Stocking Method, Animal Behavior, and Soil Nutrient Redistribution: How are They Linked?

crop science, vol. 54, september–october 2014 www.crops.org 2341

RESEARCH

Excreta deposition by cattle redistributes, separates, and concentrates nutrients, affecting pasture heterogeneity and

the environment (Auerswald et al., 2010). Stocking method may affect animal behavior and excreta distribution, consequently affecting soil nutrient redistribution in grazed swards. Short graz-ing periods and high stocking densities promote a more uniform excreta distribution on the pasture than do other stocking meth-ods (Peterson and Gerrish, 1996). The rationale is that higher stocking densities, obtained by the subdivision of the pasture, lead to greater competition for forage among the animals, reduc-ing their time spent under the shade or close to watering areas (Mathews et al., 1999).

Urination and defecation often occur near lounging areas, shade, and water troughs (Dennis et al., 2012), however, climate and stocking method may interact, affecting excreta distribution. In temperate areas, short grazing periods and high stocking rate may improve nutrient distribution; however, in warmer climates this is not always the case (Mathews et al., 1994b, 1999). In tropical and subtropical climates, the animals may congregate under shade

Stocking Method, Animal Behavior, and Soil Nutrient Redistribution: How are They Linked?

J.C.B. Dubeux, Jr.,* L.E. Sollenberger, J.M.B. Vendramini, S.M. Interrante, and M.A. Lira, Jr.

ABSTRACTChoice of stocking method may impact soil, plant, and animal responses. This 3-yr study evaluated stocking method effects on animal behavior and soil nutrient concentration in ‘Pen-sacola’ bahiagrass (Paspalum notatum Flügge) pastures. Stocking methods were continuous stocking and rotational stocking with 1-, 3-, 7-, and 21-d grazing periods and a 21-d rest-ing period. Responses were measured in three zones based on distance from shade and water (Zone 1, 0–8 m; Zone 2, 8–16 m; Zone 3, >16 m). Indices were calculated to weight number of dung and urine events and time spent by cattle in a zone by the proportion of the total pasture and paddock area represented by that zone. Indices were most uniform (~1) across zones for rotational stocking with short grazing peri-ods and generally increased linearly in Zones 1 and 2 with increasing grazing period. Except for N, soil nutrient concentration was not affected by stocking method. In zones closest to shade and water, soil nutrients accumulated for all methods in the surface 8 cm but not in the 8- to 23-cm layer. Air temperature, wind speed, and temperature–humidity index explained 49% of the variation in time cattle spent under shade, confirming the importance of the environment in animal behavior. In warm environments, structural features of stocking method (e.g., the position of shade and water) have a greater effect on animal behavior and distribution in the landscape than do stocking density-mediated effects on competition for forage.

J.C.B. Dubeux, Jr., Univ. of Florida, North Florida Research and Edu-cation Center, 3925 Hwy. 71, Marianna, FL 32446; L.E. Sollenberger, Agronomy Dep., Univ. of Florida, Gainesville, FL 32611; J.M.B. Vendramini, Univ. of Florida Range Cattle Research and Education Center, 3401 Experiment Station, Ona, FL 33865; S.M. Interrante, Samuel Roberts Noble Foundation, 2510 Sam Noble Pkwy, Ardmore, OK 73401; M.A. Lira, Jr., Univ. Fed. Rural de Pernambuco, Av. Dom Manoel de Medeiros, SN, Dois Irmãos, Recife, PE, Brazil, 52171-900. Received 28 Jan. 2014. *Corresponding author ([email protected]).

Abbreviations: AU, animal unit; DI, dispersion index.

Published in Crop Sci. 54:2341–2350 (2014). doi: 10.2135/cropsci2014.01.0076 © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA

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and close to watering points during the warmer part of the day, regardless of stocking density (Mathews et al., 1994b, 1999; White et al., 2001), reducing the effect of the stocking method. Mathews et al. (1999) found that shade sources had a greater effect on distribution of cattle in the landscape than water sources in Hawaii. In a subsequent study, Mathews et al. (2011) observed that shade in closer proximity to water sources was not preferred by cattle relative to shade farther from water sources. Thus, of shade and water sources, shade appears to be a stronger driver of animal behavior in warm environments, although further studies are needed to deter-mine the relative magnitude of their positioning on animal behavior and soil nutrient redistribution.

