Sustainable nitrogen management using Indigenous essential oils for nitrification inhibition and synergistic effects

Fertilizer is used to improve soil quality; however, the majority of these forms of nitrogen from fertilizer are lost through environmental activities. The nitrification retarding activities of the essential oils of Syzygium aromaticum, Xylopia aethiopica, Monodora myristica, and their blend were investigated. The steam distillation method was used for the extraction of essential oils, and analyzed using Gas chromatography mass spectrometry (GC-MS). The microbial analysis and chemical analysis were done by standard methods. The main composition of the essential oil of S. aromaticum was eugenol (75.08%), isocaryophyllene (29.36%), and germacrene D-4-ol (20.31%) were found to be the main constituents of M. myristica. X. aethiopica had isospathulenol (8.67%), chavibetol (6.99%), and β-elemene (6.76%) as its key constituents. Eugenol (34.25%) and chavibetol (16.57%) are the blend’s main constituents. The values of nitrosomonas, actinomycetes, and nitrobacter population when urea fertilizer was coated with the essential oils after the 7th and 14th day of incubation ranged from (1.21 × 104–2.02 × 104 CFU/g). The values of NO3− ranged from 17.50 to 19.40 mg/kg, while the quantity of NO2 − ranged from 14.90 to 17.10 mg/kg. The amount of NH4+ ranged from 26.80 to 31.20 mg/kg, while the amount of urea left in the soil ranged from 81 to 58 mg/kg. The population of bacteria during the different incubation days was higher in the controlled experiment than in the essential oil-coated urea fertilizer. M. myristica coated with urea fertilizer had the least nitrification activity, the essential oil of X. aethiopica and the blend had the highest. In conclusion, the findings showed that all essential oils had nitrification retarding activity, which will help maximize the output obtained from fertilizers applied during farming and thereby replace the synthetic nitrogen inhibitors that could be toxic to the soil and water bodies. Further study will be conducted on the field application of the study.