Defoliation Management of Bahiagrass Germplasm ... - PubAg - USDA

Defoliation Management of Bahiagrass Germplasm Affects Cover and Persistence-Related Responses S. M. Interrante, L. E. Sollenberger,* A. R. Blount, S. W. Coleman, U. R. White, and K. Liu Bahiagrass (Paspalum notatum Flügge) cultivars are valued for their persistence under grazing and low management inputs. However, they are daylength-sensitive and have minimal cool-season production, resulting in high winter feeding costs in foragebased livestock systems. New germplasm is less daylength-sensitive, possesses greater cold tolerance, and is more productive during the cool season, but its persistence under defoliation is unknown. A field experiment quantified cover and persistence-related responses of photoperiod-sensitive bahiagrass (diploids ‘Pensacola’ and ‘Tifton 9’ and tetraploids ‘Argentine’ and Tifton 7) and a less photoperiod-sensitive, cold-adapted (PCA) diploid bahiagrass (Cycle 4) at two stubble heights (4 and 8 cm) and two harvest frequencies (7 and 21 d). Argentine cover was unaffected by defoliation treatments, but harvesting every 7 d to 4 cm for 3 yr resulted in 10 yr−1 on average) occurrences of subfreezing temperatures in the northern Gulf Coast region. Examples of these species include rhizoma peanut (Arachis glabrata Benth.; Ortega-S. et al., 1992), elephantgrass (Pennisetum purpureum Schum.; Chaparro et al., 1996), and bermudagrass [Cynodon dactylon (L.) Pers.; Pedreira et al., 2000]. Breeding and selection has resulted in development of PCA Cycle 4 bahiagrass, a genotype with greater cool-season production (Blount et al., 2008) and potential to extend the grazing season and reduce winter feed costs (Blount et al., 2001). Of concern is whether the greater cool-season production of PCA Cycle 4 will affect its long-term persistence and productivity when defoliated. Specifically, it is not clear whether these plants accumulate sufficient reserve organ mass, energy, and N to ensure winter survival and to produce vigorous spring regrowth. Also, it is not known to what degree defoliation intensity and frequency during the growing season influence long-term persistence of a PCA type. Previous studies in the Gulf Coast region have shown that frequent, severe defoliation may have negative effects on the mass of reserve storage organs including stem bases, rhizomes, stolons, and roots (Ortega-S. et al., 1992; Spitaleri et al., 1994; Chaparro et al., 1996; Macoon et al., 2002). Chaparro et al. (1996) reported that sustained frequent, close defoliation of ‘Mott’ elephantgrass resulted in reduced light interception, Abbreviations: NIR, near-infrared reflectance; PCA, less photoperiodsensitive, cold-adapted; TNC, total nonstructural carbohydrate.

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Forages

ABSTRACT

rhizome mass, rhizome TNC and N reserves, and number of tillers per plant. Gates et al. (1999) reported greater spring reserves (as estimated by total etiolated initial spring growth) in bahiagrass plots cut the previous growing season every 8 wk than in those cut every 2 or 4 wk, while cutting height did not affect spring reserves. After 3 yr of grazing every 2 wk, bahiagrass stem base TNC concentration during August to early September averaged Select = procedure of the soft ware InfraSoft International (ISI, State College, PA) based on spectral dissimilarity of samples (Schenk and Westerhaus, 1991a). Reference laboratory data for N and TNC were compared with the spectral data for the calibration samples and equations were developed with the ISI soft ware using partial least squares regression (Schenk and Westerhaus, Agronomy Journal

