Purpletop is a warm-season perennial grass native to the United States that grows in dry fields or along roadsides in 36 states (Brown, 1979; USDA-NRCS, 2009b). It is able to grow within a variety of soil types and pH levels, including soils that are highly eroded (Foote and Jackobs, 1966). Removal of the palea and lemma of the caryopsis fruit (dehulling) and stratification for 14 d at 3 °C overcomes purpletop dormancy (USDA-NRCS, 2006); however, dehulling does not increase purpletop stand establishment (USDA-NRCS, 1996). Dormancy of purpletop is at least partly the result of seed-covering structures because their removal decreases time to germination, although mechanical scarification did not increase germination percentage or germination uniformity (Olszewski et al., 2009). Publications regarding seed dormancy are lacking for many grass genera, including Tridens (Simpson, 1990).
Big bluestem grows in dry open areas, along roadsides, or within fields in 43 states (Brown, 1979; USDA-NRCS, 2009a). In Pennsylvania, birds in warm-season grass fields containing big bluestem have greater nest success than those containing cool-season grasses (Giuliano and Daves, 2002). There are no specific competition effects among species of warm-season grasses during early establishment (Launchbaugh and Owensby, 1970); however, Robocker et al. (1953) determined that Canada wild rye (Elymus canadensis L.) grew more quickly than big bluestem. Among germinating members of orchardgrass (Dactylis glomerata L.), early-emerging individuals have competitive advantages over later-emerging individuals (Ross and Harper, 1972).
Presowing wet chilling (prechilling) of big bluestem caryopses in 0.2% KNO3 for 14 d at 4 °C caused an increase of the temperature at which maximum germination percentage and germination rate occur (Hsu et al., 1985). Although big bluestem laboratory testing indicated that germination increased after solid matrix priming (–6 MPa for 2 d at 17 °C or 14 d at 4 °C), sowing nontreated caryopses resulted in higher field emergence than primed caryopses under dry environmental conditions (Beckman et al., 1993). Long-duration after-ripening and scarification of big bluestem caryopses were effective seed enhancement techniques and the mechanism of dormancy was hypothesized to result from seed-covering structures restricting gas exchange (Coukos, 1944).
If seeding is delayed, then caryopses may have to be stored. Storage temperatures of 16 to 27 °C resulted in big bluestem germinating in higher percentages than those stored at cooler storage temperatures of 1 to 6 °C (Coukos, 1944). Because we know of no reports comparing H2O versus KNO3 during prechilling, the effects of posttreatment storage conditions on germination and seedling growth, and subsequent incorporation of prechilled caryopses into warm-season grass seed mixes, the following studies were undertaken using purpletop and big bluestem.
Beckman, J.J., Moser, L.E., Kubik, K. & Waller, S.S. 1993 Big bluestem and switchgrass establishment as influenced by seed priming Agron. J. 85 199 202
Emal, J.G. & Conrad, E.C. 1973 Seed dormancy and germination in Indiangrass as affected by light, chilling, and certain chemical treatments Agron. J. 65 383 385
Foote, L.E. & Jackobs, J.A. 1966 Occurrence and stand density of Tridens flavus (L.) Hitchc. as related to some soil factors Agron. J. 58 412 414
Giuliano, W.M. & Daves, S.E. 2002 Avian response to warm-season grass use in pasture and hayfield management Biological Conservation 106 1 9
Hsiao, A.I. & Quick, W.A. 1985 Wild oats (Avena fatua L.) seed dormancy as influenced by sodium hypochlorite, moist storage and gibberellin A3 Weed Res. 25 281 288
Launchbaugh, J.L. & Owensby, C.E. 1970 Seeding rate and first-year stand establishment for six native grasses J. of Range Mgt. 23 414 417
Miller, C.F. & Dickerson, J.A. 1999 The use of native warm season grasses for critical area stabilization 222 228 Proc. 2nd Eastern Grass Symp Baltimore, MD
Olszewski, M.W., Pill, W.G., Scheiblin, D.A. & Czymmek, K.J. 2009 Use of confocal microscopy to relate germination vigour to embryo morphology of dormant and non-dormant purpletop (Tridens flavus) Seed Sci. Technol. 37 52 58
Parera, C.A. & Cantliffe, D.J. 1991 Improved germination and modified imbibitions of shrunken-2 sweet corn by seed disinfection and solid matrix priming J. Amer. Soc. Hort. Sci. 116 942 945
Robocker, W.C., Curtis, J.T. & Ahlgren, H.L. 1953 Some factors affecting emergence and establishment of native grass seedlings in Wisconsin Ecol. 34 194 199
Smith, O.E., Welch, N.C. & Little, T.M. 1973 Studies on lettuce seed quality: I. Effect of seed size and weight on vigor J. Amer. Soc. Hort. Sci. 98 529 533
USDA-NRCS 1996 Establishment of native plants on disturbed sites. Jamie L. Whitten Plant Materials Center, Coffeeville, MS. Tech. Note 12(1) 5 Nov. 2008 <http://www.plant-materials.nrcs.usda.gov/pubs/mspmctn9601.pdf>.
USDA-NRCS 2006 2005 annual report. Jamie L. Whitten Plant Materials Center, Coffeeville, MS 5 Nov. 2008 <http://www.plant-materials.nrcs.usda.gov/pubs/mspmctr6778.pdf>.
USDA-NRCS 2009a Plants profile: Andropogon gerardii Vitman. Big bluestem 11 Jan 2009 <http://plants.usda.gov/java/nameSearch?keywordquery=big+bluestem&mode=comname>.
USDA-NRCS 2009b Plants profile: Tridens flavus (L.) Hitchc. Purpletop tridens 11 Jan. 2009 <http://plants.usda.gov/java/profile?symbol=TRFL2>.