Agronomy Journal 92:1184-1188 (2000)
© 2000 American Society of Agronomy
FORAGES
Winter Establishment of Eastern Gamagrass in the Southern Piedmont
J.Paul Mueller,
Timothy S. Hall,
Janet F. Spears and
Brenda T. Penny
Dep. of Crop Sci., North Carolina State Univ., Box 7620, Raleigh, NC 27695-7620 USA
paul_mueller{at}ncsu.edu
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ABSTRACT
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Eastern gamagrass [Tripsacum dactyloides (L.)] has the potential to contribute as a warm-season component in grazing systems and conservation plantings, but its seeds exhibit a strong dormancy that reduce germination and successful stand establishment. A 3-yr study was conducted on Typic Hapudult soils to determine the influence of fungicide seed treatment [Captan (N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide), 5.6 g a.i. kg-1 seed] and winter planting date (November–February) on germination, stand establishment, and herbage mass of eastern gamagrass. Eastern gamagrass was planted with and without fungicide seed treatment at monthly intervals between November and May. The May plantings (stratified and nonstratified seeds) served as controls. Fungicide seed treatment had no effect on initial or subsequent stands of eastern gamagrass. Winter plantings resulted in initial stands that were equal or superior to stands established from planting stratified seeds in May (5.9 vs. 3.4 plants m-2, respectively). Significant seed carry-over effects were observed from spring (April and May) plantings, with an average of 8.8 seedlings m-2 germinating in spring of the second year compared with 1.7 seedlings m-2 for winter treatments. Herbage mass for spring plantings (March, April, and May) was depressed up to 75% compared with winter plantings. Planting in November, December, or January is an effective alternative to planting stratified seeds in May in the southern Piedmont.
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INTRODUCTION
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EASTERN GAMAGRASS is a widely distributed warm-season, perennial grass native to North and South America. It is commonly found along stream banks, ditch banks, and other sites on alluvial soils in the southeastern USA (Blomquist, 1948). This undomesticated grass has much potential to contribute high quality summer grazing to livestock systems (Burns et al., 1992, 1996). Nevertheless, stand establishment can be particularly difficult and unreliable due to the dormant condition of the seed imposed by its morphology and possibly by physiological factors (Milby and Johnson, 1989). The caryopsis is enclosed in a cupule, which imparts dormancy to the seed (Anderson, 1985). Cold, moist stratification is required to break dormancy (Fine et al., 1990). However, this is a cumbersome procedure that limits the use of this grass. Although it is now possible to obtain commercially stratified seeds, establishment success has been variable due to the tendency of seeds to revert to the dormant condition if seeds dessicate before planting, or dry conditions persist immediately after planting (J.C. Burns and J.P. Mueller, personal communication, 1995).
An alternative strategy is to plant nonstratified seeds during the autumn and winter and then rely on natural climatic effects to stratify the seeds. The objective of this experiment was to determine if dormant-season planting of nonstratified eastern gamagrass seeds in the southern Piedmont would result in establishment that was equal or superior to spring planting with stratified seeds.
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Materials and methods
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Seed Procurement and Testing
An important aspect of this research was to characterize seed dormancy before planting. `Pete' eastern gamagrass seeds were obtained from two sources: Gamagrass Seed Company of Falls City, NE and Shepards Farms of Clifton Hill, MO. Each seedlot was tested using three methods: A rag doll germination test at a constant 30°C (Chamblee and Green, 1995, p. 153), a tetrazolium test (AOSA, 1970), and a stratification test (AOSA, 1994) to confirm the previous two estimates. The concept of autumn through winter planting relies on a high proportion of dormant seeds to allow for natural climatic conditions to break dormancy.
Site Preparation
Three separate field trials were established on a Cecil (clayey, kaolinitic, thermic, Typic Halpudult) clay loam soil in the Piedmont of North Carolina from 1994 through 1997. The research sites were located at the Lake Wheeler Field Laboratory, University Farms, Raleigh, NC (35°52' N, 78°47' W). Plantings of `Pete' eastern gamagrass with and without fungicide (Captan, 5.6 g a.i. kg-1 seed) were made at monthly intervals beginning 15 November through May using a 1.67 m wide no-till drill (Truax Flex Grass Drill, Truax Company, Minneapolis, MN). Seeds were planted approximately 2 cm deep in rows 15 cm apart. The May planting of stratified (wet, prechilled at 5°C for 8 wk) seeds served as a positive control in all experiments. In the second and third experiments, a negative control consisting of nonstratified seeds with and without fungicide treatment was planted in May.
Plantings were made into a glyphosate-killed [N-(phosphonomethyl) glycine] tall fescue (Festuca arundinacea Schreb.) sod at 11.2 kg ha-1 pure, live seed. Plot size was 3 by 9 m. Glyphosate was applied at 1.7 kg a. i. ha-1 plus 0.5% (v/v) of a nonionic surfactant in November of each year to the test site. Soil tests indicated that no P, K, or agricultural limestone was needed. No N fertilizer was applied during the first growth season, but all plots received 75 kg ha-1 of N from NH4NO3 during the second season in April.
