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Pasture Management and Forage Utilization

Bermudagrass Management in the Southern Piedmont USA

X. Coastal Productivity and Persistence in Response to Fertilization and Defoliation Regimes

USDA-ARS, 1420 Experiment Station Rd., Watkinsville, GA 30677-2373

^* Corresponding author (afranz{at}uga.edu)

Received for publication November 12, 2003.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Productivity, quality, and persistence of ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] pastures are affected by fertilization, but possible interactions with defoliation regime including animal grazing are not fully known. We evaluated three sources of fertilization with equivalent N rates [inorganic, crimson clover (Trifolium incarnatum L.) cover crop plus inorganic, and chicken (Gallus gallus) broiler litter] factorially arranged with four defoliation regimes [unharvested, cattle (Bos taurus) grazing to maintain high (4.5 ± 1.6 Mg ha^–1) and low (2.5 ± 1.1 Mg ha^–1) forage mass, and hayed monthly] on estimated forage dry matter production, forage and surface residue C/N ratio, and ground cover of pastures on a Typic Kanhapludult in Georgia during 5 yr. Mean annual forage dry matter production was 7.5 ± 0.7 Mg ha^–1 with hay harvest but declined (1.3 Mg ha^–1 yr^–1) significantly with time as a result of lower precipitation. With grazing, estimated production was 8.3 ± 1.0 Mg ha^–1 and did not change with time, suggesting that grazing cattle sustained forage productivity by recycling nutrients and creating better surface soil conditions. Coastal bermudagrass as a percentage of ground cover (initially 81%) declined 5 ± 2% yr^–1 with unharvested and grazing to maintain low forage mass, declined 3 ± 1% yr^–1 with haying, and remained unchanged (–1 ± 1% yr^–1) with grazing to maintain high forage mass. Pastures with high forage mass were more productive than with low forage mass (9.2 ± 1.6 vs. 7.5 ± 1.1 Mg ha^–1) from a forage sustainability perspective, primarily by avoiding encroachment of undesirable plant species.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
HYBRID BERMUDAGRASS, of which Coastal represents a long-term performance standard, is an important warm-season component of pastures in the southeastern USA. The effect of fertilizer rate and defoliation frequency on bermudagrass production and quality has been extensively studied (Holt and Lancaster, 1968; Monson and Burton, 1982; Wood et al., 1993; Evers, 1998). Bermudagrass hay yield and quality are maximized when N is applied frequently at levels > 400 kg ha^–1 yr^–1 (Overman et al., 1992). Although production is maximized with long defoliation intervals, it comes at the expense of lower forage quality (Monson and Burton, 1982; Holt and Conrad, 1986).

Nitrogen fertilizer is a necessary agronomic input for high forage productivity and quality (Wilkinson and Langdale, 1974). It is also a monetary input for producers (Hoveland, 1992), a costly energy input for society (Lockeretz, 1980), and a possible source of surface and ground water pollution from excessive application, especially in humid regions with abundant precipitation (Russelle, 1992). Optimum N fertilization of Coastal bermudagrass depends upon a variety of producer goals, socioeconomic constraints, and environmental factors. Maximum conversion efficiency of applied N to dry matter was estimated at 200 kg N ha^–1 yr^–1 for Coastal bermudagrass (Overman and Wilkinson, 1992), which was also the approximate breakpoint for susceptibility to N leaching loss (Wilkinson and Frere, 1993). The rising cost of inorganic N fertilizer has prompted the need to look for alternatives for supplying pastures with N. Overseeding of bermudagrass with the winter annual, crimson clover, has been shown to produce equivalent hay yield with half the inorganic N input required for bermudagrass alone (Adams et al., 1967). Broiler litter is a locally abundant resource that can supply sufficient N at a reasonable cost with many opportunities for application throughout the year in the southeastern USA (Wood et al., 1993; Evers, 1998).

Most of the studies that have determined defoliation effects on bermudagrass productivity and quality have focused on frequency or timing of mechanical defoliation. Frequency and clipping height of mechanical defoliation are sometimes used to simulate animal grazing pressure, but plants are known to respond differently to animal grazing compared with mechanical defoliation (Matches, 1992). Animal grazing not only alters the structure and quality of pastures in the short term (Roth et al., 1990) but may also affect long-term pasture productivity (Matches, 1992) and environmental quality (Russelle, 1992). For many forages, maintenance of low forage mass leads to a reduction in plant productivity although the threshold to induce this decline may vary considerably depending upon plant species and environmental conditions (Matches, 1992). In contrast, maintaining moderate forage mass can lead to enhanced plant productivity compared with ungrazed pasture (Hodgkinson and Mott, 1986). Matches (1992) presented a review of a wide diversity of plant responses to grazing and concluded that no single plant response to grazing was applicable to all pastures under all environments.

Available literature on forage responses to fertilization and defoliation regimes is fragmented and not always integrated into a continuum of information relating plant, animal, and environmental responses (Coleman, 1992). We began a long-term study focusing primarily on the effects of fertilization and defoliation regimes on soil properties under bermudagrass-based pasture (Franzluebbers et al., 2001, 2002; Stuedemann et al., 2002; Franzluebbers and Stuedemann, 2003b). Forage mass, forage and surface residue C and N concentration, and ground cover of pastures were also determined as part of a holistic approach to assess soil and water quality within the context of forage and cattle production.