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1991b). The N mean, standard error of validation, and r 2 for the equation used were: 10.6 g kg−1, 0.9 g kg−1, and 0.85, respectively. The TNC mean, standard error of validation, and r 2 for the equation used were: 52.2 g kg−1, 13.4 g kg−1, and 0.86, respectively. These equations were then used to predict N and TNC for all samples, including those used for the calibration. Statistical Analyses Statistical analyses were performed using Proc Mixed of SAS (SAS Institute, 1996). Entry, stubble height, harvest frequency, year, and their interactions were considered fi xed effects and replicate and its interactions random effects. Year was considered fi xed because of the potential for carryover effects of treatments from previous years. Year was included in the model as a subplot treatment in a split-plot arrangement, with the treatment combinations being the main plot. The PDIFF feature of the LSMEANS procedure was used to compare entry means. Differences among stubble height and harvest frequency means were assessed using F tests. Cover data were subjected to arcsine transformation before statistical analysis and back-transformed for data presentation. Interaction means were compared when the interaction P value was 0.05), but it was affected by entry × stubble height (P = 0.02) and entry × harvest frequency (P = 0.01) interactions in 2006 and entry (P = 0.01) and harvest frequency (P = 0.001) main effects in 2007. In 2006, Argentine had greatest root + rhizome mass when harvested to 4-cm stubble height, and there were no differences among the other entries (Table 2). When harvested to 8-cm stubble height, Argentine and Pensacola had greater root + rhizome mass than all entries except Tifton 9, and there were no differences between Tifton 7 and PCA Cycle 4. With the exception of Argentine, stubble height had no effect on root + rhizome mass of the entries in 2006. There also was entry × harvest frequency interaction for root + rhizome mass in 2006 (Table 2). Argentine had greater root + rhizome mass than all entries except Pensacola when Table 1. Bahiagrass cover as affected by entry × stubble height × harvest frequency interaction (P = 0.06) in October. Data are means across three replicates and 3 yr (n = 9). Harvest frequency, d 7

21 Stubble height, cm

Entry

4

8

4

8

89aA 73bA 81abA 66bcB 55cB

94aA 84abA 86abA 83bA 77bA

% cover Argentine Tifton 7 Pensacola Tifton 9 PCA Cycle 4

91aA† 42bB 46bB 32bC 36bC

90aA 73bcA 82abA 65cB 46dBC

SE‡

4.8

† Means followed by the same letter, lowercase letters within a column and uppercase letters within a row, do not differ by the LSMEANS test (P > 0.05). ‡ Standard error of an interaction mean.

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Table 2. Bahiagrass root + rhizome mass as affected by entry × stubble height (P = 0.02) and entry × harvest frequency (P = 0.01) interactions in October 2006. Data are means across two harvest frequencies or two stubble heights and three replicates (n = 6). Stubble height, cm Entry Argentine Tifton 7 Pensacola Tifton 9 PCA Cycle 4

4 2530aA† 1560bA 1740bA 1920bA 1620bA

Harvest frequency, d

8

7

g DM m–2 1620abB 2280aA 1530bA 1480bcA 2040aA 1900abA 1550abA 1240cB 1510bA 1510bA

SE‡

Table 3. Bahiagrass stem base mass as affected by entry × stubble height (P = 0.01) and entry × harvest frequency (P = 0.01) interactions in October. Data are means across two stubble heights or harvest frequencies, three replicates, and 3 yr (n = 18). Stubble height, cm

21

Entry

1870abA 1610bA 1880aA 2220aA 1610bA

Argentine Tifton 7 Pensacola Tifton 9 PCA Cycle 4

210

4


8

390aA† 270bB 390aA 230bB 210bB

7 g DM m–2 460aA 450aA 410abA 290bB 330bcA 360abA 340bA 270bA 280cA 180cB

SE‡

21 400aA 390aA 360aA 300bA 310abA

39.6

† Means followed by the same letter, lowercase letters within a column and uppercase letters within a row and treatment variable, do not differ by the LSMEANS test (P > 0.05).


