Agronomy Journal 92:472-478 (2000)
© 2000 American Society of Agronomy
FORAGE MANAGEMENT
Influence of Nitrogen on Productivity and Nutritive Value of Forage Chicory
David P. Belesky,
Kenneth E. Turner and
Joyce M. Ruckle
USDA-ARS, Appalachian Farming Systems Research Center, 1224 Airport Road, Beaver, WV 25813 USA
dbelesky{at}afsrc.ars.usda.gov
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ABSTRACT
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Chicory (Cichorium intybus L.) is highly productive and responsive to N fertilization under midsummer conditions in the eastern USA. We conducted a field experiment for 3 yr on a Ramsey soil (loamy, siliceous, subactive, mesic Lithic Dystrudept) in southern West Virginia to determine if fertilizer N influenced forage chicory nutritive value and NO3–N concentration. Each N rate (0, 80, 160, 240, or 480 kg N ha-1) was replicated three times in a randomized block design. Swards were clipped at 6-wk intervals during the growing season. Swards were virtually pure chicory in the first year (1994) regardless of N rate. By the third year (1996), chicory ranged from about 40% (0 N) to less than 5% (480 kg N ha-1) of swards. Botanical composition changes in the sward influenced dry matter (DM) response to N rate and herbage nutritive value. Dry matter production increased with N rate in 1994, but was not affected by N in 1996 when chicory was not a major sward component. More than 70% of total annual DM production in 1994 occurred after the first harvest, but by 1996 was less than 50%, reflecting productivity patterns typical of cool-season swards. Nitrate concentrations in herbage were greatest (3.5 g kg-1) in 1995, a relatively dry year, and least (2.3 g kg-1) in 1996, when there was less chicory in the sward. Crude protein (CP) and in vitro organic matter disappearance (IVOMD) values indicated high forage quality throughout the course of the experiment.
Abbreviations: CP, crude protein • DM, dry matter • IVDMD, in vitro dry matter disappearance • IVOMD, in vitro organic matter disappearance • MEF, metabolizable energy of feed
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INTRODUCTION
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CHICORY has proven forage production capabilities (Jung et al., 1996; Volesky, 1996; Collins and McCoy, 1997; Belesky et al., 1999). It is productive in summer when growth of cool-temperate species lags and nutrient requirements and feed consumption by growing livestock increase (Lancashire and Brock, 1983; Collins and McCoy, 1997; Belesky et al., 1999). Successful chicory production depends upon achieving a balance between vigorous growth, which is a function of morphogenesis, and herbage quality (Li et al., 1994). Chicory declined as a proportion of swards in field experiments in Kentucky (Collins and McCoy, 1997) and West Virginia (Belesky et al., 1999), as well as in New Zealand, where `Grasslands Puna', the cultivar used in this study, was developed (Li et al., 1994). Declines occurred despite using defoliation practices designed to optimize herbage quality and stand persistence and prevent stem development (Clark et al., 1990). Nitrogen rate influenced chicory stand density, with fewer plants persisting at higher N levels (Clark et al., 1990; Collins and McCoy, 1997). Conversely, chicory persistence in a 2-yr period was not affected in a defoliation frequency experiment conducted in central Pennsylvania by Jung et al. (1996) or a grazing experiment in Oklahoma (Volesky, 1996).
Defoliation can interact with N to affect the shoot-to-root ratio by altering photosynthetic area and resulting photosynthate available for production and storage. In addition, nitrogenous compounds allocated to the taproot in plants like chicory are involved in over-wintering and persistence (Cyr et al., 1990). Chicory production increased as fertilizer N was increased to the 200 kg N ha-1 range in forage production situations (Clark et al., 1990; Collins and McCoy, 1997). Chicory production increased each time a split N fertilizer application was made (Collins and McCoy, 1997). Insufficient N can affect the shoot-to-root ratio in chicory by influencing leaf area of shoots and carbon metabolism in the taproot (Ameziane et al., 1995). The shoot-to-root ratio occurring at the end of the first growing season has direct bearing upon production in the following year (Ameziane et al., 1997). The ratio could be affected by N, with less shoot mass being produced relative to root in N-deficient situations.