Our objective in this portion of the experiment was to assess forage productivity, forage and surface residue N content and C/N ratio, and persistence of Coastal bermudagrass–based pastures under a factorial arrangement of three sources of N fertilization and four defoliation regimes during the initial 5 yr of management.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Site Characteristics
A 15-ha upland field (33°22' N, 83°24' W) near Farmington, GA, in the Southern Piedmont resource area had previously been conventionally cultivated with various row crops for several decades before grassland establishment by sprigging of Coastal bermudagrass in 1991. Long-term mean annual conditions were 16.5°C air temperature, 1250 mm precipitation, and 1560 mm potential pan evaporation. Precipitation at the site was recorded at least twice each week throughout the study. Sampled on a 30-m grid, the frequency of soil series was 46% Madison, 22% Cecil, 13% Pacolet, 5% Appling, 2% Wedowee (fine, kaolinitic, thermic Typic Kanhapludults), 11% Grover (fine-loamy, micaceous, thermic Typic Hapludults), and 1% Louisa (loamy, micaceous, thermic, shallow Ruptic-Ultic Dystrudepts). Soil textural frequency of the Ap horizon (21 ± 12 cm) was 75% sandy loam, 12% sandy clay loam, 8% loamy sand, and 4% loam.

Experimental Design
The experimental design was a randomized complete block with treatments in a split-plot arrangement in each of three blocks, which were delineated by landscape features (i.e., slight, moderate, and severe erosion classes). Main plots were fertilization regime (n = 3), and split plots were defoliation regime (n = 4) for a total of 36 experimental units. Individual paddocks were 0.69 ± 0.03 ha. Each paddock contained a 3- by 4-m shade, mineral feeder, and water trough placed in a line 15 m long at the highest elevation. Unharvested and hayed exclosures (100 m² each) were placed side-by-side in paired low- and high-forage-mass paddocks of each fertilization regime.

Fertilization was targeted to supply 200 kg total N ha^–1 yr^–1 in one of three manners: (i) inorganic only as NH₄NO₃ broadcast in equally split applications in May and July, (ii) crimson clover cover crop plus supplemental inorganic fertilizer with half of the N assumed supplied by decomposing clover biomass derived from biological N fixation and half as NH₄NO₃ broadcast in July, and (iii) broiler litter broadcast by commercial truck spreader in split applications in May and July. A 3-yr evaluation at a site near our study suggested that hay yield (12.7 Mg dry matter ha^–1 yr^–1) from Coastal bermudagrass overseeded with crimson clover and supplied with 110 kg N ha^–1 yr^–1 was similar (13.0 Mg dry matter ha^–1 yr^–1) to that of Coastal bermudagrass supplied with 220 kg N ha^–1 yr^–1 (Carreker et al., 1977). Details of fertilizer applications each year are reported in Table 1. Diammonium phosphate and potash were applied based on soil-testing recommendations while excess P and K were applied with broiler litter as a result of meeting N requirements. Crimson clover ‘AU Robin’ seed was direct-drilled into dormant bermudagrass at 10 kg ha^–1 in October each year for the clover + inorganic treatment only. All grazed paddocks were mowed in late April immediately following collection of initial forage and surface residue samples and estimation of ground cover, and residue was allowed to decompose (i.e., clover biomass in clover plus inorganic treatment and winter annual weeds in other treatments). Paddocks were tedded occasionally to evenly distribute residue and avoid smothering the emerging bermudagrass.

Sampling and Analyses
Forage mass was determined by hand from multiple 0.25-m² subsampling locations within experimental units by collecting all aboveground forage and drying at 55°C for several days. Samples were collected during the middle of each month from April to October. Subsampling locations within grazed paddocks were within a 3-m radius of points on a 30-m grid. Due to the nonuniform dimensions of paddocks, subsampling locations within a paddock varied from four to nine, averaging 7 ± 1. Two points were established in each unharvested and hayed exclosure, around which samples were collected. At the initial and final sampling of each season, surface residue was collected from the same 0.25-m² subsampling locations by removing all surface litter to mineral soil with the aid of battery-powered hand shears. Forage and surface residue samples at the initial and final sampling times were oven-dried (55°C for several days) and ground to <1 mm, and a subsample was analyzed for organic C and total N with dry combustion at 1350°C (Leco CNS-2000, St. Joseph, MI).¹

Forage was harvested from hayed exclosures at 5-cm height each month from April to October with a vacuum mower. A 1- by 10-m strip was cut from the center of each hayed exclosure, wet forage weighed on a portable balance, and a 0.5- to 1.0-kg subsample weighed before and after drying at 55°C for several days. Dry matter yield was calculated from dry and wet weights and area harvested. The entire hayed exclosure was mowed and forage removed following subsampling.

Basal ground cover of grazed paddocks and exclosures was evaluated at monthly intervals immediately before forage mass determinations within each of the 0.25-m² sampling areas. All visual estimates of basal ground cover were made by the same experienced technician. Percentages (with separations in multiples of five) were calculated for the following six classes: (i) Coastal bermudagrass, (ii) crimson clover, (iii) common bermudagrass, (iv) winter annual grass [primarily Italian ryegrass (Lolium multiflorum Lam.) and rescuegrass (Bromus catharticus Vahl.)], (v) broadleaf weeds {primarily henbit (Lamium amplexicaule L.), chickweed (Cerastium nutans Raf.), shepherd's purse [Capsella bursa-pastoris (L.) Medik.], and horsenettle (Solanum carolinense L.)}, and (vi) bare ground.

