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Published online 3 October 2006
Published in Agron J 98:1453-1459 (2006)
DOI: 10.2134/agronj2005.0246
© 2006 American Society of Agronomy
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Spatial Heterogeneity of Herbage Response to Management Intensity in Continuously Stocked Pensacola Bahiagrass Pastures

J. C. B. Dubeux, Jr.a, R. L. Stewart, Jr.b, L. E. Sollenbergerc,*, J. M. B. Vendraminid and S. M. Interrantec

a Depto. de Zootecnia/UFRPE, Av. Dom Manoel de Medeiros, S/N, Dois Irmãos, 52171-900, Recife-PE, Brazil
b Dep. of Animal and Poultry Sciences, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061-0306
c Agronomy Dep., Univ. of Florida, Gainesville, FL, 32611-0300
d Soil and Crop Science Dep., Texas A&M Univ., Overton, TX 75684

* Corresponding author (lesollen{at}ufl.edu)

Received for publication August 24, 2005.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
Redistribution of soil nutrients often occurs on grazed swards, but the effect of these changes on herbage response is not well understood. This 3-yr study evaluated the effects of a wide range of management intensities on patterns of herbage and soil nutrient responses in continuously stocked ‘Pensacola’ bahiagrass (Paspalum notatum Flügge) pastures growing on Pomona and Smyrna sands. The three management intensities were: Low (40 kg N ha–1 yr–1 and 1.4 animal units [AU, one AU = 500 kg live weight] ha–1 stocking rate [SR]), Moderate (120 kg N ha–1 yr–1 and 2.8 AU ha–1 SR), and High (360 kg N ha–1 yr–1 and 4.2 AU ha–1 SR). Responses were measured in three zones based on distance from the watering point (Zone 1, 0–8 m; Zone 2, 8–16 m; Zone 3, > 16 m). Herbage accumulation rate increased as management intensity increased from Low to Moderate in 2 of 3 yr (14 vs. 41 kg ha–1 d–1 in 2002 and 17 vs. 42 kg ha–1 d–1 in 2003) but was not greater for High than Moderate in any year. Herbage accumulation rate was greater in Zone 1 than 3 (40 vs. 20 kg ha–1 d–1 kg ha–1 d–1). Herbage mass was lower in Zone 1 than in Zones 2 and 3 during 2 of 3 yr. Herbage nutritive value increased with management intensity and was greatest in Zone 1 for Low, but not for the other intensities. Soil P, K, and Mg accumulated in Zone 1 of all management intensities. Across management intensities, soil nutrient concentration and productivity of continuously stocked bahiagrass pastures was greatest in the zone including shade and watering locations, but zonal heterogeneity in nutritive value occurred only in the least intensively managed pastures (Low).

Abbreviations: AU, animal units • DM, dry matter • IVDOM, in vitro digestible organic matter • OM, organic matter • SR, stocking rate


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
PASTURE MANAGEMENT has a major impact on nutrient cycling in grazing systems (Sollenberger et al., 2002; Dubeux et al., 2004). Nitrogen fertilization and grazing management (stocking method and SR) are examples of practices that play an important role in nutrient dynamics in grazed swards.

Fertilization increases the amount of nutrients cycling within the soil–plant–animal continuum, acting as a catalyst in the main recycling processes, particularly in low soil-fertility environments. Fertilization increases the total plant biomass produced (below- and aboveground) that leads to an increase in: (i) SR and excreta deposition, (ii) litter production and decomposition rate, and (iii) soil organic matter (OM) mineralization rate (Dubeux et al., 2004). Increasing SR increases the proportion of herbage consumed by livestock and the proportion of nutrients being returned to the soil in excreta relative to plant litter (Thomas, 1992). Because of the greater availability to plants of nutrients in dung and urine relative to litter, SR also increases the rates of flow among nutrient pools (Haynes and Williams, 1993; Castilla et al., 1995). Stocking method may also play a role altering distribution of excreta return across the pasture surface (Peterson and Gerrish, 1996).

Soil nutrient concentration tends to be greater in areas of grazed pasture closer to animal lounging sites (e.g., shade and water sources) than in the rest of the pasture because of higher density of excreta deposition, particularly in warm environments (Mathews et al., 1996, 2004). Nutrient accumulation near shade was studied for pastures in which Holstein heifers (Bos taurus) grazed bahiagrass in humid southwestern Japan (Sugimoto et al., 1987). On warm, summer days when temperatures exceeded 27°C, 44 to 53% of urinations and 26 to 29% of defecations occurred in shaded areas. In autumn, when maximum air temperature did not exceed 23.5°C, only 11% of urine and dung deposits occurred in shaded areas.

