| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a New England Small Farm Inst., 275 Jackson St., Belchertown, MA 01007
b Box 110300, Agron. Dep., Univ. of Florida, Gainesville, FL 32611-0300
c Agric. Res. Inst. of Minas Gerais (EPAMIG), Belo Horizonte, Brazil
* Corresponding author (les{at}gnv.ifas.ufl.edu)
Received for publication October 1, 2001.
 |
ABSTRACT |
|---|
 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Abbreviations: CP, crude protein • DM, dry matter • IVDMD, in vitro dry matter digestibility • IVOMD, in vitro organic matter digestibility • NDF, neutral detergent fiber • PPFD, photosynthetic photon flux density • TNC, total nonstructural carbohydrate
|
INTRODUCTION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Florigraze rhizoma peanut is a perennial forage legume used for livestock production in the subtropics and warmer temperate areas. It is persistent and of high quality whether grazed or mechanically harvested (Sollenberger et al., 1989; Ocumpaugh, 1990; Ortega-S. et al., 1992; Venuto et al., 1998). Daily gains of 1 kg have been reported for growing cattle grazing rhizoma peanut during late spring through early autumn (Sollenberger et al., 1989).
Producer adoption of rhizoma peanut has been limited primarily by a relatively long establishment period. Johnson (1990) suggested that concurrent planting of trees and Florigraze might facilitate use of the legume and improve the quality of forage for grazing in the understory of southeastern U.S. pine plantations. Rhizoma peanut has been shown to be persistent and productive under moderate levels of shade. When grown at 54 and 78% of incident photosynthetic photon flux density (PPFD) during 2 yr, forage yields were 70% and >94%, respectively, those of unshaded plants (Johnson et al., 1994).
The light environment during plant growth affects forage nutritive value in addition to yield and persistence. The great majority of studies evaluating the effect of shade on forage nutritive value have been conducted with grasses. The data are inconsistent, with responses to increasing shade ranging from positive (Kephart and Buxton, 1993; Deinum et al., 1996) to negative (Samarakoon et al., 1990; Senanayake, 1995) to no effect (Norton et al., 1991). Eriksen and Whitney (1982) found no difference in the herbage crude protein (CP) concentration of six tropical legumes grown in 27 to 70% of full sun compared with those grown in full sun. Wilson and Wong (1982) found relatively little effect of shade on siratro [Macroptilium atropurpureum (DC.) Urb.] while Muir and Pitman (1989) reported that herbage N concentration of milkpea (Galactia elliotii Nuttall) increased as irradiance decreased from 100 to 45% of full sun. Garza et al. (1965) also found higher CP in shaded alfalfa (Medicago sativa L.) grown in the greenhouse, but soluble carbohydrates and in vitro dry matter digestibility (IVDMD) were lower. Shelton et al. (1987) concluded that the effect of shading on nutritive value often is negative but pointed out that most research evaluating this response has been from greenhouse experiments and has focused on grasses.
Several studies have pointed to the existence of shade-tolerant and shade-intolerant legumes (Wong et al., 1985). Izaguirre-Mayoral et al. (1995) concluded that the capacity to nodulate and fix N at high rates in low-light environments is key to the success of facultative shade-tolerant legumes. Thus, different N concentration responses of legumes may be a function of their shade tolerance. There are no data that describe the nutritive value responses of rhizoma peanut to shade, and the relationships between measures of plant nutritive value, other than N concentration, and shade tolerance are not well defined for forage legumes in general. These data are needed to assess the potential of legumes for use as understory crops. Also lacking in the literature are studies of shade effects on nutritive value of forage legumes that were conducted in the field and/or for more than a single growing season. Thus, this study was designed with the objective of assessing the effects of four levels of PPFD, imposed continuously in the field during two growing seasons and the winter between them, on the nutritive value of Florigraze rhizoma peanut.
|
MATERIALS AND METHODS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Before imposing treatments, all plots were clipped on 17 May 1989 to a 4-cm stubble height using a sickle-bar mower (staging cut). Following the staging cut, black nylon shade material was stretched on 5- by 5-m aluminum frames, and frames were mounted above the plots on wooden posts so that the cloth was 50 cm above soil level. Different densities of weaves of the shade material resulted in the different PPFD levels. Treatments imposed were four levels of PPFD (34, 54, 78, and 100%) arranged in three replicates of a randomized block design. With a LI-COR (LI-COR, Lincoln, NE) line quantum sensor, PPFD was quantified near midday on several clear days by measures of PPFD (µmol m-2 s-1) beneath shade structures and expressed relative to incident PPFD above the shade structure. The area covered by the shade structure and its height above soil level were such that the harvested portion of the plot was always shaded, but light quality under the cloth was not measured.
