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return to Farmers Independent Weekly

April 8, 2004

by Glenn Friesen, former M. Sc. Candidate in Plant Science*

New research on native grass establishment

Native grasses are gaining ground!

That would be the headline of every farm newspaper if only they were as easily established as “introduced” or tame species. Native grasses are indigenous to North America. Prior to European settlement, they were the predominant vegetation tall grass, mixed grass and short grass prairie regions of the North American Great Plains.

Believe it or not, the factors that make native grasses difficult to establish also add to their endurance when faced with adverse environmental conditions. The two accepted reasons for this resilience are the range of genetic diversity within each population and their vigorous root development and subsequent crown survival.

Genetic diversity is a direct result of cross-pollination. Since all grasses are cross-pollinating, genetic diversity is common in the world of grass. However, because grass breeders select new grass varieties with narrow gene pools, tame grass varieties are relatively uniform genetically and do not have the large genetic diversity seen in native grasses. This uniformity increases their ease of establishment and management, but reduces their long-term survival under harsh conditions.

In simple terms, there is a genetic trade-off between ease of establishment and management with long-term survival. In fact, many previous studies have concluded that once established, native grasses are more tolerant to environmental extremes and require fewer long-term inputs than tame species.

Historically, with the exception of innovative livestock producers, native grasses were planted for projects on government land (e.g. reclamation projects, right-of-ways, wildlife habitats). This was primarily due to three factors: 1) poor establishment success rates, 2) low seed availability, and 3) high seed cost. However, recent increases in seed availability and lower seed prices have sparked new interest in harnessing the resilience of native species for more mainstream purposes such as pastures.

Previous research studies on native plants have focused on increasing establishment success rates and seedling vigor through techniques such as scratching the seed coat to improve water uptake, soaking seeds in potassium nitrate to initiate germination, and improving phosphorus fertility to increase root development. Studies have shown that of all the factors influencing native grass establishment, soil type is consistently near the top. Given the soil types in which native grasses evolved, it is not surprising that loamy soils typically promote the growth of mixed grass prairie species, such as little bluestem, while sandy soils commonly promote the growth of short grass species such as blue grama and prairie junegrass.

In 2001 and 2002, I conducted research for an M.Sc. in Plant Science on the effects of varying seeding rates, in-furrow phosphorus fertilizer, seed treatments of phosphorus scavenging bacteria (Jumpstart™), and soil type on the seedling vigor and survival of two native short grass species. The two species I used were blue grama (Bouteloua gracilis) and prairie junegrass (Koeleria macrantha). I evaluated plant density as an estimate of establishment success and plant height and leaf stage as an estimate of seedling vigor.

Higher seeding rates did increase stand densities but not proportionately. Doubling seeding rate to 200 from 100 seeds/meter increased row densities by 40 percent for blue grama and 45 percent for prairie junegrass (Table 1). Many researchers speculate that native species will naturally establish at the proper plant density required to survive in a given environment, suggesting that different “optimum” densities exist for different environments. Since plant densities increased approximately 50 percent on average, this would suggest that perhaps 150 seeds/meter of row may be the “optimum” density for the particular environment used in the study.

Although soil fertility levels are very important in today’s conventional crops, many researchers are certain that it does not play as important a role in establishing and managing native species. This theory is supported by our study since neither native grass responded to the phosphorus fertilizer or the bacterial seed treatment intended to increase phosphorus uptake. The common understanding is that native species have adapted under environments of low fertility and, having evolved over a very long period of time, have developed their own tools necessary for survival, including symbiotic relationships with naturally occurring soil microbes.

Finally, as expected, we observed that the soil type played the largest role in establishing the two native grass species. Seedling vigor, measured as plant height and leaf stage, and plant densities were both highest in the sandy loam (SL) soil (Table 2). The texture of SL soil was an average of the sandy-clay loam (SCL) and the loamy sand (LS) soils. It is likely that the SCL soil was too fine and the LS was too coarse in texture for the proper establishment of these two grass species.

What does this tell us? The basic message is pay attention to the environment – in particular the soil type - before you choose your seed mixture of native grasses.

*Glenn Friesen graduated with an M.Sc. from the University of Manitoba in 2002 and is now the Provincial Forage Specialist based in Carman.