Responses of ryegrass, white clover, soil plant primary macronutrients and microbial abundance to application of anaerobic digestates, cattle slurry and inorganic N-fertiliser

This study compared the fertiliser effects of different types of liquid anaerobic digestates on the growth of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.), and on soil's primary plant macronutrients and microbial abundance. A factorial design with seven fertilisers and one control (five liquid anaerobic digestates, undigested cattle slurry, calcium ammonium nitrate (CAN) 27% N, and no fertiliser) and four plant schemes (monocultures of perennial ryegrass and white clover, a mix of both, and bare soil) were tested. Plant (forage yield, leaf area index (LAI), canopy height and root mass) and soil (concentrations of total N, Morgan's extracted P and K) responses were measured, as well as soil bacterial/archaeal (16S) and fungal (18S) gene copy numbers (GCN). Digestates and cattle slurry with different chemical compositions, when balanced in terms of the quantity of dry matter applied, had comparable forage yield responses (p > 0.05), with higher yields than CAN mostly observed in ryegrass and mixed vegetation (p < 0.05). The presence of white clover contributed to higher soil N (p < 0.05). Soil available P was increased by biofertiliser applications (p < 0.05). Soil available K was influenced by the interaction between biofertiliser and type of plant (p < 0.05), with ryegrass/mixed swards showing lower K concentrations than white clover and bare soil. Soil bacterial (16S) GCN responded to the interaction between fertiliser/vegetation (p < 0.05), while archaeal (16S) and fungal (18S) GCN only to the type of vegetation (p < 0.05). The application of anaerobic digestates showed low direct impacts on the microbial GCN of the soil, mostly influenced by type of vegetation. The biofertilisers showed comparable performances and effects, despite substantial differences between their chemical compositions, indicating a possible complex matrix of interactions between fertiliser-plant-soil-environment.