Productivity and Persistence of Introduced Wheatgrass Species
Rationale
Semiarid regions of the Texas Rolling Plains are characterized by relatively mild winters and hot, dry summers with prolonged drought. In these environments, C4 grasses are the dominant component of rangelands and improved pastures grazed by livestock during summer and fall. High quality winter forage is based mostly on dual-purpose wheat (Triticum aestivum L.) pastures. The gaps in forage availability from early March (termination of grazing on dual-purpose wheat) until May (grazing on warm-season grass pastures) and from October until December (low quality forage from dormant warm-season grass pastures) may be filled by improved cool-season perennial grasses. Their forage quality is generally better than that of dormant warm-season grasses. Therefore, perennial cool-season grasses may be considered as potential source of added value in beef production systems. Winter weather conditions are favorable for growth of most cool-season perennial grasses in the Texas Rolling Plains. Soil water deficits and high temperatures during summer months, however, reduce survival and significantly limit the number of potentially adapted species.
Wheatgrasses native to the Great Plains are usually less grazing tolerant and have lower nutritional quality than wheatgrasses introduced from Europe and Asia. Responses of these C3 grasses to defoliation intensity and frequency is not well understood at the margin of their survival range in C4-dominated environments. Our previous research (for summary click here) evidenced that wheatgrass productivity increased under intensive (7.5 vs. 15-cm hight) or frequent (3 vs. 6-wk interval) defoliation in the first, but declined in several species in the subsequent growing seasons, making their potential to complement forage base limited.
Objectives
The objectives of this study are: 1) to determine the effect of deferred defoliation in the first growing season on productivity and persistence of introduced wheatgrass species; 2) to determine if self-reseeding may increase swards persistence; and 3) to determine soil moisture dynamics under selected wheatgrass species during summer drought.
Methods
The experiment was established near Vernon, TX. Plots (2 x 8 m) with the following wheatgrass species and cultivars were planted in September 2002: Siberian wheatgrass (Vavilov), crested wheatgrass (CD II), pubescent wheatgrass (Manska, Luna), intermediate wheatgrass (Oahe, Rush), and tall wheatgrass (Jose). A part of the plots was defoliated during the first growing season at 3 wk or 6 wk intervals. Within this group, a half of the plots was allowed to produce seed prior to the onset of summer drought. The other part of the plots was not defoliated in the first growing season, and above management treatments were applied in the second and subsequent growing seasons.
Results
Data have been collected during 2003-2005 growing seasons.