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Effect of bermudagrass height on clover establishment.

In the hill lands of the western mid-South, many livestock producers rely on bermudagrass for pasture from May through September. Interseeding cool-season forage legumes into these pastures in the autumn can extend the grazing season. For example, white clover begins producing forage in March, peaking in production in mid-April to mid-June, and has a small peak in forage production from mid-October to mid-November (Ball et al., 1991). Cool-season legumes are also higher in forage quality compared with warm-season grasses and benefit the environment by reducing the need for N fertilizers.

Prior to seeding legumes in autumn, producers frequently graze bermudagrass pastures to remove as much canopy residue as possible and delay initiation of the winter feeding period. This practice leaves variable bermudagrass heights that may interfere with clover establishment. The objective of this research was to evaluate the effect of bermudagrass stubble height on crimson and white clover establishment in the hill lands of the western mid-South.

Materials and Methods

This study was conducted at the USDA-Agricultural Research Service, Dale Bumpers Small Farm Research Center, near Booneville, AR, on an Enders silt loam (clayey, mixed, thermic Typic Hapludults) soil. The cultivars used were common (cultivar name unknown) and Regal white clover and Dixie and Tibbee crimson clover. The common white clover was a small to intermediate type. Each legume cultivar was seeded into Tifton44 bermudagrass sod. The 16 bermudagrass main plots (7.2 by 7.6 m), arranged in a Latin square design, were mowed to either 2-, 7-, 12-, or 17-cm heights and the residue removed. Main plots were divided into four subplots (1.8 by 7.6 m) into which cultivar treatments were randomly assigned. Each cultivar was seeded at 7000 pure live seed/plot. Planting was accomplished with a beltcone type planter with eight double disk openers and press wheels spaced 20 cm apart (Kincaid Equip. Manuf., Haven, KS)(1). This is equal to seeding crimson clover at 25.0 kg/ha and white clover at 2.8 kg/ha. Seeds were inoculated with Rhizobium (LiphaTech, Inc., Milwaukee, WI) specific for each clover species at an equivalent rate of 8 g Rhizobium-peat medium per kilogram of seed. Sugar water was used to stick Rhizobium to the seed.

Establishment Year

This study consisted of two experiments planted on 15 Sep. 1992 and 1993. The experiment seeded in 1993 was adjacent to the experiment seeded in 1992. On 20 May 1993 and on 1 June 1994, the clover ground cover (percentage of ground surface covered by the legume species) of each plot was visually estimated. Each plot was rated independently by two individuals and their scores averaged. Visual estimates have been used to measure pasture and range composition (Grant, 1981). Percentage data were not transformed prior to analysis (data residuals were distributed normally). A covariance analysis with bermudagrass height as a concomitant variable and percentage legume ground cover as the dependent variable was performed on the data using PROC GLM (SAS Institute, 1988). Regression equations were generated for predicting percentage legume cover as the dependent variable and bermudagrass height as the independent variable using PROC REG (SAS Institute, 1988).

To estimate the reseeding ability of crimson clover, a 0.09- in 2 area was harvested from each plot upon maturity. Seeds were threshed by hand, cleaned using an air column separator, and weighed. Reseeding was not estimated for white clover because it generally regenerates vegetatively from year to year in this area. A hay crop was removed from each experiment about 25 July. Bermudagrass was cut to a height of 2 cm. Bermudagrass regrowth after harvest was minimal, generally less than 7 cm, due to reduced rainfall in August and September of each year.

Regeneration Year

Crimson clover was allowed to naturally regenerate from seed by allowing the plants to mature and drop seed onto the ground. Tillage (light disking) was not used to enhance establishment of crimson clover on bermudagrass sod due to the size and arrangement of the plots. White clover was allowed to regenerate from vegetative propagation. On 1 June 1994 and 1995, the percentage clover ground cover in the first year after seeding (regeneration year) was estimated. Plots were evaluated and analyzed by the same procedures as in the establishment year.

Results and Discussion

Establishment Year

Differences in percentage of legume ground cover were attributed to year of establishment, bermudagrass height, legume species, cultivars within species, and species of legume by height of bermudagrass interactions. It was not surprising to find differences between years for clover establishment. The seeding in 1992 resulted in 62% ground cover compared with 76% cover in 1993. In both years, there was enough rainfall to initiate germination and early seedling growth, but after 23 Sep. 1992 there was a 5-wk dry period which likely killed some seedlings. There was a linear response in percentage legume ground cover with increasing bermudagrass heights. Regression equations for percentage legume ground cover (Y) based on bermudagrass height (x) for the cultivars were common white clover, Y = -2.1x + 71.5 (F = 11.7; DF = 1, 30; P [is less than] 0.001); Regal, Y = -2.0x + 80.4 (F = 8.4; DF = 1, 30; P [is less than] 0.007); Dixie, Y = -0.3x + 92.4 (F = 0.96; DF 1, 30; P [is less than] 0.33); and Tibbee, Y = -0.6x + 95.6 (F 5.0; DF = 1, 30; P [is less than] 0.03). The linear decrease in legume ground cover with increasing bermudagrass heights was possibly due to a lack of good soil-seed contact caused by the inability of seeding equipment to cut through the residue to achieve proper seed placement. Similarly, shading in plots may reduce stand establishment because of decreased sunlight reaching the soil, and taller bermudagrass may also provided a better habitat for insects that feed on legume seedlings.