Nitrogen management is important from the standpoint of herbage quality as well as herbage production. Chicory clipped four times in a growing season and receiving 220 kg N ha-1 applied in equal increments after each harvest, averaged 150 g CP kg-1 in herbage DM (Jung et al., 1996). A split application of 200 kg N ha-1 applied to chicory clipped four times produced an average of 159 g CP kg-1 DM (Collins and McCoy, 1997). Grazed chicory receiving a total of 150 kg N ha-1 averaged 183 g CP kg-1 DM (Volesky, 1996). Collins and McCoy (1997) also found that chicory quality remained high, with neutral-detergent fiber less than 400 g kg-1 and in vitro dry matter disappearance (IVDMD) greater than 640 g kg-1.
Chicory produced for human consumption can accumulate relatively high NO3–N concentrations in foliage (Santamaria et al., 1998). Lack of photosynthate along with water deficit or low light conditions, as well as N availability that exceeds plant growth requirements, can lead to NO3–N accumulation (Wright and Davison, 1964). Nitrate-N concentrations and accumulation patterns have not been reported for chicory grown in forage production situations.
We conducted a field experiment, with pure swards of chicory receiving a single application of fertilizer N to determine response in terms of productivity, persistence, and nutritive value (including herbage N, CP yield, NO3–N, and estimated metabolizable energy). Single applications of N would be likely to occur in extensively managed pasture situations and high rates would be possible when applying nutrients from confined animal feeding operations. This work is part of a series of investigations concerning phenology of chicory, utility of chicory in full-season grazing regimes, and composition and in vitro digestion kinetics of chicory herbage.
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Materials and methods
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Site Preparation and Treatments
A field experiment was conducted for 3 yr (1994–1996) on a gently sloping upland site of Ramsey soil in southern West Virginia (38° N; 81° W; 850 m above sea level). Temperature and precipitation data were collected at the site and are presented along with long-term means recorded at the National Weather Service office (National Oceanographic and Atmospheric Administration) located about 5 km west of the experiment site (Fig. 1)
. Initial soil pH was 6.6 with moderate levels of available P (Olsen and Sommers, 1982) and exchangeable K (ammonium acetate-extractable) in the surface 15 cm. The plot area was prepared by spraying existing vegetation [mixed cool-season grasses, white clover (Trifolium repens L.), and forbs] of a stand previously managed for hay with glyphosate [N-(phosphono-methyl) glycine] at 1.19 kg ha-1 a.i. in late spring of 1993, rototilling to about 10 cm, followed by manual smoothing and raking to prepare a firm seedbed. No insecticides or herbicides were used once plots were sown.
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Fig. 1 Mean monthly maximum and minimum air temperatures, monthly precipitation, and 30-yr mean values for each parameter at Beckley, WV
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Plots were broadcast-sown to Grasslands Puna chicory (10 kg seed ha-1) and culti-packed to improve seed-to-soil contact. Each plot was 2 by 4 m in size with five plots in each of three blocks. Plantings were made in June of 1993, with sampling begun in 1994 and carried out for three consecutive growing seasons. Stands were clipped once in late summer of 1993 to control weeds, and at 6-wk intervals (beginning in late spring) with three harvests in 1994, and four harvests in both 1995 and 1996. Nitrogen (35 kg N ha-1 as NH4NO3) was applied after plants appeared to be actively growing in the establishment year, with 80 kg P ha-1 and 150 kg K ha-1 plus 2 kg B ha-1 applied at establishment and in spring of each subsequent year of the experiment. Nitrogen (NH4NO3) was applied (40, 160, 240, and 480 kg N ha-1) in mid-April of each year of the experiment after the establishment year when basal rosettes of chicory leaves appeared. A control (0 N applied) was maintained as well, with each N rate and control replicated three times. Control plots received 35 kg N ha-1 in the establishment year only.
