Nitrification dynamics in a soil after addition of different fumigants

Abstract

Soil fumigation has significant effects on nitrification. Better quantification of soil nitrification after fumigation can benefit fertilizer recommendation.The effects of methyl bromide (MB), sulfuryl fluoride (SF), methyl iodide (MI), metham sodium (MS) and chloroform (CF) fumigation on soil nitrification dynamics were evaluated in laboratory incubation. After removal of the fumigant, the soils were incubated at 25°C in aerobic conditions for 20 weeks. An accumulation of soil ammonium-nitrogen (-N) content was found after MB, MI, MS and CF fumigation compared to untreated control at 1 and 2 WAF (weeks after fumigation). Soil -N accumulation lasted up to 4 WAF in MI treatment. Fumigants also increased soil dissolved amino acids (DAA) significantly except for SF at 1 WAF. The levels of microbial biomass nitrogen (MBN) in all fumigated treatments were lower than the levels in the untreated control at 1 WAF and potential nitrification rates in all five fumigant treatments were significantly lower than in the untreated control during all sampling dates. To assess the effect of fumigation on nitrification, an S-shaped function was fitted to the amounts of nitrate-nitrogen (-N) in fumigated soils. The times of maximum nitrification (t max) in MB, MI, CF and MS were 1.63, 1.81, 1.33, and 1.00 wk (week), respectively, and MI was shown to have a stronger inhibitory effect on nitrification of soil -N, while t max in SF and the untreated control were −7.83 wk and −5.90 wk, respectively. The negative values of t max indicated nitrification was not affected in the untreated control and SF treatment and the conversion of soil -N to -N was finished during the first week.