Forage productivity was calculated differently for each defoliation regime. For hayed exclosures, annual forage productivity was measured from cumulative monthly machine harvests (10 m²) throughout the year. For unharvested exclosures, annual forage productivity was calculated from a yearly peak using linear + quadratic regression of monthly harvests of forage mass against day of year. Monthly harvests were by hand from two 0.25-m² areas within each exclosure. Only on 1 July 1994, the unharvested exclosures were machine-harvested for hay (before finalization of treatment designation), and this hayed forage mass was added to the calculated peak forage mass that occurred later in 1994. Peak forage mass usually occurred in August with subsequent decline later in the year due to deterioration of unharvested biomass. For high- and low-forage-mass treatments with grazing, annual forage productivity was calculated from the sum of final forage mass in October and an estimate of forage intake by grazing cattle. Forage intake was estimated based on equations established by the National Research Council using measured cattle live-weight gain specific to each experimental unit of this study and assuming 9.6 kJ of metabolizable energy g^–1 of bermudagrass forage (National Research Council, 1996, p. 116). We did not determine metabolizable energy of the forage produced in this study, so we could not verify the validity of this assumed value, nor determine whether this value might need to be seasonally adjusted. Since pastures were continuously stocked in summer, it is unlikely that seasonal differences in metabolizable energy would have been nearly as large as accumulated forage with haying or unharvested management. Sampled at 14-d intervals from grazed bermudagrass in North Carolina, in vitro dry matter digestibility declined from 54% in early June to 52% at the end of August while crude protein declined from 17.7 to 14.3% (Harvey et al., 1996). We also could not account for trampling and spoilage losses of forage by cattle, and therefore, forage productivity under grazed systems would likely have been underestimated although the relative change in productivity with time in any particular management system would be valid.

Data from multiple samples collected within an experimental unit were averaged and not considered as a source of variation in the analysis of variance using the general linear models procedure (SAS Inst., 1990). Mass, N content, C/N ratio of forage and surface residue components, and percentage ground cover were analyzed within each sampling date of each year separately according to the split-plot design with three blocks. When analyzed across years, treatment means of these same response variables were analyzed with year as an additional blocking effect. Annual changes in ground cover were analyzed using linear regression with a common intercept for all treatments to evaluate a single variable, the slope coefficient. Annual changes in forage productivity among fertilization and defoliation regimes were analyzed by linear regression of actual values and treatment residuals from an overall annual mean, in which the slope represented a management-induced difference against a normalized yearly effect, since climatic differences among years were expected to alter absolute productivity. All effects were considered significant at P 0.1.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Precipitation
During the 5 yr of this study, annual precipitation was at or above normal each year (Fig. 1). However, deviations from long-term monthly means occurred, especially regarding the consistently wetter-than-normal summer months in 1994, the alternating drier- and wetter-than-normal spring and summer months in 1997, and the consistently drier-than-normal summer months in 1998.

View larger version (46K): [in this window] [in a new window]   Fig. 1. Long-term mean (65-yr) cumulative (line) and monthly (bars) precipitation at Watkinsville, GA, and precipitation received at the site during 1994 to 1998.

Forage and Surface Residue Carbon and Nitrogen
Forage C/N ratio was positively related to forage maturity. Average forage C/N ratio was 22 at the beginning of the season and 29 at the end of the season (Table 2). Forage N concentration was 20 ± 2 mg g^–1 (mean ± standard deviation among fertilization and defoliation regimes) at the beginning of the growing season and 16 ± 2 mg g^–1 at the end of the growing season. These values represent an estimate of 125 and 100 mg crude protein g^–1 dry matter, respectively, which would represent Grade 4 hay with 85 to 100% relative feed value (van Soest, 1982). At similar N rates applied as in our study, crude protein from several bermudagrass hay harvests throughout the year was 100 ± 25 mg g^–1 in Alabama (Wood et al., 1993) and 124 ± 19 mg g^–1 in Texas (Evers, 1998).

Differences in surface residue components among fertilization regimes were mostly consistent with the trends that occurred in forage components but more significant (Table 2). Inorganic fertilization appeared to be a more effective nutrient source for sequestration of N into forage mass and subsequent surface residue components than either clover + inorganic or broiler litter fertilization.

The effect of defoliation regime on forage mass was large, but also an intentional consequence of the treatments employed (Fig. 2), which led to major changes in forage C/N ratio. Forage N content and C/N ratio were affected by defoliation regime at the beginning and end of the growing season (Table 2). At the end of the growing season, forage C/N ratio was lowest under grazing to maintain low forage mass (22 g g^–1) and highest under unharvested management (35 g g^–1). Forage C/N ratio was not different between grazing to maintain high forage mass (29 g g^–1) and hayed management (30 g g^–1) averaged across years but was lower under grazing to maintain high forage mass (28 ± 5 g g^–1) than under hayed management (33 ± 5 g g^–1) at the end of 1995, 1996, and 1997. The difference in forage C/N ratio between high and low forage mass with grazing probably reflected the change in growth form of Coastal bermudagrass in response to grazing, whereby lower forage mass resulted in more prostrate growth with predominantly young shoots compared with upright growth with a combination of mature stems and young shoots primarily at the top of the canopy under high forage mass (Roth et al., 1990). With increasing maturity, forage C/N ratio increases (Holt and Conrad, 1986; Hoveland, 1992). Nutritive value of consumed forage by grazing cattle, however, may not have been different between forage mass treatments (Roth et al., 1990), since cattle would have likely selected the top layers of forage with higher N concentration (Wilkinson et al., 1970), which could have been more similar to that of the low-growing young shoots available under grazing to maintain low forage mass. In contrast to the inverse relationship between forage mass and forage C/N ratio among fertilization regimes due to fertility, there was a positive relationship between forage mass and forage C/N ratio among defoliation regimes due to differences in maturation of forage.