Variables Measured
Plant density m-2 was measured in August of the first season and again in spring and fall of the second season. Herbage mass was measured during the second and third season of growth. Plant stands were measured by placing a 1-m2 frame at four locations within each plot and counting the number of eastern gamagrass plants within the frame. Each plot was stratified into quarters based on the major slope gradient and frames placed at random within the strata. Seedling and mature plant identification was made in the spring following initial stand establishment. Herbage mass was measured from a 0.9- by 9-m harvest strip taken from each plot and dried in a forced-air oven at 60°C for 36 h. Botanical composition of eastern gamagrass and weeds (two observers) was determined as visual estimates calibrated to six, hand-separated quadrat samples at each harvest. Adjusted yields are reported on a weed-free basis.
Statistical Design and Analysis
Trials were conducted in a randomized complete block design with a factorial arrangement of treatments in four replicates with 14 or 16 treatments. Factors included planting date (seven or eight levels) and fungicide seed treatment (two levels). An analysis of variance was performed on data from each experiment, and Error MS was used as the denominator in F-tests of the null hypotheses for the model. The analysis of variance was used to determine the effects of planting date, fungicide, and the interaction of planting date x fungicide. Preplanned contrasts were used to test for differences among various planting-date combinations.
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Results and discussion
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Establishment Year Stands
Due to a significant year x treatment interaction, data from each of the three trials were analyzed by year. None of the fungicide effects were significant. Hence, data were pooled over fungicide seed-treatment levels for the statistical analysis and treatment contrasts between planting dates in each experiment. Seeds planted during autumn through winter were exposed to prolonged cool, moist conditions (Fig. 1
and Table 1)
. These conditions provide ample opportunity for infection and subsequent deterioration of seed embryos by fungi. Lack of a fungicide effect is consistent with the observations of Ahring and Frank (1968), who noted in laboratory studies that heavy infestations of mold in the germination media did not appear to restrict germination of eastern gamagrass seeds. Furthermore, Anderson and Libreto (1986) reported the presence of fungi-inhibiting bacteria (Pseudomonas sp.) in the caryopses of eastern gamagrass that may act to protect the seed embryo from fungal decomposition.
Treatment effects were examined as a series of planned contrasts designed to answer specific questions regarding stand establishment. In all trials, planting nonstratified eastern gamagrass seeds between November and February resulted in initial stands that were equal to or significantly greater than stands from stratified seeds planted in May (Tables 2–4)
. In two of the three trials, planting in November or December resulted in the establishment of significantly more seedlings than planting in January or February. Only in 1996 (Table 1) were temperatures cold enough after February to sufficiently stratify the seeds. Plantings made from November 1995 through February 1996 produced similar numbers of established seedlings, and in all cases, stands were significantly greater than stands established in May with stratified seed (Table 3). In all trials, planting from November through February resulted in significantly greater seedling stands than spring plantings made in March and April (Tables 2–4). In the latter two trials, comparisons made between the negative controls (May planting with nonstratified seed) and spring planting (March and April) revealed no difference in first-year stand establishment (Tables 3 and 4). In one of two trials, planting stratified seed in May resulted in superior stands compared with the May planting of nonstratified seed (Tables 3 and 4). During the third trial (Table 4), both May plantings resulted in poor stand establishment. Poor stands observed from the positive control were associated with prolonged dry soil conditions after planting (only 6 mm during the first 15 d after planting).
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Table 2 The influence of planting treatment and preplanned treatment contrasts on the statistical significance of stand and herbage mass comparisons from Trial 1 established in 1994–1995 in Raleigh, NC***
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Table 3 The influence of planting treatment and preplanned treatment contrasts on the statistical significance of stand and herbage mass comparisons from Trial 1 established in 1995–1996 in Raleigh, NC
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Table 4 The influence of planting treatment and preplanned treatment contrasts on the statistical significance of stand and herbage mass comparisons from Trial 1 established in 1996–1997 in Raleigh, NC
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Second Season Stand Carry-over Effects
Soil temperatures were not available from the experimental sites. However, it is likely that recorded air temperatures were perhaps more relevant to stratification effects than soil temperatures recorded from a standard depth of approximately 10 cm because seeds were planted relatively shallow (2 cm). A summary of air temperature data and moisture are presented in Fig. 1 and Table 1. Trends over all three trials indicated that a large proportion of seeds from winter plantings germinated within 6 mo, which resulted in relatively few newly emerged seedlings in the second spring (mean = 1.7 seedlings m-2). Spring plantings (March, April, and May), however, exhibited a marked trend toward carry-over germination (mean = 8.8 seedlings m-2). In the November through February plantings, only 3.5 to 33% of the total plants present in the spring of the second season were seedlings while 57 to 67% of the plants were seedlings from carry-over seeds in the spring plantings (March–April). In some cases, this effect was dramatic, with newly emerged seedlings increasing stands three-fold by the spring of the second season (Tables 2–4). It seemed likely that these carry-over seeds did not receive sufficient climatic effects for stratification in the season immediately after planting; however, they germinated after experiencing wet, cool temperatures during the second winter. This trend was particularly strong during the spring of 1996 when March through April plantings averaged more than 10 newly emerged seedlings m2 compared with similar plantings in 1997 and 1998 that averaged 3.5 seedlings m2. Temperature data indicated that the fall through winter period of 1995 through 1996 was the coldest recorded during the trials, with the minimum temperature trend at or below 0°C between December and February (Fig. 1 and Table 1). Ahring and Frank (1968) reported similar carry-over effects from gamagrass seeds planted in March. They also reported successful results with October through December plantings, but no data were presented. The planting rate in our trials, 11.2 kg ha-1, is equivalent to about 32 seeds m2. Therefore, total plants established from various planting-date treatments during the three trials represented about 16 to 58% of the seeds initially planted.
