Effects of heavy precipitation on ammonia volatilization in wheat fields at different fertilization stages
To clarify the effects of heavy precipitation on ammonia volatilization(AV)in wheat fields at different fertilization periods against the background of frequent extreme precipitation events,this study utilized field-simulated rainfall experiment to investigate the repercussions of heavy precipitation on AV,soil ammonium N content and nitrification potential of wheat fields.Concurrently,a micro-plot experiment was conducted to elucidate the correlation between AV and soil moisture.The field trials encompassed N application treatments(CF)alongside non-N application controls(CK).Employing the fertilization schedule of the CF treatment,a heavy rainfall event(90 mm)was simulated on the 7th day subsequent to the application of basal,wintering,and panicl fertilizer.Monitoring encompassed assessments of N runoff and leaching losses in the trialed plots,alongside continuous measurements of AV over a 10-day period.The results indicated that fertilization markedly elevated ammonium N levels within the upper-middle soil layers(0-10 cm)and exacerbated precipitation-drived N runoff and leaching losses during the earlier growth stages[basal(BFS)and overwintering(WFS)fertilization stages],with comparable losses observed during the panicle fertilization stage(PFS).The results also showed that both fertilization and precipitation had insignificant effects on AV at basal fertilizer stage,but significantly altered the ammonia volatilization intensity(AVI)during the two topdressing periods.The AVI of the precipitation-fertilization treatment(CF-R)during the topdressing periods(WFS,35.02 mg·m-2·d-1;PFS,12.84 mg·m-2·d-1)was markedly higher than those observed in the other treatments(WFS,15.46-17.29 mg·m-2·d-1;PFS,7.95-11.23 mg·m-2·d-1)where AVI ranged from 15.46 to 17.29 mg·m-2·d-1 during WFS and 7.95 to 11.23 mg·m-2·d-1 during PFS.Further analysis highlighted that AV were more pronounced during the WFS compared to BFS and PFS stages.Correlation analysis substantiated a significant linear relationship between the ammonium N content in the topsoil layer(0-5 cm)and the AVI(P<0.05).Notably,in the absence of rainfall,no significant difference in AVI was detected during topdressing periods between the CF and CK treatments.Additionally,it was observed that AV inversely correlated with increasing soil water content within the incubation system.Soil nitrification potential assays revealed that fertilization exerted no discernible influence on nitrification potential across various soil layers.However,precipitation was found to significantly diminish the nitrification potential in the upper-middle soil layers.These suggested that the modulating role of precipitation on AV in fertilized plots was predominantly dictated by the synergistic influences of N concentration and nitrification potential in the topsoil.In summation,while heavy rainfall is a key factor driving N runoff and leaching losses in wheat fields,its role in enhancing AV during topdressing periods,especially during the WFS,is considerable and merits careful consideration in nutrient management strategies.
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