Bob Gillen

Producers continue to have a strong interest in cool-season perennial grasses for the western Great Plains. To answer some questions about the productivity and longevity of these grasses, we tested 4 species of cool-season perennial grasses at the Southern Plains Range Research Station at Woodward, Oklahoma. The species in our test were Jose tall wheatgrass, Luna intermediate wheatgrass, Barton western wheatgrass, and Bozoisky Russian wildrye. The grasses were seeded on a fine sandy loam soil in the fall of 1995. The winter and spring of 1995-1996 were very dry but the grasses established good stands. Paiute orchardgrass and Texas bluegrass were seeded at the same time but failed to produce a stand. Annual precipitation is about 22 inches at the site.

Since 1997, we conducted harvest management studies on these grasses. The treatments consisted of all combinations of 2 cutting heights (4 or 6 inches) and 3 cutting intervals (30, 45, or 60 days). We also had a hay treatment in which the grasses were cut only once in the spring at early heading. The treatments were started at the beginning of the third growing season. We applied 20 lb nitrogen per acre in fall and 40 lb nitrogen per acre in spring each year.

To get an idea of general adaptability, we can look at the results from the hay treatment (see figure below). Production was similar for the 4 grasses in 1998 at about 2000 lb/acre of harvested forage. In 1999, the wheatgrasses had similar production of about 2600 lb/acre but the production of Russian wildrye fell considerably. Spring precipitation in 1999 was very favorable (60% above normal) and these may be the upper limits of production at this level of fertilization. Harvested production was 23% greater with the lower cutting height. Production was about 20% higher with the 60-day harvest interval compared to the 30 or 45-day intervals. We had usable fall production from these grasses in only 1 year out of 3.

A major concern was invasion by warm-season grasses. Tall wheatgrass and Russian wildrye allowed the greatest invasion by warm-season grasses (see figure below). Tall wheatgrass and Russian wildrye are both bunchgrasses so there is more space between plants for invasion. Intermediate and western wheatgrass both form a sod and are more resistant to invasion. The main invaders were sand dropseed and windmillgrass. Intermediate and western wheatgrass also appeared to be more resistant to invasion by cheatgrass. Invasion was greatest in the 4-inch/30-day and 4-inch/45-day harvest treatments for all of the grasses.

Luna intermediate wheatgrass and Barton western wheatgrass were probably the best overall performers. Jose tall wheatgrass did fairly well while Bozoisky Russian wildrye appeared to be declining. These grasses may have a place in our production systems but they will not be exact replacements for winter annuals such as wheat. Our studies are continuing and these results should be considered preliminary. For further information, contact Bob Gillen at the Southern Plains Range Research Station, 580.256.7449, bgillen@ag.gov.