Direct palm oil mill effluent (POME) application diminishes nodulation and other physiological developments in Arachis hypogea, a leguminous plant

Abstract

Nodulation is a key biological process mediated through a symbiotic partnership between some resident soil bacteria e.g. Rhizobium and leguminous plants leading to the formation of nodules on roots of infected plants. Nitrogen fixation take place within specialized compartments in the nodules called heterocysts. Nitrogen is critical to plant metabolism and crop production. In the present study, Arachis hypogea grown in mesocosms were treated separately with different concentrations (25, 50, 75, and 100%) of aerobically and anaerobically digested POME. The plants were sampled fortnightly and checked for degree of nodulation and other growth characteristics. Results show that low (25%) concentrated POME treatments promoted beneficial responses than those amended with higher (50, 75 and 100%) concentrations. For instance, after 5 weeks, pH increased from 5.4±0.14 in the control treatment to 6.2±0.07 (aerobically digested) and 5.9±0.07 (anaerobically digested) respectively. At higher POME concentrations, there was no significant change in pH compared to the control. Nodulation was also highest in mesocosms treated with 25% POME. The number of nodules found in the control was 28.5±0.5 but in the aerobically and anaerobically digested treatments, 37.5±0.5 and 23.5±0.5 nodules were produced respectively. There was zero nodulation at 75 and 100% amendments with anaerobic POME digests. The same trend was observed with other growth features of the plant. In mesocosms treated with 100% POME, there was a significant reduction (p˂0.05) leaf length and width, stem length and root length. The application of highly concentrated POME negatively affected all the soil and plant indices monitored. Data obtained from the present study indicate that application of low concentrated (25%) POME residues could be useful as mordant, conditioner and fertilizer since microbial activity around the rhizosphere was promoted as indicated by the proliferation of nodulation and other plant features.