Journal of Environmental Protection, 2011, 2, 408-417
doi: 10.4236/jep.2011.24046 Published Online June 2011 (http://www.SciRP.org/journal/jep)
Regional Distribution of Soil Phosphorus across
Congregation-Grazing Zones of Forage-Based
Pastures with Cow-Calf Operations in Florida
Gilbert C. Sigua1, Robert O. Myer2, Samuel W. Coleman1, Cheryl Mackowiak2, Martin Adjei3,
Chad C. Chase1, Joseph Albano4
1United States Department of Agriculture-Agricultural Research Service, Brooksville, USA; 2North Florida Research and Educational
Center, University of Florida, Marianna, USA; 3University of Florida, Range Cattle Research and Education Center, Ona, USA; 4United
States Department of Agriculture-Agricultural Research Service, Fort Pierce, USA.
Received October 19th, 2010; revised February 19th, 2011; accepted March 22nd, 2011.
ABSTRACT
The arrangement of supplemental feed, water, shelter, and their concurrent interactions with topographic features may
influence the distribution of animals and their simultaneous use of pasture’s resources. The effects of grazing and/or
congregation management that control phosphorus cycling and distribution have not been sufficiently evaluated. The
objectives of this study were: 1) to determine whether cattle congregation sites typical on most Florida ranches, repre-
sented by water troughs and shaded areas, are more phosphorus-rich and may contribute more soluble phosphorus to
surface water run-off and groundwater than other pasture locations; and 2) to assess the regional distribution of Meh-
lich-1 extractable soil phosphorus (MP) across congregation-grazing zones of forage-based pastures with cow-calf
operations in Florida. Soil samples were collected at increasing distance from congregations structures (water troughs
and shades) in established (>10 yr), grazed beef cattle pastures located in three Florida regions. Samples were col-
lected in the fall and spring of 2005, 2006, and 2007, respectively; following a radial (every 90 degrees) sampling pat-
terns away from the center of the congregation structures. Averaged across years, MP and soil phosphorus saturation
in the congregation zones were comparable (p ≤ 0.05) with MP values and soil phosphorus saturation in the grazing
zones at all three Florida regions. Average MP at all three pasture locations did not exceed the crop requirement
threshold of 50 mg P kg–1 and the water quality protection threshold of 150 mg P
 kg–1, suggesting that congregation
zones in beef cattle pastures at all three regions of Florida are not phosphorus-rich.
Keywords: Beef Cattle, Congregation Structures, Congregation Zone, Grazing Zone, Total Phosphorus, Phosphorus
Saturation, Nutrient Management
1. Introduction
Livestock concentration areas in pastures can be impor-
tant point sources of nutrient pollution and are often per-
ceived to have higher amounts of soil phosphorus and
nitrogen compared with less disturbed areas of the pas-
ture. The arrangement of supplemental feed, water, shel-
ter, and their concurrent interactions with topographic
features obviously influences the distribution of animals
and their use of pasture’s resources [1]. Distribution and
movement patterns of cattle are particularly valuable in
allocating and assessing utilization impacts on a given
pasture. Movement of free-ranging cattle varies due to
spatial arrangement of forage resources within pastures
[2] and the proximity of water [3,4], mineral feeders [5],
and shades to grazing sites. Temperate British breeds
(Angus and Hereford) of Bos taurus cows grazed less
during the day in warm environments than tropically
adapted Senepol cows, but compensated for reduced
grazing activity during the hotter parts of the day by in-
creasing time spent grazing at night [6,7]. Grazing ani-
mals congregate close to the shade and watering areas
during the warmer periods of the day especially during
summer months [8,9].
Grazing animals have dominant effects on the move-
ment and utilization of nutrients through the plant-soil
system, and thus on the fertility of pasture soils [10-12].

Regional Distribution of Soil Phosphorus Across Congregation-Grazing Zones of Forage-Based 409
Pastures with Cow-Calf Operations in Florida
Grazing can accelerate and alter the timing of nutrient
transfers, and increase the amount of nutrients cycled
from soil to plant [13]. The position of shade and water
sources could influence the spatial distribution of soil
biochemical properties including soil organic carbon and
nitrogen, particulate organic carbon, nitrogen, microbial
biomass, and net nitrogen mineralization [14].
