Impact of field and laboratory techniques on the nitrification rate determined by 15N pool dilution

A number of laboratory and field-based sample taking, handling, treatment and tracer application methods exist for the determination of gross nitrification rates in soil by ¹⁵N pool dilution. However, a comprehensive evaluation of method-induced effects on nitrification rates remains challenging.

With our study, we systematically investigate if laboratory and field techniques generally produce comparable gross nitrification rates determined by the ¹⁵N pool dilution method. Our investigations are conducted on three plots with sandy soil under the different land-uses forest, grassland and arable land in the Fuhrberger Feld region, Lower Saxony, Germany. For this, we conduct on every plot five sub-test series that vary tracer application and subsequent sample handling and/or treatment in the field and in the laboratory, and compare the impact of the different methods. The five sub-tests span over a range from established pure laboratory method for the determination of nitrification rates  to almost pure field work (where soil is incubated and extracted in the field), covering different degrees of handling and treatment impacts. Because there are differences, we will use the experiment to analyze which treatment and/or handling steps change the determined rates the most.