Intraspecific and temporal variation in radiation use efficiency of Medicago sativa L. and Lolium arundinaceum

Understanding the spatial and temporal variability of aboveground net primary productivity (ANPP) is essential in extensive livestock systems, because it directly determines forage availability, stocking rates, and carbon inputs to the ecosystem. Even though radiation use efficiency (RUE) is a key variable for estimating ANPP, it is rarely measured. This study compared inter‐ and intraspecific variation in RUE in five alfalfa ( Medicago sativa L.) and five Lolium arundinaceum cultivars. RUE showed considerable temporal variation, largely explained by harvest time and its interaction with cultivar group and identity. On average, alfalfa exhibited 27% greater RUE than tall fescue. RUE differences accounted for 59% of the variation in accumulated ANPP between species. Using a fixed RUE value for intra‐annual estimations led to overestimations of up to 167% or underestimations of up to 50% in forage production. These results highlight the importance of accounting for RUE variability to improve pasture management and set the stocking rate. A better understanding of the controls of intra‐ and interannual RUE variation is crucial for developing models based on environmental conditions that allow explaining the temporal variations of this key variable.