Understanding how moisture stress affects plants is essential when designing drought management practices.
Native prairie plants are well adapted to low and variable precipitation. However, severe, prolonged drought will reduce plant numbers and vigor. And last year's precipitation and defoliation (grazing) will affect this year's forage production. Here's why:
Carbohydrates produced from photosynthesis provide energy for all plant growth and maintenance. When air temperatures are favorable for plant growth, lack of soil moisture is the limiting factor for photosynthesis.
Plant growth is reduced or delayed when green leaf area is removed, or when soil moisture limits the amount of carbohydrates that can be produced. Overgrazing and drought during the plant’s rapid growth windows will reduce next year's plant growth.
Plants rely on stored energy to survive during dormancy, and for initial growth after dormancy.Plants must rely on stored energy for unusually long periods of time when drought-induced summer dormancy is added to winter dormancy. Early spring growth that is stopped by drought or frost will deplete the plant’s energy reserves and reduce forage production potential the following year.
Multiple cadres of buds occur on little bluestem crowns ranging from 1-year-old (a) to 3-year-old (b) generations. Image: Pat Reece
Each year’s forage crop is produced by a new set of tillers that develops from buds located in the crown and on rhizomes or stolons.
Year-to-year replacement of grass tillers primarily depends on the production and survival of vegetative buds on existing plants. Few perennial grasses become established from seed on rangeland.
Reduced plant growth under drought conditions or excessive grazing before grasses head may reduce or eliminate formation of new buds. Severe drought will lead to severe die off of tillers and rhizomes.
Grazing pastures every year at the same time, when root growth, bud formation, stolon growth and/or rhizome growth are seasonally most rapid, will reduce next year’s forage production of most mid-grasses and tall-grasses.