Evaluation of Different Carrier Substances for the Development of an Effective Pelleted Biofertilizer for Rice (Oryza sativa L.) Using Co-inoculated Bacteria and Arbuscular Mycorrhizal Fungi

Aims: This study was aimed to compare aquatic weed, biochar and compost carrier substances for the development of effective pelleted biofertilizer for paddy (Oryza sativa L.) using co-inoculated bacteria, Azospirillum sp., Pseudomonas fluorescens and arbuscular mycorrhizal fungi (AMF). Place and Duration of Study: Faculty of Applied Sciences, Rajarata University of Sri Lanka, Mihintale, Sri Lanka between November 2018 and May 2019. Methodology: Pre-sterilized, 1 kg weight of ground carrier material was inoculated with 50 g of AMF propagules and 20 ml of 1.5 x 108 (CFU/ml) of each bacterial inoculant. Different types of pelleted biofertilizers were prepared as; aquatic weed and bioinoculum (P1), aquatic weed, bioinoculum and nutrient supplement mixture (P2), biochar and bioinoculum (P3), biochar, bioinoculum and nutrient supplement mixture (P4), compost and bioinoculum (P5), compost, bioinoculum and nutrient supplement mixture (P6). Rock phosphate and potassium feldspar was used as nutrient supplement mixture in developing some pelleted biofertilizers. Biofertilizer pellets were tested for the microbial survivability with the time by determining viable cell count of bacteria at two storage temperatures of 0°C and 30°C. Pot experiment was carried out to investigate the effects of prepared pelleted biofertilizers on growth and yield of rice and on some soil chemical and biological characteristics. Control (without biofertilizers) and above pelleted biofertilizers were added to the 3000 g of soil in pot with one paddy plant of variety BG 360. The treatments were arranged in a randomized complete block design (RCBD) with five replicates. Rice roots were screened for AMF colonization after harvesting. Results: According to Tukey’s Pairwise Comparison test, control and different treatments in pot experiment were significantly different for shoot height, number of seeds per panicle, 100 seeds weight and soil pH (p ≤ 0.05). However, there was no significant difference observed for bacterial count in prepared biofertilizers and biofertilizer applied soil, relative growth rate, plant dry and fresh weights and electrical conductivity. Among different pelleted biofertilizers, application of pellets consisted of compost with bioinoculant (P5), exceedingly enhanced the rice growth and yield. Compost, bioinoculum and nutrient supplement mixture (P6) added pellets were shown highest bacterial survivability at 30°C for seven days. Although AMF colonization of rice plants were low this was the first report of citing the presence of AMF in rice roots in Sri Lanka. Conclusion: These pelleted biofertilizers have the potential to be used for improved productivity of rice variety Bg 360. Therefore, developing such bioinoculants as biofertilizers and their efficient use could be considered as a sustainable solution for rice cultivation in Sri Lanka and worldwide.