It is not well established whether soil differences due to patterns of excreta deposition are large enough to affect plant response. There are very few studies that have evaluated the effect of management practices on spatial patterns of plant growth and herbage nutrient concentration in pastures. Thus, the objectives of this study were to evaluate effects of different levels of management intensity, defined in terms of N fertilization amount and SR, on spatial patterns of herbage response on continuously stocked Pensacola bahiagrass pastures and to relate these patterns to treatment effects on soil nutrient concentrations.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
Experimental Site
The experiment was performed at the University of Florida Beef Research Unit, northeast of Gainesville at 29°43' N latitude on Pensacola bahiagrass pastures. Pastures used in the study were well established, had been planted within 2 yr of each other, and were at least 10 yr old at the start of the trial. During this 10-yr period, the pastures were similarly managed, with SR ranging from 1 to 2 AU ha–1 and N fertilization ranging from 40 to 100 kg N ha–1 yr–1. Soils were classified as Spodosols (sandy siliceous, hyperthermic Ultic Alaquods from the Pomona series or sandy siliceous, hyperthermic Aeric Alaquods from the Smyrna series). Average soil pH was 5.9, and Mehlich-I soil P, K, Ca, and Mg concentrations at the beginning of the experiment were 5.3, 28, 553, and 98 mg kg–1, respectively.

Treatments and Design
Management intensities were combinations of SR and N fertilization amount and were replicated twice in a randomized block design. The three management intensities tested were Low (40 kg N ha–1 yr–1 and 1.4 AU ha–1 SR), Moderate (120 kg N ha–1 yr–1 and 2.8 AU ha–1 SR), and High (360 kg N ha–1 yr–1 and 4.2 AU ha–1 SR). Low was chosen because it approximates average bahiagrass management practice in Florida cow–calf systems, while Moderate represents the upper range of current producer practice (Chambliss, 1999). High is much greater than what is currently in use, but decreasing land area available for grassland agriculture may require greater management intensity in the future. The level of SR associated with the N levels for Moderate and High were chosen based on studies of bahiagrass yield response to N fertilizer conducted by Burton et al. (1997) and Twidwell et al. (1998).

Within management intensity treatments, three zones were defined based on distance from the watering point. Zone 1 consisted of a semicircle with an 8-m radius from the watering point and included a permanently positioned shade structure (Fig. 1 ). Zone 2 was the area located between the 8- and 16-m radii from the watering point, and Zone 3 was the remaining area of the pasture. Zones within pastures were considered a strip-plot feature of the randomized block design.


Figure 1
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  		Fig. 1. Diagram showing the three pasture zones. Zone 1 is an 8-m radius semicircle in which the shade and watering points are located. Zone 2 is the area between the 8- to 16-m radii from the watering point, and Zone 3 is the remaining area of the pasture. Figure is not drawn to scale.

 
Two crossbred (Angus x Brahman) yearling heifers were assigned to each experimental unit so that total live weight varied by no more than 5 kg per experimental unit. Average initial live weight across all animals was 344, 308, and 313 kg in 2001, 2002, and 2003, respectively. To achieve the desired SR, pasture area varied according to management intensity and was 1, 0.5, and 0.33 ha for Low (100 by 100 m), Moderate (100 by 50 m), and High (66.7 by 50 m) experimental units, respectively.

The bahiagrass pastures were continuously stocked, and the experiment was performed during the grazing seasons of 2001 (26 June–16 October, 112 d), 2002 (8 May–23 October, 168 d), and 2003 (12 May–27 October, 168 d). Late initiation of the study in 2001 was due to severe late-spring drought (Fig. 2 ). Fixed, artificial shade (3.1 by 3.1 m) was provided on all pastures, and cattle had free-choice access to water and a mineral mixture.


Figure 2
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  		Fig. 2. Monthly rainfall data at the experimental site: average of 30 yr, 2001, 2002, and 2003. Annual rainfall totals for the 30-yr avg., 2001, 2002, and 2003 were: 1341, 1008, 1237, and 1345 mm, respectively.