‡ Standard error of an interaction mean.


harvested every 7 d, while root + rhizome mass of Tifton 9 was less than all entries except Tifton 7. When harvested every 21 d, Pensacola and Tifton 9 had greater root + rhizome mass than all entries except Argentine. Tifton 9 had greater root + rhizome mass when harvested every 21 than 7 d, while there was no effect of harvest frequency on root + rhizome mass of the other entries. In October 2007, Argentine had greater (P = 0.01) root + rhizome mass than all entries except Pensacola (1660 and 1260 g DM m−2 , respectively). There was no difference in root + rhizome mass among Tifton 9, Tifton 7, and PCA Cycle 4 (1100, 910, and 950 g DM m−2 , respectively), but these values were considerably lower numerically than averages in 2006. Gates et al. (1999) reported Pensacola produced a greater root mass than Tifton 9 (33.6 and 21.4 g, respectively) from cores measuring 75 mm in diameter × 75 mm deep on plots receiving 168 kg N ha−1 yr−1. Pedreira and Brown (1996b) reported that Pensacola had more rhizomes per plant than Tifton 9. Average October rhizome + stubble mass was 1000 and 810 g DM m−2 for Pensacola and Tifton 9, respectively, when harvested every 14 d to 3.5- or 10-cm stubble height and fertilized with 200 kg N ha−1 annually (Pedreira and Brown, 1996a). In the current study, PCA Cycle 4 generally had or tended to have lower root + rhizome mass than Pensacola and Argentine during the second and third years of defoliation after having similar mass in Year 1. This greater impact of defoliation on root + rhizome mass of Cycle 4 raises some concern about its long-term persistence because numerous studies have reported decreasing belowground mass to be associated with reduced persistence in this environment (Ortega-S. et al., 1992; Spitaleri et al., 1994; Chaparro et al., 1996; Macoon et al., 2002). Bahiagrass root + rhizome mass was also affected by harvest frequency (P = 0.001) in October 2007. Root + rhizome mass was greater at 21- than 7-d harvest frequency (1440 and 915 g DM m−2 , respectively). Weekly clipping of perennial ryegrass (Lolium perenne L.) to 4 cm reduced root biomass compared to clipping every 8 wk, which was attributed to a shortage of carbohydrates available for root growth (Dawson et al., 2000). Root mass was 27% less in the first year and 46% less in the second year for heavy versus light grazing intensities of Caucasian bluestem [Bothriochloa bladhii (Retz.) S.T. Blake; Christiansen and Svejcar, 1988]. Frequent defoliation may

result in translocation of carbohydrate reserves from roots and rhizomes to the shoot for new leaf development to compensate for deficiency of photosynthate (Youngner, 1972). The reduction in root + rhizome mass in the current study was associated with frequent clipping and probably due to reduction in stored carbohydrates, which may have been translocated and utilized for regrowth.

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Stem Base

Stem base mass was measured each October during the 3-yr study. It was affected by entry × harvest frequency (P = 0.01) and entry × stubble height (P = 0.01) interactions. For the 4-cm stubble height treatment, Argentine and Pensacola had greater stem base mass than the other entries (Table 3). When harvested to 8-cm stubble height, Argentine had greater stem base mass than all entries except Tifton 7, while PCA Cycle 4 had less stem base mass than all entries except Pensacola. There was no effect of stubble height on stem base mass of Argentine and Pensacola; however, Tifton 7, Tifton 9, and PCA Cycle 4 had greater stem base mass when harvested to 8 than 4 cm. There also was entry × harvest frequency interaction for stem base mass. Argentine had greater stem base mass than all entries except Pensacola when harvested every 7 d, while stem base mass of PCA Cycle 4 was less than all entries (Table 3). When harvested every 21 d, Tifton 9 had less stem base mass than all entries except PCA Cycle 4, and there were no differences among Argentine, Tifton 7, and Pensacola. There was no effect of 7- vs. 21-d harvest frequency on stem base mass of Argentine, Pensacola, and Tifton 9; however, Tifton 7 and PCA Cycle 4 had greater stem base mass when harvested every 21 than 7 d. Overall, the root + rhizome and stem base mass data show important patterns of response that likely have implications for persistence. Across defoliation treatments, average stem base mass of Pensacola and Argentine was 60% greater than PCA Cycle 4; while at 4- and 8-cm stubble height, the comparable numbers were 86 and 41%. Similarly, when defoliated every 7 d, average stem base mass of Pensacola and Argentine was 125% greater than for Cycle 4, while the difference was only 23% for the 21-d treatment. A similar but less pronounced pattern was observed for root + rhizome mass. Across defoliation Agronomy Journal

