Applied Microbiology: Open Access
Open Access

Abstract

Effect of Liquid Digestate on Agricultural Soil-II: Microbial Population Dynamics.

Ogbonna CB, Stanley HO and Abu GO

The aim of this study was to investigate the effect of liquid digestate (produced from anaerobic digestion of organic municipal solid waste) on the population dynamics of selected soil microbial groups during cultivation of maize plants. Maize seeds where subjected to various concentrations (between 0% to 72%) of the digestate with a total of ten (10) runs. One set of experimental runs were treated with one-time application of the corresponding digestate concentration (OTDA). Another set of experimental runs were treated with two-time application of the corresponding digestate concentration (TTDA). The first application of the digestate (for OTDA and TTDA) was conducted two weeks after sowing while the second application (for TTDA alone) was conducted three weeks after the first application. During the growth of maize plants, the populations of soil aerobic bacteria (AEB), strict anaerobic bacteria (SAB), ammonia oxidizing bacteria (AOB), nitrate reducing bacteria (NRB) and fungi (FUN) where monitored using standard cultural methods. In OTDA and TTDA treatments, the population of soil AEB, SAB, AOB, NRB and FUN ranged from 3.0 × 10⁶ CFU/g to 50.2 × 10⁶ CFU/g and 3.1 × 10⁶ CFU/g to 78.6 × 10⁶ CFU/g; 1.9 × 10⁴ CFU/g to 7.2 × 10⁵ CFU/g and 2.2 × 10⁴ CFU/g to 2.53 × 10⁵ CFU/g; 0MPN/g to 4.3 × 10⁴ MPN/g and 0MPN/g to 3.9 × 10⁵ MPN/g; 0 MPN/g to 4.4 × 10⁵ MPN/g and 0 MPN/g to 1.4 × 10⁵ MPN/g and 1.3 × 10³ CFU/g to 2.6 × 10⁴ CFU/g and 1.2 ×10³ CFU/g to 9.4 × 10³ CFU/g respectively before and 70 days after applying the digestate. Bacteria species isolated appear to belong to genera such as Arthrobacter, Azotobacter, Flavobacterium, Nocardia, Bacillus, Clostridium, Cellulomonas, Micrococcus and Pseudomonas. Fungi species isolated appear to belong to genera such as Aspergillus, Cladosporium, Fusarium, Geotrichum, Penicillium, Rhizopus and Trichoderma. Digestate application appears to have increased the population of soil microbes with time during the cultivation of maize plants.