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Seed dormancy is a main factor limiting the use of eastern gamagrass (Tripsacum dactyloides L.) for forage and conservation purposes; however, there is little available information on the seed bank dynamics of eastern gamagrass plantings. Knowledge of the degree and rate of seed dormancy loss would improve decisions concerning eastern gamagrass plantings and provide a better understanding of the seed bank longevity for this species. In this study, cold, moist stratified seed or unstratified seed was planted at 2.5- and 5.0-cm depths on 16 Aug. 1999, 1 Nov. 1999, 14 April 2000, 15 May 2000, and 16 June 2000 for the first year of the study and 15 Aug. 2000, 31 Oct. 2000, 17 April 2001, 15 May 2001, and 15 June 2001 in the second year. Plants and seeds were retrieved at 3, 6, 9, and 12 mo after planting of 50 seeds for each seed treatment and planting depth combination. Intact seeds were germinated for 28 d and the viability of ungerminated seeds was determined with a tetrazolium test. Seed dormancy of both stratified and unstratified eastern gamagrass seed was lost mostly between mid-September and mid-November. No more than 12% dormant seed remained after mid-December and dormancy was completely lost by April and May. Seed dormancy in eastern gamagrass was substantially reduced with several weeks of soil temperatures below 15°C and adequate soil moisture., EASTERN GAMAGRASS is a warm-season, perennial, bunch grass found growing naturally from the northeastern and north central USA and south into Mexico, Central America, the Caribbean, and into Bolivia and [...]

Eastern gamagrass (Tripsacum dactyloides, L.), a warm season, perennial grass with great potential for forage and conservation uses, has a high level of seed dormancy, making establishment difficult. Stratification at 4°C for 6 wk is a standard method for providing germinable gamagrass seed. Earlier research showed that gibberellic acid (G[A.sub.3]) increased germinability of gamagrass caryopses removed from the cupule, but was less effective when the caryopses remained in the cupule. We hypothesized that gibberellic acid together with stratification may increase germination of seed above levels obtained by stratification or gibberellic acid alone. This study assessed the germination of three seed lots of eastern gamagrass to 1 mM G[A.sub.3] and exposure to 4°C for 0 to 7 wk. Seed soaked in G[A.sub.3] solution averaged 43% germination during the first 3 wk of stratification and was significantly higher than the germination of water soaked seed averaging 35% germination. Seed reached peak germinability after 4 wk of stratification and remained at this level during the final weeks. After 4 wk of stratification, germination levels of G[A.sub.3] and water treated seed were similar at 64 to 70%. The most pronounced effect of G[A.sub.3] was more rapid germination of seed in all of the stratification durations tested., EASTERN GAMAGRAS is a warm-season, perennial grass species found from the northeastern and north central USA and south into Mexico, Central America, the Caribbean, and into Bolivia and Paraguay in [...]

Landscape position affects legume establishment in pastures. We conducted this study to (i) determine the role of emergence and survival on establishment of legumes on summit and backslope positions and (ii) examine how competition, as influenced by sward-cutting height and N fertilization, affects legume emergence and survival across these positions. We no-till drilled a mixture composed of red clover (Trifolium pratense L.), alfalfa (Medicago sativa L.), and birds-foot trefoil (Lotus corniculatus L.) into an existing cool-season grass pasture at Rhodes, IA, in 1998 and 1999. Treatments consisted of landscape positions (summit and backslope), N fertilizer rates (0, 22, 44, and 89 kg [ha.sup.-1]), and sward heights (uncut, 5, and 13 cm). Landscape position did not affect legume emergence in swards cut at 5 and 13 cm. At those heights, emergence averaged 1041 and 831 seedlings [m.sup.-2]. In swards cut at 5 cm, 62 plants [m.sup.-2] survived on summits vs. 183 plants [m.sup.-2] on backslopes. Legume emergence and survival generally decreased as sward height and N fertilization increased but interactions with landscape position occurred. Addition of 89 kg [ha.sup.-1] N was required to reduce survival on backslopes to 39 plants [m.sup.-2], a density similar to that on summits. Our results show that seedling survival limits legume establishment on summit positions in pastures. Legume establishment is successful on backslopes because of less competition from grass. We recommend that legumes be seeded on backslope positions in pastures, N fertilizer not be applied, and grass competition be reduced before seeding legumes in pastures., LEGUMES improve the production and nutritional value of forage in cool-season grass pastures. Pastures composed of grasses and legumes produce more dry matter than grass-only pastures (Taylor and Allinson, 1983). [...]

The ability of seed quality tests to predict field performance of soybean seed lots with different incidences of infection by the causal agents of phomopsis seed decay (PD), was evaluated. Different PD seed infection levels were induced in one 'Corsoy 79' soybean seed lot by exposing naturally infected pods to 0, 3, 4, or 5 d at >95% relative humidity and 25 degrees C. Seeds were then removed from pods and dried. Seed quality was evaluated by germination tests on creped cellulose wadding (Kimpac), rolled towel, and sand and by cold, accelerated aging (A.Aging), tetrazolium (TZ), and conductivity tests. Field emergence of these seeds was evaluated at two locations and two 1991 planting dates in Iowa. Differences between laboratory germination test results for seeds with low (6.4 and 11.5%) infection levels were minor. At higher infection levels (18.2 and 32.4%), test differences were as large as 23%. Phomopsis-diaporthe infection was located primarily in the seed coat with lesser infection levels in cotyledons. Cotyledonary infection was not associated with variation in test results, but seed coat infection was, as evidenced by greater numbers of infected-abnormal seedlings in Kimpac and towel tests than in other tests. Field emergence declined with increasing PD seed infection at all sites and planting dates. Kimpac, towel, sand, A.Aging, and cold tests gave good estimates of field emergence at seed infection levels to 18.2%, but at 32.4% infection, Kimpac and towel tests underestimated field emergence. Tetrazolium and conductivity tests overestimated seed quality at low and high infection levels. AUTH-ABST