 
Low management intensity pastures received 40 kg N ha–1 in one application in late April each year. Moderate intensity pastures received 40 kg N ha–1 at each of three dates (late April, mid-July, and mid-August), while High intensity pastures received 90 kg N ha–1 at each of four dates in 2002 and 2003 (mid-June in addition to those for Moderate) and 90 kg N ha–1 at only three dates in 2001 due to delayed onset of grazing. The delay was attributable to spring drought in 2001 (Fig. 2, 50 mm rainfall in April and May vs. the 30-yr average of 181 mm). Phosphorus (17 kg ha–1 yr–1) and K (66 kg ha–1 yr–1) were applied to all management intensities with the initial N application each year. There was a second application of the same amount of P (17 kg P ha–1 yr–1) and K (66 kg K ha–1 yr–1) in mid-July 2002 for Moderate and High intensities only. This application reflects the fact that P and K recommendations for grazed bahiagrass pasture in Florida are based on the amount of N applied (Chambliss and Kidder, 1999). Micronutrients were applied in April 2003 at a rate of 360 g B, 2.7 kg Fe, 3.6 kg Mn, and 1.4 kg Zn ha–1 because iron deficiency chlorosis was observed on some pastures for a limited time during 2002. Sulfur was also applied in April 2002 at a rate of 30 kg S ha–1.

Response Variables
To determine herbage mass, 10 disk meter readings (0.25-m2 aluminum disk) were taken in each of three zones per experimental unit at each evaluation date. The disk meter was calibrated every 28 d by measuring the disk settling height and cutting the herbage below it to soil level at 18 0.25 m2 sites (3 pasture–1). These sites were chosen across the six experimental units to represent the range of herbage mass in those pastures. Regression equations were obtained to estimate herbage mass, and coefficients of determination (r2) ranged from 0.75 to 0.94. Forage allowance was calculated for each pasture during each 28-d period as the average herbage mass (mean across three sampling dates in that 28-d period) divided by the average total heifer live weight during that period (Sollenberger et al., 2005).

Because animals were present on the pasture during the entire grazing season, a cage technique was used to quantify herbage accumulation rate (Stewart et al., 2005). Two 1-m2 cages were placed in each zone of each pasture at initiation of grazing. Sites were chosen that had the average disk settling height of that particular zone so that herbage mass at time of cage placement was as similar to the surrounding pasture as possible. Fourteen days after a cage was placed, the cage was removed and disk settling height measured inside the cage. Herbage accumulation was calculated as the difference in herbage mass between the removal date and initial placement date measurements, and herbage accumulation rate was this difference divided by 14 to account for number of days of growth. Cages were then moved to new locations in the zone, and the procedure was repeated.

Herbage N, P, and in vitro digestible organic matter (IVDOM) concentrations were measured biweekly to describe forage chemical composition and digestibility. Hand-plucked samples were collected from each zone in each pasture. This technique attempts to simulate the forage actually being grazed by the animals by removing the top 5 cm of herbage at approximately 10 locations per zone per pasture. Herbage was composited across the 10 locations per zone, dried at 60°C, and ground to pass a 1-mm screen. Analyses were conducted at the University of Florida Forage Evaluation Support Laboratory using the micro-Kjeldahl technique for N and P (Gallaher et al., 1975) and the two-stage technique for IVDOM (Moore and Mott, 1974).

Soil samples were taken in each zone of each experimental unit before the beginning of the experiment and after the end of the third grazing season to aid in explaining differences in plant responses. In each pasture zone, a composite soil sample was prepared from 20 cores (2-cm diam.) of 8-cm depth that were taken in a zigzag pattern within the zone. The composite soil samples were split with one sample, air-dried and analyzed for Mehlich I P, K, and Mg. The other sample was frozen, and following a subsequent 2 M KCl extraction (2:1), shaken for 1 h, filtered in Whatman paper filter Number 5, stored in plastic vials and frozen until laboratory analysis for NH4 and NO3 using a semiautomated colorimetric analysis (USEPA Method 353.2). A subsample was taken from each frozen soil sample to determine soil moisture. Results were corrected for soil moisture and are expressed as milligrams per kilogram dry soil. Nitrogen data presented are total extractable N (NH4 plus NO3).

