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Effect of Harvest Dates on Yield Nutritive Value of Eastern Gamagrass
The Professional Animal Scientist 24 (2008):363–373 ©2008 American Registry of Professional Animal Scientists
E fand fect of Harvest Dates on Yield Nutritive Value of Eastern Gamagrass M. S. H. Mashingo,1 D. W. Kellogg,2 PAS, W. K. Coblentz,3 and K. S. Anschutz Department of Animal Science, University of Arkansas, Fayetteville 72701
ABSTRACT Yield of ‘Pete’ eastern gamagrass [Tripsacum dactyloides (L.) L.] was evaluated for 3 yr. Forage samples were harvested at 7-d intervals beginning on May 15 and ending on July 17 during 2000, 2001, and 2002. Samples from 2000 and 2001 were analyzed to determine nutrient composition. Plant height increased (P < 0.01) during the 10-wk sampling period by 132, 89, and 132 cm and maximum height reached 225, 231, and 240 cm during 2000, 2001, and 2002, respectively. Increases in DM yield over harvest dates were quadratic, linear, and cubic (P < 0.01) and ranged from 1.25 to 10.04, 4.14 to 14.51, and 2.15 to 15.19 Mg/ha during 2000, 2001, and 2002, respectively. Concentration of NDF for whole-plant samples increased (P < 0.02) from 65.9 to 78.5% with advancing plant maturity in 2000 and from 65.0 to 70.5% in 2001. The concentration of ADF increased (P < 0.001) from 31.1 to 44.5% in 2000 and from 35.3 to 41.5%
1 Current address: Ministry of Livestock Development, TAWLAE, Box 76498, Dar es Salaam, Tanzania. 2 Corresponding author: [email protected] 3 Current address: USDA-ARS, US Dairy Forage Research Center, Marshfield, WI 54449.
in 2001, respectively. The CP concentrations declined (P < 0.002) from 14.4 to 6.3% and 14.7 to 6.6% during 2000 and 2001, respectively. The least numerical value for fraction A (the immediately soluble portion) and the potential extent of DM degradability were observed with eastern gamagrass that was harvested in early July. With limited fertilization, eastern gamagrass demonstrated a tall growth habit and excellent DM yields. If hay of greater nutritive value is preferred for animals with greater nutrient requirements, then harvest should occur at the beginning of June. Key words: eastern gamagrass, yield, nutritive value
INTRODUCTION Eastern gamagrass is a perennial, warm-season bunchgrass that is native to the eastern half of the United States. It is adapted to moist areas and grows in clumps that can be greater than 1 m in diameter. Plants may attain heights of 1.7 to 3.3 m. A minimum stubble height of 20 cm should be maintained during hay production to protect the stand (Roberts and Kallenbach, 1999), and Gillen (2001) recommended a higher stubble height under grazing conditions. Interest in eastern gamagrass
gained momentum after the cultivar ‘Pete’ was developed from 70 accessions originating from native eastern gamagrass populations in Kansas and Oklahoma (Fine et al., 1990). Popularity of eastern gamagrass has increased because it usually produces large quantities of forage during the summer months. Compared with other tall-growing, perennial warmseason grasses, growth and quality characteristics of eastern gamagrass have been incompletely evaluated. Yields of DM at first harvest for eastern gamagrass depend on harvest date and maturity. In a study conducted in Florida, yields of DM increased with fertilization, but the yields declined after the second year of frequent cuttings (Kalmbacher et al., 1990). Brejda et al. (1996) recommended a 6-wk harvest interval if the goal is to produce greater DM yield, and a 4-wk interval if greater CP concentration is desired. The NDF concentrations are generally high (> 60.0%), even at immature stages of growth (Coblentz et al., 1998). Fibrous components in eastern gamagrass are of similar concentrations to those reported commonly for other warm-season grass species. In a review, Coblentz et al. (1999b) reported that ADF concentrations ranged between 29.2 to 44.8% over
364 several studies. The concentration of ADF increases in leaf, stem, and whole- plant tissues and has a positive relationship with plant maturity (Coblentz et al., 1998). There remains a need for information to determine the appropriate timing of the first harvest of eastern gamagrass. The objective of this study was to evaluate yield and nutritive value of eastern gamagrass when the harvests were performed weekly over 10 dates between mid May and early August.
MATERIALS AND METHODS Eastern gamagrass was established during spring 1999 in rows spaced 102 cm apart. The experimental site was fertilized on May 1, 2000, with ammonium nitrate at a rate of 56 kg of N/ha. On April 27, 2001, poultry litter was applied (2.4 t/ha; dry basis) and provided 147, 50, and 65 kg/ha of N, P and K. On May 8, 2002, poultry litter was applied (1.5 t/ha; dry basis) and provided 113, 39, and 51 kg/ha of N, P, and K. Plots were not burned because the field was adjacent to a residential area.
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forage samples were dried under forced air at 50°C, and yields of DM were then extrapolated to a kilogram per hectare basis. In association with each harvest, plant height was measured from the ground to the uppermost point of the leaf canopy when plants were vegetative, or the seedhead following stem elongation. After drying, tillers were counted from 1 m of row, and tiller counts were expressed as the number of tillers per square meter. For forage samples harvested in 2000 and 2001, leaf and stem tissues were hand-separated individually and the leaf was clipped at the collar to remove the leaf sheath and to obtain samples of each tissue type that were used for subsequent nutritive evaluation. Samples were ground through a 2-mm screen in a Wiley mill (Arthur H. Thomas, Swedesboro, NJ) for in situ analyses; then, subsamples of dried whole-plant, stem, and leaf samples were ground through a 1-mm screen. Neutral detergent fiber, ADF, and ADL were sequentially determined using batch
procedures outlined by ANKOM Technology Corp. (Fairport, NY) for samples from 2000 and 2001. The N concentrations were determined by a modified Kjeldahl procedure (Kjeltech Auto 1030 Analyzer, Tecator Inc., Herndon, VA), and CP was calculated by multiplying the percentage of N in each sample by 6.25.
In Situ DM and Forage Disappearance Five ruminally cannulated crossbred steers (mean BW = 388 ± 38 kg) were used as replicates to determine in situ degradation of eastern gamagrass. These animals were cannulated and managed by procedures approved by the University of Arkansas Animal Care and Use Committee. Steers were housed in individual (3.4 × 4.9 m) pens and fed a basal diet of 80% bermudagrass hay and 20% concentrate. The diet was offered at 0730 and 1600 h each day in 2 equal allotments for a cumulative daily rate of 2.2% of BW. Water supply was provided ad libitum to
Harvest Sampling Procedures and Chemical Analyses The experimental design was a randomized complete block with 4 replications and harvest dates as treatments. Each year, sampling was initiated on approximately May 15 and was continued on weekly intervals until approximately July 15, which resulted in a total of 10 harvest dates annually. Within each block, a 1-m section of 2 drill rows was harvested to a 20-cm stubble height with hand shears on each of the 10 sampling dates. Generally, sampling locations within each block were picked at random, but the large area (50 × 50 m) within each field block allowed for considerable distance (>5 m) between specific sampling locations, thereby preventing any confounding across specific harvest locations related to the availability of sunlight. After harvest,
Figure 1. Monthly rainfall totals measured at the University of Arkansas Research Farm in Fayetteville during the growing season of the 3-yr study. Monthly mean (1971 to 2000) precipitation was 110, 129, 134, 80, and 76 mm for April, May, June, July, and August (SRCC, 2008).
Yields and nutritive value of eastern gamagrass
all steers. Steers were adapted to the basal diet for 10 d before conducting the trial. Whole-plant samples harvested during 2000 were ground through a 2-mm screen in preparation for in situ incubations. Within each harvest date, forages were composited over field blocks, thereby resulting in a manageable number of forages (10) for ruminal incubation. A total of 500 Dacron bags (10 × 20 cm, 53-μm pore size; ANKOM Technology Corp.) were filled with 5 g of sample and sealed with an impulse heat sealer (Model CD-200; National Instrument Co. Inc., Baltimore, MD). Within each steer, one bag of each forage was incubated for 3, 6, 9, 12, 24, 48, 72, 96, or 120 h. Prior to insertion in the ventral rumen, all bags were soaked in tepid (39°C) water for 0.33 h to remove water-soluble components and reduce lag time associated with wetting. Bags were inserted into the rumen simultaneously, immediately before the 0730-h feeding. After removal from the rumen, all bags were rinsed in a top-loading washing machine (Whirlpool Corp., Model #LR 7144 EQ1, Benton Harbor, MI) 10 times in about 45 L of tap water with 1 min of agitation and 2 min of spin per rinse. A 0-h incubation time also was included in the analysis, and was based on bags that were soaked in tepid water and rinsed, but not inserted into the rumen (Vanzant et al., 1996; Coblentz et al., 1997). The A fraction was defined as the immediately soluble portion, although it is recognized that some minute insoluble particles may have been included (Coblentz et al., 1998; Galdámez-Cabrera et al., 2003). The NDF concentration in residues was determined as described earlier. In situ procedures were consistent with the standardized techniques described by Vanzant et al. (1998). The fractional passage rate for each steer was determined by using acid detergent insoluble ash (ADIA) as an internal marker. Mass of ruminal contents for steers at 0 h (before feeding) and 4 h after feeding were determined after evacuating
the rumen. Rumen contents were sub-sampled in triplicate after being weighed and mixed, and sub-samples were dried at 50°C for 120 h in a forced-air oven. Hay and concentrate samples were dried at 50°C for 48 h in a forced-air oven. All samples were ground to pass a 1-mm screen in a Wiley mill. Concentration of ADIA in the basal diet and digesta samples were determined by ashing ADF residues in a muffle furnace at 500°C for 8 h. The concentration of ADIA in the bermudagrass hay and concentrate comprising the basal diet were 20.2 and 3.5 g/kg, respectively. Mean ADIA concentrations in ruminal contents obtained from evacuation of steers at 0 and 4 h were 30.5 ± 0.5 and 28.3 ± 1.2 g/kg, respectively. Fractional passage rate (Kp) of ADIA for each steer was calculated by dividing the mean ADIA intake (g/h) by the mean ruminal mass (g) of
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ADIA obtained from the 0- and 4-h ruminal evacuations (Waldo et al., 1972); the mean calculated Kp for steers was 0.035 ± 0.007/h. In situ DM residues were divided into 3 fractions based on susceptibility to ruminal degradation and were defined as follows: A = the immediately soluble fraction, B = the fraction that was degraded at a measurable rate, and C = the fraction unavailable in the rumen. Degradation kinetics were determined by non-linear regression of percentage of DM remaining on incubation time, using PROC NLIN of SAS (SAS, 1985). Data were fitted according to a nonlinear regression model (Mertens and Loften, 1980): DM_REM = B e−k(t-L) + C, when time > L, and DM_REM = B + C when 0 < time < L; where, DM_REM = DM remaining, t incubation time (hours), L = lag times, and K = degradation
Table 1. Height (cm) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Item Harvest 1 2 3 4 5 6 7 8 9 10 n Best fit Cubic Quadratic Linear Intercept RMSE3 R2 P4
2000 93 118 142 173 182 196 193 202 219 225 40 Cubic1 0.24 −5.34 47.3 47.1 8.21 0.96 0.003
1
Cubic effect of harvest dates.