The rate at which soil phosphorus accumulates in ter-
restrial beef cattle agro-ecosystem is uncertain, as are the
mechanisms responsible for the current phosphorus sink
and/or source. Broad knowledge of cattle movement in
pastures is critical to understanding their impact on
agro-ecosystems. We hypothesized that cattle congrega-
tion sites are more nutrient-rich and may contribute more
nutrients to surface and groundwater supply and may
have higher concentrations of soil phosphorus than in
other pasture locations. There was a correlation between
time spent in a particular area especially close to shade
and water, and the number of excretions and this behav-
ior could lead to an increase in the concentrations of soil
nutrients [15]. Congregation areas may receive a signifi-
cantly greater daily fecal and urinary load compared with
less affected areas of the pasture [15-17].
Phosphorus management in soils is of concern to water
quality protection, as losses of phosphorus in surface
runoff can accelerate the eutrophication of surface wast-
ers [18-22]. Agricultural soils considered high in phos-
phorus can cause significant movement of phosphorus
into waterways in dissolved and particulate forms [23,24].
Forage-beef cattle operations must adopt an integrated
approach that will lead to the development of appropriate
sustainable pasture technologies that optimize beef cattle
ranching profitability. Thus, both actual and perceived
environmental problems associated with beef cattle pro-
duction systems need to be addressed when new man-
agement systems are being developed.
Although several studies have documented livestock
concentration effects on soil properties under controlled
conditions [14,25,26], the effects of animal congregation
management that control phosphorus cycling and distri-
bution have not been sufficiently evaluated and reported.
Lack of a clear relationship between grazing practices
and phosphorus dynamics may be attributed to inherent
soil variations, depth of soil sampling, and insufficient
evaluation of phosphorus distributions within pasture
system [27,28]. The objectives of this study were: 1) to
evaluate whether cattle congregation sites such as water
troughs and shade areas, typical on most Florida ranches,
are more phosphorus-rich and therefore contribute more
soluble phosphorus to surface and groundwater supply
than in other pasture locations; and 2) to assess the re-
gional distribution of soil phosphorus across congrega-
tion-grazing zones of forage-based pastures with cow-
calf operations in Florida.
2. Materials and Methods
2.1. Study Sites Location and Description
The study sites were located in three (Brooksville, Ona
and Marianna) Florida pastures with cow-calf operations.
The site in Brooksville, FL (central region) was at
Turnley Unit (82.29˚ W; 28.62˚ N) of the USDA-ARS,
Subtropical Agricultural Research Station [12]. Soil
(Candler fine sand) at this location can be described as
well-drained hyperthermic uncoated typic quartzipsam-
ments [29]. The study site in Ona, Florida (southern re-
gion) was located at the University of Florida Range Cat-
tle Research and Education Center (82.92˚ W; 27.43˚ N)
on a Pomona fine sandy soil (Sandy, siliceous, hyper-
thermic ultic alaquods). The study site in Marianna, FL
(northern region) was located at the University of Florida
North Florida Research and Education Center (85.18˚ W;
30.87˚ N) on a well drained acidic, sandy soil (fine loamy,
kaolinitic, thermic kandiudults). Figure 1 shows the lo-
cations of the different study sites.
Cattle production at these three pasture locations is
forage-based with perennial tropical grass, bahiagrass
(Paspalum notatum, Flugge), the predominant species.
The other major forage species in Brooksville, Marianna
and Ona are rhizoma peanuts (Arachis glabrata, Benth),
bermudagrass (Cynodon dactylon, L.) and limpograss
(Hemarthria altissima), respectively. All the pasture
fields that were included in this study received annual
nitrogen fertilization of 90 kg Nha–1 that was based on
the University of Florida’s recommendation [30].
Table 1 shows some of the selected properties of sur-
face (0 - 20 cm) soils at the study sites. The three-year
(2005-2007) average of rainfall distribution in the study
sites were 121 cm, 122 cm and 122 cm for Brooksville,
Ona and Marianna, respectively with approximately half
of these rainfall amounts occurring during mid-June
through mid-September (Figure 2).
2.2. Soil Sampling, Sample Preparation and Soil
Analyses
Soil samples around the congregations structures (water
troughs and shades) in established (>10 yr), grazed beef
cattle pastures at each location (Brooksville, n = 280;
Ona, n = 260; and Marianna, n = 280) were collected in
the fall and spring of 2005, 2006, and 2007, respectively.