Sample Collection and Analysis
Sample strips (0.6 by 3.0 m) located in the center of each plot were clipped to a 5-cm residue height with a collection-bag-equipped rotary mower. Herbage samples were dried at 60°C in a forced-air oven and ground for analysis. Botanical composition of stands was determined at each 6-wk sampling date using the point-quadrat method described by Warren-Wilson (1959). Each of 45 contact points in a plot was categorized as chicory, grass [orchardgrass (Dactylis glomerata L.); tall fescue (Festuca arundinacea Schreb.) and Kentucky bluegrass (Poa pratensis L.)] or legume [both red (Trifolium pratense L.) and white (T. repens L.) clover occur naturally on the site]. Weeds (includes forbs and other grasses not specifically listed above) and bare ground were noted but not included in the data analysis because the contribution to total composition was nominal.
Dry matter and organic matter (AOAC, 1990), IVOMD (Tilley and Terry, 1963; Moore, 1970), total N (1994 samples were analyzed with a LECO CHN 600, Leco,1
St. Joseph, MI; 1995–1996 samples were analyzed with a Carlo Erba Ea1108 CHNS Analyzer, Fisons Instruments, Beverly, MA), and NO3–N (Consalter et al., 1992) were determined. Ruminal fluid was obtained from two cannulated steers (Bos sp.) offered cool-season grass hay (primarily orchardgrass) and alfalfa (Medicago sativa L.) hay. After incubation, tube contents were filtered through crucibles, dried at 105°C, cooled over silica gel desiccant, and reweighed to determine IVDMD (Goering and Van Soest, 1970). Ash was determined by weighing residue after total combustion of samples at 500°C in a muffle furnace for use in calculation of IVOMD. Crude protein was calculated as N x 6.25.
Metabolizable energy of feed (MEF) was estimated from equations developed for complex feedstuffs (MAFF, 1987). Values used for crude protein and ash were derived from herbage samples, whereas ether extract and crude fiber values were obtained for the respective botanical components from tables of food composition values (MAFF, 1987) for rotationally grazed grasses, white clover at bud to 1/10th flower. Fiber components were not determined on samples collected in our experiment. Consequently, we calculated metabolizable energy with crude fiber values derived for turnip (Brassica rapa L.) (MAFF, 1987) to represent chicory, based on suggestions by Collins and McCoy (1997) that fiber concentration in chicory was similar to that of rape (B. napus L.). The sum of components based on the mean annual botanical composition of the sward for a given harvest date was used in the calculation.
Data were analyzed using PROC GLM and repeated measures analysis of variance procedures of the Statistical Analysis System (SAS Inst., 1990). Univariate procedures were applied to evaluate the influence of treatment within N rate (repeated measures for harvest dates). Variances for herbage mass, herbage quality factors, and botanical composition for years were heterogeneous; consequently, years were analyzed separately. Sources of variation were N rate, harvest date, and the interaction of N rate and harvest date. Nitrogen rate effects were tested with the N rate x block effect, and N rate x harvest date was tested with the residual error term. Regression equations were developed using orthogonal polynomial contrasts for N rate influence on cumulative yield, chicory, grass, and legume contribution to sward composition, crude protein yield, herbage N, NO3–N, and MEF of the feed.
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Results and discussion
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Botanical Composition
Nitrogen application rate and time (years) influenced the botanical composition of swards. Swards were virtually pure (99%) chicory throughout the first (1994) full growing season, regardless of N application rate. By the second (1995) growing season, the occurrence of chicory in the sward began to decline. Chicory ranged from 50 to 70% of the sward and varied as a function of N rate (Fig. 2)
. Chicory contribution to the sward was strongly influenced by N rate in the third year (1996) of the experiment. Increasing N from 0 to 480 kg N ha-1 depressed the presence of chicory from 46.0% to 3.3% (Fig. 2) in 1996. Hume et al. (1995) also recognized the complexity of sward persistence and proposed that decline in chicory as a component of mixed-species swards in New Zealand was caused by a combination of factors including soil N concentrations, defoliation regime, and pathogens.