View larger version (25K): [in this window] [in a new window]   Fig. 2. Forage mass throughout the summer as affected by defoliation regime (UH is unharvested, HFM is grazing to maintain high forage mass, LFM is grazing to maintain low forage mass, and Hay is hayed) when averaged across fertilization regimes from 1994 to 1998. Vertical bars at the top of each panel indicate the least significant difference (P = 0.1) among defoliation regimes within each month of sampling.

Ground Cover of Pastures
As intended, Coastal bermudagrass was the dominant ground cover in all management systems, except in April with clover + inorganic fertilization (Fig. 3), at which time crimson clover was a large component (Table 3). Cutting of the winter-annual crimson clover following the April evaluation reduced this component to a sporadic species thereafter. Ground cover of crimson clover in pastures, although variable among years, was positively related to forage utilization (Table 3). Under haying and grazing to maintain low forage mass, where forage mass was reduced to a minimum before the winter planting time, crimson clover established the best. Large quantities of either standing forage mass (grazing to maintain high forage mass) or surface residue mass (unharvested management) led to poor development of crimson clover, most likely due to poor surface conditions that inhibited light penetration to the developing seedlings. Springer (1997) found a negative linear relationship between bermudagrass height at the end of the growing season and establishment of either crimson clover or white clover (Trifolium repens L.), possibly due to poorer soil–seed contact caused by the inability of seeding equipment to cut through residue, increased shading of seedlings, and better habitat for insects to feed on legume seedlings with taller bermudagrass.

View larger version (55K): [in this window] [in a new window]   Fig. 3. Ground cover as affected by defoliation regime within each fertilization regime throughout the summer. An asterisk above a set of values within a botanical category, fertilization regime, and month of sampling indicates a significant difference (P = 0.01) between at least two defoliation regime means.

Annual changes in ground cover as Coastal bermudagrass were most striking under unharvested management, irrespective of fertilization regime (Table 4). The rates of change resulted in a decline from 81% at the beginning of the experiment to 60% with clover + inorganic fertilization and to 46% with broiler litter fertilization at the end of 5 yr. The decline in ground cover as Coastal bermudagrass under unharvested management resulted in an increase as bare ground (Fig. 3; Table 4), which indicated a thinning of the stand by mature forage that created shade at the soil surface and prevented new basal shoot development.

Decline in ground cover as Coastal bermudagrass was moderate under hayed management, varying from 2 to 4% per year (Table 4). Ground cover as common bermudagrass with inorganic fertilization and as broadleaves with clover + inorganic and broiler litter fertilization increased with time under hayed management (Fig. 3; Table 4). It is unclear why changes in ground cover differed among fertilization regimes, but it may have been due to differences in soil surface nutrient availability that altered competitive advantages of various species.

Ground cover as Coastal bermudagrass with grazing to maintain high forage mass did not change on an annual basis although there were declines early in the growing season with clover + inorganic fertilization (Table 4). The early-season declines were likely due to similar competitive effects that were observed under grazing to maintain low forage mass by the crimson clover cover crop.

Encroachment of common bermudagrass occurred under grazing to maintain low forage mass in all fertilization regimes from August to October (Table 4). The low forage mass may have reduced energy reserves of Coastal bermudagrass below a sustainable threshold, thereby allowing invasion with common bermudagrass following occasionally favorable precipitation events later in the summer. A similar, but lesser invasion of common bermudagrass occurred later in the summer under hayed management with inorganic and broiler litter fertilization. Common bermudagrass encroachment into pastures grazed to a low forage mass is typical in the southeastern USA (Bates et al., 1996; Gates et al., 1999), partly because its prostrate growth habit makes it more tolerant to conditions of low forage mass.

Encroachment of annual grasses during the winter dormant period of bermudagrass was greatest under grazing to maintain low forage mass with inorganic fertilization (Table 4). Annual broadleaves were even more encroaching during the winter period under all management systems. The encroachment of broadleaves was positively related to the extent of forage utilization, indicating that less forage or surface residue mass created opportunities for broadleaves to proliferate. These low-growing broadleaves did not appear to greatly inhibit the development of overseeded crimson clover, nor did they pose a serious threat to the persistence of Coastal bermudagrass. However, the development of winter annual grasses and broadleaves in this study highlights a period of opportunity to increase forage production and potential animal grazing days by overseeding of bermudagrass pastures with cool-season grasses or legumes, which has been demonstrated in several other studies (Welch et al., 1967; Carreker et al., 1977; Wilkinson and Stuedemann, 1983). Our results from overseeding crimson clover into bermudagrass with grazing to maintain low forage mass highlight the need to carefully manage the cool-season forage in the spring to avoid loss of Coastal bermudagrass stand. We allowed crimson clover to reach full bloom before cutting to maximize biological N fixation, but this likely reduced the early-season development of Coastal bermudagrass.