2
Quadratic effect of harvest dates.
3
RMSE = root mean square error.
4
2001 142 171 174 191 210 220 230 234 234 231 40 Quadratic2 — −1.3 24.5 119.7 6.9 0.95 <0.001
2002 109 127 152 190 209 216 224 229 240 240 40 Quadratic — −1.87 35.5 70.1 8.69 0.97 <0.001
P = probability that the quadratic or cubic parameter estimate was different from zero.
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366 rate constants. Lag times, K, and fractions B and C were determined directly from the model. The immediately soluble portion (fraction A) was calculated by difference [total DM – (B + C)]. Effective DM disappearance was calculated as effective disappearance = A + B × [Kd/(Kd + Kp)], where Kp = fractional passage rate of the basal diet using the mean of the steers and Kd = fractional rate of degradation of potentially degradable DM.
Statistical Analyses Data collected from 2000 to 2002 on forage growth (height and tillering) and DM yield were analyzed by regressing against harvest date using PROC REG (SAS, 1985). When data were available for more than 1 yr, the effect of year and the interaction between harvest dates were tested. If the year × harvest date interaction was significant (P < 0.05), data were analyzed separately for each year. Data of NDF, ADF, ADL, cellulose, and hemicellulose concentrations for whole plant and leaf tissues from samples collected during 2000 and 2001, and for stem tissue in 2001, were analyzed by regressing against harvest dates using PROC REG (SAS, 1985). The regression model included cubic, quadratic, and linear terms, and the highest order term was dropped from the model if it was non significant at P < 0.01. Parameters of in situ degradation for each date were analyzed as a randomized complete block design using ANOVA procedure of SAS (1985). The 5 steers were considered as blocks because of the number of samples. Excessive sample numbers prohibited the evaluation of kinetics of ruminal DM disappearance for all possible combinations of harvest date, block, and year. To reduce the number of forages to a manageable number each year (10) for this type of analysis, some procedural compromises were necessary. To accomplish this, forages were composited over field replications within each harvest date, and then kinetic evaluations
for 2000 and 2001 were conducted independently.
RESULTS AND DISCUSSION The interaction of year × harvest date was significant, so results are presented for each year. This interaction is explained by rainfall distribution during the 3-yr period (Figure 1). Rainfall at the beginning of the growing period in April and May was 31 and 181 mm in 2000, 51 and 168 mm in 2001, and 173 and 131 mm in 2002, respectively. Rainfall was exceptionally heavy (362 mm) during June 2000 compared with June 2001 (93 mm) and June 2002 (102 mm) or to normal (1971 to 2000) precipitation of 133 mm (SRCC, 2008).
Forage Height and Yield During each year height of eastern gamagrass increased (P = 0.003) with advancing maturity at 10 different
harvests (Table 1). There was a cubic increase (P = 0.003) in height relative to harvest date during 2000, but during 2001 and 2002 the trend was a quadratic (P < 0.001) increase. The respective increases in eastern gamagrass height during the three 70-d growing seasons were 132, 89, and 131 cm, and plants attained heights of 225, 231, and 240 cm during 2000, 2001, and 2002, respectively. Greater growth rates of eastern gamagrass were observed in May and June during 2001 and 2002 compared with 2000. During 2000, growth rate was most rapid during July. This may be partly explained on the basis of excellent June precipitation, which was nearly 3 times the 30-yr norm for that month (SRCC, 2008). There was a linear relationship (P < 0.001) between number of tillers and harvest date during 2000 and 2002, but the pattern was quadratic (P < 0.001) during 2001 (Table 2).
Table 2. Tillers (number per m2) of eastern gamagrass at 10 weekly dates (beginning on May 15) in Fayetteville, AR Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Quadratic Linear Intercept R2 RMSE3 P4
2000 80 88 110 183 270 325 350 377 456 471 Linear1 — 48.47 4.56 0.92 42.59 <0.001
1
Linear effect of harvest dates.
2
Quadratic effect of harvest dates.
3
RMSE = root mean square error.
4
2001 166 136 152 138 155 217 161 250 270 306 Quadratic2 3.68 −24.40 189.38 0.71 35.81 <0.001
2002 100 112 104 128 168 153 152 201 191 208 Linear — 12.11 82.80 0.52 34.04 <0.001
P = probability that the quadratic or cubic parameter estimate was different from zero.
Yields and nutritive value of eastern gamagrass
The number of tillers ranged from 80 to 471/m2 during 2000, from 136 to 306/m2 during 2001, and from 100 to 208/m2 during 2002. These plots were not burned because the research site was located adjacent to a residential area. Burning is known to have a positive effect on tillering density and growth of perennial warm-season grasses. Previously, Cuomo et al. (1998) reported increased plant vigor and tillering density when perennial warm-season grasses were burned during spring. Similarly, Mitchell et al. (1994) observed a 70% increase in forage production by big bluestem (Andropogon gerardii Vitman) in response to early or mid-spring burning. In the present study, overall annual means for tiller density during 2001 and 2002 declined to 72 and 56%, respectively, of levels observed during 2000. Yields of DM by eastern gamagrass increased in curvilinear patterns over harvest dates in each experimental year; however, responses for specific years varied (Table 3). The relationship between DM yield and harvest dates were quadratic (P = 0.008) during 2000 and cubic (P < 0.001) during the following 2 yr. Yields of DM on the final (mid-July) harvest date increased by 45 and 51% during 2001 and 2002 when compared with the yield observed on the same harvest date for 2000 (10.04 Mg/ha). In this study, the 2-yr (2001 and 2002) average of calculated daily DM accumulation values was 99 kg/ha between wk 6 and 8 and was within the range reported for western Oklahoma by Gillen (2001), who observed 59 to 112 kg/ha DM accumulations (daily) during the first 6 to 8 wk of the growing season. This range for DM yield is consistent with other reports. Douglas (1993) reported an average annual DM yield of 10.16 Mg/ha for eastern gamagrass harvested from 3 harvests spaced at 45 d without fertilization. Similarly, Faix et al. (1980) reported annual yields of 7.60 to 24.68 Mg/ha in southern Illinois. Bredja et al. (1997) reported annual yields ranging from 8.00 to 13.60
Mg/ha for eastern gamagrass fertilized with either 168 or 336 kg N/ha and harvested from a 3-cut system. Quadratic responses to N fertilization were observed within 4 of 6 siteyears. Brejda et al. (1996) reported that eastern gamagrass produced good regrowth following defoliation, which allowed multiple harvests during the growing season. Faix et al. (1980) harvested PMK-24 eastern gamagrass 3 and 4 times per growing season and reported DM yields ranging from 7.60 to 24.68 Mg /ha per year.
Crude Protein Concentrations The CP concentrations of eastern gamagrass are shown in Table 4. Whole-plant CP exhibited linear (P < 0.001) and quadratic (P = 0.002) declines with harvest dates during 2000 and 2001, respectively. The declines between the initial and
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final harvest dates ranged from 14.4% down to 6.3% during 2000, and from 14.7% down to 6.6% during 2001. Many researchers have reported declines in CP concentrations with plant maturity for eastern gamagrass (Coblentz et al., 1998, 1999b; Dickerson and van der Grinten, 1990); however, these declines are not explained strictly as a function of increased proportions of stem within the forage. Concentrations of CP within leaf tissue declined in quadratic (P = 0.006) and linear (P < 0.001) relationships with time during 2000 and 2001, respectively. Respective concentrations of CP within leaf tissue harvested in mid-July were only 46 and 61% of those observed in mid-May. Moreover, Coblentz et al. (1998) reported that stem tissue from eastern gamagrass plants harvested at the boot, anthesis, and physiologically mature stages of growth contained < 31% stem tissue
Table 3. Dry matter yields (mg/ha) of eastern gamagrass at 10 weekly dates (beginning on May 15) in Fayetteville, AR Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Cubic Quadratic Linear Intercept RMSE3 R2 P4
2000 1.25 1.75 2.22 3.83 4.84 5.13 5.67 8.12 9.63 10.04 Quadratic1 — 0.57287 0.53869 0.04446 0.725 0.95 0.008
1
Quadratic effect of harvest dates.
2
Cubic effect of harvest dates.
3
RMSE = root mean square error.
4
2001 4.14 5.28 8.96 10.10 8.52 11.04 10.35 10.78 10.73 14.51 Cubic2 0.04994 −0.88246 5.31453 −0.92218 1.334 0.82 <0.001
2002 2.15 2.75 3.24 4.79 7.39 9.01 11.76 13.44 13.97 15.19 Cubic −0.039252 0.66844 −1.58256 3.21189 0.789 0.97 <0.001
P = probability that the quadratic or cubic parameter estimate was different from zero.
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Table 4. Crude protein concentrations (% of DM) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Whole plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Quadratic Linear Intercept RMSE3 R2 P4
2000
Stem
2001
14.4 13.1 12.6 11.1 10.1 9.8 9.4 7.1 6.5 6.3 Linear1 — −0.91 15.09 1.0 0.88 <0.001
14.7 13.1 11.5 10.8 9.9 9.2 7.9 7.7 7.8 6.6 Quadratic2 0.06 −1.59 16.04 0.91 0.89 0.002
Leaf
2000
2001
9.1 8.2 6.1 5.6 4.6 4.5 3.6 3.5 3.0 3.0 Linear — −2.11 11.16 0.60 0.92 <0.001
8.3 8.1 6.9 6.3 5.8 5.3 4.0 3.7 2.9 2.8 Linear — −0.66 9.06 0.49 0.94 <0.001
1
Linear effect of harvest dates.
2
Quadratic effect of harvest dates.
3
RMSE = root mean square error.
4
P = probability that the quadratic or cubic parameter estimate was different from zero.
