Evaluation of a Cool-Season Grass-White Clover Mixture for Low-Nitrogen Input Lawns

Turfgrass lawns require supplemental nitrogen (N) to maintain green color and seasonal shoot density. Improper lawn fertilization with excess N or phosphorus has the potential to contaminate both surface and groundwater. Thus, to reduce the reliance on supplemental N fertilization, alternative strategies or novel turf systems like grass-legume mixtures need explored. White clover (Trifolium repens L.) is a stoloniferous legume that biologically fixes N from the atmosphere and adds N into the soil via mineralization. The objective of this field study was to evaluate the persistence and feasibility of a cool-season grass-clover lawn mixture. A lawn grass mixture with and without a novel white clover \u27Microclover\u27 (MC) was grown at two annual N rates (0 and 98 kg N ha-1 yr-1) for two growing seasons. Dry matter yield (DMY), yield component analysis (YCA), visual appearance, canopy greenness, clover populations, and flower production were measured. Total DMY ranged from 3815 to 15583 kg ha-1 and turf that received supplemental N produced the most DMY, 15583 and 13136 kg ha-1, respectively, for turf with and without MC. By contrast, unfertilized turf with and without MC produced 8754 and 3815 kg ha-1, respectively. The YCA in year two showed that MC contributed approximately 15% to DMY in unfertilized turf, and 3% in turf receiving supplemental N. All treatments except the unfertilized turf without MC demonstrated acceptable visual quality and where supplemental N was applied, the highest visual quality was observed. In year two, the unfertilized grass-only turf lacked vigor and was affected by two leaf blighting diseases, red thread and dollar spot, resulting in localized patches of brown, dead turf which negatively impacted visual appearance. Canopy greenness was highest in turf with MC receiving supplemental N, and lowest in unfertilized turf without MC, while unfertilized turf with MC and turf without MC receiving supplemental N were identical. Clover populations decreased over the two years regardless of supplemental N. Clover in the turf receiving supplemental N decreased substantially (17 to 1%), while slightly less in the unfertilized turf (14 to 5%), which also affected subsequent flower numbers measured in year two. In a second study, the effect of annual N-rate (0, 98, 146, 195 kg N ha-1 yr-1) on MC population changes was assessed using a poultry manure fertilizer. Although the MC populations again decreased over time, roughly 25 to 11 % across all treatments, there was surprisingly no difference due to any N-rate. This observation, demonstrates that in the future, various N-sources deserve further exploration for their compatibility with grass-legume systems. Overall, these results highlight the influence of traditional N fertilization practices on DMY, visual quality, canopy greenness, and MC persistence in a cool-season lawn grass mixture with and without MC. Further, this study demonstrated that a grass-MC lawn can persist and provide reasonable visual lawn quality and is a potentially feasible option for lawns in the cool-humid region where minimal supplemental N is the goal