Forage Productivity
Differences in hay yield due to fertilization regime occurred primarily early in the growing season from April to June each year (Table 5). Clover + inorganic fertilization produced greater quantity of hay in April than inorganic or broiler litter fertilization during 1995, 1996, and 1997. This result was an intentional consequence of overseeding the warm-season pastures with the winter-annual crimson clover, which produced peak forage mass in April. An opposite effect occurred for hay production in May where hay yield under inorganic and broiler litter fertilization was greater than under clover + inorganic fertilization in 1995, 1997, and 1998. Hay yield in June was greatest with inorganic fertilization during most years. The higher hay yields during May and June in most years and from the first cutting in July in 1994 with inorganic fertilization compared with the organic fertilization regimes occurred most likely because of the immediate availability of applied inorganic N to bermudagrass forage. Since clover forage was harvested as hay, crimson clover root and stubble were the only sources of organic N supplied, which would have likely required more time for release of biologically fixed N than that of leaves and stems (Franzluebbers et al., 1994a, 1994b). Availability of N from broiler litter can be highly variable, but analyses from 15 different broiler houses in northern Georgia revealed 34 ± 12% of total N in an immediately available pool, 31 ± 7% of total N in an intermediately available pool with a half-life of 15-29 d under ideal conditions, and 35 ± 12% of total N in a resistant pool not considered available during the first growing season (Gordillo and Cabrera, 1997).

Averaged across years, hay yield with clover + inorganic fertilization was more than double that with inorganic or broiler litter fertilization during April (Table 5). During May, June, and July, hay yield was greater with inorganic fertilization than with clover + inorganic fertilization. Hay yield was greater with broiler litter fertilization than with clover + inorganic fertilization in May and June and greater with inorganic fertilization than with broiler litter fertilization in June and July.

Total annual hay yield was not different among fertilization regimes during any single year (Table 5). However, when averaged across years, inorganic fertilization produced hay yield 12% greater than with clover + inorganic fertilization and 20% greater than with broiler litter fertilization. It appears that the immediate availability of N with the inorganic source was efficiently utilized throughout the year, considering also little evidence of leaching loss from any of the fertilization regimes (Franzluebbers and Stuedemann, 2003b). However, it can also be stated that the organic fertilization sources produced equal quantities of hay in any single year while at the same time utilizing very important resources available to producers in the southeastern USA, i.e., biological N fixation with the overseeding of crimson clover and animal manure readily available within the region that must be effectively utilized to avoid environmental degradation.

Lower hay yield with clover + inorganic fertilization than with inorganic fertilization in our study was consistent with observations of slightly lower hay yield but improved forage N concentration when various legumes were overseeded into bermudagrass compared with bermudagrass alone in Oklahoma (Mullen et al., 2000). We based supplemental inorganic N fertilization in the clover + inorganic treatment on the assumption that carryover of N from clover would be 110 kg N ha^–1 (Carreker et al., 1977). Overman et al. (1992) estimated that when overseeded crimson clover forage mass was removed as hay, actual N carryover from clover to bermudagrass would be 33 kg ha^–1 yr^–1. It is therefore possible that the reduced 5-yr-mean hay yield we observed with clover + inorganic compared with inorganic fertilization was due to lower availability of N.

Similar to our results, hay yield of bermudagrass fertilized with broiler litter (300 kg N ha^–1 yr^–1) was lower (14.9 vs. 16.4 Mg dry matter ha^–1 yr^–1) than with inorganic fertilization (220 kg N ha^–1 yr^–1) during a 2-yr evaluation in northern Alabama but statistically significant in only two of six hay cuttings (one positive and one negative) (Wood et al., 1993). In eastern Texas, hay yield of Coastal bermudagrass fertilized with broiler litter to supply the same quantity of N as with inorganic fertilizer (220 kg N ha^–1 yr^–1) was reduced (8.1 vs. 9.5 Mg dry matter ha^–1 yr^–1) during a 2-yr evaluation (Evers, 1998).

Forage mass of the unharvested treatment was typically greater with inorganic fertilization than with either clover + inorganic or broiler litter fertilization early in the summer but became more similar among fertilization regimes by the end of the growing season (Table 6). This early-season fertilization effect was evident during the first 3 yr but not during the last 2 yr of the experiment. Both the reduced early-season growth during the early years and the lack of differences at any time during the later years with organic compared with the inorganic sources of fertilization suggest that additional time was needed for mineralization of organically bound nutrients. Once that time became available, there were no major differences in forage mass among inorganic and organic sources when fertilized with equivalent rates of N.

Forage productivity was greater with inorganic fertilization (8.89 Mg ha^–1 yr^–1) than with clover + inorganic fertilization (7.83 Mg ha^–1 yr^–1) and broiler litter fertilization (7.88 Mg ha^–1 yr^–1) when averaged across defoliation regimes and years (Table 7). Although an interaction between fertilization and defoliation regimes was not significant when averaged across years, differences in forage productivity were significant in two of three fertilization comparisons with unharvested management, in none of the three comparisons under grazing to maintain high forage mass, in one of three comparisons under grazing to maintain low forage mass, and in one of three comparisons under haying (Table 7).

