Persistence and Botanical Composition of Jesup Tall Fescue w/ Varying Endophyte Status after Stockpiling and Intensive Winter Grazing

Persistence and Botanical Composition of Jesup Tall Fescue with Varying Endophyte Status after Five Years of Stockpiling and Intensive Winter Grazing

Ronaldo E. Vibart, Research Associate, Mary E. Drewnoski, Graduate Research Assistant, Matthew H. Poore, Professor and Extension Ruminant Nutrition Specialist, Department of Animal Science; and James T. Green, Jr., Professor Emeritus, Department of Crop Science; North Carolina State University, Raleigh 27695

Abstract

Long-term stand persistence data on tall fescue varieties infected with novel endophyte strains is still limited. We examined the changes in persistence of Jesup tall fescue without (E–) or with either a wild (E+) or novel endophyte (EN) after intensive winter grazing for five consecutive years using a transect method. Also, three methods of assessing botanical composition of the stands (a transect method, a step point method, and a dry weight rank method) were evaluated. Five years after the initial scoring, E+ (73.0%) had a greater proportion of tall fescue in the stand than E– (59.0%), but the relative abundance of tall fescue in 2006 compared to that of 2002 was, in average, 50% greater, and did not differ among treatments. All three methods ranked the relative abundance of tall fescue similarly. According to the transect method, EN did not differ from E+ and only tended to be different from E–. Alternatively, the other two methods established clear differences among treatments. Our data are in agreement with previous data from novel-endophyte research that indicate that tall fescue infected with the AR542 strain exhibits improved persistence compared to that of E– tall fescue, but unlike others we observed that EN showed inferior persistence compared to E+. Long-term persistence data under broader utilization strategies is still needed to verify such attributes.

Introduction

Tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire] is a cool-season perennial grass that is well adapted to much of the eastern half and northern Pacific areas of the United States, accounting for over 15 million hectares (4). The occurrence of a wild-type, alkaloid-producing, fungal endophyte (E+) [Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin] that resides within the above-ground portion of tall fescue has been associated with both desirable agronomic traits (i.e., superior stand persistence) (2) and undesirable animal responses (i.e., reduced dry matter intake and impaired weight gain, lactation, and reproduction) (19). The introduction of endophyte-free (E–) tall fescue improved animal performance, but was detrimental to plant performance (5). More recently, grazing studies have reported that tall fescue varieties that were re-infected with a non-ergot alkaloid-producing endophyte (EN) produced superior animal performance than E+ (16,17,18) and superior agronomic performance than E– (5,7).

Among the several agronomic attributes of a perennial, cool-season grass (i.e., nutritive value, forage DM production, seasonality of production), the ability to persist is probably the single most important trait (9). Although animal performance using all three tall fescue/endophyte combinations has been documented, information regarding the persistence of tall fescue infected with novel endophyte strains is still limited or in preliminary stages (5,7). The objectives of this study were twofold. The first objective was to examine the changes in persistence of Jesup tall fescue (3) without or with either a wild-type or a novel (AR542, currently marketed as MaxQ, Pennington Seed Inc., Madison, GA) endophyte after stockpiling and intensive winter grazing for five consecutive years using a transect method. The second objective was to compare three methods of assessing botanical composition of the stands. Methods of assessing botanical composition included a transect method, a step point method, and a dry weight rank method.

Establishment and Management of the Tall Fescue Stands

Four replications, each of approximately 1.0 ha, of Jesup tall fescue with three different endophyte combinations were planted in November of 1999. Tall fescue/endophyte combinations were Jesup tall fescue without (E–) or with a wild (E+) or novel (EN) fungal endophyte. The stands were established on a Georgeville silt loam (clayey, kaolinitic, thermic Typic Hapludult) soil at the Butner Beef Cattle Field Laboratory located near Butner, NC. Prior to the planting of the experimental stands, a pure stand of the endophyte-free tall fescue variety A.U. Triumph had been supplying forage for beef cattle herds since 1990. In July of 1999, the existing canopy was harvested to approximately a 7-cm stubble to remove excess growth, and sprayed three weeks later with one application of glyphosate isopropylamine salt herbicide (1.09 kg ai/ha). The sod was then disked, harrowed, and packed to prepare a clean seedbed, and seeded to Jesup tall fescue at 22 kg/ha in late November of 1999.

