FIG. 4. Flux concentrations of a tracer (i.e., a substance that is not sorbed, not transformed, nor taken up by plants) at 1 m depth in the soil as a function of time as calculated for the field and lysimeter systems. Year numbers indicate 1 January of the corresponding year. Tracer (1 kg ha^–1) was applied on 31 March in 1911, 1913, and 1915.