bok choy root colonization by VAM with a very high level of infection.