Moving artificial shades and watering points is an option for improving nutrient distribution (Russelle, 1997), but it may not be practical for more extensive sys-tems. Sollenberger et al. (2002) suggested that if there are advantages in nutrient distribution of rotational stocking or having more paddocks in a rotational system in a warm climate, these may accrue due to animals being forced to utilize a greater number of lounging or watering points (one in each paddock) more so than achieving greater uni-formity of excreta deposition within individual paddocks.

Grazing experiments in many cases fail to link man-agement practices with animal behavior and soil nutrient distribution. Thus, the objective of this research was to investigate the effect of different stocking methods and the grazing environment on animal behavior and soil nutri-ent concentration in different pasture zones based on their distance from shade and water.

MATERIALS AND METHODSExperimental SiteThe research was performed at the University of Florida Beef Research Unit, northeast of Gainesville, FL, at 29°43′ N lat on Pensacola bahiagrass pastures. Soils were classified as Spodosols and included sandy siliceous, hyperthermic Ultic Alaquods from the Pomona series and sandy siliceous, hyperthermic Aeric Alaquods from the Smyrna series. Soil (0–20 cm) pH averaged 5.9, and Mehlich-I extractable soil P, K, and Mg con-centrations at the beginning of the experiment were 5, 28, and 98 mg kg-1, respectively.

Treatments and Experimental DesignTreatments were four rotational and one continuous stocking method, and they were imposed in 2001, 2002, and 2003. The five treatments were replicated twice using a strip-split plot arrangement in a randomized complete block design. In all experimental units, three zones were identified according to distance from shade and water locations. Stocking method was the main plot and zone was the strip-split plot.

The four rotational stocking strategies differed in terms of length of the grazing period (1, 3, 7, and 21 d). All four treat-ments had the same resting period of 21 d. All four rotational strategies and the continuous stocking treatment had the same

stocking rate of 4.2 animal units (AU; 1 AU = 500 kg live-weight) ha-1 and N fertilization of 360 kg ha-1 yr-1. This high level of N input was used because these treatments were part of a larger experiment evaluating the effect of a range of man-agement intensities on grazing behavior, nutrient dynamics, and spatial heterogeneity of pasture response (Dubeux et al., 2006, 2009). To reduce the amount of land area required for the experiment, an experimental unit of a rotationally stocked treatment was a single paddock of the overall rotational system, and the size of the paddock reflected the length of the grazing period. Paddock areas were 454, 1250, 2500, and 5000 m2 for 1-, 3-, 7-, and 21-d treatments, respectively. These areas were calculated on the basis of a pasture area of 1 ha, which would in practice be subdivided into 22, 8, 4, and 2 paddocks of the areas indicated for the 1-, 3-, 7-, and 21-d treatments, respectively. The area for the continuous treatment was 3333 m2.

Zones were defined on the basis of their distance from shade and water and were also described by Dubeux et al. (2009). Briefly, Zone 1 consisted of a semicircle with an 8-m radius and included the shade structure and water trough. Zone 2 was the area located between an 8- to 16-m radius away from the water trough, and Zone 3 was the remaining area of the paddock (rotational stocking) or pasture (continuous stocking).

At the beginning of each grazing season, two crossbred (Angus × Brahman) yearling heifers were allocated to the con-tinuously stocked treatment. Heifers were formed in groups to obtain similar total live weight to graze the rotationally stocked experimental units. The heifer live weight of each group was calculated so that stocking rate was the same as on continuously stocked pastures. The target stocking rate for all treatments was 3.6 AU ha-1, but the initial weight of the heifers each year was greater than expected and actual stocking rates achieved were 4.4, 4.1, and 4.0 AU ha-1 in 2001, 2002, and 2003, respectively.