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Fig. 2 Sward composition as a function of N rate in 1995 and 1996. Error bars are standard error of the mean. 1995 chicory = (-3.89 x 10-4)(N rate)2 + (0.19)(N rate) + 41.36, R2 = 0.86; 1996 chicory = (3.26 x 10-5)(N rate)2 - (0.09)(N rate) + 37.26, R2 = 0.87; 1995 grasses = (2.31 x 10-4)(N rate)2 - (0.06)(N rate) + 28.04, R2 = 0.84; 1996 grasses = (-4.59 x 10-5)(N rate)2 + (0.09)(N rate) + 59.11, R2 = 0.84; 1995 legumes = (1.84 x 10-4)(N rate)2 - (0.15) (N rate) + 28.73, R2 = 0.95; 1996 legumes = (3.37 x 10-5) (N rate)2 - (0.02)(N rate) + 3.71, R2 = 0.69
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We made botanical assessments prior to harvest, so canopy closure had usually occurred in pure chicory swards. Gaps remaining in the sward were filled by volunteer species with time in a manner similar to that observed in New Zealand (Barry, 1998). The decrease in chicory as a component of the canopy was accompanied by an increase in grasses (Fig. 2). Grasses represented from 25 (0 N control) to 50% (480 kg N ha-1) of the sward composition in 1995 and from 55 (0 N) to 95% (480 kg N ha-1) of the sward in 1996. The increase in grasses could be a function of volunteer grass responsiveness to N and weakened chicory stands at high N rates (see Clark et al., 1990). A range of plant sizes occurs within a chicory stand so that individuals with large and rapidly developing leaves, especially under higher N rates, could shade smaller individuals within the canopy, leading to the eventual loss of smaller plants from the stand. Clipping orchardgrass–chicory mixtures that received only 35 kg N ha-1 at 3- and 6-wk intervals (Belesky et al., 1999) in an adjacent experiment, or rotational grazing of chicory–orchardgrass paddocks (Turner et al., 1999) did not lead to the same extent of chicory loss from swards as seen here. Legumes occurred in plots in 1995, but were virtually absent by 1996. The minimal presence of legumes in 1996 could be a function of competition for light arising from the long interval between clippings, N rates (80 or more kg N ha-1) that could accelerate grass growth and competitive advantage, and an extended dry period, which occurred in the summer of 1995.
We noted some differences in chicory morphology and response to treatments during this experiment that formed the basis for additional field investigations. We observed that leaves on plants receiving the higher rates of N appeared to be larger than those on control (0 N) plants and that plant density was less than at lower N rates. One assessment of basal rosette density was made in summer of 1995. The number of basal rosettes per square meter and rosettes per plant declined, by 95 and 99% respectively, as N rate was increased from 40 to 480 kg N ha-1 (data not shown). Ongoing work addresses the phenological and nutritive value aspects of chicory as a function of management; we expect to report them elsewhere. Some heaving of chicory plants occurred as a function of freeze-thaw conditions over the winter of 1994–1995, but we did not quantify our observations. The influence of root morphology on heaving warrants investigation. It would be worthwhile to quantify heaving of chicory plants in pure and mixed swards and to evaluate regional effects attributable to soil conditions in winter.
