Effect of the Nematocides Nemagon and DD on Mineralization, Nitrification, Soil Microbial Population, and Soil Fertility Status of Two Tropical Soils

Abstract

Nitrification was inhibited in an acid soil by 60 p/m or more of Nemagon; the NH₄⁺ oxidizing bacteria being affected but not the Nitrobacter, as NO₂^- accumulation was not observed. Nitrogen mineralization was not affected even at 20,000 p/m of Nemagon and an increase in available P, Mn, and a rise in pH occurred in both acid and alkaline soils. Extractable zinc increased in the acid soil. DD was extremely toxic to the nitrifying bacteria; much more so than Nemagon. It inhibited NH₄⁺ oxidizing bacteria but not the Nitrobacter. Nitrogen mineralization was progressively depressed with increasing levels of DD. It resulted in a decrease in pH and extractable P. Mn increased in both the acid and alkaline soils, whereas the effect on Fe and Mg were inconsistent. Bacteria, actinomycetes and fungi were suppressed drastically. At lower levels bacterial population was increased, indicating a possible role in detoxification of DD.