Nitrogen fertilization was split in four applications of 90 kg N ha-1 each grazing season. Because drought delayed the start of the grazing season in 2001, only 270 kg N ha-1 was applied that year. Phosphorus (17 kg ha-1 yr-1) and K (66 kg ha-1 yr-1) were applied to all treatments before N application in 2001 (17 April), and with the initial N application in 2002 (30 April) and 2003 (23 April). There was a second application of the same amount of P (17 kg ha-1 yr-1) and K (66 kg ha-1 yr-1) in 2002 (15 July). Micronutrients were applied on 23 Apr. 2003 at a rate of 400 kg ha-1 of the following formula: 0.9 g B kg-1, 6.8 g Fe kg-1, 9.1 g Mn kg-1, and 3.6 g Zn kg-1. Sulfur was also applied on 30 Apr. 2002 at a rate of 30 kg S ha-1. Application rates and frequency of S and micronutrients reflect recommended practice in the region. Constructed shade (3.1 m by 3.1 m) was provided on each experimental unit, and cattle had free-choice access to water and a mineral mixture. The water troughs were always located under the provided shade, and the mineral mix troughs (one per pasture) were moved weekly to a new, randomly selected location in the pasture.

Response VariablesSoil samples were collected in the three zones of each experi-mental unit immediately before the beginning (spring) and immediately after the end (autumn) of each of the three graz-ing seasons. In each zone of all experimental units, a composite was prepared from 20 samples (2-cm diameter core) for the 0- to 8-cm and the 8- to 23-cm depths, taken along a zigzag


temperature and relative humidity were obtained from Florida Automated Weather Network and averaged from 1000 to 1500 h on each animal behavior observation day. Cattle heat stress index was estimated from 1000 to 1500 h of each evaluation day using the equation described by Osborne (2003).

Dung and urine distribution indices were calculated by dividing the percentage of dung or urine events that occurred in a given zone by the percentage of the pasture or paddock area occupied by that particular zone. The total time index and grazing time index were calculated in the same way (i.e., divid-ing the total time spent per zone or the grazing time per zone by the percentage of the pasture or paddock area occupied by that particular zone). Information describing total number of paddocks in the systems being simulated, grazing period length, starting and ending grazing dates per treatment, number of cycles during each grazing season, paddock sizes, and stocking density are summarized in Table 1.

The spatial distribution of dung was quantified using a second method in three treatments, 1- and 7-d grazing period rotational stocking and continuous stocking. Dung deposits for a 24-h period were identified by spray painting all existing dung patches and returning to the pasture 24 h later. Flags were placed on the new dung patches, and their actual X and Y coordinates in the pasture or paddock were quantified. Treatments from the same replicate were evaluated during the same 24-h period to avoid confounding temperature and humidity differences with animal behavior. These evaluations were performed three times per year during the grazing seasons of 2002 and 2003.

Statistical AnalysesStatistical analyses of the animal behavior and soil nutrient concentration response variables were performed using Proc Mixed of SAS (SAS Institute, 1996), and the LSMEANS proce-dure was used to compare treatment means. Zonal soil samples were analyzed using the final soil nutrient concentration (Octo-ber 2003) as the response variable and the initial concentration ( June 2001) as a covariate. Animal behavior data were analyzed including evaluation date in the model. Multivariate regression between behavioral responses and climate data was performed using Proc Reg of SAS. Animal behavior means were consid-ered different when P £ 0.05, and because variability associated with soil analyses is generally high, soil chemical composition means were considered different when P £ 0.10.

The dung spatial distribution statistical analysis was per-formed after dividing each pasture in each evaluation day into

line within the zone. The composite soil samples were split with one subsample air dried and analyzed for Mehlich-I P, K, and Mg (USEPA Method 200.7). The other subsample 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 for nitrate and USEPA Method 350.1 for ammonium). A subsample was taken from each frozen soil sample to determine soil moisture. Results were corrected for soil moisture and were expressed as mg kg-1 soil.

