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Tracking soil nitrogen with stable isotopes

 

Understanding the fate of nitrogen applied to soil is vitally important if we are to improve its agronomic use efficiency and reduce its negative effects on the environment.  Very few studies have successfully used natural abundance isotope techniques to follow nitrogen transformations in agroecosystems.

In the March-April issue of the Journal of Environmental Quality, researchers report on a year-long study using stable isotope ratios to obtain a comprehensive nitrogen biogeochemical dataset before, during and after dairy manure application to soil, and combined this with continuous nitrous oxide emissions.

The team found that 56% of the ammonium (>25% of the total nitrogen application) was volatilized to the atmosphere or assimilated into organic forms within 3 days of the springtime application despite immediate incorporation of the manure into the soil.  In the 3 weeks that followed, all the remaining manure-derived ammonium was converted to nitrate (via nitrification) and nitrous oxide (via nitrifier-denitrification).

Using stable isotopes at natural abundance, the team was able to track soil transformations and differentiate gains/losses of manure-nitrogen from endogenous soil nitrogen.  This approach is an alternative to using artificially-enriched isotope materials that are costly to apply at the field scale.

Read the full article in JEQ. Free preview May 19 - May 26