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Table 4. Bahiagrass root + rhizome N content as affected by entry × stubble height (P = 0.001) and entry × harvest frequency (P = 0.01) interactions in October. Data are means across two stubble heights or harvest frequencies, three replicates, and 2 yr (n = 12). Stubble height, cm Entry Argentine Tifton 7 Pensacola Tifton 9 PCA Cycle 4

4


8

7 g N m–2 18abB 24aA 14bB 15bA 23aA 20abA 17bA 15bB 15bA 16bA

24aA† 17bA 17bB 18bA 17bA

SE‡

Table 5. Bahiagrass stem base N content in October as affected by entry × stubble height (P = 0.02) interaction. The entry × harvest frequency interaction approached significance (P = 0.08) and interaction means were compared. Data are means across two defoliation frequencies or stubble heights, three replicates, and 2 yr (n = 12).

21

Stubble height, cm Entry

19aB 16aA 21aA 20aA 16aA

4


8

7

21

g N m–2 Argentine Tifton 7 Pensacola Tifton 9 PCA Cycle 4

2.2


6.1abA† 4.6bcB 6.5aA 3.7cA 3.6cA

6.9aA 6.0abA 4.7bcB 4.9bA 4.1cA

SE‡

6.9aA 4.9bcA 5.8abA 4.1cdA 3.0dB

6.0aA 5.8aA 5.3aA 4.5aA 4.7aA

0.70




treatments, Pensacola and Argentine had 27% greater root + rhizome mass than Cycle 4, while at 4- and 8-cm stubble height the values were 32 and 21%, respectively. When defoliated every 7 and 21 d, Pensacola and Argentine root + rhizome mass was 38 and 14% greater, respectively, than Cycle 4. These plant responses could result in PCA Cycle 4 being less persistent than Argentine and Pensacola under defoliation, particularly frequent or close defoliation. Nitrogen and Nonstructural Carbohydrate Content Under defoliation, N and TNC content are often more responsive to grazing stress than are N and TNC concentration (Sollenberger and Newman, 2007), thus only content data will be presented. Nitrogen and TNC content were measured on root + rhizome and stem base plant fractions at the end of the first and second year of defoliation (October 2005 and 2006). Nitrogen Content October root + rhizome N content was affected by entry × harvest frequency (P = 0.01) and entry × stubble height (P = 0.001) interactions. Argentine had greatest root + rhizome N content when harvested to 4-cm stubble height (Table 4). At 8-cm stubble height, Pensacola had greater root + rhizome N content than all entries except Argentine. Root + rhizome N content of PCA Cycle 4 was similar to Tifton 9 at both stubble heights. When comparing the two stubble heights, Argentine and Tifton 7 had greater root + rhizome N content when harvested to 4 cm, while Pensacola had greater root + rhizome N content when harvested to 8 cm. An entry × harvest frequency interaction occurred because there were no differences in root + rhizome N content among entries when harvested every 21 d; however, Argentine had greater root + rhizome N content than all entries except Pensacola when harvested every 7 d (Table 4). There was no harvest frequency effect on root + rhizome N content of Tifton 7, Pensacola, and PCA Cycle 4. Argentine had greater root + rhizome N content when harvested every 7 d, while Tifton 9 had greater root + rhizome N content when harvested every 21 d. Stem base N content was affected by entry × stubble height interaction (P = 0.02), and the entry × harvest frequency interaction approached significance (P = 0.08) and was Agronomy Journal

