Grassland Yield Gaps and Their Impact on the Contribution to Food Security of Walloon Dairy Farms

Abstract

Current livestock systems are often criticised for their competition with food and land, but they are rarely compared to optimised livestock systems in this matter. The net productivity indicator offers insights into potential improvements. We calibrated a process-based grass growth model (LINGRA-N-Plus) for Walloon grasslands and coupled its output with an animal production model to estimate the potential net productivity achievable on commercial dairy farms in two grassland regions of Wallonia. Three mowing regimes (4C, 5C, and G), three nitrogen (N) fertilisation rates (90N, 225N, and 360N), and two energy corrections (sugar beet pulp or wheat) were tested for the years 2016–2020. Our results showed that potential net productivity ranged from 49% (4C.4C and 90N, grass-only) to 166% (5C.G and 360N, grass + sugar beet pulp) of the current farm sample productivity (267 ± 64 kg HDP ha⁻¹). Notably, similar performance (108% for 5C.G at 225N with sugar beet pulp) could be achieved by commercial farms with lower fertilisation rates than they currently use (285 ± 93 kg N), indicating room for improvement in N use. The variability in potential net productivity was mainly driven by mowing regime and fertilisation rate rather than soil and climate, emphasising management improvements. This suggests the possibility of setting regional net productivity targets. The developed model can guide discussions with farmers on enhancing their contribution to food security.