Statistical analyses were performed using Proc Mixed of SAS (SAS Institute, 1996), and the PDIFF test of the LSMEANS procedure was used to compare management intensity and zone means. Differences referred to in the text are significant at P ≤ 0.05 except for soil responses where significance was indicated at P ≤ 0.10. This was done because of the inherent large variability in pasture soil nutrient concentrations (Russelle, 1996). Replicate and interactions of zone and management intensity with replicate were considered random effects. Management intensity, zone, year, and their interactions were fixed effects; year was considered fixed because in perennial-crop experiments its effects can carry over into subsequent years. The herbage data used for analysis were averages across evaluation dates within year because analysis of seasonal trends was not an objective of the experiment. In the analysis of herbage data, year was considered the main plot, management intensity the subplot, and zone the strip-split plot. The soil data reported are from the end of the third yr of grazing (one sampling date), thus year was not included in the model. Pretreatment soil data were used as a covariate in the analysis.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
SUMMARY AND CONCLUSIONS
 REFERENCES
 
Soil Nutrient Concentration
There were no management intensity or zone differences in pretreatment soil nutrient concentrations (data not shown); therefore, concentrations at the beginning of the experiment were not responsible for differences observed. After 3 yr of grazing, there were no management intensity x zone interaction effects on soil nutrient concentrations (P > 0.20), but there were main effects of both management intensity and zone for most nutrients measured (Table 1).


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  		Table 1. Total extractable N and Mehlich I soil P, K, and Mg concentrations in the 0- to 8-cm soil depth in continuously stocked bahiagrass pastures after 3 yr of grazing.

 
Averaged across zones, the High management intensity pastures had greater total extractable N and Mehlich I extractable soil P, K, and Mg than Low (Table 1). Soil nutrient concentrations were greater for High vs. Moderate pastures for all but soil P. Differences between High and Low reflect the addition of greater amounts of N, P, and K fertilizer to High than Low pastures across the 3 yr. It must be noted, however, that the same response was observed for Mg, and no Mg-containing fertilizer was applied to any of the management intensities during the study. In addition, High and Moderate intensities received the same amounts of all fertilizers except N, yet soil concentrations of both K and Mg were greater for High than Moderate. This suggests a role of SR in the response, likely due to the effect of SR on the proportion of nutrients that are cycling in excreta (Thomas, 1992). Studies with pastured lactating dairy cows showed a SR effect on Mehlich I extractable soil P concentrations when fertilizer P was constant across treatments (Sollenberger et al., 2002). In pasture areas closest to shade and water, soil P increased in the greater and lesser SR treatments by 25 and 4 mg kg–1 (0–15 cm soil depth) during 2 yr of grazing. In areas that were 8 m or more from shade or water, P concentrations increased by 7 mg kg–1 for the greater SR and decreased by 10 mg kg–1 for the lesser SR. Thus, the greater SR increased P redistribution across the pasture, but the size of the increase in P concentration was greatest in lounging areas. In contrast, Capece et al. (2006) found no effect of SR on soil-P concentrations of bahiagrass pastures in South Florida, but in their study the greatest SR was similar to that of the Low management intensity in the current study. Under these very low SR, they reported that previous P fertilizer history and soil P concentrations were better predictors of P in surface water runoff than current SR, but they cautioned that these conclusions may not apply to situations where SR is greater.

Assessing the zone effect, it can be noted that inorganic N concentrations were similar among zones (Table 1). Soil P, K, and Mg concentrations, however, were greater in Zone 1 than Zone 3, with Zone 2 generally intermediate (Table 1). Mathews et al. (1999) reported increasing soil N, P, K, and Mg around cattle lounging areas on kikuyugrass (Pennisetum clandestinum Hochst. ex Chiov.) pastures in Hawaii. In the current study, the increasing soil nutrient concentrations in areas near shade and water affected the herbage responses described in the following sections.

