Modeling the biomass production of grasslands of Wallonia according to their functional type

Permanent grasslands are complex ecosystems which respond with a great variability - in terms of specific richness - to soil type and management strategies. Modelling is a valuable tool to explore these relationships. Our work consisted in adapting the Moorepark St Gilles grass growth model (MoSt GG) designed to model Lolium perenne plant functional type (PFT) pastures (PFT A) to a different PFT (Dactylis glomerata, PFT B) through literature-based parametrization. The model was evaluated under Walloon (Belgium) conditions using growth trials from 2014 to 2018 in two sites with contrasting pedo-climatic conditions. Three to five cuts were performed over the course of the growing seasons depending on the rainfall yielding a total of 20 and 25 biomass measurements (kg of DM per ha), for PFT A and B respectively. No site effects were observed in the performance of the model. The relative root mean square error (RRMSE), normalized deviation (ND) and model efficiency (EF) across all cuts, sites and PFTs were 33%, 3% and 68% respectively. PFT B was better simulated than A for the criteria RRMSE (33% vs 33%), ND (4% vs. 9%), and EF (75% vs. 54%). Although this first evaluation was satisfactory, a complementary parametrization for additional pedoclimatic conditions and PFTs is called for to use the model under the diversity of Walloon conditions