2000
2001
16.9 15.1 14.0 11.6 11.1 9.9 9.9 — 7.9 7.8 Quadratic 0.07 −1.81 18.48 1.21 0.85 0.006
14.5 14.4 13.1 11.9 11.7 11.1 9.9 9.3 8.8 8.8 Linear — −0.69 15.14 1.06 0.78 <0.001
Table 5. Neutral detergent fiber concentrations (% of DM) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Whole plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Quadratic Linear Intercept RMSE3 R2 P4
2000 65.9 67.4 69.8 73.3 72.3 75.0 73.1 77.4 78.5 75.3 Quadratic1 −0.137 2.73 63.0 1.73 0.82 <0.001
Stem 2001 66.6 65.0 66.8 71.7 68.8 67.4 71.1 67.7 70.5 68.9 Linear2 — 0.372 66.4 2.05 0.22 0.002
Leaf
2000
2001
71.8 71.9 76.6 79.4 79.5 81.7 80.6 82.8 82.2 82.1 Linear — 3.40 67.8 1.45 0.89 0.003
64.5 65.7 68.4 66.5 68.1 67.2 66.6 68.4 68.5 68.5 Linear — 1.18 63.7 2.49 0.66 <0.001
1
Quadratic effect of harvest dates.
2
Linear effect of harvest dates.
3
RMSE = root mean square error.
4
P = probability that the quadratic or cubic parameter estimate was different from zero.
2000 66.8 66.3 69.2 72.9 75.0 74.7 73.3 74.0 77.8 75.9 Quadratic −0.137 2.64 63.3 1.92 0.77 0.002
2001 66.4 66.2 62.7 69.6 71.3 71.2 72.2 72.4 73.2 76.4 Linear — 0.63 62.8 2.46 0.36 <0.001
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by weight, thereby further indicating that dilution by developing stems plays only a limited role in declines in whole-plant CP over time.
Neutral Detergent Fiber Concentrations Whole-plant NDF for eastern gamagrass sampled in 2000 exhibited a quadratic (P < 0.001) increase with harvest date and ranged from 65.9 at the first harvest to 78.5% at the ninth harvest (Table 5). These results are consistent with those summarized previously (Coblentz et al., 1998), where an increase of 8.6 percentage units was observed between boot stage and physiological maturity. In this study, NDF concentrations in stem tissues increased linearly (P = 0.003) across harvest dates in 2000. There was a linear relationship (P < 0.001) between NDF concentrations and harvest dates for
stem and leaf tissues in 2001. There was a quadratic relationship (P = 0.002) between NDF concentrations and harvest dates for leaf tissues in 2000. These results from 2001 are consistent with those observed by Fick and Coblentz (1994) who reported that the NDF concentration of leaf and stem portions harvested over 3 yr maintained a narrow range of 65.3 to 67.5%. Griffin and Jung (1983) suggested that NDF concentration of leaf and stem tissue may have a narrow range that is indistinguishable during early stages of growth and increases slightly with plant maturity. Coblentz et al. (1999b) noted that cell wall content of whole-plant eastern gamagrass is not dependent on leafto-stem ratio through the anthesis stage of growth. This is corroborated by 2001 data of this study where NDF was generally reduced on most dates for stem tissue, relative to leaf.
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Acid Detergent Fiber Concentrations There were quadratic (P < 0.001) and cubic (P < 0.001) increases of ADF concentration and with advancing maturity (harvest dates) for whole-plant samples harvested in 2000 and 2001, respectively (Table 6). The ADF concentrations for whole-plant eastern gamagrass increased from 31.1 to 44.5% during 2000 and from 35.3 to 41.5% during 2001; however, the maximum concentration during 2001 occurred on the fourth harvest date with relatively limited change thereafter. Concentrations of ADF for stem tissue during 2001increased over harvest dates by 7.7 percentage units, thereby exhibiting a cubic (P = 0.002) relationship with time. The relationship with leaf tissue was also cubic (P = 0.003), and ADF concentrations of leaf tissue during 2001
Table 6. Acid detergent fiber concentrations (% of DM) of eastern gamagrass at 10 different harvest dates (beginning on May 15) in Fayetteville, AR Whole plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Cubic Quadratic Linear Intercept RMSE3 R2 P4
2000 31.1 32.5 34.9 37.9 42.5 39.5 38.2 43.6 44.1 44.5 Quadratic1 — −0.266 4.27 25.9 2.50 0.76 <0.001
Stem 2001 35.3 35.0 38.3 41.5 38.2 35.2 37.8 37.3 39.9 36.8 Cubic2 0.159 −2.897 14.78 22.0 4.79 0.38 <0.001
2000 38.2 42.3 44.1 46.1 46.4 49.3 48.3 50.3 47.6 51.0 Quadratic — −0.064 5.21 33.73 1.76 0.83 0.024
Leaf 2001 39.3 39.8 40.0 42.1 43.3 42.1 43.6 44.9 44.9 47.0 Cubic 0.120 −2.068 10.23 30.4 4.03 0.25 0.002
1
Quadratic effect of harvest dates.
2
Cubic effect of harvest dates.
3
RMSE = root mean square error.
4
P = Probability that the quadratic or cubic parameter estimate was different from zero.
2000 31.1 31.2 34.3 36.5 39.6 38.5 37.8 38.1 43.7 41.3 Quadratic — −0.191 3.36 26.8 2.89 0.67 0.003
2001 33.1 37.4 37.3 35.2 35.0 33.9 35.7 37.3 43.1 36.1 Cubic 0.136 −2.363 11.02 25.3 4.66 0.34 0.003
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370 were generally less than observed for stem tissue. Similarly, Coblentz et al. (1999b) reported that ADF concentrations in stem increased with maturity.
Hemicellulose Concentrations Hemicellulose concentrations are shown in Table 7; whole-plant concentrations during 2000 and 2001 increased quadratically (P = 0.008) and cubically (P < 0.001), respectively, with harvest date. Concentrations of hemicellulose varied little across harvest dates, indicating there was relatively limited practical effect of advancing plant maturity. Hemicellulose concentration in stem tissue did not vary significantly in 2000, but during 2001 had a linear increase (P < 0.001) in relation to harvest dates. However, the difference in concentrations between the first
and last harvest date was only 2.3 percentage units. The relationship between hemicellulose concentrations in leaf tissue and harvest dates was linear (P = 0.002) during 2001, but no relationship was observed during 2000 (P = 0.275). Hemicellulose concentrations in leaf tissue generally were greater than that observed in stem tissue.
Cellulose Concentrations Cellulose concentrations increased (P < 0.001) for whole-plant samples harvested during 2000 and 2001, respectively (Table 8). Cellulose concentrations in stem tissue sampled during 2001 increased (P = 0.005) in relation to harvest date, and that of leaf tissue harvested 2000 and 2001 exhibited quadratic (P = 0.002) and cubic (P = 0.002) increases. Stem
samples were not analyzed for cellulose during 2000.
Lignin Concentrations The ADL concentrations for eastern gamagrass are shown in Table 9. The concentration of ADL in wholeplant tissues of eastern gamagrass harvested in 2000 was explained by a quadratic response (P < 0.001), and samples harvested in 2001 were explained by a linear (P < 0.001) relationship with harvest date. Stem and leaf tissue ADL generally increased with plant maturity. There was a cubic (P < 0.001) and linear relationship (P < 0.001) for stem and leaf tissue, respectively, sampled in 2001, and a linear relationship for leaf tissue harvested during 2000. Samples were not analyzed for ADL during 2000. Coblentz et al. (1999b) reported increased lignin concentra-
Table 7. Hemicellulose concentrations (% of DM) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Whole plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Cubic Quadratic Linear Intercept RMSE4 R2 P5
2000 34.8 34.9 34.7 35.4 29.8 35.5 34.9 33.8 34.4 33.9 Quadratic1 — 0.137 −1.622 37.23 2.24 0.19 0.008
Stem 2001 31.2 29.9 28.5 30.2 30.6 32.2 31.4 30.4 30.6 32.2 Cubic2 −0.094 1.706 −8.40 38.5 3.15 0.34 <0.001
2000 33.6 29.6 32.4 33.3 33.1 32.4 32.2 32.5 34.6 31.1 Linear — — −1.64 33.9 2.24 0.06 0.321
Leaf 2001 27.1 26.4 27.4 27.5 27.9 29.1 28.6 27.4 31.4 29.4 Linear3 — — 0.573 25.5 2.49 0.32 <0.001
1
Quadratic effect of harvest dates.
2
Cubic effect of harvest dates.
3
Linear effect of harvest dates.
4
RMSE = root mean square error.
5
P = probability that the quadratic or cubic parameter estimate was different from zero.
2000
2001
35.6 34.1 34.9 36.4 33.4 29.4 35.6 35.9 34.1 35.6 Linear — — −0.199 36.0 3.28 0.03 0.275
31.4 28.3 31.0 31.2 33.0 33.2 30.9 31.2 30.2 32.4 Linear — — 0.63 29.0 3.24 0.25 0.002
Yields and nutritive value of eastern gamagrass
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Table 8. Cellulose concentrations (% of DM) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Whole-plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Cubic Quadratic Linear Intercept RMSE4 R2 P5
2000 28.4 30.0 35.0 37.4 37.1 35.1 33.8 38.0 38.3 36.4 Quadratic2 — −0.199 3.19 24.8 2.04 0.727 <0.001
Stem 2001 31.9 31.2 37.1 34.2 33.7 30.4 34.4 31.6 33.9 30.6 Cubic3 0.16 −2.927 14.65 18.5 4.73 0.431 <0.001
Leaf
2000
2001
NA1 NA NA NA NA NA NA NA NA NA — — — — — NA — —
29.93 33.76 33.0 31.2 30.7 29.2 30.5 31.8 32.0 30.2 Cubic 0.11 −1.877 8.89 27.7 4.01 0.248 0.005
1
NA = not analyzed.
2
Quadratic effect of harvest dates.
3
Cubic effect of harvest dates.
4
RMSE = root mean square error.
5
P = probability that the quadratic or cubic parameter estimate was different from zero.
tions as a function of plant maturity. Horner et al. (1985) reported a mean lignin concentration of 9.3% for eastern gamagrass regrowth hay.