During the period from 29 July through 5 Sept. 1989, ambient air temperature was monitored for all treatments of one replicate using automated thermocouple sensors. Temperatures peaked for all plots at approximately 1400 h. Between 1200 and 1800 h, air temperatures were generally in the order 78 > 100 > 34 > 54% PPFD, but in no case was the range among all treatments >2°C.
All treatments were harvested on 23 June, 29 July, and 5 Sept. 1989 and on 22 May, 18 July, and 12 Sept. 1990. A three-harvest system with 5- to 8-wk regrowth intervals is recommended for rhizoma peanut in north Florida (Prine et al., 1981). Regrowth intervals were 5 to 6 wk in 1989 and closer to 8 wk in 1990. Shorter intervals were used in 1989 because the staging cut delayed the date of first harvest. At harvest, 1.95-m2 strips were clipped to a 4-cm stubble from the center of each plot using a sickle-bar mower. Shade structures were removed for harvest, reset the following day, and maintained over the plots year-round throughout the experiment.
A subsample of herbage harvested from the 1.95-m2 strip in each plot was taken for hand separation into leaf and stem fractions. After separation, they were dried to constant weight at 60°C. After drying, samples were ground to pass a 1-mm screen and analyzed for N, in vitro organic matter digestibility (IVOMD), total nonstructural carbohydrate (TNC) concentration, neutral detergent fiber (NDF), and lignin. Samples were digested for N determination using a modification of the aluminum block digestion procedure of Gallaher et al. (1975). Ammonia in the digestate was determined by semiautomated colorimetry (Hambleton, 1977), and CP was calculated as N x 6.25. The two-stage procedure of Tilley and Terry (1963), as modified by Moore and Mott (1974), was used to determine IVOMD. The donor cow (Bos taurus) was fed a diet of bermudagrass [Cynodon dactylon (L.) Pers.] hay, with 900 g of soybean [Glycine max (L.) Merr.] meal fed 2 h before collection of inoculum. Neutral detergent fiber was analyzed as described by Golding et al. (1985) and is reported on an ash-free basis. Lignin was determined using the permanganate method of Van Soest and Wine (1967), and TNC concentration was measured using the procedure described by Chaparro et al. (1996).
Data were analyzed using analysis of variance with PPFD as a fixed effect. Repeated-measures analysis of variance was used to assess harvest date effects for each response variable using the SAS system for mixed models (Littell et al., 1996; SAS Inst., 1996). Differences were considered to be significant at P < 0.05. There were numerous treatment x harvest date interactions; thus, data are presented by harvest date. When there was an effect of PPFD on the response, regression analysis with PROC REG (SAS Inst., 1996) was used to determine the nature of the response function, and the equation was plotted. Where there was no effect of PPFD, only the means across levels of PPFD are reported.
|
RESULTS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
|
|
Stem CP increased with increasing PPFD in Harvests 1 and 2 of 1989 (Fig. 3) . The increase was quadratic from 128 to 145 g kg-1 in Harvest 1 and linear from 133 to 143 g kg-1 in Harvest 2. In all harvests of 1989, stem IVOMD increased linearly with increasing PPFD (Fig. 4) . Across the range of PPFD, the magnitude of the increase was >65 g kg-1 in each harvest, and for most treatment–harvest combinations, stem IVOMD was between 650 and 750 g kg-1. In Harvests 1 and 2, the increase in IVOMD with increasing PPFD was associated with a linear decrease in NDF, from approximately 587 to 531 g kg-1 in Harvest 1 and 507 to 430 g kg-1 in Harvest 2 (Fig. 5) . Stem lignin also decreased as PPFD increased (Fig. 6) , and most concentrations were between 80 and 110 g kg-1. The response was linear in Harvests 2 and 3 and quadratic in Harvest 1. The magnitude of the decline was 15 to 22 g kg-1 over the range of PPFD evaluated.