Soil samples were collected at 0 - 15 cm and 15 - 30 cm
from different locations around the congregation struc-
tures following a radial (every 90 degrees) sampling pat-
tern at 0.9, 1.7, 3.3, 6.7, 13.3, 26.7, and 53.3 m from the

Regional Distribution of Soil Phosphorus Across Congregation-Grazing Zones of Forage-Based
Pastures with Cow-Calf Operations in Florida
410
Figure 1. Location of study sites in Florida (Brooksville, Ona and Marianna).
Table 1. Average properties of surface soil (0 - 20 cm) across the congregation-pasture interface of three Florida pastures
(Brooksville, Marianna, and Ona).
Soil Properties Brooksville, FL Marianna, FL Ona, FL
Particle Size
Sand (gkg–1) 825 ± 38 944 ± 24 962 ± 24
Silt (gkg–1) 125 ± 38 44 ± 14 12 ± 2
Clay (gkg–1) 50 ± 6 12 ± 0.2 25 ± 4
pH (in H2O) 6.4 ± 0.1 5.9 ± 0.8 5.7 ± 0.8
Calcium (mgkg–1) 603±171 273 ± 37 593 ± 65
Magnesium (mgkg–1) 89 ± 4.6 35 ± 6 134 ± 24
Potassium (mgkg–1) 48 ± 11 70 ± 11 135 ± 44
Soil Organic Carbon (gkg–1) 4 ± 0.4 3 ± 1.7 6 ± 2.0

Regional Distribution of Soil Phosphorus Across Congregation-Grazing Zones of Forage-Based 411
Pastures with Cow-Calf Operations in Florida
Figure 2. Monthly rainfall distribution in the study area (Brooksville, FL; Ona, Florida; Marianna, FL).
approximate center of water troughs and shaded areas
(Figure 3). For the purpose of this study, sampling sites
at 0.9, 1.7, and 3.3 from the center of the congregation
structures were referred to as the “congregation zone”
while sites located at 13.3, 26.7 and 53.3 m away from
the center of the congregation structures were referred to
as the “grazing zone”.
Soil samples were air-dried and passed through a
2-mm mesh sieve prior to chemical extraction of soil
phosphorus. Sample extractions were conducted at
USDA-ARS Laboratory located in Brooksville, FL. Soil
available phosphorus was extracted with double acid
(0.025 N H2SO4 + 0.05 N HCl) [31] and analyzed using
an inductively coupled spectrophotometer at USDA Hor-
ticultural Laboratory located in Fort Pierce, FL. The de-
gree of soil saturation with phosphorus (DPS) as de-
scribed in Equation (1) was computed using the phos-
phorus, iron, and aluminum contents (mgkg–1) of the soils.
DPS(%)([P]100) [FeAl]  (1)
2.3. Statistical Analysis
Data were analyzed with a three-way ANOVA using
PROC GLM [32]. The model included year (Y), pasture
location (PL), and pasture zone (PZ). The pooled data
(2005-2007) were tested initially for normality [32]. For
this study, F-test indicated highly significant (p < 0.0001)
year and pasture location effects, so means of PZ effects
on soil phosphorus and DPS were separated following
the procedures of Duncan Multiple Range Test [32] by
year. PROC REG method [32] was used to evaluate the
relationship of soil phosphorus concentration with dis-
tance away from the center of congregation structures.
3. Results and Discussion
3.1. Mehlich-1 Extractable Soil Phosphorus
Soil phosphorus concentration varied among the pasture
locations (p ≤ 0.0001) and pasture zone (p ≤ 0.001).
There was an interaction between pasture location and
pasture zone (p ≤ 0.001) and interaction effects among
year, pasture location, and pasture zone (p ≤ 0.0001).