Ruminal In Situ Degradation of Dry Matter In situ degradation kinetics of whole-plant eastern gamagrass are presented in Table 10. Fraction A comprised 24.2 and 22.7% of DM on the first and third harvest dates and was comparable to that found at boot (26.8%) and anthesis (22.8%) stages by Coblentz et al. (1998). Fraction B differed (P < 0.05) among harvest dates and ranged from 58 to 62.7% across all sampling dates. Coblentz et al. (1998) observed that fraction B for eastern gamagrass harvested at boot, anthesis, and mature stages as 53.6, 53.6 and 48.1% of DM, respectively. Fraction B contains fiber
components that are digested incompletely. Undegradable fraction C increased (P < 0.05) with maturity. In this study, the least numerical value for fraction A and greatest numerical value of fraction C were observed for eastern gamagrass harvested on the July 3 harvest. Fraction C decreased (P < 0.05) following the first harvest date until the last. Lag time of DM degradation was not affected (P > 0.05) by harvest date. The declining estimates of effective degradability of DM are related to declining decay rates in the rumen, and to a lesser extent to declining pools of soluble (fraction A) DM. Decay rates declined from 4.6 to 2.3%/h over harvest dates, which is a huge change with respect to utilization and is consistent with responses for Coblentz et al. (1998). An 18.1 percentage unit decline in effective degradability of DM over time is
2000 28.7 28.6 31.1 31.9 37.1 39.1 33.3 33.6 38.0 35.6 Quadratic — −0.174 2.80 25.0 2.42 0.599 0.002
2001 35.4 35.1 33.4 36.3 37.5 36.1 37.1 38.2 37.4 39.3 Cubic 0.14 −2.407 10.90 22.2 4.63 0.426 0.002
enormous, although changes over the first 4 and last 4 harvest dates appear minimal.
IMPLICATIONS Concentrations of NDF, ADF, and CP and degradation of DM are important criteria for deciding when, and at what stage of maturity, to harvest eastern gamagrass as hay. If hay of greater nutritive value is preferred, then harvest should occur at the beginning of June. According to this study, the expected CP would be greater than 10%, but average DM yield would likely be < 8 Mg/ha. If hay is harvested later in June, CP would probably be less than 10%, but DM yields may be >10 Mg/ha. Degradation characteristics of DM indicated a decline with advancing harvest dates. A decision to harvest earlier would result in greater nutri-
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372
Table 9. Acid detergent lignin concentrations (% of DM) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Whole-plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Cubic Quadratic Linear Intercept RMSE5 R2 P6
2000 2.66 2.48 3.28 4.14 5.41 4.37 4.40 5.53 5.83 5.01 Quadratic2 — −0.074 1.17 0.96 0.79 0.69 <0.001
Stem 2001
Leaf
2000 NA1 NA NA NA NA NA NA NA NA NA — — — — — NA NA
3.47 3.85 4.13 4.40 4.47 4.77 5.33 5.68 6.04 6.17 Linear3 — — 0.31 3.15 0.28 0.93 <0.001
2001 3.81 4.66 5.40 5.73 5.88 6.02 6.48 6.73 7.32 7.65 Cubic4 0.0102 −0.183 1.31 2.70 0.19 0.97 <0.001
1
NA = not analyzed.
2
Quadratic effect of harvest dates.
3
Linear effect of harvest dates.
4
Cubic effect of harvest dates.
5
RMSE = root mean square error.
6
P = Probability that the quadratic or cubic parameter estimate was different from zero.
2000
2001
2.42 2.67 3.31 4.48 4.50 6.38 4.46 4.51 5.67 5.43 Linear — — 0.34 2.44 0.80 0.61 <0.001
3.16 3.61 3.87 4.07 4.29 4.82 5.21 5.44 5.75 5.87 Linear — — 0.31 2.91 0.12 0.98 <0.001
Table 10. In situ DM degradation of whole plant eastern gamagrass at 10 weekly harvest dates (beginning on May 15) during 2000 and 2001 in Fayetteville, AR Item
A1
B2
C3
EFF4
(%) Harvest 1 2 3 4 5 6 7 8 9 10 SEM
24.2a 22.7ab 22.7ab 19.2bc 19.1c 15.7cd 17.7cd 14.5d 16.1cd 17.7c 7.7
61.8ab 62.7a 61.2ab 60.0ab 60.3ab 62.3a 62.3a 60.9ab 60.3ab 58.0b 11.1
14.0e 14.6ed 16.3d 20.8c 20.6c 21.9bc 21.2c 24.6a 23.7ab 24.3a 3.1
58.8a 55.6b 55.4b 50.4c 46.9d 44.0e 42.5ef 41.0f 40.5f 40.7f 3.2
Lag
Kd
(h)
(%/h)
1.5 0.7 1.7 1.8 1.2 1.2 1.1 2.3 1.6 1.6 2.0
4.6a 3.9b 4.1ab 3.9b 3.0c 2.9cd 2.5cde 2.7cde 2.5de 2.3e 0.001
a-f
Means in a column with different superscript differ (P < 0.05).
1
A = immediately soluble fraction: [total DM – (B + C)].
2
B = fraction degradable at a measurable rate.
3
C = undegradable fraction.
4
EFF = effective degradability of DM. EFF = A + B × Kd/(Kd + Kp), where Kp is the fractional passage rate of the basal diet using the mean of the 5 steers. The experimentally determined passage rate was 0.035 ± 0.007/h.
Yields and nutritive value of eastern gamagrass
tive value and also permit regrowth of the forage.
LITERATURE CITED Brejda, J. J., J. R. Brown, T. E. Lorenz, J. Henry, and S. R. Lowry. 1997. Variation in eastern gamagrass forage yield with environments, harvests, and nitrogen rates. Agron. J. 89:702. Brejda, J. J., J. R. Brown, T. E. Lorenz, J. Henry, J. L. Reid, and S. R. Lowry. 1996. Eastern gamagrass response to different harvest intervals and nitrogen rates in northern Missouri. J. Prod. Agric. 9:130. Coblentz, W. K., I. E. O. Abdelgadir, R. C. Cochran, J. O. Fritz, W. H. Fick, K. C. Olson, and J. E. Turner. 1999a. Degradability of forage proteins by in situ and in vitro enzymatic methods. J. Dairy Sci. 82:343. Coblentz, W. K., K. P. Coffey, and J. E. Turner. 1999b. A review: Quality characteristics of eastern gamagrass forages. Prof. Anim. Sci. 15:211. Coblentz, W. K., J. O. Fritz, R. C. Cochran, W. L. Rooney, and K. K. Bolsen. 1997. Protein degradation responses to spontaneous heating in alfalfa hay by in situ and ficin methods. J. Dairy Sci. 80:700. Coblentz, W. K., J. O. Fritz, W. H. Fick, R. C. Cochran, and J. E. Shirley. 1998. In situ dry matter, nitrogen, and fiber degradation of alfalfa, red clover, and eastern gamagrass at four maturities. J. Dairy Sci. 81:150. Cuomo, G. J., B. E. Anderson, and L. J. Young. 1998. Harvest frequency and burning effect on vigor of native grasses. J. Range Manage. 51:32.
Dickerson, J. A., and M. van der Grinten. 1990. Developing eastern gamagrass as a haylage crop for northeast. p. 194 in Proc. Am. Forage Grassl. Council Ann. Meeting, Bellville, PA. Am. Forage Grassl. Council, Georgetown, TX. Douglas, J. 1993. Effects of clipping frequency and N rate on yield and quality of eastern gamagrass. MS Thesis. Stephen F. Austin State Univ., Nacogdoches, TX. Faix, J. J., C. J. Kaiser, and F. C. Hinds. 1980. Quality, yield, and survival of Asiatic bluestems and an eastern gamagrass in southern Illinois. J. Range Manage. 33:388. Fick, W. H., and W. K. Coblentz. 1994. Production and quality of 12 eastern gamagrass progeny. p. 16 in Proc. Soc. Range Management Ann. Meeting, Colorado Springs, CO. (Abstr.). Fine, G. L., F. I. Barnett, K. L. Anderson, R. D. Lippert, and E. T. Jacobson. 1990. Registration of ‘Pete’ eastern gamagrass. Crop Sci. 30:741. Galdámez-Cabrera, N. W., K. P. Coffey, W. K. Coblentz, J. E. Turner, D. A. Scarbrough, Z. B. Johnson, J. L. Gunsaulis, M. B. Daniels, and D. H. Hellwig. 2003. In situ ruminal degradation of dry matter and fiber from bermudagrass fertilized with different nitrogen rates and harvested on two dates. Anim. Feed Sci. Technol. 105:185. Gillen, R. L. 2001. Production and grazing management for eastern gamagrass. Proc. 56th Southern Pasture Forage Crop Improvement Conf., Springdale, AR. Am. Forage Grassl. Counc., Georgetown, TX. Griffin, J. L., and G. A. Jung. 1983. Leaf and stem forages quality of big bluestem and switchgrass. Agron. J. 75:723.
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Horner, J. L., L. J. Bush, G. D. Adams, and C. M. Taliaferro. 1985. Comparative nutritional value of eastern gamagrass and alfalfa hay for dairy cows. J. Dairy Sci. 68:2615. Kalmbacher, R. S., L. S. Dunavin, and F. G. Martin. 1990. Fertilization and harvest season of eastern gamagrass Ona and Jay. Soil Crop Sci. Soc. Florida. Proc. 49:166. Mertens, D. R., and J. R. Loften. 1980. The effect of starch on forage fiber digestion kinetics in vitro. J. Dairy Sci. 63:1437. Mitchell, R. B., R. A. Masters, S. S. Waller, K. J. Moore, and L. E. Moser. 1994. Big bluestem production and forage quality responses to burning date and fertilizer in tallgrass prairies. J. Prod. Agric. 7:355. SAS. 1985. Users guide: Statistics, Version 5 ed. SAS Inst. Inc., Cary, NC. Roberts, C., and R. Kallenbach. 1999. Eastern gamagrass. Univ. of Missouri Guide #G 4671. Univ. of Missouri Outreach and Ext., Columbia. SRCC. 2008. Southern Regional Climate Center, Baton Rouge, LA. http://www.srcc. lsu.edu/southernClimate/atlas/images/ ARprcp.html/view?searchterm=Fayetteville Accessed January 2008. Vanzant, E. S., R. C. Cochran, and E. C. Titgemeyer. 1998. Standardization of in situ techniques for ruminant feedstuff evaluation. J. Anim. Sci. 76:2717. Vanzant, E. S., R. C. Cochran, E. C. Titgemeyer, S. D. Stafford, K. C. Olson, D. E. Johnson, and G. St. Jean. 1996. In vivo and in-situ measurements of forage protein degradation in cattle. J. Anim. Sci. 74:2773. Waldo, D. R., L. W. Smith, and E. L. Cox. 1972. Model of cellulose disappearance from rumen. J. Dairy Sci. 55:125.