|
|
|
|
|
DISCUSSION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Several studies have pointed to the existence of shade-tolerant and shade-intolerant legumes, with tissue N concentration being one of several adaptive mechanisms used by some plants. For example, Watson et al. (1984) found that berseem clover (Trifolium alexandrinum L.) and ‘Nangeela’ subclover (T. subterraneum L.) yielded nearly as much dry matter (DM) under 50% shade as in full sun, and both had as great or greater tissue N concentration when shaded as when grown in full sun. These authors also reported that hairy vetch (Vicia villosa Roth) yielded only 33% as much DM at 50% sun compared with 100% sun, and it had lower tissue N concentration when grown in shade. Wong and Wilson (1980) showed very large reductions in weight and number of nodules on roots of shaded siratro. In addition, Eriksen and Whitney (1982) reported that acetylene reduction rates of six tropical legumes were highly positively correlated with PPFD. Izaguirre-Mayoral et al. (1995) concluded that the ability of facultative shade-tolerant legumes to grow under shade is associated with their capacity to nodulate and fix N at high rates in low-light environments. Wong et al. (1985) suggest that shade-intolerant legumes have reduced leaf/stem ratio and very large increases in shoot/root ratio, whereas shade-tolerant legumes maintain a balance between leaf and stem under shaded conditions. Poor performance of intolerant types is associated with a reduced root system and lower nodulation and N fixation (Wong et al., 1985). Both of these factors directly influence N status of the plant, either by limiting N uptake from the soil or N fixed by the legume. Shade-intolerant legumes would therefore be likely to have lower N concentrations in shaded compared with full-sun conditions. Thus, there is an increasing body of literature that suggests that the variation in N response to shade among legumes may reflect real differences in shade tolerance and in strategies for coping with low-light environments.
In the specific case of rhizoma peanut, when shaded, it has lower DM yield (Johnson et al., 1994), lower leaf/stem ratio (Johnson et al., 1991), decreased rhizome mass (Johnson et al., 1994), and lower tissue N concentration. In the current study, we did not measure nodule characteristics or acetylene reduction, but if shaded rhizoma peanut responds similarly to the legumes tested by Wong and Wilson (1980) and Eriksen and Whitney (1982), it is logical that lower CP concentration would result. That is especially the case when shaded peanut is grown on sandy, low organic matter soils like the Kendrick fine sand used in the current study. All of these factors imply that rhizoma peanut is at least moderately intolerant of shade.
Leaf IVOMD and NDF were affected by light level only in 1990 and only in two of three harvests that year. Increases in IVOMD with greater PPFD were of considerably lesser magnitude for leaf than those observed for stem, but the response was linear across the range of PPFD. Leaf NDF decreased with increasing PPFD, and low NDF likely was responsible, in part, for higher IVOMD at higher light levels. We did not detect changes in leaf lignin concentration due to PPFD.
Redfearn et al. (1999) found no effect of light environment on leaf fiber constituents of shaded vs. full-sun soybean, and Wilson and Wong (1982) reported that shade had no effect on siratro leaf IVDMD. In contrast, shaded green panic (Panicum maximum Jacq. var. trichoglume Robijns) leaves had 30 to 50 g kg-1 lower IVDMD than full-sun across a wide range of leaf age (Wilson and Wong, 1982). In that study, lower IVDMD of shaded leaves could not be explained by cell wall concentration because it decreased with shading. Increasing shade was associated, however, with lower leaf TNC concentration, which likely reduced IVDMD. Similar results were found with kermes oak (Quercus coccifera L.) browse (leaf plus small twigs) when it was grown as an understory and compared to unshaded plants (Koukoura, 1988). Lower IVDMD of shaded plants in that study was associated with lower TNC concentration and increased lignin concentration.
Stem Nutritive Value
In two harvests each year, stem CP increased with increasing PPFD. This response was similar to that of the leaf fraction. At a given PPFD, stem CP was often at least 20 g kg-1 greater in 1989 than 1990 harvests, primarily due to the shorter regrowth intervals in 1989.
Stem IVOMD increased linearly with increasing PPFD in all harvests of both years and was greater by approximately 50 to 100 g kg-1 organic matter in 1989 than 1990. This response can be explained by concentration and composition of NDF. As PPFD increased, NDF concentration decreased in five of six harvests. This decrease was approximately 50 g kg-1 across the range of PPFD evaluated. Along with decreasing NDF, lignin concentration also decreased with increasing PPFD in five of six harvests. Within a harvest, this decrease was often in the range of 10 to 15 g kg-1 across PPFD from 34 to 100%.
