Irrigated pasture with cool-season perennial grasses

Properly managed irrigated pasture can result in substantial forage production that can support relatively high stocking rates that, in turn, generate a high-dollar return per acre.

Jerry Volesky

Irrigated pasture can balance and complement other forage resources of a farm or ranch and mitigate some of the effects of drought.

There are a number of management considerations and details associated with irrigated pasture. Individual livestock operations should carefully evaluate their production goals, current resources, forage needs and economic returns when considering irrigated pasture.

Important planning and management considerations associated with irrigated pasture are shown below.

Economics
Grazing forage or hay needs
Soils and site selection (erosion potential, fertility, livestock working facilities)
Pasture type (species, varieties, mixtures)
Establishment (seeding rates, seedbed preparation, seeding method and date)
Irrigation (frequency and amounts)
Fertilization (types and rates)
Grazing management (livestock water, fencing, pivot fence crossings, grazing records, pasture monitoring)

Forage types

There are a number of different annual and perennial forage species that could be used. Annuals do allow for flexibility in terms of crop rotations, and the length of time between seeding and grazing can be relatively short.

However, the expense of planting a cool- and warm-season annual in a double-crop strategy can be significant.

Once established and if managed properly, irrigated perennial grasses will have consistent production for multiple years.

Cool- or warm-season perennial grasses could be used, but cool-season grasses generally have the advantage because of their longer growing period, quicker establishment time, persistence under grazing and response to irrigation and fertilizer.

Cool-season perennial grasses

There are a considerable number of introduced, cool-season perennial grasses that have potential for use in irrigated pasture. There can also be multiple varieties for each of these species as well.

Suitability of some of the species may vary by climate, soil type or planned irrigation amount. Some of the more commonly used species include orchardgrass, smooth bromegrass, pubescent and intermediate wheatgrass, meadow bromegrass, perennial ryegrass and endophyte-free tall fescue.

Others that might be used include reed canarygrass, hybrid wheatgrass, festulolium or timothy.

Mixtures of several grass species are most often recommended rather than the use of a single species. Most fields have variation in soil type, fertility and moisture, and each of the grass species have some differences in their adaptation to the sites within a field.

Creeping foxtail and reed canarygrass, for example, are two well-adapted species to low, wet soil sites. Additionally, there are growth rate differences between species within the growing season, and the use of a mixture may help provide a more balanced supply of forage.

Another important consideration is the inclusion of both sod-forming and bunchgrass species in the mixture. Sod-forming species are more aggressive with respect to filling in bare areas or moving into areas where plants have died.

Legumes

Combining legumes into the grass mixture provides several benefits but also can create additional challenges with respect to fertilization, irrigation, weed and grazing management. Common legumes might include alfalfa, red clover, white clover or birdsfoot trefoil.

The addition of a legume in a pasture may result in increased forage yield and quality. Another important benefit of a grass-legume mixture is reduced requirements for nitrogen fertilizer because the grass is able to utilize some of the nitrogen fixed by the legume.

The amount of nitrogen fixed by legumes and the corresponding grass response varies with the amount of legume in the mixture. On the downside, options for broadleaf weed control become limited in a pasture that contains both grasses and legumes.

Seeding and establishment

Most cool-season perennial grasses will thrive on a variety of soil types. Sandy soils can produce substantial forage when properly irrigated and fertilized. Soil samples should be taken to determine fertilizer needs. The seedbed for grasses should be firm, similar to alfalfa.

Check for residual herbicides that might have been used on the crop the previous year. The total seeding rate for all species in a mixture will be about 15 to 25 pounds per acre.

There can be considerable variation in this and the number of seeds per square foot that are sown depending on the species in the mixture.

Spring or late-summer seeding is recommended, but the late-summer seeding is usually better because of more rapid and uniform germination and less weed competition.

Irrigation and fertilizer

Irrigation management for pasture is important with respect to efficient water use and optimizing forage production. Generally, frequent and smaller applications (0.75 to 1 inch) result in the best use of water by the grasses. Many of the cool-season grasses have relatively shallow root systems.

Water is usually applied to a paddock after a grazing period has been completed. For pasture mixtures that include a deep-rooted legume such as alfalfa, it is still desirable to irrigate more frequently using lesser amounts to maintain consistent and active growth of the grasses.

In grass-only irrigated pastures, nitrogen will be the key nutrient affecting production. Irrigated cool-season grasses have been found to continue to respond to nitrogen at rates as high as 200 to 250 pounds per acre.

The level of fertilization used should depend on what level of forage production or stocking rates are desired as well as fertilizer costs. Soil tests are recommended to assist in determining proper fertilizer rates.

Phosphorus levels will be important for mixtures containing legumes. Both irrigation water and fertilizer-use efficiency is greatest when temperatures are moderate and the grasses are rapidly growing.

Grazing management

There are two grazing management principles essential to good irrigated pasture production. The first is limiting the number of times a plant is grazed, which can be accomplished by rotational grazing.

The second is the maintenance of sufficient residual leaf area to keep plants productive. A target level of residual plant material after a grazing period is about 6 to 8 inches.

At a minimum, divide the field into five or six paddocks so each paddock has 24 to 40 days to regrow following each grazing. This will require each paddock to be grazed for about six to eight days.

Depending on a manager’s objectives and desired management intensity, a greater number of paddocks may be established.

Growth of irrigated cool-season pasture is very rapid during spring and early summer and then slows during the warmer part of the summer.

To accommodate this difference in growth rate in a multiple-paddock grazing system, one or more paddocks could be cut for hay in the spring while the other paddocks are grazed.

Another option to manage this change in growth rate is to reduce the number of livestock after the rapid growth period or to have additional pasture available during mid- to late-summer.

The extent of the stocking rate reduction needed during this period can range from 25 percent to as high as 50 percent.