Differential Effects of Plant Growth-Promoting Rhizobacteria Used as Soil Application vis-à-vis Root Dip of Seedlings on the Performance of Onion (Allium cepa L.) in Three Distinct Agro-climatic Zones of Indian Punjab

Abstract

ABSTRACT The effects of plant growth-promoting rhizobacteria (PGPRs) vary with their mode of inoculation, location, and dose of inorganic fertilizers applied. Therefore, it is imperative to identify the proper PGPR along with its mode of inoculation for each soil–plant system. Here, six combinations of PGPRs applied through root dip of onion seedlings were used with both 75% NPK and 100% NPK. Their performance was compared with a biofertilizer commercialized by Punjab Agricultural University as soil application (T9), two biofertilizers from Indian Agricultural Research Institute used as root dip of seedlings (T7 and T8), and two uninoculated controls [100% NPK (T0) and 75% NPK (T16)] at three locations of Punjab, India. Since interaction (PGPR × location) effects were significant, only one out of six PGPR treatments, viz. T6 (100% NPK + Azotobacter + Sphingobacterium + Burkholderia), performed consistently well across locations and gave maximum 20-bulb weight, bulb yield, net returns, and benefit:cost ratio. This treatment (T6) yielded at par with T7 and T8 but was superior to T9, which in turn yielded at par with T0 and T16 at all locations. Colonization of onion roots by beneficial natural resident arbuscular mycorrhizal fungi was higher in T6 than in control and penetration was higher when PGPRs were integrated with 75% NPK than with 100% NPK. Utilization of PGPRs with 100% NPK in light textured soils having low fertility along with poor water holding capacity and with 75% NPK in heavy textured soils having high fertility coupled with high moisture holding capacity is advocated.