Crimson clover establishment (89%) was greater than white clover (51%; Table 1) when averaged across years, bermudagrass height, and cultivars. The larger crimson clover seed likely exhibited greater seedling vigor compared to the smaller white clover seed. Cultivars of crimson clover had equal ground cover percentages (89%), whereas, a difference occurred between white clover cultivars. Regal white clover averaged 56% ground cover compared to 46% for common white clover (Table 1). Regal white clover was likely better adapted for use in the hill-lands than the common white clover. Bermudagrass height had little effect on establishment of crimson clover, but a significant effect on white clover. Regression equations for percentage legume ground cover based on bermudagrass height for the species were white clover, Y = -2.1x + 76.0 (F = 19.3; DF = 1, 62; P [is less than] 0.001) and crimson clover, Y = -0.43x + 94.0 (F = 4.9; DF = 1, 62; P [is less than] 0.03). Seed size and seedling vigor differences between the two species may account for the interaction. In denser bermudagrass canopies once the seeds germinate, crimson clover may have a better chance of survival because of its more upright growth habit and its ability to compete for sunlight.

Table 1. Mean percent ground cover in establishment year and regeneration year of crimson clover (CC) and white clover (WC) established into bermudagrass sod.
                             Establishment       Regeneration
                             year([dagger])   year([double dagger])

Variable        Level            CC    WC      CC         WC
Year              1              84    44      70         41
                  2              93    58      54         47
Bermudagrass      2              94    75      64         56
   height (cm)    7              93    60      64         46
                 12              87    43      53         40
                 17              82    28      68         33
Species                          89    51      62         44
Cultivar    Dixie CC/Regal WC    89    56      64         62
           Tibbee CC/common WC   89    46      60         25




([dagger]) LSD (0.05) = 17.5 for the establishment year.

([double dagger]) LSD (0.05) = 20.3 for the regeneration year.

Regeneration Year

Significant effects in the regeneration year were similar to the establishment year with the addition of year by species interactions. White clover ground cover remained fairly steady with 44% ground cover compared to 51% in the establishment year. Regal white clover slightly increased in percentage ground cover from 56% in the establishment year to 62% in the regeneration year. Common white clover declined from 46% in the establishment year to 25% in the regeneration year. Cover percentages for crimson clover decreased from 89% in the establishment year to 62% in the regeneration year. Reproduction was not a problem for the crimson clover cultivars.

Averaged across regeneration years, Dixie averaged 984 kg seed/ha and Tibbee averaged 939 kg seed/ha. Lower ground cover percentages in the regeneration years are more likely due to the amount of seed that over-summered and seed quality. In the summer of 1993 (1 June-15 September), each significant rainfall event was followed by 1 or 2 wk of drying. In 1994, rainfall was relatively continuous without drying periods. During saturated soil conditions, soft seeds may have germinated or decayed in the ground. Seed decay has been observed in subterranean clover with saturated soil conditions (Fairbrother and Rowe, 1995). Hoveland and Elkins (1965) observed 89% seed germination for Dixie crimson clover after 4 d in a diurnal cycle of 38 [degrees] C for 8 h and 21 [degrees] C for 16-h. These temperatures are similar to the summer diurnal temperature in the area.

Crimson clover seed size may also affect regeneration. Crimson clover seed used in the establishment year averaged 5.12 mg/seed with 82% germination and 3% hard seed compared to 3.33 mg/seed with 80% germination and 11% hard seed in the regeneration year. Improved establishment and increased dry matter production would be expected for larger seed sizes. Seed size and seedling vigor are correlated in crimson clover (Knight, 1985).

Conclusions

The height of bermudagrass at planting affects the establishment of white clover (small seed) more than crimson clover (large seed). The shorter the bermudagrass height at planting the better the establishment of the legume. This research demonstrated that for every 5-cm increase in bermudagrass height there was approximately a 2% reduction in ground cover for crimson clover and 10% for white clover. Stand regeneration was constant for white clover, but crimson clover stands declined in the regeneration year. In years when soils remain wet for extended time periods during the summer, it would be advisable to lightly reseed crimson clover to maintain the stand.

Acknowledgments

I thank T.Y. Horton, USDA-ARS, Booneville, AR, for her excellent assistance during this study.

(1) Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by USDA or the University of Arkansas and does not imply approval to the exclusion of other suitable products.

References

Ball, D.M., Hoveland, C.S., and Lacefield, G.D. 1991. Southern for ages. Potash & Phosphate Institute and Foundation for Agronomic Research, Atlanta, GA.

Fairbrother, T.E., and D.E. Rowe. 1995. Temperature and soil water effects on dormancy and mortality of subterranean clover seed. Agron. J. 87:252-257.

Grant, S.A. 1981. Sward components. p. 7192. In J. Hodgson et al. (ed.) Sward measurement handbook. Brit. Grassi. Soc., Grassi. Res. Inst., Hurley, Maidenhead, Berkshire, UK.

Hoveland, C.S., and D.M. Elkins. 1965. Germination of arrowleaf, ball, and crimson clover varieties to temperature. Crop Sci. 5:244-246.

Knight, W.E. 1985. Crimson clover. p. 491-502. In N.L. Taylor (ed.) Clover science and technology. ASA, CSSA, SSSA. Madison, WI.

SAS Institute. 1988. SAS/STAT user's guide, release 6.03 ed. SAS Institute, Cary, NC.

T. L. Springer(*)

USDA-ARS, Dale Bumpers Small Farm Res. Center, 6883 South State Highway 23, Booneville, AR 72927-9214. Joint contribution of USDA-ARS and the Univ. of Arkansas Agric. Exp. Stn. Received 12 Nov. 1996. T. L. Springer, Corresponding author (tlspring@ag.gov).
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Author:Springer, T.L.
Publication:Crop Science
Date:Sep 1, 1997
Words:1946
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