Effects of Pesticide Application on the Growth of Soil Nitrifying Bacteria

Abstract

This research studied the effects of pesticide application on the growth of soil nitrifying bacteria. Nitrosomonas sp. was isolated from the Soil samples gotten from five different locations within the University of Benin, Benin City and cultured using Winogradsky medium. The bacterial isolate was characterized and identified based on its cultural, morphological and biochemical characteristics. After 4 to 5 days of growth, Nitrosomonas Counts obtained from Winogradsky medium ranged from 4.8×10³ to 9.2×10³cfu/g. There was an increase in bacteria growth at lower pesticide concentration which began to decrease as the pesticide concentration increased with time. The percentage nitrite accumulation gradually decreased with time, the LC₅₀ values were higher than EC₅₀ values which shows that the bacteria could survive and grow at lower pesticide concentrations but were completely inhibited at higher pesticide concentrations. It is therefore very important to examine pesticides so as to determine its toxicity to soil bacteria before application.