Effect of individual grass species and grass species mixtures on soil quality as related to root biomass and grass yield

For the purpose of feeding value, drought resistance and nitrogen utilization, other grasses (e.g. Festuca arundinacea and Dactylis glomerata) than the currently widely used perennial rye grass (Lolium perenne) are introduced in dairy farming, either as a monoculture or in a mixture. To study the effect of these grasses on yield and soil chemical and biological quality, the three species were sown in a field experiment in monoculture and in two mixtures. Within two growing seasons, the grass species tested under high soil fertility conditions did not show significant effects on most of the tested soil biological parameters. Only for the mixture of L. perenne and D. glomerata a higher soil NO3− and mineral N content were most probably related to a higher bacterial activity, possibly induced by dying roots of L. perenne. This was the likely cause of the high aboveground dry matter yield of this mixture. The N-efficiencies of the monocultures of L. perenne, F. arundinacea and D. glomerata were not different when only considering the aboveground biomass. In L. perenne and F. arundinacea the total N in root biomass was higher while under D. glomerata the NO3− in the soil was higher. The lower fraction of mineral N to total N for L. perenne, F. arundinacea and the mixture of the two suggests that their organic matter build-up/mineralization ratio was higher than for D. glomerata. Furthermore, the mixture of L. perenne and F. arundinacea showed significantly lower soil mineral N levels than the monocultures of each. We conclude that grassland systems with a mixture of L. perenne and F. arundinacea are more sustainable than the monocultures of each, in terms of reduction of nitrogen losses and the build-up of soil organic matter. D. glomerata should only be used in a mixture in which the companion grass(es) are maintained.