Evaluating the nitrification inhibition potential of selected botanicals and their non-target effects

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 ten plant species [neem (Azadirachta indica), lantana (Lantana camara), karanda (Pongamia pinnata), 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 ten 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.