View this table: [in this window] [in a new window]   Table 7. Forage productivity as affected by fertilization and defoliation regimes during the first 5 yr of management.

View larger version (38K): [in this window] [in a new window]   Fig. 4. Annual forage productivity as affected by defoliation regime averaged across fertilization regimes during 1994 to 1998 and treatment deviations from annual means (to account for differences in climatic conditions) as a function of years since initiation of the study among defoliation regimes.

Forage productivity was greater when unharvested than when hayed in 1994 and 1996 (Fig. 4; Table 7) and when averaged across years (8.62 vs. 7.52 Mg ha^–1 yr^–1). This result is in accordance with several previous studies where forage yield of less frequently harvested Coastal bermudagrass has been greater than that of more frequently harvested (Holt and Lancaster, 1968; Monson and Burton, 1982; Holt and Conrad, 1986). The difference in productivity between unharvested and hayed forage in our study could have also been related to cumulative changes in soil properties with time due to the continuous removal of forage mass with haying, which lowered the recycling of nutrients from plant residues into (i) soil organic and surface residue C and N pools (Franzluebbers et al., 2001), (ii) N-supplying capacity of surface soil (Franzluebbers and Stuedemann, 2001), and (iii) exchangeable soil K (Franzluebbers et al., 2004). The change in ground cover with time may have also contributed to the difference in productivity, in which the more productive Coastal bermudagrass component declined and the less productive common bermudagrass and broadleaf components increased with time under haying compared with unharvested management (Table 4).

Estimated forage productivity was greater under high than under low forage mass with grazing in 1994, 1997, and 1998 (Fig. 4; Table 7) and when averaged across years (9.2 vs. 7.5 Mg ha^–1 yr^–1). Maintenance of greater ground cover as Coastal bermudagrass, lower encroachment of common bermudagrass, and lower development of bare ground (Table 4) under high than low forage mass with grazing could partly explain the greater estimated productivity under grazing to maintain high forage mass. Soil organic matter components and surface soil compaction were not greatly affected between high and low forage mass with grazing (Franzluebbers et al., 2001; Franzluebbers and Stuedemann, 2003a), suggesting soil nutrient supply and soil surface conditions affecting rooting and water dynamics would have been similar.

The difference in estimated forage productivity between high and low forage mass with grazing was 1.7 ± 1.2 Mg ha^–1 yr^–1 among years, nearly equivalent to the difference in forage mass at the end of the growing season, which averaged 4.53 ± 1.59 Mg ha^–1 under grazing to maintain high forage mass and 2.54 ± 1.11 Mg ha^–1 yr^–1 under grazing to maintain low forage mass (Fig. 2). Despite the higher estimated forage productivity with grazing to maintain high forage mass, cattle stocking density was lower with high forage mass (5.9 ± 2.1 head ha^–1) than with low forage mass (8.4 ± 2.8 head ha^–1) (mean ± standard deviation among fertilization regimes, years, and stocking periods). Stocking density gives no indication of cattle performance or production, which will be reported elsewhere (J.A. Stuedemann, unpublished data,1998). Forage allowance (calculated from forage mass before a 28-d period divided by total cattle weight stocked during that period) was 2.64 ± 1.18 kg forage kg^–1 body weight (mean ± standard deviation among fertilization regimes, years, and periods; n = 23) under high forage mass and 0.92 ± 0.40 kg forage kg^–1 body weight under low forage mass. Coastal bermudagrass is known to alter its morphology toward a less prehensible, prostrate growth habit with grazing to maintain low forage mass, allowing it to achieve a similar growth rate to that under grazing to maintain high forage mass (Roth et al., 1990). More prostrate morphology with grazing to maintain low forage mass was associated with greater rhizome mass of ‘Florakirk’ bermudagrass compared with grazing to maintain high forage mass at the end of 2 yr (Pedreira et al., 2000), suggesting that energy reserve of closely grazed bermudagrass might be maintained without sacrificing productivity. Our results, however, indicate that grazing to maintain low forage mass reduced forage productivity of Coastal bermudagrass pastures across several years and that a long-term optimum forage mass target might be between the two forage masses maintained in our study.

From an environmental quality perspective, forage production under either grazing to maintain high forage mass or unharvested management would be more desirable than under grazing to maintain low forage mass because the greater forage and surface residue coverage would reduce water runoff and particulate-borne nutrient transport across the landscape (Phillips, 1998). From an agronomic perspective, higher forage productivity under grazing to maintain high rather than low forage mass effectively contributed to a surface buffer of forage mass that suppressed winter annual growth (Table 2) and allowed greater persistence of Coastal bermudagrass by limiting encroachment of undesirable forage components (Table 4). From an animal production perspective, the 46 ± 47% greater cattle stocking density under low than under high forage mass could lead to greater short-term economic gain although at the risk of reducing medium-term forage productivity and economic outcome.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Pastures grazed to maintain high forage mass, whether fertilized inorganically or organically, had the highest productivity with the highest persistence of Coastal bermudagrass. Cattle producers in the Piedmont region could use information from this experiment to (i) sustain medium-term forage productivity and preserve Coastal bermudagrass stands by stocking cattle to moderately utilize forage (high forage mass) or (ii) maximize short-term economic gain and risk losing long-term forage productivity by stocking cattle to fully utilize forage (low forage mass). Although we acquired revealing ecosystem responses from the first 5 yr of this study, more time is needed to appropriately relate short- and long-term economics with pasture productivity and environmental consequences.