Soil phosphorus concentration also varied with radial
distance away from the center of the congregation struc-
tures (p ≤ 0.001). Averaged across years and pasture zones,
pasture located in Brooksville, FL ((46.6 ± 5.3) mgkg–1)
had the greatest available soil phosphorus while pasture
at Marianna, FL had thelowest concentrations of

Regional Distribution of Soil Phosphorus Across Congregation-Grazing Zones of Forage-Based 412
Pastures with Cow-Calf Operations in Florida
Figure 3. Sampling location and sampling scheme following radial (every 90 degrees: north, south, east and west direction)
patterns at 0.9, 1.7, 3.3, 13.3, 26.7 and 53.3 meters away from the approximate center of congregation structures (e.g. water
troughs, shades/tree).
soil phosphorus ((26.7 ± 1.4) mgkg–1). The amount of
soil phosphorus in pasture located in Ona, FL was about
(45.5 ± 4.2) mgkg–1 (Table 2). The average concentra-
tions of soil phosphorus at all three regions were still not
high enough to be of environmental concern. Average
concentration of phosphorus at all three pasture locations did
not exceed the crop requirement threshold of 50 mg Pkg–1
[33] nor exceeded the water quality protection threshold of
150 mg Pkg–1 [34]. Losses of soil phosphorus by over-
land flow can become a big concern when the concentra-
tions for soil phosphorus exceeded 150 mgkg–1.
Spatial trends of soil phosphorus in our study may be a
function of feces and urine deposition where animals
clustered. Where animals congregate may tend to de-
velop some hot spots in the pasture. Our results did not
support the idea that hot spots were likely had the highest
concentration of soil phosphorus. Soil phosphorus con-
centrations in the congregation zones were comparable (p
≤ 0.05) with the concentrations of soil phosphorus in the
grazing zones at all the three regions, except for Brooks-
ville site (Table 2). The grazing zone of pastures located
in Brooksville, FL had the highest concentrations of soil
phosphorus ((51.6 ± 5.1) mgkg–1) while congregation
zone of pastures in Marianna, FL had the lowest levels of
soil phosphorus ((26 ± 1.3) mgkg–1).
The concentrations of soil phosphorus decreased line-
arly with distance away from center of the congregation
structures at all three Florida regions. Figure 4 shows the
relationships between extractable soil phosphorus and
distance away for the center of the shaded areas in
Brooksville, Ona and Marianna, FL. The regression
models that described the relationship of Mehlich-1 ex-
tractable (MP) soil phosphorus with distance away from
the center of shaded areas are given below.
MPBKV = –5.6x + 65.7; R2 = 0.78** (2)
MPONA = –4.4x + 41.8; R2 = 0.87** (3)
MPMAR = –1.4x + 43.6; R2 = 0.46* (4)
Regression models that describe the relationship of
MP and distance away from the center of water troughs
in Brooksville, Ona and Marianna, FL are shown in Fig-
ure 5. These regressions models are further described
below (Equations 5-7).
MPBKV = –9.6x + 80.4; R2 = 0.74** (5)
MPONA = –6.5x + 80.5; R2 = 0.59* (6)

Regional Distribution of Soil Phosphorus Across Congregation-Grazing Zones of Forage-Based 413
Pastures with Cow-Calf Operations in Florida
Table 2. Comparative concentrations of Mehlich-1 extractable phosphorus, aluminum, iron and percent phosphorus satura-
tion in soils (0 - 20 cm) among the different pasture zones of three Florida pastures (Brooksville, Ona and Marianna).
Pasture
Location Pasture Zone Sample Number (n) Phosphorus (mgkg–1) Aluminum (mgkg–1) Iron (mgkg–1) Soil Phosphorus Saturation (%)
1. Brooksville, FL Congregation 211 39.7 ± 4.3b† 289.8 ± 47.0b 8.9 ± 2.1a 13.2
Grazing 187 51.6 ± 5.1a 457.1 ± 55.3a 11.1 ± 2.3a 11.0
Transition 70 49.2 ± 6.4a 416.1 ± 57.1a 11.9 ± 2.8a 11.5
Mean 46.6 ± 5.3 387.7 ± 53.1 10.6 ± 2.4 11.9
2. Ona, FL Congregation 244 45.1 ± 4.5b 71.8 ± 4.5a 11.9 ± 1.1a 53.8
Grazing 224 39.2 ± 3.4b 68.1 ± 4.1a 13.6 ± 1.2a 47.9
Transition 82 52.2 ± 4.7a 62.2 ± 3.3a 12.1 ± 0.9a 70.2
Mean 45.5 ± 4.2 67.4 ± 3.9 12.5 ± 1.1 57.3
3. Marianna, FL Congregation 240 26.5 ± 1.3a 118.2 ± 3.3b 2.2 ± 0.09a 22.1
Grazing 188 29.0 ± 1.4a 135.5 ± 4.7a 1.8 ± 0.08b 21.1
Transition 78 24.7 ± 1.5a 144.9 ± 5.0a 2.2 ± 0.09a 16.8
Mean 26.7 ± 1.4 132.9 ± 4.3 2.1 ± 0.08 20.0
Sources of Variations F-Value F-Value F-Value F-Value
Year (Y) 140.9***‡ 244.7*** 26.4*** 103.7***
Pasture Location (PL) 114.2*** 298.1*** 51.9*** 38.2**
Pasture Zone (PZ) 61.7** 1.9ns 3.4* 7.4**
PL × PZ 110.9*** 1.4ns 3.6* 1.6ns
Y × PL × PZ 11.1** 1.6ns 3.9** 0.4ns
†Means in column within each subheading followed by common letter(s) are not significantly different from each other at p ≤ 0.05. ‡*** - (p ≤ 0.0001), ** - (p ≤
0.001), * - (p ≤ 0.01), ns - not significant.
