Light-use-efficiency (LUE) – the efficiency with which absorbed photosynthetically active radiation (APAR) is converted into plant biomass – is a key variable necessary for assessing aboveground net primary productivity (ANPP) using remotely sensed data. If grazing management impacts LUE, estimates of productivity could be biased by inaccurate values of LUE.

The goal of this project was to investigate the degree to which grazing management impacts LUE and how those impacts vary over the course of the growing season. We quantified LUE using ground-based measurements for different pasture grazing treatments at two sites – in southwestern Virginia and central Tennessee. The impact of grazing treatments – rotational versus continuous grazing – on LUE was characterized by measuring ANPP and APAR under controlled conditions. APAR and ANPP were significantly greater for rotationally grazed plots over two growing seasons at the Virginia site, but APAR and ANPP were not significantly different at the Tennessee site. Light-use efficiency (LUE) was not impacted by grazing management treatments at either site. ANPP differences between treatments were due not to differences in LUE, but to differences in leaf area and the amount of light harvested. This suggests that production efficiency models need not account for different grazing management-strategies when using LUE to estimate ANPP from APAR.