Yield and chemical composition of the plant parts and total herbage of switchgrass (Panicum virgatum L.) and timothy (Phleum pratense L.) at anthesis were studied in growth chambers. The grasses were established in pots of Plano silt loam soil by transplanting young, unelongated tillers. They were grown to anthesis in four day/night temperature regimes (32/26, 27/21, 21/15, and 15/10 C) at two soil N levels; 60 and 260 kg/ha.

Days required for the grasses to reach anthesis decreased as day/night temperatures increased to 27/21 C and then remained the same at 32/26 C. N fertilization did not affect time to anthesis. Neither N nor temperature affected inflorescence numbers of either species, but N increased inflorescence lengths.

Vegetative growth measures at anthesis were greatest for switchgrass in the highest temperature regime (32/26 C) and for timothy in the low or mid-temperature regimes (15/10 C and 21/15 C). N increased these parameters for both species.

Total nonstructural carbohydrate (TNC) percentages in the herbage, stubble, and rhizomes of switchgrass at anthesis were not affected greatly by temperatures or N. TNC percentages for the plant parts of timothy were generally highest in the lowest temperature regime and lowest in the highest temperature regime. N decreased TNC percentages for the herbage and stubble of timothy, but had little effect on those of the roots.

Mineral concentrations in the herbage of both species at anthesis were generally highest in the temperature regimes where the species produced the least growth (15/10 C to 21/15 C for switchgrass and 32/26 C for timothy). N generally increased nutrient element concentrations.