Development of a Botanical Formulation Using <em>Cinnamomum verum</em> and <em>Pongamia pinnata</em> Leaves for Suppression of Nitrification in Soil

There is a growing interest in controlling nitrification by using botanical nitrification inhibitors to enhance the nitrogen (N) fertilizer use efficiency. The main objective of this study was to develop a botanical formulation (BF) with Cinnamomum verum (cinnamon) and Pongamia pinnata (karanda) leaves to suppress the nitrification rate of two soils (Red Yellow Podzolic (RYP) and Reddish-Brown Earth (RBE)) commonly used for vegetable cultivation in Sri Lanka. A BF was prepared using dried and powdered leaves of cinnamon and karanda, biochar and corn flour. The two soils were treated with BF at three rates (0, 5 and 10%, w/w) and the potential nitrification rate (PNR) was determined using the shaken slurry method in a laboratory incubation. The obtained data were analysed by Statistical Analysis Software (SAS) adopting a two factor factorial design. The BF application significantly delayed (P<0.05) nitrate formation in both soils. The RBE soil had significantly lesser (P<0.05) PNR compared to RYP soil. Application of 5 and 10% BF, significantly reduced PNR in both soils at 4 h of incubation. However, only a 10% BF application rate remained effective in suppressing PNR at 21 h of incubation. Results indicate the possibility of using dried, powdered leaves of cinnamon and karanda for suppressing nitrification in soil. Further studies are required to investigate the effect of developed BF on soil biological properties.