Herbage Accumulation Rate and Herbage Mass
Herbage accumulation rate was affected by management intensity x year interaction (P = 0.01, Table 2). In the first yr, herbage accumulation rate was similar among management intensities, but in 2002 and 2003, greater management intensity increased herbage accumulation rate. Herbage accumulation rates for High were approximately three times those for Low in Years 2 and 3 (Table 2), but Moderate and High were not different in any year. In 2001, the High management intensity pastures received less fertilizer N than in 2002 and 2003, but herbage accumulation rate was also less for Moderate in 2001 than in subsequent years, suggesting that dry weather in 2001 affected the herbage response. April, May, and August 2001 rainfall was much less than average (121 mm vs. the 30-yr avg. of 384 mm) and was lower than in 2002 or 2003 (260 mm in 2002, and 190 mm in 2003; Fig. 2). Another possible explanation for the increase in the herbage accumulation rate for Moderate and High in Years 2 and 3 of the study is the carryover effect of more intensive management on soil fertility. These effects may have been mediated through excreta (Russelle, 1996) and decomposition of plant litter (Dubeux et al., 2006b) instead of residual inorganic N fertilizer because inorganic N is rapidly leached from these sandy soils. This observation is supported by a companion study that showed that greater management intensity was associated with increasing C and N concentrations and C/N ratio in the low density soil OM fraction (Dubeux et al., 2006a). Changes in this fraction correlate positively with soil net N mineralization and reflect recent changes in soil OM due to land management. The authors concluded that increasing management intensity (N fertilization and SR) can increase soil fertility and C sequestration (Dubeux et al., 2006a).


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  		Table 2. Herbage accumulation rate and herbage mass on continuously stocked bahiagrass pastures during 2001 through 2003.{dagger}

 
The results of the current study do not support the use of the highest N fertilization amount, i.e., 360 kg N ha–1 yr–1, on continuously stocked bahiagrass pastures because there was no increase in herbage accumulation rate from Moderate to High management intensity (Table 2). In clipping studies, increasing bahiagrass yield with greater N fertilization was reported by several authors (Blue, 1972; Burton et al., 1997; Gates and Burton, 1998), but the responses varied. For example, in the range of 0 to 168 kg N ha–1, bahiagrass produced 26 kg of dry matter (DM) kg–1 of N applied, but the response to N fertilization between 168 and 336 kg ha–1 was marginal (Stanley and Rhoads, 2000). Overman and Stanley (1998) stated that maximal incremental OM yield response to applied N on bahiagrass occurred at 140 kg N ha–1. In contrast, Burton et al. (1997) showed increasing yield response across the range of N rates from 56 to 448 kg ha–1.

There was no zone x year or management intensity x zone interaction (P > 0.20) for herbage accumulation rate. Herbage accumulation rate differed among pasture zones; however, and was greater in Zone 1 (40 kg ha–1 d–1) than Zone 3 (20 kg ha–1 d–1). Zone 2 was intermediate (33 kg ha–1 d–1) and not different than the other zones. Because animals congregate in lounging areas (e.g., shade and watering locations), soil fertility tends to be greater in those sites due to greater excreta return (Mathews et al., 1996; 2004). This pattern of increasing soil nutrient concentration occurred for the pastures in the current study, with Mehlich I extractable P, K, and Mg all greater in Zone 1 than in Zone 3 (Table 1). Greater herbage accumulation rate in Zone 1 was likely due in part to greater soil fertility.

Herbage mass averaged 2780 kg ha–1 (SE = 330 kg ha–1) and did not differ (P > 0.05) among management intensities. There was no management intensity effect on herbage mass because the additional forage growth of High and Moderate intensities was compensated for by greater SR. There was a year x zone interaction for herbage mass (P = 0.02, Table 2). Interaction occurred because herbage mass was least in Zone 1 in 2001 and 2003, but there were no zone effects in 2002. In a companion study, Dubeux (2005) evaluated the total time spent by grazing cattle in the three pasture zones. The results indicated that cattle spent proportionally more time in Zone 1 than in the other zones, likely contributing to the lower herbage mass observed.

Herbage Nutritive Value
There was management intensity x year interaction for herbage N (P = 0.003), P (P < 0.001), and IVDOM (P = 0.002) concentrations in hand-plucked herbage (Table 3). Herbage N concentration increased with each increase in management intensity in 2001 and 2003. In 2002, N concentration was greatest for herbage from the High intensity, but it was not different between Low and Moderate intensities. Herbage P and IVDOM concentrations were greater for the High than Low intensity in all but the first year (Table 3).


