Impact of Organic and Inorganic Fertilizers on Microbial Populations and Biomass Carbon in Paddy Field Soil

A field experiment was conducted to examine the microbial populations and microbial biomass carbon under organic and inorganic farming practices in paddy (variety IR-64) fields. The organic fertilizer used was a mixture of farmyard manure, rock phosphate and neem cake, while on the other hand for inorganic fertilizer, a mixture of urea, single super phosphate and muriate of potash was used. Microbial population counts were analysed from samples collected from the surface (0-15 cm) and sub-surface (15-30 cm) soil depths of the treated plots by soil plate and dilution plate methods for fungi and bacteria, respectively. Results obtained showed that the organically treated plot recorded the maximum microbial population counts (fungal and bacterial) and microbial biomass carbon, followed by the inorganically treated plot and control. A significant variation in fungal population was found between control and treated plots (organic and inorganic) at the surface soil depth, whereas at the sub-surface soil depth it was between all the plots (Tukey’s test at p≤0.05). Organic plot exhibited a significant variation in bacterial population (both the soil depths) with the inorganically treated plot and control (Tukey’s test at p≤0.05). Organic carbon showed significant positive correlation with fungal and bacterial populations (p≤0.05). The application of organic fertilizers increased the organic carbon content of the soil and thereby increasing the microbial counts and microbial biomass carbon. The use of inorganic fertilizers resulted in low organic carbon content, microbial counts and microbial biomass carbon of the soil, although it increased the soil’s NPK level which could be explained by the rates of fertilizers being applied.