PDF version
for printing

Impact
Statement

© 2008 Plant Management Network.
Accepted for publication 24 January 2008. Published 29 April 2008.

Influence of Grazing Frequency on Cynodon Grasses Grown in Peninsular Florida

P. Mislevy, Range Cattle Research and Education Center, Ona, FL 33865-9706; O. P. Miller, Okeechobee County Extension Service, Okeechobee, FL 34972-2303; and F. G. Martin, retired, Statistics Department, University of Florida, Gainesville 32611-0840

Corresponding author: Paul Mislevy. pmislevy@ufl.edu

Mislevy, P., Miller, O. P., and Martin, F. G. 2008. Influence of grazing frequency on cynodon grasses grown in peninsular Florida. Online. Forage and Grazinglands doi:10.1094/FG-2008-0429-01-RS.

Abstract

Bermudagrass and Stargrass are among the most important of the warm-season perennial grasses used for livestock grazing and hay production in warmer regions of the world. The purpose of this experiment was to test four stargrasses (Cynodon nlemfuensis Vanderyst var. nlemfuensis) and four bermudagrasses (C. dactylon L. Pers.) at four grazing frequencies (GF) for dry biomass (DB) yield, nutritive value, and persistence. Experimental design was a split-plot arrangement of a randomized complete block with three replications. The main plot consisted of GF (2, 4, 5, and 7 weeks) and grass entries (cvs. Stargrass 2000, Florona, Okeechobee, and Ona Pasture No. 2 stargrass; Bermudagrass 2000, Jiggs, World Feeder, and Tifton 85 bermudagrass) as subplots. There was a grass entry × GF interaction for DB yield during the warm-season. Decreasing GF from 2 to 7 weeks resulted in a linear increase in DB yield and generally a linear decrease in CP and IVDOM. Bermudagrass 2000 and Jiggs bermudagrass were generally the two highest yielding entries at GF of 2 (3.4 and 3.1), 4 (6.5 and 5.7), 5 (6.9 and 7.9), and 7 weeks (9.3 and 8.2 ton/acre), respectively, and most persistent. Delaying GF from 2 to 7 weeks decreased CP and IVDOM by 39 and 22%, respectively. Winter forage production was highest for Bermudagrass 2000 and Jiggs and averaged 1.1 ton/acre when harvested after 12 weeks regrowth.

Introduction

To provide commercial growers with forage grasses that produce well throughout the year, there is a constant need for screening and testing new germplasm under grazing. Temperature, rainfalls, and edaphic conditions all indicate which forages can be grown within a specific location.

In peninsular Florida, high temperatures, humidity, and wet soils are commonplace on flatwood pastures especially during long days (April-September). In addition, during short days (October-March) moisture is generally limited averaging 2.5 inch/month and average low temperatures are 55°F (4). Cold fronts periodically traverse the state and may drop temperatures to 21°F. This makes cool season forage production extremely important in Florida and subtropical regions of the world. Consequently only tropical forages (C₄ plants) are productive and persistent during warm, wet conditions. However, most tropical forages are not productive during the cool season when frosts and freezes occur (6).

When selecting perennial forage grasses for hay and/or grazing, persistence is an important variable to consider. Regardless how great the production and nutritive value of an entry, if a forage species does not persist it is of little value to a commercial producer. Approximately 70% of Florida’s pastures are seeded to bahiagrass (Paspalum notatum Flugge) which are persistent and tolerant to variations in edaphic and environmental conditions. However, these grasses produce little forage during short days (10), and are susceptible to mole crickets (Scapteriscus spp.) (1). The number of perennial grass choices that produce high biomass yields and have good nutritional value are limited.

The purpose of this study was to use the mob-grazing technique to compare eight Cynodon entries at 2-, 4-, 5-, and 7-week GF for warm-season dry biomass (DB) production, persistence, and nutritive value and influence of grass entry on cool-season DB yield.