Dry Matter Productivity
Weather patterns varied substantially for each year of the experiment, with a severe and relatively prolonged water deficit occurring in midsummer of 1995 (Fig. 1). Herbage DM increased with each increment of N greater than 80 kg ha-1 in 1994 when stands were essentially pure chicory (Fig. 3)
. Dry matter productivity increased from 3.5 to 6 Mg ha-1 as N was increased from 80 kg N ha-1 to a single application of 480 kg N ha-1. Yields ranged from 3.0 to 5.0 Mg ha-1 in 1995 and from 3.0 to 4.0 Mg ha-1 in 1996 as N was increased from 0 to 480 kg ha-1. Mean DM yield was 18% greater in 1994 than 1996 at 0 N but was 52% greater at 480 kg N ha-1 for the same comparison, indicating a strong responsiveness of chicory to applied N and the value of including chicory in swards where total herbage production is important. Chicory stand longevity, however, seems to be compromised with single-dose applications of high N rates. Single applications of N would be a typical practice in extensive pasture situations where fertilizer or livestock manure accumulated from confinement feeding operations might be applied in spring.
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Fig. 3 Cumulative herbage dry matter yield as a function of N rate from 1994 to 1996. Error bars are standard error of the mean. 1994 cumulative yield = (5.67 x 10-3)(N rate) + 3.45, r2 = 0.94; 1995 cumulative yield = (3.59 x 10-3)(N rate)+ 3.07, r2 = 0.72; 1996 cumulative yield = (2.28 x 10-3)(N rate) + 2.79, r2 = 0.91
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Season total DM accumulation changed as the experiment progressed, primarily as a function of changes in botanical composition. This is reflected in the distribution of mean DM production by harvest, averaged over N rate (harvest date x N rate; P < 0.01). More than 70% of the mean 1994 season total yield occurred after the first harvest (1994), when chicory dominated the sward (Fig. 4)
. The increasing occurrence of species other than chicory, primarily grasses, in swards in 1995 and 1996 caused peak DM production to occur in spring. In 1995, about 60% of the cumulative yield occurred after the first harvest, but by 1996, slightly less than 50% of the season total yield occurred after the first harvest. Increased mid- to late-summer herbage production is one reason to consider including chicory in permanent pastures. Midseason forage production often lags in cool-temperate-origin pastures and often forces producers to determine livestock numbers for their particular operation based on the occurrence of a mid- to late-season forage deficit. Including plants like chicory in pasture could enhance midseason forage production and increase the likelihood of improved production efficiency. Maintaining an adequate amount of chicory in the sward could help improve available forage distribution. Botanical changes occurring in swards over time compensate for the loss of chicory plants in terms of plant numbers but do not recoup total herbage production.
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Fig. 4 Distribution of mean season total yield during each growing season. Error bars are standard error of the mean
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Nutritive Value
Nitrogen and Nitrate Concentration
Nitrogen concentrations in herbage increased linearly as N increased
in 1994, ranging from 22 g kg-1 at 0 N to 35 g kg-1 at 480 kg N ha-1 (Fig. 5)
when the canopy was virtually pure chicory. Mean herbage N concentration was not a function of N rate in 1995 or 1996 and probably reflects the change in botanical composition occurring over years and N rate. The herbage N concentrations arising from single-dose N applications were similar to those obtained by Collins and McCoy (1997) for chicory receiving a split application of N.
