Microbially synthesised agriculturally useful urea nanoparticles have no phytotoxicity and show enhanced fertilising effects in Kharif (monsoon) paddy

Abstract

Abstract Urea has been used as a conventional nitrogenous fertiliser since long, however, the nutrient use efficiency of the conventional urea is low due to issues related to ammonia volatilisation. Nanotechnology-based fertilisers are now proposed to reduce the dose of conventional fertilisers and enhance nutrient use efficiency. In the present study, we proposed a novel microbial-assisted synthesis approach for urea nanoparticles (TERI NanoUrea: TNU) using a microbial co-culture approach that included two species from the Bacillaceae family. This approach is an eco-friendly method as opposed to the synthesis of conventional urea. In brief, the synthesis reaction was modelled using Monod’s kinetics for bacterial growth in presence of substrate. Two species of Bacilluswere co-cultured and during the algorithmic growth phase were exposed to the bulk substrate (conventional urea: 46% N). Difference in release patterns of organic acids, carbohydrates, lipids, and proteins during microbial culture exposure to bulk substrate was observed, which resulted in the synthesis of urea nanoparticles (TNU) after 24 hr of incubation. Also, biomolecules released during synthesis of nanoparticles contributed to a biomolecular corona over the nanoparticles. The prepared TNU was thoroughly characterised by using various physicochemical and analytical techniques and it was observed that via microbial synthesis approach, 5-15 nm sized spherical particles possessing inherent characteristics of urea were synthesised. Along with the synthesis and characterisation we also investigated the effects of TNU on the early development of seedlings of a monocot (maize) and two dicot (tomato and okra) species. It was found that the novel biogenic TNU did not show any phytotoxicity to the selected monocot and dicot species and resulted in enhanced seed vigour and plant growth. Further, the TNU was used in Kharif (monsoon) field trials on paddy for nitrogen supplementation to the conventional urea fertilisers. The field trial observations showed the agronomic efficiency of replacing 25% of the conventional urea with TNU (TNU + 75% urea along with 100% treatment with recommended doses of phosphorus and potassium fertilisers). These results suggest that biogenic TNU, can be explored further for its application to various crop systems and can aid in supplementation of conventional urea fertilisers.