The new stands were clipped in the spring and fall of 2000. Spring management included the making of hay (2001, 2002, and 2006) and rotational grazing with beef heifers (2003, 2004, and 2005). Every year, residual herbage mass from late spring and summer growth was harvested and baled as hay in mid-August. Plots were fertilized with 30% urea-ammonium nitrate on 28 August 2001, 24 September 2002, 4 September 2003, 21 September 2004, and 5 October 2005 at an N rate of 86, 96, 85, 95, and 57 kg/ha, respectively. Forage was allowed to accumulate until December when winter grazing began. Estimates of pre-grazing herbage mass were obtained in late November using a 0.25-m² falling plate meter (15) at 25 randomly selected sites in each plot. The falling plate readings were calibrated by clipping forage within nine quadrats (0.25 m² each) to ground level using battery-powered sheep shearing equipment (Sunbeam, Botany, New South Wales, Australia). Forage was dried at 60°C for 72 h and weighed. Regression was used to develop an equation relating the harvested forage samples with the falling plate meter readings taken at each quadrat location (14). A detailed description of the agronomic performance of all three tall fescue/endophyte combinations (i.e., herbage mass yield, herbage mass nutritive value, ergot alkaloid concentration, and toxicity) is presented in a separate report (8). Briefly, pre-grazing herbage mass averaged 5570, 2280, 4736, 3759, and 2518 kg DM/ha in 2002 through 2006, respectively. Across the 5-year period, pre-grazing herbage mass averaged 3508, 3979, and 3829 kg DM/ha for treatments E–, E+, and EN, respectively. Forty-eight Angus-cross tester cattle (4 per individual plot that averaged 254 kg bodyweight before the initiation of winter grazing) grazed the plots from early December to mid- to late February using strip-grazing management with daily allocation (i.e. frontal grazing). Plots were grazed following the same management decision rules across treatments to a target residual height of approximately 5.0 cm for an average of 86, 70, 86, 72, and 56 days in 2002 through 2006, respectively. Measurements of residual herbage mass were obtained in a similar fashion to that of pre-grazing herbage mass in 2004, 2005, and 2006, and averaged 1491, 1614, and 1541kg DM/ha for treatments E–, E+, and EN, respectively.

Endophyte Status and Toxicity

Tall fescue tiller infestation levels (10) and alkaloid production (1) were assessed by random collection of 60 tillers in four replicates for each grass/endophyte combination. Samples were collected in November of 2001 and in August of 2006. Infestation levels in E– stands were 4.6% in 2001 and 5.4% in 2006. Conversely, in 2001, 85.8% of the E+ tillers and 91.3% of the EN tillers were endophyte infested. By 2006, the corresponding levels of infestation were 97.5 and 87.1%, respectively. All endophyte-infested tillers in E– and E+ stands produced ergot alkaloids in 2001, while in 2006 94% and 100% of the endophyte-infested tillers produced ergot alkaloids in the E+ and E– stands, respectively. In contrast, only 3.2% (2001) and 0.5% (2006) of the infested tillers in EN stands produced ergot alkaloids.

Estimating Botanical Composition

Transect method. Starting in 2002 and through 2006, a transect method (7) was used to estimate the species composition of the stands. Six permanent transect lines were established in each tall fescue paddock using pre-established landmarks and field measurements prior to the initial readings in September of 2002. Three permanent observation sites (out of a total of 10 equally-spaced potential sites on each transect) were randomly selected along each transect line. The same transect lines (and observation sites within lines) were used from year 1 (2002) to year 5 (2006). A 1-m acrylic ruler was placed on the ground, perpendicular to and centered on the line to pinpoint shoots at the site. Botanical composition was assessed by identifying the species and counting the individuals that came in contact with a 2-mm line that was placed at 5-cm intervals on the graded ruler. Twenty readings (5-cm intervals on the 1-m ruler) were obtained at each observation site, and each treatment was characterized by 1,440 individual readings (4 replicates, 6 transect lines, 3 observation sites per line, and 20 readings per observation site). The botanical composition of the stands was assessed on the same field sites on 4 September 2002; 3 September 2003; 1 October 2004; 1 August 2005; and 28 September 2006.

Step point method. On the same date in 2006 that the transect measurements were taken, species composition was assessed by using a step point method (13). Botanical composition was obtained by identifying the species and recording the foliage hits that came in contact with the tip of the boot of 6 independent, trained observers who walked evenly spread across the plots. Each treatment was characterized by 3,136 individual readings. If the tip of the boot did not contact any plant tissue, the reading was recorded as "bare."