E fand fect of Harvest Dates on Yield Nutritive Value of Eastern Gamagrass M. S. H. Mashingo,1 D. W. Kellogg,2 PAS, W. K. Coblentz,3 and K. S. Anschutz Department of Animal Science, University of Arkansas, Fayetteville 72701
ABSTRACT Yield of ‘Pete’ eastern gamagrass [Tripsacum dactyloides (L.) L.] was evaluated for 3 yr. Forage samples were harvested at 7-d intervals beginning on May 15 and ending on July 17 during 2000, 2001, and 2002. Samples from 2000 and 2001 were analyzed to determine nutrient composition. Plant height increased (P < 0.01) during the 10-wk sampling period by 132, 89, and 132 cm and maximum height reached 225, 231, and 240 cm during 2000, 2001, and 2002, respectively. Increases in DM yield over harvest dates were quadratic, linear, and cubic (P < 0.01) and ranged from 1.25 to 10.04, 4.14 to 14.51, and 2.15 to 15.19 Mg/ha during 2000, 2001, and 2002, respectively. Concentration of NDF for whole-plant samples increased (P < 0.02) from 65.9 to 78.5% with advancing plant maturity in 2000 and from 65.0 to 70.5% in 2001. The concentration of ADF increased (P < 0.001) from 31.1 to 44.5% in 2000 and from 35.3 to 41.5%
1 Current address: Ministry of Livestock Development, TAWLAE, Box 76498, Dar es Salaam, Tanzania. 2 Corresponding author: [email protected] 3 Current address: USDA-ARS, US Dairy Forage Research Center, Marshfield, WI 54449.
in 2001, respectively. The CP concentrations declined (P < 0.002) from 14.4 to 6.3% and 14.7 to 6.6% during 2000 and 2001, respectively. The least numerical value for fraction A (the immediately soluble portion) and the potential extent of DM degradability were observed with eastern gamagrass that was harvested in early July. With limited fertilization, eastern gamagrass demonstrated a tall growth habit and excellent DM yields. If hay of greater nutritive value is preferred for animals with greater nutrient requirements, then harvest should occur at the beginning of June. Key words: eastern gamagrass, yield, nutritive value
INTRODUCTION Eastern gamagrass is a perennial, warm-season bunchgrass that is native to the eastern half of the United States. It is adapted to moist areas and grows in clumps that can be greater than 1 m in diameter. Plants may attain heights of 1.7 to 3.3 m. A minimum stubble height of 20 cm should be maintained during hay production to protect the stand (Roberts and Kallenbach, 1999), and Gillen (2001) recommended a higher stubble height under grazing conditions. Interest in eastern gamagrass
gained momentum after the cultivar ‘Pete’ was developed from 70 accessions originating from native eastern gamagrass populations in Kansas and Oklahoma (Fine et al., 1990). Popularity of eastern gamagrass has increased because it usually produces large quantities of forage during the summer months. Compared with other tall-growing, perennial warmseason grasses, growth and quality characteristics of eastern gamagrass have been incompletely evaluated. Yields of DM at first harvest for eastern gamagrass depend on harvest date and maturity. In a study conducted in Florida, yields of DM increased with fertilization, but the yields declined after the second year of frequent cuttings (Kalmbacher et al., 1990). Brejda et al. (1996) recommended a 6-wk harvest interval if the goal is to produce greater DM yield, and a 4-wk interval if greater CP concentration is desired. The NDF concentrations are generally high (> 60.0%), even at immature stages of growth (Coblentz et al., 1998). Fibrous components in eastern gamagrass are of similar concentrations to those reported commonly for other warm-season grass species. In a review, Coblentz et al. (1999b) reported that ADF concentrations ranged between 29.2 to 44.8% over
364 several studies. The concentration of ADF increases in leaf, stem, and whole- plant tissues and has a positive relationship with plant maturity (Coblentz et al., 1998). There remains a need for information to determine the appropriate timing of the first harvest of eastern gamagrass. The objective of this study was to evaluate yield and nutritive value of eastern gamagrass when the harvests were performed weekly over 10 dates between mid May and early August.
MATERIALS AND METHODS Eastern gamagrass was established during spring 1999 in rows spaced 102 cm apart. The experimental site was fertilized on May 1, 2000, with ammonium nitrate at a rate of 56 kg of N/ha. On April 27, 2001, poultry litter was applied (2.4 t/ha; dry basis) and provided 147, 50, and 65 kg/ha of N, P and K. On May 8, 2002, poultry litter was applied (1.5 t/ha; dry basis) and provided 113, 39, and 51 kg/ha of N, P, and K. Plots were not burned because the field was adjacent to a residential area.
Mashingo et al.
forage samples were dried under forced air at 50°C, and yields of DM were then extrapolated to a kilogram per hectare basis. In association with each harvest, plant height was measured from the ground to the uppermost point of the leaf canopy when plants were vegetative, or the seedhead following stem elongation. After drying, tillers were counted from 1 m of row, and tiller counts were expressed as the number of tillers per square meter. For forage samples harvested in 2000 and 2001, leaf and stem tissues were hand-separated individually and the leaf was clipped at the collar to remove the leaf sheath and to obtain samples of each tissue type that were used for subsequent nutritive evaluation. Samples were ground through a 2-mm screen in a Wiley mill (Arthur H. Thomas, Swedesboro, NJ) for in situ analyses; then, subsamples of dried whole-plant, stem, and leaf samples were ground through a 1-mm screen. Neutral detergent fiber, ADF, and ADL were sequentially determined using batch
procedures outlined by ANKOM Technology Corp. (Fairport, NY) for samples from 2000 and 2001. The N concentrations were determined by a modified Kjeldahl procedure (Kjeltech Auto 1030 Analyzer, Tecator Inc., Herndon, VA), and CP was calculated by multiplying the percentage of N in each sample by 6.25.
In Situ DM and Forage Disappearance Five ruminally cannulated crossbred steers (mean BW = 388 ± 38 kg) were used as replicates to determine in situ degradation of eastern gamagrass. These animals were cannulated and managed by procedures approved by the University of Arkansas Animal Care and Use Committee. Steers were housed in individual (3.4 × 4.9 m) pens and fed a basal diet of 80% bermudagrass hay and 20% concentrate. The diet was offered at 0730 and 1600 h each day in 2 equal allotments for a cumulative daily rate of 2.2% of BW. Water supply was provided ad libitum to
Harvest Sampling Procedures and Chemical Analyses The experimental design was a randomized complete block with 4 replications and harvest dates as treatments. Each year, sampling was initiated on approximately May 15 and was continued on weekly intervals until approximately July 15, which resulted in a total of 10 harvest dates annually. Within each block, a 1-m section of 2 drill rows was harvested to a 20-cm stubble height with hand shears on each of the 10 sampling dates. Generally, sampling locations within each block were picked at random, but the large area (50 × 50 m) within each field block allowed for considerable distance (>5 m) between specific sampling locations, thereby preventing any confounding across specific harvest locations related to the availability of sunlight. After harvest,
Figure 1. Monthly rainfall totals measured at the University of Arkansas Research Farm in Fayetteville during the growing season of the 3-yr study. Monthly mean (1971 to 2000) precipitation was 110, 129, 134, 80, and 76 mm for April, May, June, July, and August (SRCC, 2008).
Yields and nutritive value of eastern gamagrass
all steers. Steers were adapted to the basal diet for 10 d before conducting the trial. Whole-plant samples harvested during 2000 were ground through a 2-mm screen in preparation for in situ incubations. Within each harvest date, forages were composited over field blocks, thereby resulting in a manageable number of forages (10) for ruminal incubation. A total of 500 Dacron bags (10 × 20 cm, 53-μm pore size; ANKOM Technology Corp.) were filled with 5 g of sample and sealed with an impulse heat sealer (Model CD-200; National Instrument Co. Inc., Baltimore, MD). Within each steer, one bag of each forage was incubated for 3, 6, 9, 12, 24, 48, 72, 96, or 120 h. Prior to insertion in the ventral rumen, all bags were soaked in tepid (39°C) water for 0.33 h to remove water-soluble components and reduce lag time associated with wetting. Bags were inserted into the rumen simultaneously, immediately before the 0730-h feeding. After removal from the rumen, all bags were rinsed in a top-loading washing machine (Whirlpool Corp., Model #LR 7144 EQ1, Benton Harbor, MI) 10 times in about 45 L of tap water with 1 min of agitation and 2 min of spin per rinse. A 0-h incubation time also was included in the analysis, and was based on bags that were soaked in tepid water and rinsed, but not inserted into the rumen (Vanzant et al., 1996; Coblentz et al., 1997). The A fraction was defined as the immediately soluble portion, although it is recognized that some minute insoluble particles may have been included (Coblentz et al., 1998; Galdámez-Cabrera et al., 2003). The NDF concentration in residues was determined as described earlier. In situ procedures were consistent with the standardized techniques described by Vanzant et al. (1998). The fractional passage rate for each steer was determined by using acid detergent insoluble ash (ADIA) as an internal marker. Mass of ruminal contents for steers at 0 h (before feeding) and 4 h after feeding were determined after evacuating
the rumen. Rumen contents were sub-sampled in triplicate after being weighed and mixed, and sub-samples were dried at 50°C for 120 h in a forced-air oven. Hay and concentrate samples were dried at 50°C for 48 h in a forced-air oven. All samples were ground to pass a 1-mm screen in a Wiley mill. Concentration of ADIA in the basal diet and digesta samples were determined by ashing ADF residues in a muffle furnace at 500°C for 8 h. The concentration of ADIA in the bermudagrass hay and concentrate comprising the basal diet were 20.2 and 3.5 g/kg, respectively. Mean ADIA concentrations in ruminal contents obtained from evacuation of steers at 0 and 4 h were 30.5 ± 0.5 and 28.3 ± 1.2 g/kg, respectively. Fractional passage rate (Kp) of ADIA for each steer was calculated by dividing the mean ADIA intake (g/h) by the mean ruminal mass (g) of
365
ADIA obtained from the 0- and 4-h ruminal evacuations (Waldo et al., 1972); the mean calculated Kp for steers was 0.035 ± 0.007/h. In situ DM residues were divided into 3 fractions based on susceptibility to ruminal degradation and were defined as follows: A = the immediately soluble fraction, B = the fraction that was degraded at a measurable rate, and C = the fraction unavailable in the rumen. Degradation kinetics were determined by non-linear regression of percentage of DM remaining on incubation time, using PROC NLIN of SAS (SAS, 1985). Data were fitted according to a nonlinear regression model (Mertens and Loften, 1980): DM_REM = B e−k(t-L) + C, when time > L, and DM_REM = B + C when 0 < time < L; where, DM_REM = DM remaining, t incubation time (hours), L = lag times, and K = degradation
Table 1. Height (cm) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Item Harvest 1 2 3 4 5 6 7 8 9 10 n Best fit Cubic Quadratic Linear Intercept RMSE3 R2 P4
2000 93 118 142 173 182 196 193 202 219 225 40 Cubic1 0.24 −5.34 47.3 47.1 8.21 0.96 0.003
1
Cubic effect of harvest dates.