Testing Cynodon Grasses at Four Grazing Frequencies

This experiment was established during the summer of 2001 on a sandy siliceous, hyperthermic Ultic Alaquod (Pomona fine sand) and conducted from 2002 to 2004 at the University of Florida (UF), Range Cattle Research and Education Center (RCREC), Ona, FL (longitude 82°55’W, latitude 27°26’N, altitude 80 ft). The experimental design was a randomized complete block on a split-plot arrangement with three replications. Grazing frequency (2, 4, 5, and 7 weeks) was the main plot and grass entries (Bermudagrass 2000, Jiggs, World Feeder, and Tifton 85 bermudagrasses; Stargrass 2000, Florona, Okeechobee, and Ona Pasture No. 2 stargrass) as subplots. The sources of grasses were: Bermudagrass 2000, Stargrass 2000, Florona, and Ona Pasture No. 2 stargrass (UF, RCREC, Ona, FL) Jiggs (Texas A & M University), World Feeder (Oklahoma, farmer), Tifton 85 (USDA-ARS Tifton, GA), and Okeechobee stargrass (Okeechobee, FL, farmer). Each subplot measured 25 by 25 ft. Whole plots were arranged in three randomized complete blocks. Florona stargrass and Tifton 85 were used as commercial standards. Test entries were planted on a well prepared, weed-free, moist seedbed. All vegetative material was planted from well-fertilized, mature, vegetative above ground stem material at a rate of 1500 lb/acre (7). All grasses were fertilized following emergence with N-P₂O₅-K₂O at 50-30-60 lb/acre, respectively, plus Cu, Zn, Mn, and Fe (sulfate form) at 1.5 lb/acre, and B at 0.15 lb/acre and S at 3.0 lb/acre. Thirty five days after planting, N was applied at 50 lb/acre. A 2.0-ft border surrounding each subplot was maintained free of vegetation using glyphosate (isopropylamine salt 4 lb/gal of N-phosphonomethyl glycine), at a 2-qt/acre solution applied at 15 gal/acre. Ammonium sulfate (sprayable) was added to the water at a rate of (17 lb/100 gal) prior to the addition of glyphosate.

In the spring of each year, N-P₂O₅-K₂O at 0-30-60 lb/acre plus Cu, Zn, Fe, and Mn (sulfate form) at 1.5 lb/acre, B at 0.15 lb/acre, and S at 2.6 lb/acre were applied. A total of 200 lb of N per acre was applied annually, with 55 lb/acre applied April-May, July-August, October, and 35 lb/acre applied in September. Soil Ca was 627 and Mg was 105 ppm, respectively, and pH was 6.3.

The grazing season extended from May to December 2002, April to December 2003, and May to November 2004. Prior to each grazing an area of 16 ft² was harvested from each subplot to a stubble height of 3.0 inch to determine DB yield and nutritive value. Dry biomass yield was monitored during the warm (May-December) and cool-season (December-March) over a 3 year period. Each main plot was fenced, allowing cattle to randomly graze all entries. Thirteen cross-bred yearling steers (Boss sp., 95 head/acre, about 800 lb) were allowed to consume (mob graze) forage to approximately 3 to 5 inch stubble within a 1-to 3-day period. Cattle were then removed from each main plot and a 2.0 by 20 ft area was staged again at 3.0 inch to remove residue from each subplot. This area was marked and then sampled for DB yield and forage nutritive value at the next scheduled sampling. This strip was rotated to a new sample site in each subplot for residue removal and future sampling for DB yield and nutritive value. Percentage ground cover occupied by common bermudagrass (CB) [C. dactylon (L) Pers. var. dactylon] was estimated prior to the start of the study and in the fall of each year.

On 15 December of each year grass plots were staged back to a 3.0 inch stubble and fertilized with N at 50 lb/acre. Cool season forage DB yields were determined after 12 weeks from 15 December to March 2003, 2004, and 2005. Crude protein concentration and IVDOM was documented after June - July, August-September, October, and November-December 2002 and April-May, August, and October 2003.