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  		Table 3. Herbage N, P, and in vitro digestible organic matter (IVDOM) concentrations in hand-plucked samples from continuously stocked bahiagrass pastures during 2001 through 2003.{dagger}

 
There are several potential explanations for these responses. An important factor associated with greater herbage N and P concentrations was greater N and P fertilization (Blue, 1988; Burton et al., 1997) in High and Moderate pastures than Low. Greater N fertilizer also may have affected the IVDOM response, but the effect of N fertilizer on digestibility is variable and the causes are complex (Wilson, 1982). Tillering may increase at greater N rates (Chapman and Lemaire, 1993) contributing to the formation of new tissue resulting in greater IVDOM (Coleman et al., 2004). Greater nutritive value with increasing management intensity also may have been due in part to decreasing herbage allowance (kg forage kg–1 animal live weight) as management intensity increased. Average herbage allowance was less for High (1.4 kg forage kg–1 heifer live weight) than for Moderate (2.0) and Low (4.8). As a result, on High pastures the interval between cattle visits to a particular patch was likely less than on Low pastures. This would result in less mature plant tissue in the grazed portion of the High canopy compared to Low, leading to greater nutritive value (Coleman et al., 2004). A third possibility is that greater SR with increasing management intensity played a role in herbage N and P concentration responses to management intensity. The rate of flow of nutrients among nutrient pools increases with greater SR because the nutrients in dung and urine are more readily available than in litter (Haynes and Williams, 1993). As a result, increasing nutrient availability due to greater excreta return likely resulted in greater forage N and P concentrations as management intensity increased.

There also was management intensity x zone interaction (P = 0.031) for herbage N concentration (Table 4). This interaction approached significance for herbage P (P = 0.174) and IVDOM (P = 0.126) concentrations, thus interaction means were compared for herbage P and N (Table 4). Herbage N, P, and IVDOM were greater in Zone 1 than Zone 3 in the Low management intensity but not in Moderate or High. There are two likely explanations for this response. In Low pastures, there was less fertilizer N and P applied, and as a result soil N and P concentrations were less in Low than in High pastures (Table 1). Within this context of lesser soil nutrient concentration, nutrients provided by excreta have greater potential to influence herbage response. Proportionate to the size of the zone, animals spent more time and had a greater number of excreta events in Zone 1 (Dubeux, 2005); this resulted in greater concentrations of soil P, K, and Mg in Zone 1 than 3. Thus, it is likely that nutrients from excreta were partially responsible for the zone effect in Low pastures. A second explanation relates to the lesser herbage mass in Zone 1 across management intensities and the lesser herbage accumulation rate on Low pastures. These two factors in combination with animals spending a proportionally greater amount of time around shade and water (Zone 1 vs. Zones 2 and 3, Dubeux, 2005) likely resulted in more frequent visits by cattle to grazing patches in Zone 1 of the Low management intensity. The expected outcome is less mature herbage with greater nutritive value in Zone 1 vs. 3 of Low pastures, and this is what was observed.


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  		Table 4. Herbage N, P, and in vitro digestible organic matter (IVDOM) concentrations in hand-plucked samples from continuously stocked bahiagrass pastures during 2001 through 2003.{dagger}

 

   SUMMARY AND CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
REFERENCES
 
Herbage responses of continuously stocked bahiagrass pastures varied spatially across the pasture. Herbage accumulation rate was twice as great (40 vs. 20 kg ha–1 d–1) in areas near shade and watering points as in areas 16 m or further away. This was associated with greater soil P, K, and Mg concentrations near shade and watering locations than in other areas of the pasture. Herbage mass was lower near shade and water than in the other areas of the pasture during 2 of the 3 yr of study, and this may be due to cattle spending proportionally more time near shade and water. Herbage nutritive value was greatest near shade and watering points for only the lowest management intensity. This was likely due to greater soil nutrient concentrations in these areas of the pasture and to more frequent grazing events, the latter resulting in lesser herbage mass and herbage maturity. From these data it can be concluded that spatial heterogeneity in herbage response occurs in continuously stocked bahiagrass pastures, with areas close to shade and watering points most likely to show greater herbage accumulation rate and nutritive value due at least in part to greater soil nutrient concentrations. Future research on producer-scale pasture systems would be useful in confirming these results.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 SUMMARY AND CONCLUSIONS
 REFERENCES
 
Contribution from the Florida Agric. Exp. Stn. This research was sponsored in part by USDA-CSREES Tropical and Subtropical Agricultural Research Program Grant 34135-12348.


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




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J. C. B. Dubeux Jr., L. E. Sollenberger, B. W. Mathews, J. M. Scholberg, and H. Q. Santos
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