Abstract
Nitrification inhibitors (NI) are aimed at improving N-fertilizer use efficiency in cropping systems. This study aimed to assess the nitrification inhibition potential and non-target effects of dry leaf powders (botanicals) of 10 plant species (neem (Azadirachta indica), lantana (Lantana camara), karanda (Pongamia pinnata), Brachiaria (Brachiaria humidicola), cinnamon (Cinnamomum verum), clove (Syzygium aromaticum), wild-sunflower (Tithonia diversifolia), mee (Madhuca longifolia), nutmeg (Myristica fragrans), and pepper (Piper nigram)). The effect of botanicals on the growth of three ammonia oxidizing bacteria isolates (M4, M5, and M7) and NO3− formation in soil were tested in laboratory experiments. In a pot-experiment, botanicals were applied with urea to assess their effect on vegetative-growth of tomato and capsicum. The non-target effects of botanicals on soil bacteria and fungi, and seed germination were assessed separately. Dicyandiamide (DCD) was used as the positive control in all experiments. Only the growth of M7 was significantly suppressed by all botanicals except neem, Brachiaria, and pepper. The highest shoot-biomass of tomato was obtained when urea was applied with pepper. Nitrate leaching from pots was significantly reduced (P < 0.05) when urea was added with botanicals except for clove and wild-sunflower at basal-dressing. The abundance of culturable fungi and bacteria were not affected significantly by botanicals while seed germination was reduced significantly and consistently by clove only. From the 10 botanicals tested leaf powders of nutmeg, lantana, cinnamon, mee, and pepper were identified as materials with better potential to suppress nitrification with minimum non-target effects.
Highlights
Nitrification inhibitors (NIs) are being used to improve N-fertilizer use efficiency and crop yield (Amberger 1989; Zerulla et al, 2001; Di and Cameron, 2004)
Characteristics of botanicals and soils used in the study Total N content in botanicals ranged from 1.31 to 3.79 % with the highest and the lowest values observed in leaf powders of lantana and clove, respectively (Table S22)
Effect of botanicals on population growth of nitrifiers All five ammonia-oxidizing bacteria (AOB) isolates used in bioassays were gram-negative
Summary
Nitrification inhibitors (NIs) are being used to improve N-fertilizer use efficiency and crop yield (Amberger 1989; Zerulla et al, 2001; Di and Cameron, 2004). Synthetic NIs such as DCD and DMPP are known to suppress the activity of lithoautotrophic ammonia-oxidizing bacteria (AOB) (Amberger 1989; Weiske et al, 2001; Gong et al, 2013). Plant-based natural NIs are known to affect both AOB and nitrite-oxidizing bacteria (NOB), mostly by reducing their abundance and/or retarding their activity (Patra et al, 2006; Norton and Ouyang, 2019). NIs are applied with the aim of suppressing nitrifiers, some could have nontarget effects by affecting soil enzyme activity, and reducing the culturable bacteria and actinomycete populations in soils (Patra et al, 2006; Tindaon et al, 2013). The non-target effects of the botanical NIs on soil culturable bacteria and fungi, and seed germination were investigated
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