Wilson and Wong (1982) found lower TNC concentration in shaded than unshaded siratro stems, but there was no effect on NDF and lignin concentrations or IVDMD. For black medic (M. lupulina L.), acid detergent fiber and lignin concentrations increased as shade increased from 0 to 80% (Interrante et al., 2001). In contrast, Redfearn et al. (1999) reported greater concentrations of NDF, acid detergent fiber, and lignin in full-sun vs. shaded soybean stems. Other studies have found overall positive effects (lesser NDF and greater IVDMD) of shading on nutritive value of grass stem or total herbage (Kephart and Buxton, 1993; Deinum et al., 1996). Data from the current study are consistent in showing lower CP and IVOMD of shaded compared with full-sun rhizoma peanut stems. Shaded stems had greater concentrations of NDF and lignin, factors which likely played a significant role in reducing IVOMD. The effect of shade on leaf/stem ratio also is important. Johnson et al. (1991) reported that rhizoma peanut leaf percentage increased linearly from 52 to 61% as PPFD increased from 34 to 100% in 1989. In 1990, leaf percentage increased from 54 to 56% as PPFD increased from 34 to 54%, but it remained relatively constant with further increases in PPFD. Thus, not only is nutritive value of plant parts greater under full sun, but so is the proportion of leaf.
In some cases, higher nutritive value has been reported for plants grown under moderate drought stress compared with well-watered plants (Wilson, 1983). This has relevance to the current study because, despite spring irrigation, first-harvest yields were lower in both years in the 100 vs. 78% PPFD plots (Johnson et al., 1994). Lower yield was associated with lower leaf water and turgor potentials in the 100 vs. 78% treatments (Johnson et al., 1994). In subsequent harvests, when rainfall amounts were average (Harvests 2 and 3 of 1989 and Harvest 3 of 1990) or much above average (Harvest 2 of 1990), rhizoma peanut forage yield increased with increasing PPFD through 100%. The nutritive value responses to shade were quite consistent whether rainfall was quite low, average, or much above average; thus, we do not attribute the overall response of increasing herbage nutritive value with increasing PPFD to differences among treatments in soil moisture. There were, however, no measures taken of soil moisture under shades.
Nor do the data from the current study suggest that ambient temperature differences among treatments caused the responses attributed to shading. Between 1200 and 1800 h, air temperatures were generally greatest in the 78 and 100% treatments and least in the 34 and 54% plots, but in no case was the range between highest and lowest temperature >2°C. The general nutritive value response to increasing temperature is negative (Pitman and Holt, 1982). Rhizoma peanut CP and IVOMD followed this pattern (Fritschi et al., 1999) although differences were considered small even across a range of temperatures more than twice those in the current study. Thus, if temperature differences among treatments affected the responses measured, they would most likely have attenuated the shade effect rather than accentuated it.
Data from the current study strongly support the premise that nutritive value of shaded rhizoma peanut is less than that of herbage grown in full sun. This was consistent across measures of both chemical composition and digestibility. It should be noted, however, that the lower nutritive value observed for shaded rhizoma peanut was still considerably greater than that of many warm-season grasses used for livestock in the region. Consequently, nutritive value, though lower in shaded conditions, does not appear to be a factor that would limit the use of rhizoma peanut as an understory in pine plantations.
Anderson et al. (1988) reported that, in the southeast USA, PPFD ranged from 32 to 70% in mature pine stands, depending on configuration and planting density. Additionally, light transmission of a mature pine stand in Florida approximated 55% when planted at 1120 trees ha-1 in a 0.6- by 14.4-m configuration for pulpwood (W. Sequira, personal communication, 1990). These light intensities are within the range imposed in this study. Thus, data from the current study and previous work on yield under shade (Johnson et al., 1994) support the conclusion that rhizoma peanut merits field evaluation as a component of silvopastoral systems in the region.
|
NOTES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
|
REFERENCES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  Y. C. Newman, L. E. Sollenberger, K. J. Boote, L. H. Allen Jr., J. C. V. Vu, and M. B. Hall Temperature and Carbon Dioxide Effects on Nutritive Value of Rhizoma Peanut Herbage Crop Sci., January 1, 2005; 45(1): 316 - 321. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Crop Science | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
): y = 254 - 1.12x + 0.013x2, R2 = 0.85, root mean square error (RMSE) = 7.4; Harvest 2 (
): y = 222 + 0.34x, r2 = 0.40, RMSE = 11.3; Harvest 3 (•): y = 188 + 1.43x - 0.0067x2, R2 = 0.93, RMSE = 4.5] and 1990 [Harvest 1: not significant, mean = 207 g kg-1; Harvest 2 (
