Inhibition of Bacterial Nitrification by Extracts of Velvet Beans Plant Mucuna Pruriens in Sandy Loam Soils in Owerri, Nigeria

In order to maintain soil fertility, nitrification inhibitors are used to reduce the loss of nitrogen caused by nitrification. This is vital to ensure food and environmental sustainability. Therefore extracts of the velvet beans plant Mucuna pruriens were used to determine their nitrification inhibiting activities in agricultural soil samples and simulate its possible effect in the field. Moistened soil samples amended with ammonium sulphate at 0.5mg/kg soil and different concentrations of velvet beans plant extracts (1%, 2% and 4%) at 60% water holding capacity. The soil samples were analyzed at weekly intervals for 5 weeks for ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3+-N). Data obtained were subjected to statistical analyses using the SPSS® software. Simple percentages, Analysis of Variance (ANOVA) at 95% limit and the nitrification inhibition rate of the various extracts and the inhibitory threshold times were determined using the sigmoid dose-response model. Result indicates that the sandy loamy soil samples recorded nitrification inhibition ranging from 5.63% to 90.53% and nitrification stimulation (21.2% to 2.97%). Application of 4% of extract exhibited the highest rate of nitrification inhibition. There is no significant difference in the extent of nitrification inhibition at different concentrations of extracts for the sandy loamy soil treatments except for the 4% treatment level and at week 5. It can be concluded that the extracts of Mucuna pruriens provides little effective nitrification inhibitors in sandy loam soils but its effectiveness can be improve by increasing its application rate and extending the application time.