Roger Gates: Grazing of crested wheatgrass |

Roger Gates: Grazing of crested wheatgrass

Crested wheatgrass occurs widely in pastures and hayfields across the northern Great Plains. Persistence and adaptation of this plant have been clearly demonstrated from decades of use. Seedling vigor and hardiness were traits that contributed to its successful use in reclamation of extensive areas that were cultivated and then abandoned following the Dust Bowl. Planting of crested wheatgrass can be credited for minimizing soil loss on thousands of acres. Competitive success has led to many stands which are essentially crested wheatgrass monocultures; with very little diversity.

Growth very early in spring provides an additional benefit to livestock producers. Grazing can be safely initiated on crested wheatgrass several weeks in advance of recommended dates for native pastures, potentially shortening the duration of hay feeding. Scheduling grazing of crested wheatgrass to minimize pressure on native pastures can therefore provide a useful complement as part of a pasture system.

In contrast to the early benefits, rapid maturation reduces the value of crested wheatgrass later in the growing season. Low nutritive value of mature forage can be expected to compromise the performance of livestock forced to graze crested wheatgrass after early summer. In operations where the proportion of crested wheatgrass pasture is balanced by other grazing resources, such as later maturing native pasture, the combination is beneficial. However, extensive stands on many operations create an imbalance.

Several alternatives might be considered to create better balance between animal demand and vegetation nutrient supply:

1) Stocking strategies could be developed to narrow the period of animal demand. Running yearlings from April through June might be an example. A reduction in the cow-calf herd would also be necessary to approach better balance.

2) Crested wheatgrass stands could be replaced with later maturing vegetation, such as a blend of native grasses. Removing crested wheatgrass could be accomplished with cultivation of herbicide, but this begins an expensive, high risk process. Removing vegetative cover exposes the soil to potential erosion, both wind and water. Re-establishment of cover requires time, at least one growing season, and represents a loss of feed resources during that establishment period.

3) A lower risk approach might be adding a desirable plant to the existing crested wheatgrass stand. Species which would complement crested wheatgrass should be well adapted to the environment, establish reliably, persist under grazing and grow actively and provide high nutritive content later in the growing season. Alfalfa could provide a complementary addition to crested wheatgrass if it could be successfully introduced and persist with grazing.

A wild population of predominantly yellow-flowered alfalfa was found growing and reseeding naturally in the Grand River National Grassland in northwestern South Dakota. This naturalized alfalfa population demonstrates persistence in this semiarid environment. Experimental strains were developed from plant materials collected from this feral population.

A study initiated in May 2006 at the Antelope Range and Livestock Research Station near Buffalo, South Dakota, evaluated survival and performance of 11 alfalfa populations. Entries included predominantly falcata materials derived from the yellow-flowered Grand River plants, pure falcata, and conventional purple-flowered pasture-type, and hay-type populations. Transplants were space planted into existing sod and either mob grazed by cattle or protected from mob grazing. Mob grazing began in August 2007 and continued periodically through 2008 and 2009. Survival, plant height, canopy volume, biomass, and reproduction data were collected. Grazing, dry spells, and ice sheets subjected alfalfa plants to substantial stress. High mortality of grazed plants occurred during the 2008-2009 winter. Final survival revealed that conventional hay-type and pasture-type populations had poor grazing survival, less than 19 percent. However, pure falcata and most predominantly falcata populations had survival rates better than 40 percent. Low mortality and high vigor of plants protected from grazing indicated that accumulated stress weakened grazed plants, increasing environment related mortality such as winterkill.

Locally adapted alfalfa, which has been demonstrated to persist under grazing and severe environmental conditions, might be expected to provide a valuable addition to crested wheatgrass stands.

Locally adapted yellow-flowered alfalfa (Medicago sativa L. subsp. falcata (L.) Arcang.) would complement crested wheatgrass and increase the value of stands for livestock production and ecosystem benefits. Interseeding is a method to introduce alfalfa in crested wheatgrass stands.

Our objective was to evaluate initial establishment of yellow-flowered alfalfa no-till interseeded in crested wheatgrass. Research was initiated in August 2008 at Newcastle, WY; Fruitdale, SD; Buffalo, SD; and Hettinger, ND. Effects of seeding date, sod suppression, and seeding rate on seedling frequency, seedling height, and crested wheatgrass below canopy photosynthetically active radiation (PAR) were investigated in 2009 and 2010. Initial establishment in 2009 and 2010 was strongly influenced by amount and timing of growing season precipitation. Seedling height measured in July of late summer seeded alfalfa was greater (p<0.05) than alfalfa seeded the following spring. Clethodim {(E,E)-(±)-2-[1-[[(3-chloro-2-propenyl)oxy]imino]propyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} sod suppression increased (p<0.05) seedling frequency, seedling height, and below canopy PAR compared to control. Seedling frequency in July generally increased as seeding rate increased from 0.56 to 7.84 kg pure live seed ha-1. High seeding rates and clethodim sod suppression did not greatly improve initial establishment when growing conditions were poor. Alfalfa establishment is dynamic because of seedling mortality with time.

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