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evaluated. Pensacola had greater stem base N content than all entries except Argentine when harvested to 4-cm stubble height, while Argentine had greater stem base N content than all entries except Tifton 7 when harvested to 8-cm stubble height (Table 5). Stem base N content of PCA Cycle 4 was similar to Tifton 9 and Tifton 7, the other upright-growing genotypes, when harvested to 4 cm; however, PCA Cycle 4 had less stem base N content than all entries except Pensacola when harvested to 8-cm stubble height. There was no stubble height effect on stem base N content of Argentine, Tifton 9, or PCA Cycle 4. Pensacola had greater stem base N content when harvested to 4 cm, while Tifton 7 had greater stem base N content when harvested to 8 cm. The entry × harvest frequency interaction was assessed for stem base N content. There was no difference in stem base N content among entries when harvested every 21 d (Table 5). When harvested every 7 d, Argentine had greater stem base N content than all entries except Pensacola, while PCA Cycle 4 had lesser stem base N content than all entries except Tifton 9. Only stem base N content of PCA Cycle 4 was affected by harvest frequency; it was greater when harvested every 21 than every 7 d. Considering N content overall, PCA Cycle 4 had lower root + rhizome N content than Argentine when defoliated to 4 cm or every 7 d, but not at 8-cm stubble or every 21 d. Differences in stem base N content were more pronounced than root + rhizome, and Cycle 4 had less stem base N than both Argentine and Pensacola when defoliated to 4 cm or every 7 d and less than Argentine when defoliated to 8 cm. There were no differences among entries with the 21-d harvest interval. Thus, the pattern of N content response was similar to that of storage organ mass, with PCA Cycle 4 generally having less N than Argentine, and in some cases Pensacola, and the differences being most pronounced with frequent or close defoliation. Total Nonstructural Carbohydrate Content Root + rhizome TNC content was affected by the entry × harvest frequency × year interaction (P = 0.05), so data were analyzed by year. There was entry effect in 2005 (P = 0.01) and entry × harvest frequency interaction in 2006 (P = 0.01). 1385

Table 6. Bahiagrass root + rhizome TNC content as affected by entry (P = 0.01) and entry × harvest frequency interaction (P = 0.01) in October 2005 and 2006, respectively. Data are means across two stubble heights, two harvest frequencies, and three replicates (October 2005; n = 12), and two stubble heights and three replicates (October 2006; n = 6).

Table 7. Bahiagrass stem base TNC content as affected by entry × stubble height interaction (P = 0.04) in October. Data are means across two harvest frequencies, three replicates, and 2 yr (n = 12). Stubble height, cm Entry

October 2006 Harvest frequency, d Entry Argentine Tifton 7 Pensacola Tifton 9 PCA Cycle 4 SE‡

October 2005 120ab† 60c 150a 100bc 70c 19

7 g TNC m–2 110aA 50bB 100aA 50bB 60bA

21 90abA 110aA 100aA 120aA 80bA 23

† Means followed by the same letter, lowercase letters within a column and uppercase letters within a row and year, do not differ by the LSMEANS test (P > 0.05). ‡ Standard errors of entry and entry × harvest frequency interaction means, respectively.

In October 2005, Pensacola had greater root + rhizome TNC content than all entries except Argentine, while PCA Cycle 4 and Tifton 7 had less root + rhizome TNC content than all entries except Tifton 9 (Table 6). In October 2006, Argentine and Pensacola had greater root + rhizome TNC content than the other entries when harvested every 7 d, while PCA Cycle 4 had lesser root + rhizome TNC content than all entries except Argentine when harvested every 21 d (Table 6). Argentine and Pensacola had an average of 75% greater root + rhizome TNC content than Tifton 7, Tifton 9, and PCA Cycle 4 in 2005 and 27% greater in 2006, suggesting that the upright types (Tifton 7 and 9 and Cycle 4) have less stored energy for regrowth than Argentine and Pensacola. When compared with PCA Cycle 4 only, Pensacola and Argentine had an average of 93% more TNC in 2005 and 43% more in 2006. Root + rhizome TNC content of Argentine and Pensacola was not affected by harvest frequency, while Tifton 7 and Tifton 9 had greater root + rhizome TNC content when harvested every 21 than 7 d. Stem base TNC content was affected by entry × stubble height interaction (P = 0.04). Argentine had greater stem base TNC content than all entries except Pensacola when harvested to 4 cm, while Argentine and Tifton 7 had greater stem base TNC content than the other entries when harvested to 8-cm stubble height (Table 7). Tifton 9 and PCA Cycle 4 had less stem base TNC content than all entries except Tifton 7 when harvested to 4 cm, while there was no difference in stem base TNC content among the diploid entries when harvested to 8 cm. Stubble height affected stem base TNC content only for Tifton 7 which had greater TNC when harvested to 8- than 4-cm stubble height. These data show that after 2 yr of defoliation PCA Cycle 4 generally had less stored TNC than Argentine and Pensacola. These differences were most pronounced when bahiagrass was defoliated frequently (root + rhizome) or closely (stem base). SUMMARY AND CONCLUSIONS Persistence of a less daylength-sensitive, more cold-tolerant bahiagrass was evaluated under a wide range of defoliation practices. Persistence was assessed based on percent cover, 1386

