Application of biogas-slurry and biochar improves soil multifunctionality in a poplar plantation during afforestation processes

Aims Management can largely influence the sustainability and functionality of forest plantations. However, the role of biogas-slurry and biochar application in supporting soil’s multifunctionality during afforestation remains poorly understood. Methods We conducted a six-year field experiment to examine the responses of soil ecosystem multifunctionality (EMF) to the application of biogas-slurry applied annually as four treatments, and a single initial application of four treatments of biochar in a new poplar plantation based on a reclaimed coastal area. The EMF was calculated as the standardized average of multiple soil surrogates of soil functions linked with C, N, and P cycles. Results Both biogas-slurry and biochar had significantly positive effects on EMF and individual functions, with biogas-slurry having the strongest positive effect, thus promoting carbon stocks and nutrient availability. Furthermore, interactions between biochar and biogas-slurry produced a substantial synergistic effect on soil multifunctionality. The application of biogas-slurry significantly and directly increased the C, N, and P cycle multifunctionality (CCMF, NCMF, and PCMF, respectively). In contrast, a single application of biochar profoundly increased the CCMF but decreased the NCMF, thus requiring a trade-off of multiple elements of soil multifunctionality. Conclusions We show that organic management has the potential to boost multiple ecosystem functions during afforestation. These findings further highlight the importance of rational fertilization strategies for long-term forest management.