Figure 4. Concentration of Mehlich-1 extractable soil phosphorus (MP) at and/or away from the center of congregation
structure (shade/tree).

Regional Distribution of Soil Phosphorus Across Congregation-Grazing Zones of Forage-Based 414
Pastures with Cow-Calf Operations in Florida
Figure 5. Concentration of Mehlich-1 extractable soil phosphorus (MP) at and/or away from the center of congregation
structure (water trough).
MPMAR = –0.8x + 17.1; R2 = 0.25ns (7)
Results from our study did not support our hypothesis
that cattle congregation sites in Florida ranches may have
greater potential to sequester soil phosphorus. Early re-
sults of a study suggest that congregation zones may not
be as nutrient-rich as previously thought, therefore may
not contribute more nutrients to surface and groundwater
[12]. The Mehlich-1 extractable soil phosphorus in our
study area is less than 150 mgkg–1, the threshold above
which a crop production and environmental caution.
However, the congregation zones usually do not have
vegetation, which makes soil phosphorus more suscepti-
ble to surface runoff during rainfall events.
Intensive cattle trampling in areas around cattle con-
gregation sites, especially within the congregation zone
(0.9 to 3.3 meters away) may help to explain our results.
Trampling by cattle during certain periods of the year
may substantially damage the main components of pas-
ture and/or grassland systems (plants, soil structure and
soil biology). The effects of trampling on plant produc-
tivity, root growth and physical soil properties have been
studied [35]. Trampling within a congregation zone may
lead to destruction of a large portion of aerial system,
stolons and roots, followed by removal of vegetation
cover resulting to at least 50% bare surface [35].
The effects of trampling, especially at or within the
congregation zone may also lead to the destruction of soil
aggregates, which could have some significant effects on
soil phosphorus dynamics within the congregation zones
[36]. Mixing or total destruction of soil aggregates within
the congregation zone may result to mixing and spread-
ing of phosphorus as a result of the separations among
the different aggregate sizes. Total phosphorus increased
with decreasing soil aggregate size [37]. The extent to
which individual soil aggregates influence soil phospho-
rus concentrations will partly depend on the soil aggre-
gate’s phosphorus buffering capacity (PBC). The soil
aggregate’s PBC represents a means of quantifying the
relative strength with which soil aggregate can influence
surrounding solution and is derived by dividing the quan-
tity (Q) of phosphorus that a given amount of soil aggre-
gates can sorbed by the intensity (I) of phosphorus that
the soil aggregates can maintain in solution [38]. Mixing
or total destruction of soil aggregates could result in
much lower Q and I when compared to the other parts of
the pasture with less soil compaction.

Regional Distribution of Soil Phosphorus Across Congregation-Grazing Zones of Forage-Based 415
Pastures with Cow-Calf Operations in Florida
3.2. Soil Phosphorus Saturation
The degree of phosphorus saturation in soils was signifi-
cantly (p≤ 0.0001) affected by year, pasture location and
pasture zone (Table 2). Averaged across years and pas-
ture zones, the pastures at Ona, FL had the highest esti-
mated degree of soil phosphorus saturation at 57.3% fol-
lowed by pastures located at Marianna, FL (20.0%).