	ACKNOWLEDGMENTS

 
We appreciate the technical expertise of Steven Knapp, David Lovell, Dwight Seman, Fred Hale, and Robert Sheats.

	NOTES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
¹ Trade and company names are included for the benefit of the reader and do not imply any endorsement or preferential treatment of the product listed by the USDA.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Adams, W.E., M. Stelly, H.D. Morris, and C.B. Elkins. 1967. A comparison of coastal and common bermudagrasses (Cynodon dactylon (L.) Pers.) in the Piedmont region: II. Effect of fertilization and crimson clover (Trifolium incarnatum) on nitrogen, phosphorus, and potassium contents of forage. Agron. J. 59:281–284.[Abstract/Free Full Text]
• 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.
• Bransby, D.I. 1989. Compromises in the design and conduct of grazing experiments. p. 53–67. In G.C. Marten (ed.) Grazing research: Design, methodology, and analysis. CSSA Spec. Publ. 16. CSSA and ASA, Madison, WI.
• Carreker, J.R., S.R. Wilkinson, A.P. Barnett, and J.E. Box. 1977. Soil and water management systems for sloping land. ARS-S-160. U.S. Gov. Print. Office, Washington, DC.
• Coleman, S.W. 1992. Plant–animal interface. J. Prod. Agric. 5:7–13.
• Evers, G.W. 1998. Comparison of broiler poultry litter and commercial fertilizer for coastal bermudagrass production in the southeastern US. J. Sustain. Agric. 12:55–77.
• Franzluebbers, A.J., and J.A. Stuedemann. 2001. Bermudagrass management in the Southern Piedmont USA: IV. Soil-surface nitrogen pools. The Sci. World 1(S2):673–681.
• Franzluebbers, A.J., and J.A. Stuedemann. 2003a. Bermudagrass management in the Southern Piedmont USA: III. Particulate and biologically active soil carbon. Soil Sci. Soc. Am. J. 67:132–138.[Abstract/Free Full Text]
• Franzluebbers, A.J., and J.A. Stuedemann. 2003b. Bermudagrass management in the Southern Piedmont USA: VI. Soil-profile inorganic nitrogen. J. Environ. Qual. 32:1316–1322.[Abstract/Free Full Text]
• Franzluebbers, A.J., J.A. Stuedemann, and S.R. Wilkinson. 2001. Bermudagrass management in the Southern Piedmont USA: I. Soil and surface residue carbon and sulfur. Soil Sci. Soc. Am. J. 65:834–841.[Abstract/Free Full Text]
• Franzluebbers, A.J., J.A. Stuedemann, and S.R. Wilkinson. 2002. Bermudagrass management in the Southern Piedmont USA: II. Soil phosphorus. Soil Sci. Soc. Am. J. 66:291–298.[Abstract/Free Full Text]
• Franzluebbers, K., R.W. Weaver, and A.S.R. Juo. 1994a. Mineralization of labeled N from cowpea [Vigna unguiculata (L.) Walp.] plant parts at two growth stages in sandy soil. Plant Soil 160:259–266.
• Franzluebbers, K., R.W. Weaver, A.S.R. Juo, and A.J. Franzluebbers. 1994b. Carbon and nitrogen mineralization from cowpea plants part decomposing in moist and in repeatedly dried and wetted soil. Soil Biol. Biochem. 26:1379–1387.
• Franzluebbers, A.J., S.R. Wilkinson, and J.A. Stuedemann. 2004. Bermudagrass management in the Southern Piedmont USA: VIII. Soil pH and nutrient cations. Agron. J. 96:1390–1399 (this issue).[Abstract/Free Full Text]
• 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.[Abstract/Free Full Text]
• Gordillo, R.M., and M.L. Cabrera. 1997. Mineralizable nitrogen in broiler litter: I. Effect of selected litter chemical characteristics. J. Environ. Qual. 26:1672–1679.[Abstract/Free Full Text]
• Harvey, R.W., J.P. Mueller, J.A. Barker, M.H. Poore, and J.P. Zublena. 1996. Forage characteristics, steer performance, and water quality from bermudagrass pastures fertilized with two levels of nitrogen from swine lagoon effluent. J. Anim. Sci. 74:457–464.[Abstract/Free Full Text]
• Hawkins, J.A., B.H. Wilson, C.L. Mondart, B.D. Nelson, R.A. Farlow, and P.E. Schilling. 1979. Leafhoppers and planthoppers in coastal bermudagrass: Effect on yield and quality and control by harvest frequency. J. Econ. Entomol. 72:101–104.
• Hodgkinson, K.C., and J.J. Mott. 1986. On coping with grazing. p. 171–192. In F.P. Horn et al. (ed.) Grazing-lands research at the plant-animal interface. Winrock Int., Morrilton, AR.
• Holt, E.C., and B.E. Conrad. 1986. Influence of harvest frequency and season on bermudagrass cultivar yield and forage quality. Agron. J. 78:433–436.[Abstract/Free Full Text]
• Holt, E.C., and J.A. Lancaster. 1968. Yield and stand survival of ‘Coastal’ bermudagrass as influenced by management practices. Agron. J. 60:7–11.[Abstract/Free Full Text]
