Efforts to decrease supplemental nitrogen (N) applications to turfgrass justify alternative fertility strategies such as legume inclusion. Legumes such as clovers (Trifolium spp.) are present within many turfgrass scenarios. Legume persistence is partly due to an ability to biologically fix atmospheric N, which is incorporated into the plant as proteins and other compounds. N is subsequently shared with associated grasses through the decomposition of legume -roots and -foliage.

A 3-year study evaluated the effects of white clover inclusion within a hybrid bermudagrass lawn. Supplemental N (0, 0.5, 1, 2, 4, and 8 g N m^-2) was applied monthly, April to August, in order to evaluate the effects of supplemental N upon biomass composition, N fixation, N transfer, and soil carbon.

Mixed grass plus clover swards yielded higher clipping biomass than grass-alone swards, which was evidence of enhanced bermudagrass growth due to biological N fixation. Likewise, grass biomass of mixed swards was increased relative to that of grass-alone swards at supplemental N rates ≤ 10 g N m^-2 year^-1 but was decreased at higher supplemental N rates. N fixation was estimated to be 6.6 g m^-2 year^-1 during the 3-year study, with an apparent increase in fixation as years progressed. Results indicate that N fixation was suppressed at the lower and upper extremes of supplemental N rates. N transfer to the associated bermudagrass sward was estimated to be 24% during the latter two years of the study. Soil carbon levels were similar among all treatments.