Effect Of Fumigants On Soil Nitrogen Transformation

Soil fumigants are extensively used to control nematodes, weeds, soil-borne pathogen, and insects for planting of high value cash crops. The ideal pesticide should be toxic only to the target organisms; however, fumigants are a class of pesticide with broad biocidal activity and affect many non-target soil organisms. The aim of this study was to quantify the effect of soil fumigation on N mineralization and nitrification through lab incubation and field experiments, in order to adjust N fertilizer application and improve nitrogen use efficiency。The results of lab incubation presented that the concentration of ammonium nitrogen was increased significantly within a short-term period after treated with Pic, MeI , 1,3-D and DMDS. Nitrification was inhibited at least 2 weeks after treated with Pic, 1,3-D, MeI and at least 1 week treated with DMDS.. Nitrification and mineralization were recovered gradually after a long-term incubation. Correlation analysis showed that there was a significant positive correlation between ammonium nitrogen and MeI dosage. With the reduction or removal of fumigants, the inhibition would decrease or eliminate.Therefore, inhibition of fumigant on nitrification belongs to reversible inhibition. Nitrite bacteria were inhibited after treated with 4 fumigants and the inhibition lasted for 4 weeks, of which 1,3-D and DMDS lasted for 11 weeks. The results also indicated that there were not significant correlation between nitrifying capacity and nitrite bacteria, which need to be better quantify in further study. The results of fumigation in ginger field showed that inhibitory effect on nitrification was stronger after Pic and MB fumigation compared with DMDS. MeI fumigation increased soil ammonium nitrogen and reduced soil nitrate with different dosages. The correlation coefficient between soil ammonium and MeI dosage was 0.9310. Regression analysis was used to evaluate the influence of MeI dosage on soil ammonium and nitrate. The regression equation was y=69.90+0.1424?x1-0.9260?x2 (R2=0.9582, x1=MeI dosage, x2=soil nitrate, y=soil ammonium).Soil ammonium and nitrate was significantly increased after Pic cap fumigation in strawberry field in short-term study. The correlation analysis indicated that Pic dosage have a positive correlation with soil ammonium and mineral nitrogen. The short-term accumulation of ammonium and long-term reduction of nitrate reflected inhibition on nitrification. Soil organic matter and microbial biomass had a direct influence on soil mineral nitrogen after fumigation.The content of soil nitrate was reduced by 83%-91% and nitrification rate was decreased by 52%-61% after fumigation. On the contrary, the content of soil ammonium increased by 83%-204%.Nitrification was inhibited after fumigation and the conversion of soil ammonium to nitrate was retarded, which resulted in reduction of soil nitrate.