EFFECT OF ORGANIC AMENDMENT ON THE RESISTANCE AND RESILIENCE OF FUMIGATED SOILS

Effects of soil fumigation with chloropicrin and metam sodium on organic matter decomposition activity and the number of ammonium oxidizers were compared between a soil (CF-soil) amended with only chemical fertilizers and a soil (CF+FYM-soil) with CF and farmyard manure for 14 years. Decomposition of chitin and glucose in the soils was suppressed by soil fumigation. While the inhibitory effect was not different in chitin decomposition between CF- and CF+FYM-soils, glucose decomposition seemed to be more damaged in the CF-soil than in the CF+FYM-soil. Glucose decomposition ability recovered both in the soils 4 weeks after fumigation, while chitin decomposition ability was suppressed throughout the 12 weeks incubation period. In the chloropicrin-fumigated soils, the number of ammonium oxidizers greatly decreased by the fumigation and never recovered throughout the incubation period. Although the number of ammonium oxidizers decreased by the metam sodium-fumigation, the decreased number of ammonium oxidizers recovered to the level of the non-fumigated control in the CF+FYM-soil, but not in the CF-soil. These results might suggest that soil resistance and resilience enhanced by the repeated application of organic matter