Optimization of carriers and packaging for effective biofertilizers to enhance Oryza sativa L. growth in paddy soil

Abstract

For a biofertilizer to promote plant growth after application, cell survival during storage must be ensured, while the carrier formulation and packaging are important factors during storage. This study aimed to optimize the ratio of rubber wood ash (RWA), decanter cake (DCC), rice husk ash (RHA), and spent coffee grounds (SCG) as a mixed carrier of biofertilizer of purple non-sulfur bacteria (PNSB), Rhodopseudomonas palustris and Rubrivivax gelatinosus. Different packaging materials, and different sealing methods were investigated. The phytotoxicity of PNSB biofertilizers in a solid form, and their effectiveness to enhance rice (Oryza sativa L.) seedling growth in paddy soil were also investigated in comparison with a liquid form. A mixed carrier of RWA, DCC, RHA and SCG at a ratio of 3:4:2:1 most effectively maintained viability. After 6-month storage at 25 ± 3 °C, PNSB population of a mixed carrier containing R. palustris at roughly 10 log CFU/g in nylon-linear low density polyethylene (nylon-LLDPE) bags that were vacuum sealed at 500 W decreased by only 3 log cycles compared with 7 log cycles in the control. The PNSB biofertilizers, each genus and a mixed culture at 1: 1, either in solid or liquid form at their optimal dilutions showed no phytotoxicity. However, the mixed carrier itself as a control was slightly toxic. At these optimal dilutions, all PNSB biofertilizers in both liquid and solid formulations significantly increased rice growth in paddy soil compared with controls. A suitable mix of agro-industrial waste and suitable packing prolonged the shelf-life and potency of PNSB biofertilizers.