Grazing Effects on Water Relations of Caucasian Bluestem

Abstract

Caucasian bluestem [Bothriochloa caucasica (Trin.) C. E. Hubb.] is a warm-season grass introduced from Eurasia that is currently used for reseeding rangelands in the southern Great Plains [USA]. Although this species is thought to be grazing tolerant, no specific information is available concerning its repsonse to grazing. This study was conducted to evaluate the effect of 2 levels of grazing on xylem water potential (.psi.) and total leaf conductance (gT) of Caucasian bluestem. During the grazing period (mid May to mid September) diurnal .psi. and gT measurements were made on 3 days in 1983 and 1984, and afternoon measurements were taken at weekly intervals in 1984. Soil moisture at 15, 45, and 75 cm depths was monitored in 1984. Heavily grazed plants exhibited consistently higher (less negative) .psi., and generally higher gT than lightly grazed plants. Averaged over the season, heavy grazing increased mean afternoon .psi. and gT by 28 and 76%, respectively, compared to light grazing. Soil moisture was conserved with heavy grazing; treatment differences were greatest during July, which is generally the driest summer months in central Oklahoma. Thus, for Caucasian bluestem, leaves from heavily grazed swards were under less water stress than leaves from lightly grazed swards.