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Effect of Crust Rigidity and Osmotic Potential of Emergence of Six Grass Species¹

Nonporous wax crusts were used to compare seedling emergence of tall wheatgrass (Agropyrun elongatum Host), pubescent wheatgrass [Agropyron trichophorum (Link) Richt.], basin wildrye (Elymus cinereus Scribn. and Merr.), Russian wildrye (Elymus junceus Fisch.), tall fescue (Festuca arundinacea Schreb.) and smooth bromegrass (Bromus inermus Leyss.). Seedlings were grown at O, –2.3, –4.4, –6.7, and –8.4 bars osmotic potential under soft, medium, and hard wax crusts, 3 mm thick. The treatments were designed to simulate the separate and combined effects of salty soils and crusts as limiting factors in seedling establishment in arid regions. The germination and emergence phases were separated by using only seeds that germinated as a basis for percent emergence.

Emergence of all six species was lower under hard crust than under soft wax crust. Pubescent wheatgrass and smooth bromegrass were most affected by the crust hardness. In the range of osmotic potential used, there was no reduction in emergence as osmotic potential was reduced when the emergence was taken at 2 weeks; however, reduction in osmotic potential did delay emergence. The delay was slightly longer for hard crust than for soft crust.

Although osmotic potential did not reduce emergence under soft crusts, a combination of low osmotic potential and hard crust did reduce the emergence of tall wheatgrass, basin wildrye, and Russian wildrye. The emergence of pubescent wheatgrass smooth bromegrass, and tall fescue was reduced principally by the hardness of the crust. Tall fescue was least able to penetrate the crust.

The results indicate that osmotic potential may be less important in reducing emergence of field seedlings than is the presence of a crust. In a field situation the slower rate of emergence and low osmotic potential may involve additional crust strength as the soil surface dries.

Key Words: seedling emergence • wax crusts • Pubescent wheatgrass • Basin wildrye • Russian wildrye • Tall fescue • Smooth bromegrass

² Formerly graduate research assistant, Professor of Agronomy, and Professor of Soil Physics, respectively, University of Nevada, Reno.

Received for publication February 24, 1972.