• Hoveland, C.S. 1992. Grazing systems for humid regions. J. Prod. Agric. 5:23–27.
• Lockeretz, W. 1980. Energy inputs for nitrogen, phosphorus, and potash fertilizers. p. 23–24. In D. Pimentel (ed.) Handbook of energy utilization in agriculture. CRC Press, Boca Raton, FL.
• Matches, A.G. 1992. Plant response to grazing: A review. J. Prod. Agric. 5:1–7.
• McNaughton, S.J. 1985. Interactive regulation of grass yield and chemical properties by defoliation, a salivary chemical, and inorganic nutrition. Oecologia 65:478–486.
• Monson, W.G., and G.W. Burton. 1982. Harvest frequency and fertilizer effects on yield, quality, and persistence of eight bermudagrasses. Agron. J. 74:371–374.[Abstract/Free Full Text]
• Mullen, R.W., S.B. Phillips, W.R. Raun, G.V. Johnson, and W.E. Thomason. 2000. Forage yield and crude protein of interseeded legume-bermudagrass mixtures as affected by phosphorus fertilizer. J. Plant Nutr. 23:673–681.
• National Research Council. 1996. Nutrient requirements of beef cattle. 7th ed. National Academy Press, Washington, DC.
• Overman, A.R., and S.R. Wilkinson. 1992. Model evaluation for perennial grasses in the southern United States. Agron. J. 84:523–529.[Abstract/Free Full Text]
• Overman, A.R., S.R. Wilkinson, and G.W. Evers. 1992. Yield response of bermudagrass and bahiagrass to applied nitrogen and overseeded clover. Agron. J. 84:998–1001.[Abstract/Free Full Text]
• 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.[Abstract/Free Full Text]
• Phillips, W.A. 1998. Use of manure on grazing lands. p. 157–171. In J.L. Hatfield and B.A. Stewart (ed.) Animal waste utilization: Effective use of manure as a soil resource. Ann Arbor Press, Chelsea, MI.
• Reardon, P.O., C.L. Leinweber, and L.B. Merrill. 1972. The effect of bovine saliva on grasses. J. Anim. Sci. 34:897–898.
• Roth, L.D., F.M. Rouquette, Jr., and W.C. Ellis. 1990. Effects of herbage allowance on herbage and dietary attributes of coastal bermudagrass. J. Anim. Sci. 68:193–205.[Abstract/Free Full Text]
• Russelle, M.P. 1992. Nitrogen cycling in pasture and range. J. Prod. Agric. 5:13–23.
• SAS Institute. 1990. SAS user's guide: Statistics. Version 6 ed. SAS Inst., Cary, NC.
• Springer, T.L. 1997. Effect of bermudagrass height on clover establishment. Crop Sci. 37:1663–1665.[Abstract/Free Full Text]
• Stuedemann, J.A., A.J. Franzluebbers, and D.H. Seman. 2002. The Salem Road study: Restoration of degraded land with pasture—experimental layout and animal responses [Online]. Available at http://spfcic.okstate.edu/procedures/2002/utilization/stuedemann.htm (accessed 30 June 2003; verified 18 June 2004). Proc. Southern Pasture and Forage Crop Improvement Conf., 57th, Athens GA. 23–25 Apr. 2002. Southern Pasture and Forage Crop Improvement Conf., Oklahoma State Univ., Stillwater.
• van Soest, P.J. 1982. Nutritional ecology of the ruminant: Ruminant metabolism, nutritional strategies, the cellulolytic fermentation and the chemistry of forages and plant fibers. O & B Books Inc., Corvallis OR.
• Vigil, M.F., and D.E. Kissel. 1991. Equations for estimating the amount of nitrogen mineralized from crop residues. Soil Sci. Soc. Am. J. 55:757–761.[Abstract/Free Full Text]
• Welch, L.F., S.R. Wilkinson, and G.A. Hillsman. 1967. Rye seeded for grain in coastal bermudagrass. Agron. J. 59:467–472.[Abstract/Free Full Text]
• Wilkinson, S.R., W.E. Adams, and W.A. Jackson. 1970. Chemical composition and in vitro digestibility of vertical layers of coastal bermudagrass (Cynodon dactylon L.). Agron. J. 62:39–43.[Abstract/Free Full Text]
• Wilkinson, S.R., and M.H. Frere. 1993. Use of forage nitrate-nitrogen to improve nitrogen-use efficiency in Coastal bermudagrass. p. 1450–1451. In Proc. XVII Int. Grassland Congr., Palmerston, New Zealand. 13–16 Feb. 1993. New Zealand Grassl. Assoc., Palmerston, New Zealand.
• Wilkinson, S.R., and G.W. Langdale. 1974. Fertility needs of the warm-season grasses. p. 119–145. In Forage fertilization. ASA, CSSA, and SSSA, Madison, WI.
• Wilkinson, S.R., and J.A. Stuedemann. 1983. Increased use of Southern Piedmont land and climatic resources by interseeding small grains in dormant coastal bermudagrass. p. 568–571. In J.A. Smith and V.W. Hays (ed.) Proc. XIV Int. Grassland Congr., Lexington, KY. 15–24 June 1981. Westview Press, Boulder, CO.
• Wood, C.W., H.A. Torbert, and D.P. Delaney. 1993. Poultry litter as a fertilizer for bermudagrass: Effects on yield and quality. J. Sustain. Agric. 3:21–36.

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