Estimates of dry matter losses during harvest and storage of herbaceous biomass are needed to determine harvest efficiency and net biomass yield. Losses of switchgrass (Panicum virgatum L.) biomass stored in large round bales as affected by protected and unprotected conditions in three experiments during 1992 to 1995. We also measured the losses of dry matter (DM) during the harvesting operation each year and determined the quantity and quality of runoff water from stored bales during one year. In Experiment 1, ''Alamo'' switchgrass was harvested in August 1992 and stored in 275 kg bales unprotected outside on a grass sod for six months. In Experiments 2 and 3, switchgrass was harvested in November of 1993 and 1994, respectively, and stored in 370 kg bales for one year inside on concrete, outside on a grass sod unprotected from the elements, or outside on a gravel pad. In each experiment, the biomass was field dried to 11 to 19% moisture and baled. The bales were weighed at the beginning and end of the storage period to determine DM losses. In Experiment 1, DM losses during six months of storage were 13% of the original bale dry weight. In Experiments 2 and 3, there were no differences (P > 0.05) in DM losses (average of 5%) among outside treatments during the 12 months of storage. There were no biomass Losses for bales stored inside in Experiment 2; however, there was a 2% loss in Experiment 3. Losses of DM during baling ranged from 1 to 5% depending on moisture concentration in the biomass at baling. Larger losses were associated with drier biomass, presumably because of more shattering. Quality and quantity of runoff water from bales were not different (P > 0.05) from runoff water of control plots. (C) 1997 Elsevier Science Ltd.