Enhanced vermicomposting of rice straw and pressmud with biogas slurry employing Eisenia fetida: Production, characterization, growth, and toxicological risk assessment

Abstract

The biogas plant plays a dual role: it directly provides energy and indirectly promotes organic farming through outlet slurry. However, agricultural biomass wastes such as rice straws (RS) and pressmud (PM), which can't be used as fertilizers on their own, were vermicomposted (60 days) with biogas slurry (BS), using earthworm, into four blends: T1(BS, 100%), T2(3:2, BS: RS), T3(3:2, BS: PM), and T4(3:1:1, BS: RS: PM). The characterization, elemental analysis, and toxicological risk assessment of derived vermimanure were carried out using various analytical tools, such as an organic elemental analyzer such as CHNS, FT-IR, FESEM-EDXA, XPS, and ICP-OES. The pH, electrical conductivity, and C/N values were within 7.1–7.8, 3.2–6.0 dSm−1, and 12–15, respectively, for all treatments. The proportions of N (38%), P (70%), K (58%), Mg (67%), Ca (42%), and ash (44%), increased significantly (P < 0.05) over the initial feedstocks. The ecological risks of heavy metals (Zn, Cu, Ni, Pb, Cd, and Cr) in all feedstocks were found to be under WHO-permitted levels. The growth performance of earthworms was also considerably higher (P < 0.05) over the control feedstock group. The analytical methods verified that feedstock T4 (3:1:1, BS: RS: PM) was more porous, containing NH4+, PO43−, K+, and other nutrients. Pellets of all vermimanure groups keep 65–75% of the original volume. As well, when these pellets have been employed for agronomy and dispersed in the field, they will cause less dust than traditional or powdered compost or manure. In comparison to the control group, the synergistic approach of RS, PM, and BS in vermimanure significantly (P < 0.05) enhanced seed germination (83%), vigour index (42.5%), and decreased mean germination time by 27%. Furthermore, pot trials with Abelmoschus esculentus seed indicated that seedlings cultivated with 40% vermimanure of T4 (3:1:1, BS: RS: PM) mixed soil showed high growth in shoot, root, and plant yield.