Forage samples were dried at 140°F, ground, using a 0.03937 inch (1 mm) stainless steel screen, and analyzed for total N concentration (2,3). Crude protein concentration was calculated as 6.25 × N. Additionally, IVDOM content was determined for forage samples by the two-stage procedure of Tilley and Terry (13) modified by Moore and Mott (12).

Dry biomass yield, CP, and IVDOM data were analyzed using PROC GLM (SAS Institute Inc., Cary, NC) with the model statement appropriate for a split-plot design, year, and sampling date. Year was significant in the model therefore was analyzed separately. For the non-significant interactions, entry differences were examined using the Waller-Duncan k-ratio test. To investigate the effect of GF, polynomial regression equations were estimated. To investigate entry mean differences within the significant interaction Duncan’s Multiple Range Test was used for each GF. A significant level of 0.05, 0.01, and 0.001 percent was used through out the paper. To obtain a long-term effect over environments, data were pooled over years for DB yield.

Dry Biomass Yield and Persistence

Total DB yield was analyzed for each year. Significant differences due to entries and GF were found each year. For 2002 and 2003 these differences were independent. In 2004, however the entry × GF interaction was significant (P ≤ 0.01).

Bermudagrass 2000 and Jiggs produced greatest total DB yields in 2002 averaging 7.0 and 6.9 ton/acre, respectively, when compared with all other Cynodon grasses tested, except Florona stargrass (Table 1). In 2003 Bermudagrass 2000 continued to out yield all other grasses, except Jiggs and Florona. Stargrass 2000 always produced a lesser yield, mainly because of an open (low tilling, less dense) plant-growth pattern. Delaying GF from 2 to 7 weeks during both 2002 and 2003 resulted in a linear increase in DB yield. Yields increased from 3.2 to 8.8 ton/acre, during 2002 and from 2.7 to 7.9 ton/acre in 2003 (Fig. 1). Data indicated about a 1.0 ton/acre increase in total seasonal yield with each week delay in harvest. This type of increase is routine for tropical grasses when GF is delayed (8,9,11). In 2004 grass entries interacted with GF. At the 2-week GF dry biomass yield averaged 3.3 ton/acre with no differences found between entries (data not shown). Stargrass 2000 was not sampled due to stand loss at the 2-week GF. Delaying harvest from 2 to 4 weeks increased DB yield 66% (3.3 to 5.5 ton/acre). Greatest yield at the 4-week GF was 6.9 ton/acre by Bermudagrass 2000, which was not different from Jiggs (6.1 ton/acre) or Tifton 85 (5.6 ton/acre). Delaying harvest from 4 to 5 weeks increased yield by an additional 16%, with Bermudagrass 2000 and Jiggs, Florona, and Okeechobee stargrass among the greatest yielders. Delaying harvest from 5 to 7 weeks had little effect on average biomass yield, however Bermudagrass 2000 and Tifton 85 bermudagrass increased in yield by 10 and 23%, respectively. The greatest yield increase was between 2 and 4 weeks (66%) and 2 and 5 weeks (93%).

Table 1. Influence of grass entry on total seasonal dry biomass yield during 2002 and 2003.

 * Harvest period 6 June to 15 December 2002; 7 April to 24 November 2003.

**Means within columns followed by different letters are different (P ≤ 0.05 Waller-Duncan k-ratio Test).

Fig. 1. Effect of grazing frequency (weeks) on total seasonal dry biomass yield during 2002 and 2003.