Mature Stands
In contrast to the initial stands, the stands measured at the end of the second growing season were much improved. This result indicated that dormant seeds continued to germinate and become established during the second season of growth. Even in the negative control (May, unstratified) average stand counts were above 3 plants m-2 by the end of the second season (Tables 3 and 4). Nevertheless, the general response to the planting-date treatments was consistent with the trends observed for the initial stand counts. In all three trials, winter planting treatments contained significantly more plants m-2 than the positive control (May, stratified) or the unstratified spring (March, April, and May) plantings (Tables 2–4).
Herbage Mass
During the initial season of growth, all treatments were vigorously invaded by weedy annual grasses including, large crabgrass [Digitaria sanguinalis (L.) Scop.], fall panicum (Panicum dichotomiflorum Michaux), yellow foxtail [Setaria lutescens (Weigel) F.T. Hubb.], goosegrass [Eleusine indica (L.) Gaertner], and barnyardgrass [Echinochloa crusgalli (L.) Beauv.]. In all trials, no herbage yields were taken during the initial growing season. After making stand counts, growth that had accumulated during the first season was clipped and removed or burned following the first killing frost. In all three trials, herbage mass from harvests taken in the second and third year following establishment generally reflected differences observed for stand (plants m-2) among the treatments (Tables 2–4). Herbage yields from March and April plantings were severely reduced (43–75%) in the second season after establishment relative to the winter (November–February) plantings, but this reduction diminished considerably by the third season (17–26%) due to size compensation by the established plants.
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Conclusions
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Winter (November–February) planting of eastern gamagrass in the southern Piedmont can be a better alternative to May planting of stratified or nonstratified seeds. In our trials, stands established from winter plantings were equal or superior to May plantings and were consistently superior to stands established from March or April plantings. In two of three trials, initial stands from November and December plantings were superior to stands from January and February plantings. Planting in fall and winter gives producers added flexibility in removing these operations from competition with the many routine farm operations normally occurring during spring.
Winter establishment is a method that relies on a high level of dormancy in the seeds. Having specific knowledge of the condition of each seedlot through rag doll, tetrazolium, and stratification germination tests is an essential prerequisite to making November through February planting a simple and effective method for the establishment of eastern gamagrass in the southern Piedmont because it gives a precise estimate of the degree of dormancy present.
Received for publication September 7, 1999.
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REFERENCES
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- Ahring R.M., Frank H. Establishment of eastern gamagrass from seed and vegetative propagation. J. Range Manage. 1968;21:27-30.
- Anderson R.C. Aspects of the germination ecology and biomass production of eastern gamagrass (Tripsacum dactyloides L.). Bot. Gaz. 1985;146:353-364.
- Anderson R.C., Libreto A.E. Occurance of fungal-inhibiting Pseudomonas on caryopses of Tripsacum dactyloides L., and its implication for seed survival and agricultural application. J. Appl. Bacteriol. 1986;61:195-199.
- Association of Official Seed Analysts (AOSA). Tetrazolium testing hanbook for agricultural seeds. Contrib. 29 to the Hanb. on Seed Testing. AOSA, Lincoln, NE. Association of Official Seed Analysts (AOSA) 1994. Rules for testing seeds. J. Seed Technol. 1970;16:22-23.
- Blomquist H.L. The grasses of North Carolina. Durham, NC: Duke Univ. Press, 1948.
- Burns J.C., Fisher D.S., Pond K.R. Quality of eastern gamagrass compared with switchgrass and flaccidgrass when preserved as hay. Postharvest Biol. and Biotechnol. 1996;7:261-269.
- Burns J.C., Fisher D.S., Pond K.R., Timothy D.H. Diet characteristics, digesta kinetics, and dry matter intake of steers grazing eastern gamagrass. J. Anim. Sci. 1992;70:1251-1261.[Abstract]
- Chamblee, D.S., and J.T. Green. 1995. Production and utilization of pastures and forages in North Carolina. North Carolina Agric. Res. Serv. Tech. Bull. 305.
- Fine G.L., Barnett F.L., Anderson K.L., Lippert R.D., Jacobson E.T. Registration of `Pete' eastern gamagrass. Crop Sci. 1990;30:741-742.[Free Full Text]
- Milby T.H., Johnson F.L. Variation in response to stratification and ageing in gamagrass seeds from different geographic locations. Seed Sci. Technol. 1989;17:413-419.
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ABSTRACT
INTRODUCTION