In addition to the zonal samples, soil grid samples were collected along five transects in each experimental unit. The middle transect bisected the pasture or paddock in half, and the two transects on either side of the middle transect were spaced equidistant from each other and the edge of the pasture or pad-dock. A given transect was considered to begin (0 m) at the end of the pasture where the shade structure and water trough were located, and shade and water were placed at the end of the middle transect. Sampling points were at 2, 6, 10, 14, and 18 m along each transect, with additional sampling points at 26, 42, and 74 m for those treatments in which the paddock or pasture area was sufficiently large to accommodate those distances. At the beginning of the first year and again after the end of the third year of the experiment, three soil cores were taken to a 0- to 15-cm depth near (within 10-cm) each designated sam-pling point along each transect. The three samples per transect point were composited into a single sample for analysis. These samples were analyzed for Mehlich-I extractable P, K, and Mg.

Animal behavior was monitored during 12-h periods (0700 to 1900 h) for each treatment. Two heifers per experimental unit were observed continuously during the 12-h period. Observ-ers were stationed outside the pasture or paddock to minimize effect on animal behavior. Because of the grazing calendar for the rotational treatments and the number of observers required, one replicate of each treatment was observed during a given day. The second replicate was observed 1 wk later. Animal behavior evaluations were performed in early June, late June or early July, mid-August, and late September 2002 and 2003. Behavior observations were not made in 2001. Behavior obser-vations included quantity of time spent grazing and lounging in each zone, as well as location (zone) and time of every dung and urine event. The three zones were delimited by colored flags in a way that allowed the observers to visualize each zone from a distance without disturbing the heifers’ behavior. Air

Table 1. Summary information for stocking method treatments and starting and ending dates of grazing during 2002 and 2003.

Stocking treatment

Length of grazing period cycle-1

Number of paddocks in the system

Number of cycles per

grazing seasonPaddock

sizeStocking density

Starting date by year†

Ending date by year†

2002 2003 2002 2003

d m2 AU‡ ha-1

1-d rotational 1 22 7 454 92.5 4 June 9 June 16 Oct. 20 Oct.

3-d rotational 3 8 6 1250 33.6 2 June 7 June 3 Oct. 8 Oct.

7-d rotational 7 4 6 2500 16.8 29 May 3 June 22 Oct. 28 Oct.

21-d rotational 21 2 4 5000 8.4 15 May 20 May 9 Oct. 14 Oct.

Continuous Continuous 1 – 3333 4.2 8 May 12 May 23 Oct. 27 Oct.† Starting and ending dates for the first replicate (block); second replicate starting and ending dates were 1 wk later to allow cattle behavior observations.‡ AU, animal unit (1 AU = 500 kg liveweight).


100 quadrats of equal size and allocating each individual dung record according to its X and Y coordinates in the respective quadrat. To evaluate the possibility of adjusting the observed frequencies to the Poisson or to the negative binomial models, a Dispersion Index (DI; Krebs, 1999) was estimated for each experimental unit at each evaluation day. The DI is defined as:

2

observed

observed

VarianceDI

MeanS

X= =

The null hypothesis was that the Poisson distribution applied to the observed frequencies. It was not rejected when the variance was not different from the mean (i.e., DI was not different than 1 and the distribution model was considered randomly distributed) (Braz, 2001). To statistically test DI, the chi-square test was used as follows:

2observed DI( 1)nc = -

Where 2observed observedchi-squarec = and n = number of quadrats

counted (100 quadrats).The chi-square value was obtained in statistical tables with

n-1 degrees of freedom. The two-tail chi-square test was used to test the null hypothesis, as following:

If 2 2 20.975 observed 0.025c < c < c Þ

the variance is not different from the mean and DI is 1, the dung patches are randomly distributed. In this case, the Poisson distribution adequately describes the dataset, and the null hypothesis is true.

If 2 2observed 0.975c £ c Þ the variance is less than the

mean and DI is close to zero, the dung patches are uniformly distributed on the pasture.

If 2 2observed 0.025c ³ c Þ the variance is greater than the

mean and DI is >1, the dung patches are clustered and the negative binomial distribution describes the dataset adequately.

After calculating the DI for each experimental unit and evaluation day, the data were transformed to 1/x to normalize the distribution and then analyzed using Proc Mixed from SAS. Contour maps were constructed using the software SigmaPlot Version 10 (Systat Software, San Jose, CA). Soil P, K, and Mg concentrations from June 2001 (initial sampling) were sub-tracted from their final concentrations in October 2003. Data were presented as changes in concentration from 2001 to 2003. Positive values indicate soil nutrient enrichment and negative values indicate soil nutrient depletion.