Pastures at Brooksville, FL had the lowest estimated de-
gree of soil phosphorus saturation (11.9%).
The degree of soil phosphorus saturation in the con-
gregation zones (13.2%) of pastures located in Brooks-
ville, FL was comparable to the levels of phosphorus
saturation in the grazing zones (11.0%). Similarly, the
degree of soil phosphorus saturation did not vary be-
tween the congregation zones (22.1%) and grazing zones
(21.1%) of pastures at Marianna, FL. The degree of soil
phosphorus saturation in congregation zones and grazing
zones of pastures located in Ona, FL were 53.6% and
47.9%, respectively (Table 2). The varying amount of
aluminum and iron among the different pasture locations
and pasture zones may have had affected the spatial dis-
tribution of soil phosphorus saturations in the soils. The
low concentrations of aluminum and iron within pasture
zones of pastures located in Ona, FL may explained the
highest degree of soil phosphorus saturation at this re-
gional site when compared with the average levels of
aluminum and iron in pastures located at Brooksville, FL
and/or Marianna, FL. Averaged across pasture zones and
years, the levels of aluminum (mgkg–1) in three regions
are as follows: Brooksville (387.7 ± 53.1) > Marianna
(132.9 ± 4.3) > Ona (67.4 ± 3.9). The levels of iron
across pasture zones and were as follows: Ona (12.5 ±
1.1) > Brooksville (10.6 ± 2.4) > Marianna (2.1 ± 0.1).
Results of multiple regression analyses on the levels of
Mehlich-1 extractable soil phosphorus (MP) saturation
with concentrations of aluminum and iron in the region
were significant, but rather weak relationship with R2
values ranged from 0.12 to 0.67. The levels of MP satu-
ration in three regions can be explained by the following
relationships:
MPBKV = 22.2 – 0.01 [Al] + 1.8 [Fe]; R2 = 0.67** (7)
MPONA = 43.9 + 0.22 [Al] – 1.2 [Fe]; R2 = 0.12* (8)
MPMAR = 22.8 – 0.05 [Al] + 5.2 [Fe]; R2 = 0.14* (9)
Our results (Equations 7 to 9) showed variable effects
of iron and aluminum concentrations on the levels of soil
phosphorus among the different pasture locations. Our
observations are quite similar to the observations re-
ported earlier [39]. Their studies support the absence of
significant and positive correlations between phosphorus
retention and iron and added phosphorus may have been
preferred onto aluminum over iron. The preference of
phosphorus for either aluminum or iron may have re-
sulted because the soil iron may be more saturated in
phosphorus than aluminum or because the soil aluminum
was more saturated in phosphorus than iron.
The degree of soil phosphorus saturation has been
suggested as an indicator for the risk of phosphorus loss
from agricultural soils [40,41]. Overall, the degree of soil
phosphorus saturation from pastures in our study did not
exceed the environmental threshold of phosphorus satu-
ration. Other studies [41,42] have found that the degree
of phosphorus saturation in soils needs to exceed 60%
before dissolved reactive phosphorus becomes an envi-
ronmental problem. Our results were below this satura-
tion, suggesting that phosphorus buildup and/or release is
unlikely anywhere in the pasture, including the congre-
gation zones.
4. Summary and Conclusions
Results from this study suggest that congregation zones
in pastures with beef cattle operations in three regions of
Florida are not phosphorus-rich, therefore may not con-
tribute more phosphorus to surface and groundwater
supply under Florida conditions. Averaged across years,
phosphorus concentrations and soil phosphorus satura-
tion of the congregation zones were comparable (p ≤
0.05) with soil phosphorus and soil phosphorus satura-
tion in the grazing zones of all the three regions. Average
phosphorus in all three pasture locations did not exceed
the crop requirement threshold of 50 mg Pkg–1 and the
water quality protection threshold of 150 mg Pkg–1.
The degree of soil phosphorus saturation in the three
pastures were below the environmental threshold of
phosphorus saturation (DPS ≥ 60%), suggesting that
phosphorus buildup and/or release is not a predicament
anywhere in the pasture, including the congregation zones.
These results may have significant implications for the
transport of phosphorus to surface waters and our ability
to predict and model losses of phosphorus from congre-
gation zone or grazing zone of pastures with cow-calf
operations.
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