Dry weight rank method. In 2006, botanical composition was also assessed by using a dry weight rank (DWR) method (12). Briefly, thirty 0.18-m² quadrats were randomly placed in each paddock, and visually scored. The three dominant plant species present in the quadrats were ranked in order of greatest (1) to least (3) based on an estimate of the dry weight of each. The rankings of 1, 2, and 3 were assigned proportional values (i.e., multipliers) of 0.70, 0.24, and 0.06, respectively. The combined ranking weight was used to estimate proportional dry weight composition (%) of each species found in the pasture community. The DWR method was not designed to measure bare spots (i.e., ground with no cover).

Statistics. Data were analyzed using repeated-measures analysis in a randomized complete block design with 4 replicates. Statistical analysis included linear mixed models using the PROC MIXED procedure of SAS (SAS Institute Inc., Cary, NC). The model for persistence (2002 vs. 2006) and method comparison (transect, step point, and DWR) included the fixed effects of treatment, year, and treatment × year; and treatment, method, and treatment × method, respectively. Replicate and the correspondent two- and three-way combinations were considered random effects. Denominator degrees of freedom were calculated using the Kenward-Rogers option in SAS. Significance and trends were established at P ≤ 0.05 and P ≤ 0.10, respectively.

Persistence of Tall Fescue after Five Years of Intensive Winter Grazing

Botanical composition of the pastures became progressively more dominated by tall fescue for all tall fescue/endophyte combinations (Table 1). As the tall fescue population aged, the stem material became more densely and uniformly distributed yielding increasingly greater occupation numbers. To a much lesser degree, treatment differences were also detected, due primarily to greater (P = 0.01) proportions of tall fescue in E+ (73.0%) relative to E– (59.0%) stands 5 years after the initial scoring. The relative rankings of the tall fescue/endophyte combinations were similar for both years, but only numerical differences were detected for 2002. The relative abundance of tall fescue in 2006 compared to that of 2002 was, in average, 50% greater, and this did not differ among treatments. The proportion of nonsown species differed among treatments due primarily to differences in 2006 (P = 0.02). The proportion of nonsown species in 2006 was greatest in E– stands, and least in E+ stands. Nonsown species included predominantly large crabgrass (Digitaria sanguinalis L.), Johnsongrass (Sorghum halepense L.), bluegrass (Poa pratensis L.), and white clover (Trifolium repens L.).

Table 1. Persistence (%) of Jesup tall fescue stands without (E–) or with a wild-type (E+) or novel (EN) endophyte in year 1 (2002) vs. year 5 (2006) after 5 years of stockpiling and intensive winter grazing. Data was obtained using a transect method.

		Tall fescue (% stand)^x		F-I^y	Nonsown sp. (% stand)^x		F-I^y
		2002	2006	F-I^y	2002	2006	F-I^y
Treatments	E–	39.5	59.0	19.6	30.9	38.5	7.6
	E+	45.8	73.0	27.2	24.1	24.0	–0.1
	EN	46.5	66.3	19.7	25.2	32.5	7.3
Significance (P)	Treatment	0.28	0.03	0.43	0.29	0.02	0.46
	E– vs. E+	0.20	0.01	0.27	0.15	0.007	0.28
	E– vs. EN	0.15	0.15	0.98	0.22	0.20	0.96
	E+ vs. EN	0.87	0.17	0.27	0.81	0.08	0.30
	2002 vs 2006	0.009		–	0.38		–

^x Proportion of individuals that came in contact with the 5-cm intervals on the 1-m graded ruler. Proportion of tall fescue + nonsown species + uncovered ground = 100%.

^y Final minus initial (2006-2002).

Treatment × year effects lacked significance (P > 0.25).

The agronomic advantages of the symbiotic relationship between host and fungal endophyte have been reported elsewhere (5,6,7,9,11). Compared with previous grazing research, E– appeared to be more persistent in our study, possibly due to increased ability of Jesup E– to persist relative to other cultivars (3), to the management practices pursued in our study (i.e., the tall fescue stands not being intensively used or stressed in the spring/summer periods), or both. Recently, Burns et al. (7) reported a significant reduction in Jesup E– stands (75% reduction) after 3 years of stockpiling and intensive winter grazing in North Carolina, but reductions in E+ (29% reduction) and EN (42% reduction) stands were not statistically different. Despite these differences in persistence, stockpiled forage mass and forage removed by grazing did not differ among the tall fescue/endophyte combinations (7). In our study, however, stockpiled forage mass differed (P < 0.01) among tall fescue/endophyte combinations; across the five-year period, pre-grazing herbage mass of E+ and EN did not differ (P = 0.09) and averaged 3979 and 3829 kg DM/ha, respectively, but both were greater (P ≤ 0.01) than E– (3508 kg DM/ha) (8).