Dry biomass yields were pooled over 3 years to obtain long term effects of environments on yield. There were no entries × year interaction (P ≥ 0.05). There was, however, a significant interaction (P ≤ 0.05) between entries and GF (Table 2). There was an overall increase in DB yield of 66, 22, and 23% as GF was delayed from 2 to 4, 4 to 5, and 5 to 7 weeks. No difference was obtained between entry means when sampled at the 2-week GF except Stargrass 2000, which was lesser (P < 0.05). Forage sampling at the 4-week GF resulted in Bermudagrass 2000 producing greater yields than all other entries except Jiggs. Delaying sampling frequency to 5 and 7 weeks resulted in Bermudagrass 2000 and Jiggs producing greatest yields. At the 5-week grazing frequency Jiggs yielded higher (P < 0.05) DB averaging 7.9 ton/acre and at the 7-week frequency Bermudagrass 2000 (9.3 ton/acre) produced the greatest yield. These yield data were greater than those presented in an earlier study testing stargrass, bermudagrass, rhodesgrass (Chloris gayana Kunth), etc. (11).

Table 2. Influence of grass entry × grazing frequency on total dry biomass yield pooled over 3 year (2002-2004).

 * Means within columns followed by different letter(s) are different (P ≤ 0.05, Duncans Multiple Range Test).

Grasses in this study were allowed to grow during the cool season and yields were averaged over three years. Bermudagrass 2000 and Jiggs were the greatest yielding entries averaging 1.2 and 1.07 ton/acre with Tifton 85 among the lesser yielders averaging 0.45 ton/acre (10).

Four grasses (Bermudagrass 2000, Jiggs, Tifton 85, and Florona stargrass) tested in this study had less than 2% weeds (CB) consequently these grasses averaged 98% purity over all treatments after 3 years of grazing. Stargrass 2000 was not able to persist under the intensive mob grazing treatments resulting in ~64% weeds. Because of its poor persistence this entry will be dropped from further testing, regardless of its high nutritive value. In general, weed ground cover decreased as grazing frequency decreased. For each week GF was delayed, weed ground cover decreased by 3.2 percentage units (data not shown).

Forage Nutritive Value

Differences among entries for CP and IVDOM were found for every sampling date except for August-September 2002 CP. There were significant entry × GF interactions for both 2002 and 2003 responses.

Grass entry differences for CP at five sample dates during 2002 and 2003 were independent of GF. Average CP for June-July of 2002 was 15.9% with little difference between entries (Table 3). Crude protein concentration for August-September samples averaged 12.7% with no difference among entries. The lower CP concentration for this mid-summer sampling may be a reflection of excessive soil moisture when the 5 August N was applied. Nearly 6.0 inches of rainfall fell the four days prior to fertilizer application and another 6.0 inches over the next 4 weeks (5).

Table 3. Effect of grass entry on CP concentration for sample dates during 2002 and 2003.

 * Means within columns followed by different letter(s) are different (P ≤ 0.05 Waller-Duncan k-ratio Test).

October 2002, and April-May, and August 2003 harvested forage all had adequate CP concentration for beef cattle, averaging 14.4, 14.4, and 17.3%, respectively. Research over years has demonstrated little difference in CP concentration among perennial grasses, of the same genera, when fertilized with a similar N rate and harvested at a similar physiological stage (7,9,11).

Crude protein concentration of grass entries harvested during November-December, 2002 interacted with GF. Protein concentration decreased 2.5% per week as GF was delayed from 2 to 7 weeks (data not shown). However, little change in CP concentration was found between grass entries. Jiggs, World Feeder, and Tifton 85 bermudagrasses contained the lowest CP concentration averaging 23.6% at the 2-week GF. The forage CP concentration decreased from 22.0 to 13.7 % as GF was delayed from 4 to 7 weeks, in addition no difference (P ≥ 0.05) in CP were observed among entries averaging 22.0, 20.0, and 14.0% when harvested at the 4-, 5-, and 7-week GF, respectively.

Grass entries also interacted with GF for CP during October 2003. Protein for this sampling date was lesser by 5.5, 2.5, and 3.3% for the 2-, 4-, and 5-week GF, respectively, when compared with the November-December 2002 harvest and only decreased by 1.2% per week as GF was delayed from 2 to 7 weeks. There is no entry that had the greatest CP concentration at all GF, although Florona stargrass did have higher or equal CP.

