EFFECT OF ORGANIC (NEEM OIL) AND INORGANIC PESTICIDES (PROTRIN AND PHOSKILL) ON SOIL MICROFLORA AND EVALUATION OF THE GROWTH CHARACTERISTICS OF AGROBACTERIUM SP. AND PSEUDOMONAS SP. SOIL ISOLATES

Abstract

Pesticides are used to protect plants from harmful insects. This helps in increasing the crop yield. An unintended consequence of its application, is its effect on physicochemical properties of soil that could lead to changes in microbial populations and their activities. This influences the microbial ecological balance by altering the soil fertility and metabolic activity of soil microbial communities. The study examines the response of microbial populations in soil after incorporation of pesticides [phoskill, protrin, neem oil]. The samples of soil were taken from an agricultural land from a depth of 10-15cm with no traces of pesticide application in the past 3years. The soil was fine sand with about 1.65% organic matter, pH of 6.53 and a water holding capacity of 10%. Enumeration of total bacteria, nitrogen fixing bacteria, fungi were done in control soil and pesticide applied soil at regular time intervals for a period of 21days. Growth characteristics of Agrobacterium and Pseudomonas isolated from the soil was studied in the presence and absence of the pesticides. Protein was isolated from their microbial cultures and quantified. The results indicated that the use of pesticides affected the total number of heterotrophic bacteria, fungi and bacteria involved in nitrogen fixation. The observed effects strongly correlated with pesticide type and the duration of exposure. The stress induced by the presence of pesticides showed changes in the growth pattern of bacteria and the quantity (in g) of protein expression.