Nitrogen transformations and availability in soils with application of fumigants

Gross rates of N mineralization, immobilization, and nitrification in soil (Brown Andosol, U.S. Soil Taxonomy: Typic Hapludands), where chloropicrin (28 g m(-2)) or D-D(1,3-dichloropropene) (20 g m(-2)) was applied, were determined using the (NH4+)-N-15-N isotope dilution technique. Before sowing/planting, the rates of PIT transformations in fumigated soils were less than 49% of non-fumigated soils. Before harvest, the rates of N transformations in fumigated soil recovered to the level of non-fumigated soil for a sugar beet (Beta vulgaris L.) plot. However, these rates did not recover for spring wheat (Triticnm aestivum L.) and azuki bean (Phaseolus angularis L.) plots. Based on the kinetic analysis of an 84-d incubation, the k(25 degrees C) (rate constant for net N mineralization at 25 degrees C) values of the fumigated soils were 118-123% of the values of the non-fumigated soils and E(a), (apparent activation energy) values of the fumigated soils were 82-96% of the non-fumigated soils. Our results indicated that the application of chloropicrin or D-D increased the N availability in soil in spite of a decrease in the gross rates of N transformations.