In vitro digestible organic matter of grass entries for June-July 2002 and April-May 2003 were independent of GF. During both sampling periods Tifton 85 bermudagrass and stargrass 2000 had the greatest IVDOM content (Table 4). Average IVDOM content for the four stargrass entries was always higher (61.8 and 60.2%) when compared with the bermudagrass entries (57.9 and 58.4%) for the June-July and April-May sampling, respectively. Digestibility of grass entries sampled during August-September, October, and November-December 2002 all interacted with GF. As fall approached forage nutritional values tended to increase over all GF and entries averaging 57.9, 61.0, and 65.8% for the August-September, October, and November-December sampling dates. This occurs because plants growing in the cool fall produce fewer and larger cells with thinner walls incorporating less soluble carbohydrates into cell structure. Studies conducted by Wilson (14) indicated that high temperature reduced digestibility and increased the cell wall content of recently expanded leaves of both tropical and temperate grasses. As shown in numerous previous studies IVDOM always decreases as GF is delayed from 2 to 7 weeks (8,9,11). Harvesting stargrass at the 2-week GF (74.6%) and 4-week GF (64.6%) during the fall and winter period, nearly always produced greater IVDOM than bermudagrass, which averaged 67.6% and 62.3% for the 2- and 4-week sampling period, respectively, during the same time of season.

Table 4. Influence of grass entry on in vitro digestible organic matter during 2002 and 2003.

 * Means within columns followed by different letter(s) are different (P ≤ 0.05 Waller-Duncan k-ratio Test).

However, as GF was delayed to 5- and 7-week IVDOM between the stargrasses and bermudagrasses tended to be similar averaging 58.9% for stargrass and 58.2% for bermudagrass at the 5-week and 53.4 for stargrass and 53.1% for bermudagrass at the 7-week sampling date. One reason for the lesser overall IVDOM for the bermudagrasses in this study may be due to the World Feeder entry. This entry was nearly always lower (P ≤ 0.05) than most other entries tested at nearly all GF averaging 52.2, 55.7, and 58.9 for the August-September, October, and November-December 2002 sampling, respectively, possibly due to the higher lignin content. During this same sampling period, Bermudagrass and stargrass averaged 58.3 and 59.1% during August-September, 61.3 and 62.1% during October, and 66.0 and 67.5% during November-December, respectively. Stargrass 2000 and Tifton 85 bermudagrass were the two grass entries with generally the greatest IVDOM content regardless of GF or sampling date. However, due to its sparse growth pattern and lack of persistence Stargrass 2000 may never be released as a cultivar. Because of its high nutritive value this entry may be used in a breeding program. In 2003 the August and October sampling dates for IVDOM interacted between grass entry and GF. There was an overall decrease in IVDOM as GF was delayed from 2 weeks (65.5%) to 7 weeks (52.9%) for the August sampling. The influence of GF for the October sampling generally followed a quadratic pattern for most grass entries. The average IVDOM for the bermudagrasses and stargrasses was 54.7 and 63.5%, respectively at the 2-week GF. This increased to 58.8, 63.0, 61.2, and 61.9% for the bermudagrass and stargrass, respectively at 4- and 5-week GF. After the 7-week GF IVDOM averaged 48.3 and 48.5% which appears normal after 7 weeks for Cynodon grasses. The poor nutritive value forage after the 2- and 4-week GF during October may have been due to the timing of N application which was applied one week prior to harvest of the 2- and 4-week GF. This short interval between N application and harvest does not allow adequate time for the plants to develop new tillers, consequently the digestibility is low for tillers developed during the low fertility plant growth phase. Similar to 2002, World Feeder always had significantly (P ≤ 0.05) lesser amounts of IVDOM concentration than Tifton 85 during 2003.