RESULTS AND DISCUSSIONAnimal BehaviorThere were treatment × zone interactions for dung and urine distribution indices (Tables 2 and 3). These indices were greater in Zone 1 than Zone 3 for both the 21-d and the continuous treatments. In contrast, there was no zone

effect for shorter grazing period rotationally stocked pastures (7 d or less) indicating better proportional excreta distribu-tion among zones for these treatments than for the 21-d and continuous treatments. The distribution index increased linearly as length of the rotational grazing period increased for dung in Zones 1 and 2 and for urine in Zone 1, but the index was not affected by grazing period in Zone 3.

Stocking strategies also affected the total time spent index (Table 4). Cattle spent time more nearly proportion-ate to zone area in the 1-d grazing period treatment com-pared with the other treatments. Because there is a correla-tion between time spent per zone and number of excreta events occurring in that zone (White et al., 2001), the more uniform distribution of time spent across zones in the 1-d treatment helps to explain the smaller urine and dung indi-ces observed in Zone 1 for that treatment vs. longer graz-ing periods. There was a linear increase in the total time spent index with increasing length of the grazing period under rotational stocking for both Zones 1 and 2 (Table 4). Continuous stocking was different from the average of rotational stocking treatments in Zone 1, but not in Zones 2 and 3, with the index in Zone 1 of continuous stocking presenting values closer to the 21-d rotational treatment.

Evaluation date affected animal behavior. During July and August evaluation dates, animals spent more time in Zone 1 and less time in Zone 3 compared with other dates (data not shown). Animals also spent more time under the shade and less time grazing Zone 3 in July and August. Heat stress has a pronounced effect on animal behavior and performance, and reducing feed intake, seeking shade, and increasing drinking water are behavioral mechanisms cattle develop to reduce heat stress (Blackshaw and Blackshaw, 1994). It is not surpris-ing therefore that mid-summer evaluation resulted in more time spent under the shade and less time spent graz-ing during the daylight observation period. Total grazing time during the 12-h observation period averaged 338 ± 21 min per evaluation, which is approximately 48% of total evaluation time. Considering this relatively large amount of time, if management practices alter grazing behavior they will probably alter nutrient distribution.

The heat stress index takes into account both tem-perature and relative humidity to estimate cattle stress (Osborne, 2003). Armstrong (1994) considered the follow-ing ranges for this index: normal, <23.3; alert, 23.9 to 25.6; danger, 26.1 to 28.3; emergency, >28.9 (in °C). Except for 11 June and 12 Aug. 2002, which had an index <26.1, all other evaluation dates had a heat stress index >26.1 (data not shown). A regression equation (P = 0.04) relating the time cattle spent under the shade with weather variables included in the model air temperature (Tair; °C), wind speed (WSP, km h-1), and temperature–humidity index (THI) [Y = -126.7 + 27.3*Tair – 9.7*WSP – 15.7*THI]. This equation explained 49% of the variation in time spent


paddock occupied by each zone and, as a result the graz-ing time index, was similar among zones. Cattle behav-ior observations were performed from 0700 to 1900 h. Although most grazing activity occurs during daylight, on warmer days cattle compensate by reducing grazing activity during the day and increasing nighttime grazing. Macoon (1999) observed that daytime grazing in Florida in summer was shorter on days when temperature and solar radiation intensity were greater. On these days, ani-mals attempted to compensate by grazing longer at night.

Considering the indices results together, they show that animal behavior responses were most uniform across pasture

under shade. Tucker et al. (2008) observed that as average ambient solar radiation increased, total use of the shade structures increased by grazing dairy cows in New Zealand. Standing was the most common behavior under shade.

There was a treatment × zone interaction for the grazing time index, with a linear increase occurring in Zone 2 as length of grazing period increased. No effect of length of grazing period was observed in Zones 1 and 3 (Table 5). For the continuous treatment, the grazing time index was greater in Zones 1 and 2 than in Zone 3. For shorter grazing period treatments (7 d or less), grazing time was proportional to the area of the total pasture and

Table 2. Dung distribution index (% of total dung deposits that occurred in a zone/% of the total paddock or pasture area occupied by that zone) on rotationally and continuously stocked bahiagrass pastures according to distance from shade and water (Zones 1, 2, and 3) during 2002 and 2003.