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Fig. 5 Nitrogen concentration in herbage as a function of N rate. Error bars are standard error of the mean. 1994 N concentration = (2.6 x 10-2)(N rate) + 22.58, r2 = 0.89. Nitrogen did not influence herbage N concentrations in 1995 or 1996
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Previous work has shown that water deficit influences NO3–N accumulation in herbage, and that members of the Compositae, including chicory, are NO3–N accumulators (Wright and Davison, 1964). Our data reflect these observations in the NO3–N concentrations of chicory-dominated stands in 1994 as well as herbage grown in the relatively dry conditions occurring in 1995. Mean NO3–N concentration increased as N rate increased within each year (Fig. 6)
. Nitrate-N concentrations exceeded 4.0 g kg-1 herbage DM in 1994 when 240 kg N ha-1 (4.55 g NO3–N kg-1) or 480 kg N ha-1 (4.29 g NO3–N kg-1) were applied to chicory. Nitrogen rate and harvest date interacted, with greater NO3–N accumulation occurring early in the season in 1994 rather than late (data not shown). Chicory accumulated NO3–N as a function of N in the first two harvests in 1994, but by the third harvest, N had no effect on NO3–N concentration. In 1995, mean NO3–N concentrations, irrespective of N rate, were greatest early in the growing season (first harvest averaged 4.3 g NO3–N kg-1) and least (1.7 NO3–N g kg-1) at the last harvest of the season. Nitrate-N concentrations were 1.5 g NO3–N kg-1 at 0 N and 4.7 g NO3–N kg-1 when 480 kg N ha-1 was applied in 1995. Nitrate-N concentrations ranged from 1.4 (0 N) to 3.6 g NO3–N kg-1 (480 kg N ha-1) in 1996 when the contribution of chicory to the sward was the least and rainfall was adequate.
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Fig. 6 Nitrate-N concentration of herbage as a function of N rate in each growing season. Error bars are standard error of the mean. 1994 NO3–N = (5.64 x 10-3)(N rate) + 1.94, r2 = 0.67; 1995 NO3–N = (5.80 x 10-3)(N rate) + 2.10, r2 = 0.93; 1996 NO3–N = (4.75 x 10-3)(N rate) + 1.41, r2 = 0.97
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The amount of NO3–N in herbage at 480 kg N ha-1 and early in the growing season could create livestock health concerns. Herbage NO3–N concentrations in the range of 3.4 to 4.5 g NO3–N kg-1 DM present a potential livestock health concern (Mayland and Wilkinson, 1996), although actual NO3–N concentrations that cause toxicity are not clearly defined. Nitrate-N concentrations in excess of 4.0 g kg-1 occurred when 480 kg N ha-1 was applied in 1994 and 1995, especially in the first and second harvest herbage (data not shown). Mean NO3–N concentrations were about 20% less in 1996 (3.6 g kg-1) than in previous years (4.4 g kg-1) reflecting the lack of chicory in swards receiving 480 kg N ha-1 in 1996. Pure swards of chicory receiving N fertilizer should be used with caution in livestock production situations.
Crude Protein Yield
Cumulative protein yield increased with increasing N from 80 kg N ha-1, which is a function of both N concentration and DM production (Fig. 7)
. The strongest relationship of protein yield with N occurred in 1994, when swards were virtually pure chicory. Crude protein yield as a function of N increased at twice the rate in 1994 compared with that occurring in 1995 and 1996, again reflecting sward composition and growing season conditions. Cumulative crude protein yield was a function of dry matter yield, whereas N concentration was influenced by botanical composition.
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Fig. 7 Cumulative protein yield of herbage as a function of N rate in each growing season. Error bars are standard error of the mean. 1994 cumulative protein yield = (1.53 x 10-3)(N rate) + 0.49, r2 = 0.93; 1995 cumulative protein yield = (8.11 x 10-4)(N rate) + 0.42, r2 = 0.71; 1996 cumulative protein yield = (4.95 x 10-4)(N rate) + 0.46, r2 = 0.69
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In Vitro Organic Matter Disappearance
The IVOMD of herbage in 1994 (pure chicory) was not influenced by N rate, but did increase with each successive harvest date (data not shown). Digestibility ranged from 576 g kg-1 in spring to 621 g kg-1 by the last harvest in 1994. The IVOMD data in the 1995 and 1996 growing seasons reflect shifts in botanical composition and maturity of swards that included clovers and cool season grasses. Values ranged from 750 g kg-1 at first harvest to 550 g kg-1 by the end of the 1995 growing season. Increasing N led to a slight decline (P < 0.05) in IVOMD in 1995
. Digestibility ranged from 600 to 650 g kg-1 throughout 1996, and did so irrespective of time. Herbage IVOMD decreased (P < 0.05) in 1996 as N rate increased
, which reflected botanical changes (see Fig. 2) in the sward occurring by 1996. For example, IVOMD at 0 N was 623 g kg-1 and 593 g kg-1 at 480 kg N ha-1.
