Synergistic action of humic acid substances and bio-inoculants in guava (Psidium guajava']java L.): impact on growth traits, fruiting, nutrient profiling and rhizosphere stochiometry in meadow rainy season plant-soil interface

The present investigation was conducted on guava cv. Lalit spaced at 2 m x 1.5 m in meadow plant-soil interface during two consecutive rainy seasons of 2017 and 2018. Foliar application of humic acid was carried out at bud burst stage in two different levels i.e. 30 ml/L (HA(30)) and 60 ml/L (HA(60)), bio-inoculants were applied to the rhizosphere of the trees at two combinations, B-1: PSB @ 10 ml/plant + Azotobacter chroococcum @ 10 g/plant, and B-2: PGPR @ 25 ml/plant + AM fungi @ 25 g/plant along with reduced recommended dose of fertilizers (RDF) of N:P:K (360:740:200) i.e. 90 per cent of RDF (NPK90) and 80 per cent of RDF (NPK80). The experiment was laid out in Randomized Complete Block Design with eight treatment combinations, replicated thrice along with a control. The results showed that application of humic acid at 60 ml/L along with each of PSB and A. chroococcum at 10 ml/plant along with 80 per cent of NPK resulted in growth and fruiting over control. This combination also recorded significant increase in fruit set with marked reduction in fruit drop. Fruit yield was 1.89 times compared to control. Both physical and biochemical fruit quality traits were also significantly affected by this conjoint application. Microbial biomass in terms of actinomycetes, A. chroococcum, PSB and AM fungi were also tremendously increased compared to control. This combination also exhibited considerably greater amount of leaf N (2.55%), leaf P (0.24%) and leaf K (1.32%) under meadow plant-soil interface.