4

8 g TNC m–2

Argentine Tifton 7 Pensacola Tifton 9 PCA Cycle 4

25aA† 16bcB 22abA 11cA 12cA

SE‡

25aA 24aA 16bA 16bA 14bA 2.8

† Means followed by the same letter, lowercase letters within a column and uppercase letters within a row, do not differ by the LSMEANS test (P > 0.05). ‡ Standard error of entry × stubble height interaction means.

rhizome + root and stem base mass, and rhizome + root and stem base N and TNC content. Argentine cover was unaffected by defoliation treatments, but Tifton 9 and PCA Cycle 4 were much more sensitive to defoliation management. Harvesting every 21 d to an 8-cm stubble height resulted in greatest cover for both Tifton 9 and PCA Cycle 4 (83 and 77%, respectively), while cover for both entries was less than 40% if harvested every 7 d to 4 cm. The PCA Cycle 4 entry often had less root + rhizome and stem base mass, N content, and TNC content than Argentine and Pensacola. These differences were most pronounced when the entries were harvested closely or frequently. From these data, it can be concluded that defoliation management of PCA Cycle 4 will likely be more critical than for Pensacola and Argentine bahiagrass and that Cycle 4 responds more like Tifton 9 than Argentine or Pensacola. The upright growth habit of PCA Cycle 4, as well as generally less TNC and N in storage organs, and greater reduction in cover with close, frequent defoliation than Argentine and Pensacola imply that defoliation management of PCA Cycle 4 is more critical than for those cultivars, and longer regrowth intervals (21 d or longer) and taller residual heights (8 cm or taller) may be required to ensure its persistence. REFERENCES Bates, G.E., C.S. Hoveland, M.A. McCann, J.H. Bouton, and N.S. Hill. 1996. Plant persistence and animal performance for continuously stocked alfalfa pastures at three forage allowances. J. Prod. Agric. 9:418–423. Beaty, E.R., R.H. Brown, and J.B. Morris. 1970. Response of Pensacola bahiagrass to intense clipping. p. 538–542. In M.J.T. Norman (ed.) Proc. Intl. Grassl. Cong., 11th, Surfers Paradise, Queensland. 13–23 Apr. 1970. Univ. Queensland Press, St. Lucia, QLD, Australia. Blount, A.R., C.L. Mackowiak, K.H. Quesenberry, T.R. Sinclair, and P. Mislevy. 2008. Bahiagrass breeding for the U.S. southern Coastal Plain. In 2008 annual meetings abstracts [CD-ROM]. ASA, CSSA, and SSSA, Madison, WI. Blount, A.R., K.H. Quesenberry, P. Mislevy, R.N. Gates, and T.R. Sinclair. 2001. Bahiagrass and other Paspalum species: An overview of the plant breeding efforts in the Southern Coastal Plain. Available at http://spfcic. okstate.edu/proceedings/2001/breeders/blount.htm [cited 29 Nov. 2008; verified 27 Aug. 2009]. In Proc. 56th Southern Pasture Forage Crop Improvement Conf., Springdale, AR. 21–22 Apr. 2001. Oklahoma State Univ., Stillwater. Chaparro, C.J., L.E. Sollenberger, and K.H. Quesenberry. 1996. Light interception, reserve status, and persistence of clipped Mott elephantgrass swards. Crop Sci. 36:649–655.