Previously, Bouton et al. (5) examined the stand survival of Jesup and Georgia 5 tall fescue varieties that were re-infected with the novel endophyte strains AR502 and AR542. After two years of intensive summer plus early fall grazing with sheep in two locations in Georgia, only Jesup tall fescue re-infected with the AR542 strain persisted as well as its E+ counterpart and was more persistent than its E– counterpart. Despite these findings, persistence of Jesup E+ was numerically (and consistently) greater than Jesup EN, and led the authors to suggest that the stand survival of E+ would be difficult to accomplish with re-infected fescues in such stressful conditions (5). Although shorter in nature compared with our study, research data from these and other southeastern locations also indicated increased persistence for EN compared with E–, and similar to E+ stands (9).

Methods Comparison of Assessing Botanical Composition

Three methods of assessing botanical composition (transect, step point, and DWR) were used in 2006 (Table 2). All three methods ranked the relative abundance of tall fescue in the stands similarly. According to the transect method, EN did not differ from E+ (P = 0.12) and only tended to be different from E– (P = 0.09). Alternatively, the other two methods established clear differences among all three tall fescue/endophyte combinations. Similar patterns were observed when assessing the relative abundance of nonsown species in the stands, except for the significance (P = 0.04) detected between E+ and EN when using the transect method.

Table 2. Botanical composition (%) of Jesup tall fescue stands without (E–) or with a wild-type (E+) or novel (EN) endophyte in year 5 (2006) using 3 methods of assessment.

		Tall fescue (% stand)			Nonsown sp. (% stand)
		Tran- sect^x	Step point^y	DWR^z	Tran- sect^x	Step point^y	DWR^z
Treat- ments	E–	59.0	32.8	48.3	38.5	66.9	51.7
	E+	73.0	57.3	70.2	24.0	42.4	29.9
	EN	66.3	45.3	59.4	32.5	54.2	40.6
Signif- icance (P)	Treatment	0.01	<0.001	<0.001	0.006	<0.001	<0.001
	E– vs. E+	0.003	<0.001	<0.001	0.002	<0.001	<0.001
	E– vs. EN	0.09	0.007	0.01	0.14	0.004	0.01
	E+ vs. EN	0.12	0.009	0.02	0.04	0.007	0.01
	Method	<0.001			<0.001
	T vs SP	<0.001			<0.001
	T vs DWR	0.04			0.02
	SP vs. DWR		0.002			0.002

^x Proportion of individuals that came in contact with the 5-cm intervals on the 1-m graded ruler.

^y Proportion of individuals that came in contact with the tip of the boot of 6 trained observers.

^z Proportion of individuals based on the proportional dry weight composition of each species.

Treatment × method effects lacked significance (P > 0.25).

The differences in botanical composition among the three methods are most probably attributable to differing measurements of the vertical and horizontal structure of the sward. The lower sward layers contain mostly petioles, stems, leaf sheaths, dead material, and a more visible uncovered ground, which came in contact with the graded ruler placed on the ground (transect method). The upper sward layers, however, consist mainly of live leaves, and are characteristically recorded when assessing botanical composition based on visual estimates (i.e. point step and DWR methods). Plant architecture is also perceived differently by the assessing methods. Among the nonsown species, white clover was greatest in E– and least in E+ and EN stands (P = 0.05) using the step point and DWR methods, but not the transect method (data not shown). White clover leaves are usually arranged in a horizontal plane within the plant canopy, an easy and more abundant target for visual assessment, whereas grass leaves are more vertical. Johnsongrass (10.5% of the stand) and white clover (10.1% of the stand) were the most abundant nonsown species in 2006.

Conclusions

Our data are in agreement with previous data from novel-endophyte research that indicate that tall fescue infected with the AR542 strain exhibits improved persistence compared to that of E– tall fescue, while persistence of EN appeared to be intermediate between E– and E+. However, E– appeared to be more persistent in our study compared with previous findings. Long-term persistence data under broader utilization strategies is still needed to verify these attributes. Although the three methods ranked the relative abundance of tall fescue in the stands similarly, the transect method was not able to clearly differentiate all three treatments. Alternatively, the other two methods established clear differences among all three tall fescue/endophyte combinations.

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