Accounting for the fate of inorganic N fertilizer in agricultural systems is critical to sustainable production. Sebilo et al. (1) provide a unique long-term record of 15NO3 fertilizer fate that demonstrates N molecules from a discrete fertilizer application are transferred to soil organic matter (SOM) and subsequently mineralized over the course of ca.100 years during which they contribute to NO3 leaching. The authors conclude “attempts to reduce agricultural nitrate contamination of aquatic systems must consider the long-term legacy of past applications of synthetic fertilizers”. Further, they suggest a recent decrease in anthropogenic N inputs to the Mississippi River Basin, without a concomitant decrease in riverine NO3 loads, is consistent with their conclusion