Treatment

Zone†

1 2 3

Rotational1 d 1.0A‡ 0.8A 2.1A

3 d 1.4A 1.4A 0.8A

7 d 2.3A 0.6A 1.0A

21 d 4.1A 3.1A 0.8B

Effect (P value) linear§ (<0.01) linear (0.01) NS¶

Continuous 4.4A 1.4B 0.8B

C ontrast rotational vs. continuous (P value)

0.13 0.91 0.27

† Zone indicates distance from shade and water (Zone 1, 0–8 m; Zone 2, 8–16 m; Zone 3, >16 m).

‡ Within rows, means followed by the same letter are not significantly different according to SAS least square mean test (PDIFF) (P > 0.05). SE = 0.6.

§ Polynomial contrast for effect of length of grazing period of rotational treatments.¶ Not significant (P > 0.05).

Table 3. Urine distribution index (% of total urine deposits that occurred in a zone/% of the total paddock or pasture area occupied by that zone) on rotationally and continuously stocked bahiagrass pastures according to distance from shade and water (Zones 1, 2, and 3) during 2002 and 2003.

Treatment

Zone†

1 2 3


3 d 2.5A 1.2A 0.7A

7 d 3.7A 1.5A 0.8A

21 d 9.6A 2.7B 0.7B

Effect (P value) linear§ ( < 0.01) NS¶ NS¶

Continuous 5.6A 1.1B 0.8B


0.64 <0.01 0.19




Table 4. Total time index (% of total time animals spent in a particular zone/% of the total paddock or pasture area occu-pied by that zone) on rotationally and continuously stocked bahiagrass pastures according to distance from shade and water (Zones 1, 2, and 3) during 2002 and 2003.

Treatment

Zone†

1 2 3


3 d 3.3A 0.8B 0.7B

7 d 4.4A 0.7B 0.9B

21 d 13.3A 1.4B 0.7B

Effect (P value) linear§ (P < 0.01) linear (P = 0.01) NS¶

Continuous 9.3A 0.9B 0.7 B


<0.01 0.26 0.09




Table 5. Grazing time index (% of total grazing time that occurred in a zone/% of the total paddock or pasture area occupied by that zone) during 12-h evaluation periods on dif-ferent pasture zones of rotationally and continuously stocked bahiagrass pastures during 2002 and 2003.

Treatment

Zone†

1 2 3


3 d 1.1A 1.1A 0.9A

7 d 1.1A 1.0A 1.0A

21 d 1.2AB 1.6A 0.9B

Effect (P value) NS¶ linear§ (0.003) NS¶

Continuous 1.4 A 1.4A 0.9B

R otational vs. continuous (P value)

0.41 0.03 <0.01





and paddock zones when using rotational stocking with short grazing periods. A question of interest is whether this response was due to differences among treatments in amount of time that animals performed particular activities during daylight in specific pasture and paddock zones, or if it was more related to pasture and paddock area. As a first step in exploring this ques-tion, it was noted that actual time during daylight observations that animals spent under shade as well as actual number of dung and urine deposits per zone did not differ among stocking methods (data not presented). This indicates that the increases in animal behavior indices for Zones 1 and 2 of longer grazing period treatments occurred because the index denominator decreased (i.e., Zones 1 and 2 occupied a smaller percentage of the total area of larger pastures and paddocks). These results support conclusions that (i) animal behavior measured in this study was less affected by stocking method during summer daylight hours due to the overriding attraction of shade and water and (ii) reports of more uniform distribution of animal activities across rotationally stocked pastures with short vs. long grazing periods or vs. continuously stocked pastures may primarily be a function of more frequent movement of animals to new paddocks, in effect causing the animals to move to different shade and water locations. These conclusions are sup-ported by previous work showing animals congregate under shade and close to watering points in a warm, humid environ-ment regardless of stocking density (Mathews et al., 1994b) (i.e., high levels of competition for forage were not enough to ensure homogeneous distribution of excreta across the pad-dock). They also support a previously stated hypothesis that if more uniform nutrient distribution occurs with greater vs. fewer paddocks under rotational stocking in a warm climate it

is primarily because animals are forced to utilize more loung-ing and watering points when paddock number is greater (Sol-lenberger et al., 2002). This reasoning implies that if shade and watering points were moved in the same manner under con-tinuous and rotational stocking, patterns of soil nutrient distri-bution would be much the same across stocking methods. This was shown to be the case by Mathews et al. (1994a).