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Christiansen, S., O.C. Ruelke, W.R. Ocumpaugh, K.H. Quesenberry, and J.E. Moore. 1988. Seasonal yield and quality of ‘Bigalta’, ‘Redalta’, and ‘Floralta’ limpograss. Trop. Agric. 65:49–55. Christiansen, S., and T. Svejcar. 1988. Grazing effects on shoot and root dynamics and above- and below-ground nonstructural carbohydrates in caucasian bluestem. Grass Forage Sci. 43:111–119. Dawson, L.A., S.J. Grayston, and E. Paterson. 2000. Effects of grazing on the roots and rhizosphere of grasses. p. 61–84. In G. Lemaire et al. (ed.) Grassland ecophysiology and grazing ecology. CAB International, New York. Gallaher, R.N., C.O. Weldon, and J.G. Futral. 1975. An aluminum block digester for plant and soil analysis. Soil Sci. Soc. Am. Proc. 39:803–806.

Pedreira, C.G.S., and R.H. Brown. 1996a. Yield of selected and unselected bahiagrass populations at two cutting heights. Crop Sci. 36:134–137. Pedreira, C.G.S., and R.H. Brown. 1996b. Physiology, morphology, and growth of individual plants of selected and unselected bahiagrass populations. Crop Sci. 36:138–142. Pedreira, C.G.S., L.E. Sollenberger, and P. Mislevy. 2000. Botanical composition, light interception, and carbohydrate reserve status of grazed ‘Florakirk’ bermudagrass. Agron. J. 92:194–199. SAS Institute. 1996. SAS statistics user’s guide. v. 6. SAS Inst., Cary, NC.

Gates, R.N., G.M. Hill, and G.W. Burton. 1999. Response of selected and unselected bahiagrass populations to defoliation. Agron. J. 91:787–795.

Schenk, J.S., and M.O. Westerhaus. 1991a. Population defi nition, sample selection, and calibration procedures for near infrared reflectance spectroscopy. Crop Sci. 31:469–474.

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Interrante, S.M., L.E. Sollenberger, A.R. Blount, U.R. White, K. Liu, and S.W. Coleman. 2009. Defoliation management of bahiagrass germplasm affects dry matter yield and herbage nutritive value. Agron. J. 101(989–995).

Sinclair, T.R., P. Mislevy, and J.D. Ray. 2001. Short photoperiod inhibits winter growth of subtropical grasses. Planta 213:488–491.

Kalmbacher, R. 1997. Basic perennial grasses for south Florida: Bahiagrass and limpograss. p. 4–8. In Range cattle. Res. Rep. RC-1997-2. Res. Educ. Center, Ona, FL. Macoon, B., L.E. Sollenberger, and J.E. Moore. 2002. Defoliation effects on persistence and productivity of four Pennisetum spp. genotypes. Agron. J. 94:541–548. Mislevy, P., G.W. Burton, and P. Busey. 1991. Bahiagrass response to grazing frequency. Proc. Soil Crop Sci. Soc. Fla. 50:58–64. Mislevy, P., and P.H. Everett. 1981. Subtropical grass species response to different irrigation and harvest regimes. Agron. J. 73:601–604. Ortega-S., J.A., L.E. Sollenberger, J.M. Bennett, and J.A. Cornell. 1992. Rhizome characteristics and canopy light interception of grazed rhizoma peanut pastures. Agron. J. 84:804–809.

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Sollenberger, L.E., and Y.C. Newman. 2007. Grazing management. p. 651–659. In R.F. Barnes et al. (ed.) Forages—The science of grassland agriculture. Blackwell Publ., Ames, IA. Spitaleri, R.F., L.E. Sollenberger, S.C. Schank, and C.R. Staples. 1994. Defoliation effects on agronomic performance of seeded Pennisetum hexaploid hybrids. Agron. J. 86:695–698. Thornton, B., P. Millard, and U. Bausenwein. 2000. Reserve formation and recycling of carbon and nitrogen during regrowth of defoliated plants. p. 85–99. In G. Lemaire et al. (ed.) Grassland ecophysiology and grazing ecology. CAB International, New York. Youngner, V.B. 1972. Physiology of defoliation and regrowth. p. 293–303. In V.B. Youngner and C.M. McKell (ed.) The biology and utilization of grasses. Academic Press, New York.

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