In conclusion, Bermudagrass 2000, Jiggs bermudagrass and Florona stargrass are among the best yielding grasses in this experiment during the warm season averaging 6.5, 6.2, and 5.9 ton/acre, respectively, when averaged over all GF. World Feeder produced the lowest yields among the bermudagrasses averaging 5.1 ton/acre. Bermudagrass 2000 and Jiggs, were most productive during short days (cool-season) averaging 1.2 and 1.07 ton/acre, respectively with all other grasses producing about 40% less forage mass. Bermudagrass 2000, Jiggs, Tifton 85, and Florona stargrass were also most persistent averaging less that 2% weeds after three years of grazing. Weed content decreased in all grass entries as GF was delayed, due to greater desirable grass competition. Forage nutritive value for Bermudagrass 2000, Jiggs, and Florona averaged 16.3% CP and 59.3% IVOMD.

Acknowledgment

This research was supported by the Florida Agricultural Experiment Station.

Literature Cited

1. Adjei, M. B., Crow, W. T., Smart, Jr., G. C., Frank, J. H., and Leppla, N. C. 2001. Biological control of pasture mole crickets with nematodes. Online. Florida Coop. Ext. Serv., IFAS, Univ. of Florida, Gainesville.

2. Gallaher, R. N., Weldon, O. C., Futral, J. G. 1975. An aluminum block digester for plant and soil analysis. Soil Sci. Soc. Am. Proc. 39:803-806.

3. Hambleton, L. G. 1977. Semiautomated method for simultaneous determination of phosphous, calcium, and crude protein in animal feeds. J. Assoc. Off. Anal. Chem. 60:845-854.

4. Kalmbacher, R. S. 2002. Climatalogical Report 2001. Range Cattle Res. and Educ. Center, Res. Rpt. RC-2002-1. Univ. of Florida, Gainesville.

5. Kalmbacher, R. S. 2003. Climatological Report 2002. Range Cattle Res. And Educ. Center, Res. Rpt. RC-2003-1. Univ. of Florida, Gainesville.

6. Kalmbacher, R. S. 2004. Climatological Report. 2003. Range Cattle Res. And Educ. Center, Res. Rpt. RC-2004-1 Univ. of Florida, Gainesville.

7. Mislevy, P., Brown, W. F., Kalmbacher, R. S., Dunavin, L. S., Judd, W. S., Kucharek, T. A., Ruelke, O. C., Noling, J. W., Sonoda, R. M., and Stanley, R. L., Jr. 1995. Florakirk bermudagrass. Florida Agric. Exp. Stn. Circ. S395. Univ. of Florida, Gainesville.

8. Mislevy, P., Martin, F. G., Burton, G. W., and Santos, L. F. 1996. Influence of grazing frequency on production and quality of Paspalum, Brachiaria, Setaria grasses. Soil Crop Sci. Soc. Florida Proc. 55:97-103.

9. Mislevy, P., and Martin, F. G. 1998. Comparison of Tifton 85 and other Cynodon grasses for production and nutritive value under grazing. Soil Crop Sci. Soc. Florida Proc. 57:77-82.

10. Mislevy, P., Sinclair, T. R., and Ray, J. D. 2001. Production and quality of warm season perennial grasses as influenced by extended day length. Cattle and Forage Field Day, Range Cattle Res. and Educ. Center, Res. Rpt. RC-2001- 2. Univ. of Florida, Gainesville.

11. Mislevy, P., Martin, F. G., Pate, F. M., Miller, O. P., and Rethman, N. F. G. 2002. Influence of grazing frequency on subtropical grass cultivars. Soil and Crop Sci. Soc. Florida Proc. 61:23-30.

12. Moore, J. E., and Mott, G. O. 1974 Recovery of residual organic matter from in vitro digestion of forages. J. Dairy Sci. 57:1258 -1259.

13. Tilley, J. A., and Terry, R. A. 1963 A two-stage technique of the in vitro digestion of forage crops. J. Br. Grassl. Soc. 18:104-111.

14. Wilson, J. R. 1976. Temperature and atmospheric humidity effects on cell wall content and dry matter digestibility of some tropical and temperate grasses. N.Z.J. Agric. Res. 19:41-46.