Evaluation of selected medicinal plant materials and dicyandiamide on nitrification of urea‐derived ammonium under laboratory conditions

Background: Poor utilization of urea fertilizer and N losses from agriculture lands demands alternate fertilization practices to reduce N losses and improve utilization, i.e., application of nitrification inhibitors. Aims: This study was aimed to evaluate and compare the influence of dicyandiamide (DCD) and selected medicinal plant materials and on N transformations, nitrification inhibition and recovery of applied N. Methods: Treatments included: urea nitrogen (UN), UN + DCD, UN + Gingiber officinale, UN + Viola odorata, UN + Sewertia chirata, UN + Azadirachta indica, UN + Sphaenathus indicus, UN + Allium sativus, UN + Artemisia absenthium, UN + Fumaria indicus, UN + Caesalpinea bondusella, UN + Barberis lyceum, and an un‐amended control. Urea was applied at 200 mg N kg⁻¹ soil, while DCD and medicinal plant materials were applied at of 1% and 20% of applied urea, respectively. Results: Medicinal plant materials inhibited nitrification of urea‐derived NH4+-N. On an average of medicinal plant materials treatments, 51% of NH4+-N was still present in soil compared to 17% NH4+-N in UN treatment without medicinal plant materials after 28 days. Similarly, NO3--N was 76.54 mg kg⁻¹ in UN treatment compared to 34.40 mg kg⁻¹ in UN + medicinal plant materials treatments, indicating 55% reduction in nitrification. Apparent nitrogen recovery (ANR) in UN treatment was 65% compared to 74% in UN + DCD treatment. ANR in treatments, where UN was amended with medicinal plant materials, varied between 58 to 70%. Conclusions: The use of DCD and medicinal plant materials with UN significantly reduced NH4+-N oxidation and nitrification (NO3--N). In general, medicinal plant materials were more effective in regulating N transformations and, thus, offer a suitable alternate fertilization practice to reduce N losses and improve fertilizer utilization.