Effect of Fumigation on Soil Microorganisms of Tobacco Nurseries at Hunsur

Durofume, a soil fumigant (which is presently used in tobacco nursery practices at Hunsur to control root-knot nematodes) was evaluated for its effect on microorganisms inhabiting the soil before fumigation and after fumigation too at various intervals for a period upto 630 days. The results revealed that rapid changes took place in the biological properties of fumigated soils. Immediately after fumigation nitrogen fixing Azotobacter, nitrifiers Nitrosomonas, Nitrobacter and nitrogen fixing cyanobacteria Calothrix, Plectonema, Scytonema and Tolypothrix were observed in the soil. After 180 days the microbial population in fumigated soil is almost close to that of non-fumigated soil quantitatively and microorganisms such as Aspergillus, Pythium, Mucor, Rhizopus and Rhizoctonia which were eliminated due to fumigation reappeared at this stage. Along with the pathogens, the useful microorganisms colorized following fumigation, persisted even after one year but the quantity decreased gradually. The present investigation clearly indicates that soil fumigation does not offer any threat to beneficial microorganisms and the soil microflora developed after fumigation is rather useful in stimulating the growth of seedlings.