Formulation of Carrier for Bioinoculant and its Evaluation on Maize (Zea mays L.)

Abstract

Biofertilizers are formulations containing agriculturally beneficial microorganisms, mass multiplied under laboratory conditions, inoculated in a carrier and supplied to the farmers for field applications. Carriers are inert materials with high absorptive capabilities when added in the preparations, provide strength and shape to the active ingredient. In Pakistan, dissemination of biofertilizer technology is facing a serious constraint due to non-availability of a suitable carrier for bioinnoculant. The aim of present study was to formulate suitable carriers from locally available cheap material and evaluate for shelf life by using locally isolated plant growth promoting rhizobacteria (PGPR) strains from maize rhizosphere as well as to test efficacy of PGPR inoculated carriers on maize plants under sterilized conditions of laboratory, greenhouse and unsterilized field conditions. Carrier material was prepared using different combinations between 35-50% clay soil, 30-45% fly-ash, 5-15% press mud and 5-15% lignite by weight. Soil containing 53% clay content was utilized to enhance adhesion capacity with the seeds. As essential quality of an acceptable carrier is that it should be free of lump formation, 40% clay soil with other materials was found suitable. Six different combinations in the range mentioned above were developed and subjected to physico-chemical analysis. Four treatments including 40% clay, 30-40% fly-ash, 10-15% press mud and 10-15% lignitic coal were developed considering good adhesion capacity, high moisture holding capacity, adequate nutrient availabilty and designated as formulated carrier (FC). These formulated carriers along with biozote carrier were investigated for PGPR shelf life. Different inoculated carriers revealed significant difference regarding microbial survival. Different incubation intervals also indicated a significant decline in population density of bacteria. Among the investigated carrier, the FC-4 (Clay soil 40%, fly-ash 30%, press-mud 15%, lignitic coal 15%) was categorized superior which supported 33.5x108 to 10.8x108 cfu g-1 for MR8 while 32.6x108 to 7.2x108 cfu g-1 for MR5. However all the tested carriers maintained the required population of viable cells upto six months of incubation period. All the inoculated carriers showed a significant increase over un-inoculated control to different plant growth parameters and plant mineral composition as well as nutrient uptake of maize plant in the pot, greenhouse and field study. Bioinoculant of FC-4 performed best followed by FC-1 and FC-3 conpared to BC. Among the two PGPR strains tested, MR8 was moderately better compared to MR5 while non-significant interaction between bacterial strains and carrier’s treatments was observed for most of the measured parameters. It is concluded from the pot, greenhouse and field experiments that FC-4 can be utilized as a carrier for the production of PGPR biofertizer for maize crop. Further experimentation related to other beneficial bacteria isolated from different crops should be conducted for utilization of FC-4 as carrier for biofertilizer production.