Estimation of Metabolizable Energy
Environment and management interact to influence the proportion of N and carbohydrate in plants, and thus nutritive value and utilization of herbage by grazing livestock. Level of dietary protein and fiber influence the value of digestible energy lost via urine or available as metabolizable energy for growth and maintenance (NRC, 1985). Asynchrony of N capture by rumen microorganisms and energy from structural carbohydrate breakdown can occur especially when high-quality fresh herbage is ingested (MacRae, 1996). Nitrogen is lost as ammonia and excreted as urea by the ruminant when energy is deficient. Capturing herbage N is important for livestock production efficiency as well as from an environmental perspective.
Predicted MEF averaged across harvest dates was variable and tended to be higher in 1995 and 1996 than in 1994 (Fig. 8)
. The shift in botanical composition over the 3 yr of the experiment influenced MEF trends, with MEF differing in response to N rate (Fig. 8). Years reflect differences in botanical composition of the sward over time, with MEF increasing from a mean of 9.1 ± 0.9 in 1994 to 10.9 ± 0.6 MJ kg-1 DM by 1996. The MEF values obtained in 1994 when swards were mostly chicory, were the lowest obtained in the experiment. However, Barry (1998) noted that MEF of vegetative chicory grown in New Zealand was very high relative to other commonly grown pasture forages such as red clover. By 1996, plots in our experiment had substantial amounts of grass at all N levels and legumes at low N rates and less chicory overall, of which the combined effects probably contributed to greater herbage MEF. The MEF declined as the season progressed, regardless of year. Unusual trends in 1995 (Fig. 9)
could be associated with the extremely dry conditions occurring during midsummer (Fig. 1), which caused changes in sward and chemical composition.
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Fig. 8 Metabolizable energy of feed (MEF) as a function of N rate and growing season. Error bars are standard error of the mean. 1994 MEF = (-1.40 x 10-5)(N rate)2 + (8.4 x 10-3)(N rate) + 8.41, R2 = 0.81; 1995 MEF = (1.45 x 10-5)(N rate)2 - (7.12 x 10-3)(N rate) + 10.79, R2 = 0.49; 1996 MEF = (8.64 x 10-6)(N rate)2 - (4.18 x 10-3)(N rate) + 11.13, R2 = 0.59
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Fig. 9 Mean metabolizable energy of feed (MEF) during each growing season. Error bars are standard error of the mean
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Volesky (1996) points to the merits of growing chicory in mixtures with other species. We concur that vigorous growth and high nutritive value of swards containing chicory would enhance mid- to late-summer forage production. Our results reinforce the need to use chicory in forage mixtures to meet the energy concentrations required for optimal herbage and N utilization. In our environment, chicory swards can be invaded by volunteer grasses and legumes, with the process accelerated by the demise of chicory, especially at higher N rates. Responsiveness of chicory to N affects not only productivity but nutritive value and persistence as a function of management and growing conditions. Single-dose nutrient applications are likely to be used in extensive pasture situations, and could lead to NO3–N accumulation in chicory herbage. Livestock health concerns could arise, especially where high N inputs occur.SAS Institute 1990
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ACKNOWLEDGMENTS
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This work was accomplished with the diligent assistance of J.M. Fedders and G.D. Lambert, and consultation with J.G. Phillips (USDA-ARS, North Atlantic Area, consulting statistician) on statistical methodology.
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NOTES
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1 Trade names or vendors are noted for the convenience of the reader and do not imply endorsement by USDA over comparable products or vendors. 
Received for publication April 26, 1999.
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ABSTRACT
INTRODUCTION
