Trace gas fluxes from a Northern mixed-grass prairie interseeded with Alfalfa

Abstract

That legumes improve soil fertility is well established, however the extent that N fixed by legumes may increase trace gas emissions is poorly understood. Our aim was to determine if greater soil N in native prairies interseeded with alfalfa would increase trace gas emissions of nitrous oxide (N2O) and methane (CH4). A chronosequence study to investigate interseeded alfalfa on the fluxes of N2O and CH4 was undertaken on three prairie sites. At each site, native grasslands interseeded with alfalfa for 38, 16 and 5 years, along with adjacent native grassland controls and native grasslands fertilized with a one-time addition of N fertilizer, were measured for NO2 and CH4 using static chambers. Across interseeding years there were few significant differences between the three treatments (Native, Alfalfa, Fertilized). Despite increased soil N, the interseeded treatment released no more N2O than native grasslands. Methane uptake was generally greatest on interseeded grasslands and least on fertilized grasslands. Our results suggest that while alfalfa can increase soil N and improve productivity, it did not increase trace gas production relative to native grasslands. This is a win-win situation for ranchers wishing to increase soil fertility and thus their overall productivity and forage quality without increasing trace gas emissions.