Rimrock Indian Ricegrass

Rimrock is a selected cultivar of Indian ricegrass [Achnatherum hymenoides (Roem. & Schult.) Barkw.; syn. Oryzopsis hymenoides (Roem. & Schult.) Ricker, Stipa hymenoides (Roem. & Schult.)] originally collected in 1960 from the bench atop the rims on the north edge of Billings, Montana. The collection site is a sandy range site (elev: 1,101 meters/3,610 feet) which receives 350-400 mm (14-16 in) of annual precipitation.

Eighty-three native collections of Indian ricegrass, primarily from Montana and Wyoming, were evaluated at the USDA-NRCS Plant Materials Center at Bridger, Montana. Field testing in comparison with ‘Nezpar’ (Idaho origin) and ‘Paloma’ (New Mexico origin) was done at the following sites: Cardwell, Kalispell, Moccasin, and Missoula valley, Montana; Gillette, Greybull, Point of Rocks, and Sheridan, Wyoming; Coffee Point, Curlew National Grassland, Mountain Home, and Orchard, Idaho; Jackpot and Winnemucca, Nevada; and North Logan, Cache Valley and Grantsville, Utah. Rimrock and Nezpar performed similarly.

The seed shatter and floral indeterminacy of Indian ricegrass combine to reduce harvestable seed yield. Rimrock was released primarily because of its ability to retain mature seed better than Paloma and Nezpar. The angle between the glumes (glume pair angle) of Rimrock is 44o compared to 66o for Paloma. Duration of seed retention from glume opening to shatter is 91% longer for Rimrock than Paloma.

Description

Rimrock is a perennial, cool-season, bunchgrass found on sandy soils that are neutral to mildly saline, with low water holding capacity, and with few rock fragments. The culms are densely tufted and typically 30 to 60 cm (1 to 2 ft) tall. The leaf blades are slender, usually rolled, with membranaceous ligules (6mm /1/4 in long). The diffuse panicle has dichotamously branched, thin pedicels. The seeds are dark brown to black in color, subtended by white pilose hairs. Indian ricegrass has deep, extensive, fibrous roots, capable of adjusting to shifting sands by elongating basal internodes and producing adventitious roots at these nodes.

Adaptation

Rimrock’s adaptation extends from the northern Great Plains west across the Rocky Mountains to the Columbia Plateau and Snake River Plain and north through the prairies of southern Alberta and Saskatchewan. As well as being adapted to sandy soil, Rimrock is more persistent in medium and heavy-textured soils than Nezpar or Paloma.

Uses

Spring growth is initiated in late April and is relished by both livestock and wildlife. Crude protein levels during the growing season range from 11% in early June to 5% in late August. Dormant winter forage will drop to 4%. Indian ricegrass is readily utilized as winter forage in the high deserts of Wyoming. Indian ricegrass is, however, very susceptible to overgrazing.

Rimrock can be used in seed mixtures for the reclamation of disturbed sandy soils. On sand dune sites, Indian ricegrass will be the major grass component of the establishing plant community. Indian ricegrass exhibits both mechanical and physiological dormancy, so not all seeds will germinate at once. This characteristic helps ensure plant establishment in arid, critically disturbed sites. Dormant fall seeding provides natural stratification, allowing seed to take advantage of early spring moisture conditions.

Indian ricegrass produces an abundance of plump seed with protein levels of 15 to 17 percent. This seed is excellent food for upland game birds and songbirds. Indian ricegrass can be planted with, or adjacent, to taller plants for food and cover for a wide variety of wildlife.

Indian ricegrass was commonly used as a food source by Native Americans in the Southwest and Great Basin regions. A flour made from seed of ricegrass (known as Wye or Wai to the Paiute, Shoshone and Ute tribes) was used to make a mush with a pleasing, nutlike flavor. Montana State University-Bozeman has determined that flour derived from Rimrock Indian ricegrass is gluten free. This flour (‘Montina’) is commercially available for use by people who cannot consume gluten without dire health consequences.

Establishment

For best results seed should be planted into a firm, weed-free seedbed at a rate of 7.5 kg/ha (7 lbs/a) for pure stands and 3 kg/ha (2.5 lbs/a) in mixtures. Rimrock has 340,000 seeds per kilogram (155,000 seeds per pound). It is recommended that seeding be done with a drill that will ensure a uniform 6 to 12 mm (1/4 to 1/2 inch) seed placement depth. In very sandy soil conditions, Indian ricegrass has the ability to emerge from planting depths of up to 5 cm (2 in). Rimrock, planted with narrow row spacing (18-30 cm/7-12 in), ensures good ground cover and soil stabilization. Dormant fall planting has produced the best results, but early spring (March to early April) planting can be successful.

Seed Production

Rimrock Indian ricegrass can be grown for seed in areas with greater than 380 mm (15 in) annual precipitation or under irrigated conditions. Seed fields of Rimrock are established in 60-90 cm (24-36 in) spaced rows and maintained in rows by cultivation. Seeding rates for seed production should be at a rate of 80 PLS per linear meter (25 PLS per linear foot) of row. Dormant fall seeding is recommended to utilize winter conditions for stratification of the highly dormant seed. Although little or no seed can be expected the first growing season, good production can be expected for 3 to 4 years thereafter. Seed production under dryland conditions ranges from 110 to 350 kg/ha (100 to 300 lbs/a) and with irrigation ranges from 350 to 900 kg/ha (300 to 800 lbs/a).

Rimrock can be either direct combined or swathed and combined out of dried windrows. Swathing should be done at the firm dough stage when just a few seeds have shattered from the upper portion of the diffuse panicle. Because of the light, fluffy nature of the windrow, they are susceptible to wind damage. With direct combining, the seed must be in the hard dough stage, and thus the plants are more susceptible to shatter and the producer has a shorter harvest opportunity. The average harvest date at the Bridger Plant Materials Center has been July 20.

Availability

The USDA-NRCS Bridger Plant Materials Center maintains the breeders and foundation seed. Rural Route 2, Box 1189, Bridger, MT 59014. For more information on the availability of seed, use, and seed production contact your local NRCS or conservation district office.

Authors
M.E. Majerus, J.G. Scheetz, and L.K. Holzworth

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Last Modified: 04/18/2005