Root trait complementarity improves yield of ryegrass (Lolium perenne L.) and tall fescue (Festuca aurundinacea Schreb.) in a low P soil

Phosphorus (P) fertilisation is a key environmental and agronomic issue for grassland management. This motivates the introduction of smart combinations of grasses with the ability to access poorly soluble P pools in soils and decrease reliance on external inputs. In this field experiment, we cultivated Lolium perenne L. and Festuca arundinacea Schreb. in monocultures and in combination, as well as a combination of the latter species with a tetraploid variety of Lolium and Phleum pratense L. Plants were grown in an unfertilized low P sandy soil with and without P fertilization for two growing seasons in Wageningen, The Netherlands. We monitored biomass production through time and measured root traits, nutrient uptake, microbial biomass and enzymatic activities. We observed that, in the unfertilized plots, the combination of Lolium and Festuca generated the highest cumulative yields, relative total yield (RYT) and P nutrition index (PNI). These results can be explained by the complementarity found in root traits between Festuca and Lolium. Festuca showed a significantly higher root biomass at deeper soil layers compared to Lolium. Lolium had finer roots than Festuca through the soil profile. The combination of 4 different grasses did not result in higher yields, but lead to increased soil C, microbial P biomass, alkaline phosphatase and β-glucosidase in the unfertilized plots. Our results show that, in low P soils, combinations of grass species with contrasting root traits could lead to significantly higher yields than monocultures and decrease the need for fertiliser application.