2
Quadratic effect of harvest dates.
3
RMSE = root mean square error.
4
2001 142 171 174 191 210 220 230 234 234 231 40 Quadratic2 — −1.3 24.5 119.7 6.9 0.95 <0.001
2002 109 127 152 190 209 216 224 229 240 240 40 Quadratic — −1.87 35.5 70.1 8.69 0.97 <0.001
P = probability that the quadratic or cubic parameter estimate was different from zero.
Mashingo et al.
366 rate constants. Lag times, K, and fractions B and C were determined directly from the model. The immediately soluble portion (fraction A) was calculated by difference [total DM – (B + C)]. Effective DM disappearance was calculated as effective disappearance = A + B × [Kd/(Kd + Kp)], where Kp = fractional passage rate of the basal diet using the mean of the steers and Kd = fractional rate of degradation of potentially degradable DM.
Statistical Analyses Data collected from 2000 to 2002 on forage growth (height and tillering) and DM yield were analyzed by regressing against harvest date using PROC REG (SAS, 1985). When data were available for more than 1 yr, the effect of year and the interaction between harvest dates were tested. If the year × harvest date interaction was significant (P < 0.05), data were analyzed separately for each year. Data of NDF, ADF, ADL, cellulose, and hemicellulose concentrations for whole plant and leaf tissues from samples collected during 2000 and 2001, and for stem tissue in 2001, were analyzed by regressing against harvest dates using PROC REG (SAS, 1985). The regression model included cubic, quadratic, and linear terms, and the highest order term was dropped from the model if it was non significant at P < 0.01. Parameters of in situ degradation for each date were analyzed as a randomized complete block design using ANOVA procedure of SAS (1985). The 5 steers were considered as blocks because of the number of samples. Excessive sample numbers prohibited the evaluation of kinetics of ruminal DM disappearance for all possible combinations of harvest date, block, and year. To reduce the number of forages to a manageable number each year (10) for this type of analysis, some procedural compromises were necessary. To accomplish this, forages were composited over field replications within each harvest date, and then kinetic evaluations
for 2000 and 2001 were conducted independently.
RESULTS AND DISCUSSION The interaction of year × harvest date was significant, so results are presented for each year. This interaction is explained by rainfall distribution during the 3-yr period (Figure 1). Rainfall at the beginning of the growing period in April and May was 31 and 181 mm in 2000, 51 and 168 mm in 2001, and 173 and 131 mm in 2002, respectively. Rainfall was exceptionally heavy (362 mm) during June 2000 compared with June 2001 (93 mm) and June 2002 (102 mm) or to normal (1971 to 2000) precipitation of 133 mm (SRCC, 2008).
Forage Height and Yield During each year height of eastern gamagrass increased (P = 0.003) with advancing maturity at 10 different
harvests (Table 1). There was a cubic increase (P = 0.003) in height relative to harvest date during 2000, but during 2001 and 2002 the trend was a quadratic (P < 0.001) increase. The respective increases in eastern gamagrass height during the three 70-d growing seasons were 132, 89, and 131 cm, and plants attained heights of 225, 231, and 240 cm during 2000, 2001, and 2002, respectively. Greater growth rates of eastern gamagrass were observed in May and June during 2001 and 2002 compared with 2000. During 2000, growth rate was most rapid during July. This may be partly explained on the basis of excellent June precipitation, which was nearly 3 times the 30-yr norm for that month (SRCC, 2008). There was a linear relationship (P < 0.001) between number of tillers and harvest date during 2000 and 2002, but the pattern was quadratic (P < 0.001) during 2001 (Table 2).
Table 2. Tillers (number per m2) of eastern gamagrass at 10 weekly dates (beginning on May 15) in Fayetteville, AR Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Quadratic Linear Intercept R2 RMSE3 P4
2000 80 88 110 183 270 325 350 377 456 471 Linear1 — 48.47 4.56 0.92 42.59 <0.001
1
Linear effect of harvest dates.
2
Quadratic effect of harvest dates.
3
RMSE = root mean square error.
4
2001 166 136 152 138 155 217 161 250 270 306 Quadratic2 3.68 −24.40 189.38 0.71 35.81 <0.001
2002 100 112 104 128 168 153 152 201 191 208 Linear — 12.11 82.80 0.52 34.04 <0.001
P = probability that the quadratic or cubic parameter estimate was different from zero.
Yields and nutritive value of eastern gamagrass
The number of tillers ranged from 80 to 471/m2 during 2000, from 136 to 306/m2 during 2001, and from 100 to 208/m2 during 2002. These plots were not burned because the research site was located adjacent to a residential area. Burning is known to have a positive effect on tillering density and growth of perennial warm-season grasses. Previously, Cuomo et al. (1998) reported increased plant vigor and tillering density when perennial warm-season grasses were burned during spring. Similarly, Mitchell et al. (1994) observed a 70% increase in forage production by big bluestem (Andropogon gerardii Vitman) in response to early or mid-spring burning. In the present study, overall annual means for tiller density during 2001 and 2002 declined to 72 and 56%, respectively, of levels observed during 2000. Yields of DM by eastern gamagrass increased in curvilinear patterns over harvest dates in each experimental year; however, responses for specific years varied (Table 3). The relationship between DM yield and harvest dates were quadratic (P = 0.008) during 2000 and cubic (P < 0.001) during the following 2 yr. Yields of DM on the final (mid-July) harvest date increased by 45 and 51% during 2001 and 2002 when compared with the yield observed on the same harvest date for 2000 (10.04 Mg/ha). In this study, the 2-yr (2001 and 2002) average of calculated daily DM accumulation values was 99 kg/ha between wk 6 and 8 and was within the range reported for western Oklahoma by Gillen (2001), who observed 59 to 112 kg/ha DM accumulations (daily) during the first 6 to 8 wk of the growing season. This range for DM yield is consistent with other reports. Douglas (1993) reported an average annual DM yield of 10.16 Mg/ha for eastern gamagrass harvested from 3 harvests spaced at 45 d without fertilization. Similarly, Faix et al. (1980) reported annual yields of 7.60 to 24.68 Mg/ha in southern Illinois. Bredja et al. (1997) reported annual yields ranging from 8.00 to 13.60
Mg/ha for eastern gamagrass fertilized with either 168 or 336 kg N/ha and harvested from a 3-cut system. Quadratic responses to N fertilization were observed within 4 of 6 siteyears. Brejda et al. (1996) reported that eastern gamagrass produced good regrowth following defoliation, which allowed multiple harvests during the growing season. Faix et al. (1980) harvested PMK-24 eastern gamagrass 3 and 4 times per growing season and reported DM yields ranging from 7.60 to 24.68 Mg /ha per year.
Crude Protein Concentrations The CP concentrations of eastern gamagrass are shown in Table 4. Whole-plant CP exhibited linear (P < 0.001) and quadratic (P = 0.002) declines with harvest dates during 2000 and 2001, respectively. The declines between the initial and
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final harvest dates ranged from 14.4% down to 6.3% during 2000, and from 14.7% down to 6.6% during 2001. Many researchers have reported declines in CP concentrations with plant maturity for eastern gamagrass (Coblentz et al., 1998, 1999b; Dickerson and van der Grinten, 1990); however, these declines are not explained strictly as a function of increased proportions of stem within the forage. Concentrations of CP within leaf tissue declined in quadratic (P = 0.006) and linear (P < 0.001) relationships with time during 2000 and 2001, respectively. Respective concentrations of CP within leaf tissue harvested in mid-July were only 46 and 61% of those observed in mid-May. Moreover, Coblentz et al. (1998) reported that stem tissue from eastern gamagrass plants harvested at the boot, anthesis, and physiologically mature stages of growth contained < 31% stem tissue
Table 3. Dry matter yields (mg/ha) of eastern gamagrass at 10 weekly dates (beginning on May 15) in Fayetteville, AR Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Cubic Quadratic Linear Intercept RMSE3 R2 P4
2000 1.25 1.75 2.22 3.83 4.84 5.13 5.67 8.12 9.63 10.04 Quadratic1 — 0.57287 0.53869 0.04446 0.725 0.95 0.008
1
Quadratic effect of harvest dates.
2
Cubic effect of harvest dates.
3
RMSE = root mean square error.
4
2001 4.14 5.28 8.96 10.10 8.52 11.04 10.35 10.78 10.73 14.51 Cubic2 0.04994 −0.88246 5.31453 −0.92218 1.334 0.82 <0.001
2002 2.15 2.75 3.24 4.79 7.39 9.01 11.76 13.44 13.97 15.19 Cubic −0.039252 0.66844 −1.58256 3.21189 0.789 0.97 <0.001
P = probability that the quadratic or cubic parameter estimate was different from zero.
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Table 4. Crude protein concentrations (% of DM) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Whole plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Quadratic Linear Intercept RMSE3 R2 P4
2000
Stem
2001
14.4 13.1 12.6 11.1 10.1 9.8 9.4 7.1 6.5 6.3 Linear1 — −0.91 15.09 1.0 0.88 <0.001
14.7 13.1 11.5 10.8 9.9 9.2 7.9 7.7 7.8 6.6 Quadratic2 0.06 −1.59 16.04 0.91 0.89 0.002
Leaf
2000
2001
9.1 8.2 6.1 5.6 4.6 4.5 3.6 3.5 3.0 3.0 Linear — −2.11 11.16 0.60 0.92 <0.001
8.3 8.1 6.9 6.3 5.8 5.3 4.0 3.7 2.9 2.8 Linear — −0.66 9.06 0.49 0.94 <0.001
1
Linear effect of harvest dates.
2
Quadratic effect of harvest dates.
3
RMSE = root mean square error.
4
P = probability that the quadratic or cubic parameter estimate was different from zero.
