Urease and Nitrification Retardation Properties in Natural Essential Oils and Their By‐products

Abstract

A laboratory incubation experiment was conducted with the natural essential oil of peppermint (Mentha spicata, MS), dementholized oil (DMO), terpenes, and a chemical inhibitor dicyandiamide (DCD), as coating materials for retardation of soil urea hydrolysis and nitrification. Retardation of nitrification was highest with DCD. The urea hydrolysis and nitrification processes were inhibited by all three natural products. Intensity of inhibition of both the processes increased with the level of application of the coating materials. With 0.50% level of coating, urea hydrolysis inhibition was in this decreasing order: DMO>terpenes>DCD>M. spicata oil; whereas at 1.00%, inhibition followed this order: terpenes>DMO>M. spicata oil>DCD. At 0.50% level of coating nitrification inhibition decreased in this order: M. spicata oil>DCD>DMO>terpenes; with 1.00%, the order was DCD>DMO>M. spicata oil>terpenes. All the three natural products (DMO, terpenes, and M. spicata oil) significantly retarded soil urease activity. These natural nitrification inhibitors significantly retarded Nitrosomonas. Nitrobacter, and total bacterial and actinomycete populations. Microbial activity retardation was more intense at a higher level of coating. We concluded that the different coating materials used could be used as potential retardants of urease activity as well as nitrification, unlike DCD, which is a potential retardant of nitrification and has little effect on the urea hydrolysis. The natural products, unlike chemical nitrification inhibitors, are less persistent, biodegradable, ecofriendly, and cheap.