Low legume-grass seeding ratio combined with phosphorus fertilization promotes forage yield and soil quality in managed grasslands

Forage yield of 4 monocultures and 5 legume-grass mixtures at 3 study sites over 5 years, Cangzhou, Taiyian and Yinchuan, and soil quality parameters were included in this dataset. Legume and grass seeds were combined into one of five different legume:grass mixtures of 3:7, 4:6, 5:5, 6:4, or 7:3, and each legume:grass ratio received P fertilization at a rate of 0, 9, 18, or 27 kg P ha^-1 year^-1. Forage yield of each plant community was measured at the initial flowering stage of alfalfa and all plants were mowed at 5 cm above ground by species, dried in an oven (65 ◦C, 48 h), and weighed. Soil sampling was collected to measure soil organic matter, total nitrogen, plant-available phosphorus, pH value, soil ezymatic activity and microbial biomass. Our results showed legume-grass mixture at seeding ratio of 3:7 with moderate P fertilization of 18 kg P ha^-1 year^-1 resulted in the highest forage yield among all monocultures and mixtures, for each of the three sites, with persistent and consistent transgressive overyielding. Moreover, significantly greater soil organic matter, total nitrogen, enzymatic activity, and microbial biomass were also observed in the 3:7 mixture, compared with monoculture or other seeding ratios.The file named as Forage yield at 3 sites supplied total forage yield of 4 monocultures and 5 legume-grass mixtures at each of study sites, Cangzhou, Taiyuan and Yinchuan, over 2016-2020. <i>Ms</i>, <i>Ov</i>, <i>Dg</i>, and <i>Fa</i> mean monoculture of alfalfa, sainfoin, orchardgrass and tall fescue, respectively. LG means legume-grass seeding ratio. P0, P1, P2 and P3 mean phosphorus fertilization rate of 0, 9, 18, or 27 kg P ha^-1 year^-1. The file named as Soil quality parameters supplied the results of soil nutrient, enzymatic activities, and microbial variables. MM means the treatment of mean monoculture. Best means the treatment of the best-performed monoculture. SOM, soil organic matter; TN, total nitrogen; AP, plant-available phosphorus; pH, pH-value; ACP, acid phosphatase; NR, nitrate reductase; UR, urease; SU, sucrose; MBC, soil microbial carbon; MBN, soil microbial nitrogen; PLFAs, phospholipid fatty acids; bacteria, bacterial PLFA; fungi, fungal PLFA.