2000
2001
16.9 15.1 14.0 11.6 11.1 9.9 9.9 — 7.9 7.8 Quadratic 0.07 −1.81 18.48 1.21 0.85 0.006
14.5 14.4 13.1 11.9 11.7 11.1 9.9 9.3 8.8 8.8 Linear — −0.69 15.14 1.06 0.78 <0.001
Table 5. Neutral detergent fiber concentrations (% of DM) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Whole plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Quadratic Linear Intercept RMSE3 R2 P4
2000 65.9 67.4 69.8 73.3 72.3 75.0 73.1 77.4 78.5 75.3 Quadratic1 −0.137 2.73 63.0 1.73 0.82 <0.001
Stem 2001 66.6 65.0 66.8 71.7 68.8 67.4 71.1 67.7 70.5 68.9 Linear2 — 0.372 66.4 2.05 0.22 0.002
Leaf
2000
2001
71.8 71.9 76.6 79.4 79.5 81.7 80.6 82.8 82.2 82.1 Linear — 3.40 67.8 1.45 0.89 0.003
64.5 65.7 68.4 66.5 68.1 67.2 66.6 68.4 68.5 68.5 Linear — 1.18 63.7 2.49 0.66 <0.001
1
Quadratic effect of harvest dates.
2
Linear effect of harvest dates.
3
RMSE = root mean square error.
4
P = probability that the quadratic or cubic parameter estimate was different from zero.
2000 66.8 66.3 69.2 72.9 75.0 74.7 73.3 74.0 77.8 75.9 Quadratic −0.137 2.64 63.3 1.92 0.77 0.002
2001 66.4 66.2 62.7 69.6 71.3 71.2 72.2 72.4 73.2 76.4 Linear — 0.63 62.8 2.46 0.36 <0.001
Yields and nutritive value of eastern gamagrass
by weight, thereby further indicating that dilution by developing stems plays only a limited role in declines in whole-plant CP over time.
Neutral Detergent Fiber Concentrations Whole-plant NDF for eastern gamagrass sampled in 2000 exhibited a quadratic (P < 0.001) increase with harvest date and ranged from 65.9 at the first harvest to 78.5% at the ninth harvest (Table 5). These results are consistent with those summarized previously (Coblentz et al., 1998), where an increase of 8.6 percentage units was observed between boot stage and physiological maturity. In this study, NDF concentrations in stem tissues increased linearly (P = 0.003) across harvest dates in 2000. There was a linear relationship (P < 0.001) between NDF concentrations and harvest dates for
stem and leaf tissues in 2001. There was a quadratic relationship (P = 0.002) between NDF concentrations and harvest dates for leaf tissues in 2000. These results from 2001 are consistent with those observed by Fick and Coblentz (1994) who reported that the NDF concentration of leaf and stem portions harvested over 3 yr maintained a narrow range of 65.3 to 67.5%. Griffin and Jung (1983) suggested that NDF concentration of leaf and stem tissue may have a narrow range that is indistinguishable during early stages of growth and increases slightly with plant maturity. Coblentz et al. (1999b) noted that cell wall content of whole-plant eastern gamagrass is not dependent on leafto-stem ratio through the anthesis stage of growth. This is corroborated by 2001 data of this study where NDF was generally reduced on most dates for stem tissue, relative to leaf.
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Acid Detergent Fiber Concentrations There were quadratic (P < 0.001) and cubic (P < 0.001) increases of ADF concentration and with advancing maturity (harvest dates) for whole-plant samples harvested in 2000 and 2001, respectively (Table 6). The ADF concentrations for whole-plant eastern gamagrass increased from 31.1 to 44.5% during 2000 and from 35.3 to 41.5% during 2001; however, the maximum concentration during 2001 occurred on the fourth harvest date with relatively limited change thereafter. Concentrations of ADF for stem tissue during 2001increased over harvest dates by 7.7 percentage units, thereby exhibiting a cubic (P = 0.002) relationship with time. The relationship with leaf tissue was also cubic (P = 0.003), and ADF concentrations of leaf tissue during 2001
Table 6. Acid detergent fiber concentrations (% of DM) of eastern gamagrass at 10 different harvest dates (beginning on May 15) in Fayetteville, AR Whole plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Cubic Quadratic Linear Intercept RMSE3 R2 P4
2000 31.1 32.5 34.9 37.9 42.5 39.5 38.2 43.6 44.1 44.5 Quadratic1 — −0.266 4.27 25.9 2.50 0.76 <0.001
Stem 2001 35.3 35.0 38.3 41.5 38.2 35.2 37.8 37.3 39.9 36.8 Cubic2 0.159 −2.897 14.78 22.0 4.79 0.38 <0.001
2000 38.2 42.3 44.1 46.1 46.4 49.3 48.3 50.3 47.6 51.0 Quadratic — −0.064 5.21 33.73 1.76 0.83 0.024
Leaf 2001 39.3 39.8 40.0 42.1 43.3 42.1 43.6 44.9 44.9 47.0 Cubic 0.120 −2.068 10.23 30.4 4.03 0.25 0.002
1
Quadratic effect of harvest dates.
2
Cubic effect of harvest dates.
3
RMSE = root mean square error.
4
P = Probability that the quadratic or cubic parameter estimate was different from zero.
2000 31.1 31.2 34.3 36.5 39.6 38.5 37.8 38.1 43.7 41.3 Quadratic — −0.191 3.36 26.8 2.89 0.67 0.003
2001 33.1 37.4 37.3 35.2 35.0 33.9 35.7 37.3 43.1 36.1 Cubic 0.136 −2.363 11.02 25.3 4.66 0.34 0.003
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370 were generally less than observed for stem tissue. Similarly, Coblentz et al. (1999b) reported that ADF concentrations in stem increased with maturity.
Hemicellulose Concentrations Hemicellulose concentrations are shown in Table 7; whole-plant concentrations during 2000 and 2001 increased quadratically (P = 0.008) and cubically (P < 0.001), respectively, with harvest date. Concentrations of hemicellulose varied little across harvest dates, indicating there was relatively limited practical effect of advancing plant maturity. Hemicellulose concentration in stem tissue did not vary significantly in 2000, but during 2001 had a linear increase (P < 0.001) in relation to harvest dates. However, the difference in concentrations between the first
and last harvest date was only 2.3 percentage units. The relationship between hemicellulose concentrations in leaf tissue and harvest dates was linear (P = 0.002) during 2001, but no relationship was observed during 2000 (P = 0.275). Hemicellulose concentrations in leaf tissue generally were greater than that observed in stem tissue.
Cellulose Concentrations Cellulose concentrations increased (P < 0.001) for whole-plant samples harvested during 2000 and 2001, respectively (Table 8). Cellulose concentrations in stem tissue sampled during 2001 increased (P = 0.005) in relation to harvest date, and that of leaf tissue harvested 2000 and 2001 exhibited quadratic (P = 0.002) and cubic (P = 0.002) increases. Stem
samples were not analyzed for cellulose during 2000.
Lignin Concentrations The ADL concentrations for eastern gamagrass are shown in Table 9. The concentration of ADL in wholeplant tissues of eastern gamagrass harvested in 2000 was explained by a quadratic response (P < 0.001), and samples harvested in 2001 were explained by a linear (P < 0.001) relationship with harvest date. Stem and leaf tissue ADL generally increased with plant maturity. There was a cubic (P < 0.001) and linear relationship (P < 0.001) for stem and leaf tissue, respectively, sampled in 2001, and a linear relationship for leaf tissue harvested during 2000. Samples were not analyzed for ADL during 2000. Coblentz et al. (1999b) reported increased lignin concentra-
Table 7. Hemicellulose concentrations (% of DM) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Whole plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Cubic Quadratic Linear Intercept RMSE4 R2 P5
2000 34.8 34.9 34.7 35.4 29.8 35.5 34.9 33.8 34.4 33.9 Quadratic1 — 0.137 −1.622 37.23 2.24 0.19 0.008
Stem 2001 31.2 29.9 28.5 30.2 30.6 32.2 31.4 30.4 30.6 32.2 Cubic2 −0.094 1.706 −8.40 38.5 3.15 0.34 <0.001
2000 33.6 29.6 32.4 33.3 33.1 32.4 32.2 32.5 34.6 31.1 Linear — — −1.64 33.9 2.24 0.06 0.321
Leaf 2001 27.1 26.4 27.4 27.5 27.9 29.1 28.6 27.4 31.4 29.4 Linear3 — — 0.573 25.5 2.49 0.32 <0.001
1
Quadratic effect of harvest dates.
2
Cubic effect of harvest dates.
3
Linear effect of harvest dates.
4
RMSE = root mean square error.
5
P = probability that the quadratic or cubic parameter estimate was different from zero.
2000
2001
35.6 34.1 34.9 36.4 33.4 29.4 35.6 35.9 34.1 35.6 Linear — — −0.199 36.0 3.28 0.03 0.275
31.4 28.3 31.0 31.2 33.0 33.2 30.9 31.2 30.2 32.4 Linear — — 0.63 29.0 3.24 0.25 0.002
Yields and nutritive value of eastern gamagrass
371
Table 8. Cellulose concentrations (% of DM) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Whole-plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Cubic Quadratic Linear Intercept RMSE4 R2 P5
2000 28.4 30.0 35.0 37.4 37.1 35.1 33.8 38.0 38.3 36.4 Quadratic2 — −0.199 3.19 24.8 2.04 0.727 <0.001
Stem 2001 31.9 31.2 37.1 34.2 33.7 30.4 34.4 31.6 33.9 30.6 Cubic3 0.16 −2.927 14.65 18.5 4.73 0.431 <0.001
Leaf
2000
2001
NA1 NA NA NA NA NA NA NA NA NA — — — — — NA — —
29.93 33.76 33.0 31.2 30.7 29.2 30.5 31.8 32.0 30.2 Cubic 0.11 −1.877 8.89 27.7 4.01 0.248 0.005
1
NA = not analyzed.
2
Quadratic effect of harvest dates.
3
Cubic effect of harvest dates.
4
RMSE = root mean square error.
5
P = probability that the quadratic or cubic parameter estimate was different from zero.
tions as a function of plant maturity. Horner et al. (1985) reported a mean lignin concentration of 9.3% for eastern gamagrass regrowth hay.
