Forage Grasses Matching Production to Favorable Water Supply.

A bimodal pattern of precipitation with peaks in May and September, severe water deficits accompanied by extreme heat in summer, and relatively mild winters have shaped the primary and secondary production from agroecosystems in the Southern Great Plains. One of the most important crops with the ability to compensate for these weather extremes is winter wheat (Triticum aestivum L.), cultivated on approximately 6.5 million hectares. In this region, wheat is a dual-use crop, providing winter forage for cattle and grain crop. In the past decade, the disturbed pattern of autumn precipitation has threatened timely planting of dual-use wheat, resulting in a lack of forage for cattle to graze into the winter and early spring. In the 70’s and 80’s, introduced cool-season perennial grasses (summer-active types) were an important source of high quality forage to complement dual-use wheat and perennial warm-season grass pastures. Changing climatic conditions are considered one reason for failure of traditional (summer-active), introduced cool-season perennial grasses at the margin of their existence in C-4 dominated ecosystems of the Southern Great Plains. As a result, improved cool-season perennial grasslands based on traditional, summer-active cultivars are short-lived and require frequent reestablishment, increasing costs of winter forage for cattle. The only adaptation strategy to ensure forage availability during autumn to spring grazing season in the changing climatic conditions will be adoption of a new type of forage grasses with improved tolerance to heat and drought. In 2000, we introduced to pastures of the Southern Great Plains perennial cool-season forage grasses of Mediterranean origin. These grasses express a summer dormancy trait, e.g., they cease growth during summer months and actively grow during autumn to early spring. This growth pattern enables summer-dormant cool-season grasses to adapt to the precipitation patterns usually occurring in the Southern Great Plains and makes them  more persistent than any other, traditional cool-season perennial grass species. In this presentation, we summarize long-term data on forage productivity, persistence, and soil water use during growing season of summer-dormant versus summer-active cool-season perennial grasses in an environment representative of the Southern Great Plains. We also discuss mechanisms of adaptation to summer drought and the potential implementation of summer-dormant cool-season grasses into grazing systems in the Southern Great Plains.