Ruminal In Situ Degradation of Dry Matter In situ degradation kinetics of whole-plant eastern gamagrass are presented in Table 10. Fraction A comprised 24.2 and 22.7% of DM on the first and third harvest dates and was comparable to that found at boot (26.8%) and anthesis (22.8%) stages by Coblentz et al. (1998). Fraction B differed (P < 0.05) among harvest dates and ranged from 58 to 62.7% across all sampling dates. Coblentz et al. (1998) observed that fraction B for eastern gamagrass harvested at boot, anthesis, and mature stages as 53.6, 53.6 and 48.1% of DM, respectively. Fraction B contains fiber
components that are digested incompletely. Undegradable fraction C increased (P < 0.05) with maturity. In this study, the least numerical value for fraction A and greatest numerical value of fraction C were observed for eastern gamagrass harvested on the July 3 harvest. Fraction C decreased (P < 0.05) following the first harvest date until the last. Lag time of DM degradation was not affected (P > 0.05) by harvest date. The declining estimates of effective degradability of DM are related to declining decay rates in the rumen, and to a lesser extent to declining pools of soluble (fraction A) DM. Decay rates declined from 4.6 to 2.3%/h over harvest dates, which is a huge change with respect to utilization and is consistent with responses for Coblentz et al. (1998). An 18.1 percentage unit decline in effective degradability of DM over time is
2000 28.7 28.6 31.1 31.9 37.1 39.1 33.3 33.6 38.0 35.6 Quadratic — −0.174 2.80 25.0 2.42 0.599 0.002
2001 35.4 35.1 33.4 36.3 37.5 36.1 37.1 38.2 37.4 39.3 Cubic 0.14 −2.407 10.90 22.2 4.63 0.426 0.002
enormous, although changes over the first 4 and last 4 harvest dates appear minimal.
IMPLICATIONS Concentrations of NDF, ADF, and CP and degradation of DM are important criteria for deciding when, and at what stage of maturity, to harvest eastern gamagrass as hay. If hay of greater nutritive value is preferred, then harvest should occur at the beginning of June. According to this study, the expected CP would be greater than 10%, but average DM yield would likely be < 8 Mg/ha. If hay is harvested later in June, CP would probably be less than 10%, but DM yields may be >10 Mg/ha. Degradation characteristics of DM indicated a decline with advancing harvest dates. A decision to harvest earlier would result in greater nutri-
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372
Table 9. Acid detergent lignin concentrations (% of DM) of eastern gamagrass at 10 weekly harvest dates (beginning on May 15) in Fayetteville, AR Whole-plant Item Harvest 1 2 3 4 5 6 7 8 9 10 Best fit Cubic Quadratic Linear Intercept RMSE5 R2 P6
2000 2.66 2.48 3.28 4.14 5.41 4.37 4.40 5.53 5.83 5.01 Quadratic2 — −0.074 1.17 0.96 0.79 0.69 <0.001
Stem 2001
Leaf
2000 NA1 NA NA NA NA NA NA NA NA NA — — — — — NA NA
3.47 3.85 4.13 4.40 4.47 4.77 5.33 5.68 6.04 6.17 Linear3 — — 0.31 3.15 0.28 0.93 <0.001
2001 3.81 4.66 5.40 5.73 5.88 6.02 6.48 6.73 7.32 7.65 Cubic4 0.0102 −0.183 1.31 2.70 0.19 0.97 <0.001
1
NA = not analyzed.
2
Quadratic effect of harvest dates.
3
Linear effect of harvest dates.
4
Cubic effect of harvest dates.
5
RMSE = root mean square error.
6
P = Probability that the quadratic or cubic parameter estimate was different from zero.
2000
2001
2.42 2.67 3.31 4.48 4.50 6.38 4.46 4.51 5.67 5.43 Linear — — 0.34 2.44 0.80 0.61 <0.001
3.16 3.61 3.87 4.07 4.29 4.82 5.21 5.44 5.75 5.87 Linear — — 0.31 2.91 0.12 0.98 <0.001
Table 10. In situ DM degradation of whole plant eastern gamagrass at 10 weekly harvest dates (beginning on May 15) during 2000 and 2001 in Fayetteville, AR Item
A1
B2
C3
EFF4
(%) Harvest 1 2 3 4 5 6 7 8 9 10 SEM
24.2a 22.7ab 22.7ab 19.2bc 19.1c 15.7cd 17.7cd 14.5d 16.1cd 17.7c 7.7
61.8ab 62.7a 61.2ab 60.0ab 60.3ab 62.3a 62.3a 60.9ab 60.3ab 58.0b 11.1
14.0e 14.6ed 16.3d 20.8c 20.6c 21.9bc 21.2c 24.6a 23.7ab 24.3a 3.1
58.8a 55.6b 55.4b 50.4c 46.9d 44.0e 42.5ef 41.0f 40.5f 40.7f 3.2
Lag
Kd
(h)
(%/h)
1.5 0.7 1.7 1.8 1.2 1.2 1.1 2.3 1.6 1.6 2.0
4.6a 3.9b 4.1ab 3.9b 3.0c 2.9cd 2.5cde 2.7cde 2.5de 2.3e 0.001
a-f
Means in a column with different superscript differ (P < 0.05).
1
A = immediately soluble fraction: [total DM – (B + C)].
2
B = fraction degradable at a measurable rate.
3
C = undegradable fraction.
4
EFF = effective degradability of DM. EFF = A + B × Kd/(Kd + Kp), where Kp is the fractional passage rate of the basal diet using the mean of the 5 steers. The experimentally determined passage rate was 0.035 ± 0.007/h.
Yields and nutritive value of eastern gamagrass
tive value and also permit regrowth of the forage.
LITERATURE CITED Brejda, J. J., J. R. Brown, T. E. Lorenz, J. Henry, and S. R. Lowry. 1997. Variation in eastern gamagrass forage yield with environments, harvests, and nitrogen rates. Agron. J. 89:702. Brejda, J. J., J. R. Brown, T. E. Lorenz, J. Henry, J. L. Reid, and S. R. Lowry. 1996. Eastern gamagrass response to different harvest intervals and nitrogen rates in northern Missouri. J. Prod. Agric. 9:130. Coblentz, W. K., I. E. O. Abdelgadir, R. C. Cochran, J. O. Fritz, W. H. Fick, K. C. Olson, and J. E. Turner. 1999a. Degradability of forage proteins by in situ and in vitro enzymatic methods. J. Dairy Sci. 82:343. Coblentz, W. K., K. P. Coffey, and J. E. Turner. 1999b. A review: Quality characteristics of eastern gamagrass forages. Prof. Anim. Sci. 15:211. Coblentz, W. K., J. O. Fritz, R. C. Cochran, W. L. Rooney, and K. K. Bolsen. 1997. Protein degradation responses to spontaneous heating in alfalfa hay by in situ and ficin methods. J. Dairy Sci. 80:700. Coblentz, W. K., J. O. Fritz, W. H. Fick, R. C. Cochran, and J. E. Shirley. 1998. In situ dry matter, nitrogen, and fiber degradation of alfalfa, red clover, and eastern gamagrass at four maturities. J. Dairy Sci. 81:150. Cuomo, G. J., B. E. Anderson, and L. J. Young. 1998. Harvest frequency and burning effect on vigor of native grasses. J. Range Manage. 51:32.
Dickerson, J. A., and M. van der Grinten. 1990. Developing eastern gamagrass as a haylage crop for northeast. p. 194 in Proc. Am. Forage Grassl. Council Ann. Meeting, Bellville, PA. Am. Forage Grassl. Council, Georgetown, TX. Douglas, J. 1993. Effects of clipping frequency and N rate on yield and quality of eastern gamagrass. MS Thesis. Stephen F. Austin State Univ., Nacogdoches, TX. Faix, J. J., C. J. Kaiser, and F. C. Hinds. 1980. Quality, yield, and survival of Asiatic bluestems and an eastern gamagrass in southern Illinois. J. Range Manage. 33:388. Fick, W. H., and W. K. Coblentz. 1994. Production and quality of 12 eastern gamagrass progeny. p. 16 in Proc. Soc. Range Management Ann. Meeting, Colorado Springs, CO. (Abstr.). Fine, G. L., F. I. Barnett, K. L. Anderson, R. D. Lippert, and E. T. Jacobson. 1990. Registration of ‘Pete’ eastern gamagrass. Crop Sci. 30:741. Galdámez-Cabrera, N. W., K. P. Coffey, W. K. Coblentz, J. E. Turner, D. A. Scarbrough, Z. B. Johnson, J. L. Gunsaulis, M. B. Daniels, and D. H. Hellwig. 2003. In situ ruminal degradation of dry matter and fiber from bermudagrass fertilized with different nitrogen rates and harvested on two dates. Anim. Feed Sci. Technol. 105:185. Gillen, R. L. 2001. Production and grazing management for eastern gamagrass. Proc. 56th Southern Pasture Forage Crop Improvement Conf., Springdale, AR. Am. Forage Grassl. Counc., Georgetown, TX. Griffin, J. L., and G. A. Jung. 1983. Leaf and stem forages quality of big bluestem and switchgrass. Agron. J. 75:723.
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Horner, J. L., L. J. Bush, G. D. Adams, and C. M. Taliaferro. 1985. Comparative nutritional value of eastern gamagrass and alfalfa hay for dairy cows. J. Dairy Sci. 68:2615. Kalmbacher, R. S., L. S. Dunavin, and F. G. Martin. 1990. Fertilization and harvest season of eastern gamagrass Ona and Jay. Soil Crop Sci. Soc. Florida. Proc. 49:166. Mertens, D. R., and J. R. Loften. 1980. The effect of starch on forage fiber digestion kinetics in vitro. J. Dairy Sci. 63:1437. Mitchell, R. B., R. A. Masters, S. S. Waller, K. J. Moore, and L. E. Moser. 1994. Big bluestem production and forage quality responses to burning date and fertilizer in tallgrass prairies. J. Prod. Agric. 7:355. SAS. 1985. Users guide: Statistics, Version 5 ed. SAS Inst. Inc., Cary, NC. Roberts, C., and R. Kallenbach. 1999. Eastern gamagrass. Univ. of Missouri Guide #G 4671. Univ. of Missouri Outreach and Ext., Columbia. SRCC. 2008. Southern Regional Climate Center, Baton Rouge, LA. http://www.srcc. lsu.edu/southernClimate/atlas/images/ ARprcp.html/view?searchterm=Fayetteville Accessed January 2008. Vanzant, E. S., R. C. Cochran, and E. C. Titgemeyer. 1998. Standardization of in situ techniques for ruminant feedstuff evaluation. J. Anim. Sci. 76:2717. Vanzant, E. S., R. C. Cochran, E. C. Titgemeyer, S. D. Stafford, K. C. Olson, D. E. Johnson, and G. St. Jean. 1996. In vivo and in-situ measurements of forage protein degradation in cattle. J. Anim. Sci. 74:2773. Waldo, D. R., L. W. Smith, and E. L. Cox. 1972. Model of cellulose disappearance from rumen. J. Dairy Sci. 55:125.