Dung Spatial DistributionThe dung spatial distribution evaluation showed that the stocking strategies have different degrees of clustering, and no evaluation date effect was observed. The 1-d treat-ment had a lower DI than the 7-d or continuous treat-ments (1.12, 1.67, and 1.31, respectively) which means that the variance was closer to the mean than in the other treatments. Therefore, less clustering and more unifor-mity in the dung distribution occurred for the 1-d treat-ment, and it followed a Poisson distribution model. Both the 7-d and continuous treatments followed a negative binomial distribution model, which describes the cluster-ing and overlaying of dung pats. Thus, the 1-d promoted a more uniform dung distribution than the 7-d and con-tinuous treatments (Fig. 1). This result is in contrast to the lack of differences among treatments in number of dung events per zone (data not presented), but it is probably due to 24-h sampling periods for dung spatial distribution in contrast to observation of activities in pasture zones that occurred only during daylight hours when temperatures and solar radiation were very high.

The random dung distribution observed in the 1-d treatment was associated with less spatial variability of soil

Figure 1. Dung spatial distribution on Pensacola bahiagrass pastures that were rotationally stocked with 1- and 7-d grazing periods or that were continuously stocked. Dots represent dung pats deposited during 24-h evaluation periods. Figure is not drawn to the scale.


P, K, and Mg concentrations for this treatment compared with 7 d and continuous (Fig. 2). All treatments, however, showed greater soil P, K, and Mg concentrations near shade and watering areas, gates, and camping sites (Fig. 2). Magnitudes of differences were not equal among treat-ments, with longer grazing periods (7 d and continuous) presenting greater soil nutrient variability, expressing the less even distribution of cattle excreta.

Soil Nutrient ConcentrationThere was a stocking method × depth interaction for soil nitrate N and total extractable N (Table 6), but this inter-action was not significant for soil P, K, or Mg. There was no stocking method × zone interaction for soil N, P, K, or Mg concentrations (data not presented).

Nitrate-N and total-extractable N increased linearly with increasing length of grazing period at both depths (Table 6). The continuous and 21-d rotational treatments generally presented similar soil N concentrations that were greater than those observed for the short-grazing period treatments, especially for the 0- to 8-cm depth. Considering that all treatments received the same amount of N fertilizer, treatment differences are probably due to the stocking method applied. Total-extractable N and

NH4–N were greater at the 0- to 8-cm than for 8- to 23-cm depth, but NO3–N did not differ between the depths (Table 6). Nitrate is more mobile in the soil pro-file than NH4, while NH4 interacts with soil colloids due to its positive charge (Tinker and Nye, 2000; Brady and Weil, 2002). Since soil organic matter is greater at shal-lower depths, NH4–N released after the ammonification reaction probably was adsorbed by negative charges, pre-senting higher concentrations at the 0- to 8-cm depth.

Zone × soil depth interactions occurred for all soil nutrients. At the 0- to 8-cm depth, N concentrations were greatest in Zone 1, but there were no zone differences observed at the 8- to 23-cm depth (Table 7). The total-extractable N concentrations obtained in this research are lower than the ones reported by Mathews et al. (1999) for areas within 15 m of the shade, and differences are prob-ably due to different soil characteristics between the sandy low organic matter Spodosol in the Florida site and the Kohala and Maile soil series in the Hawaii sites, which have greater silt and clay concentrations. Phosphorus, K, and Mg concentrations were greater in Zone 1 at the 0- to 8-cm depth, but not at the 8- to 23-cm depth (Table 8). Woodard et al. (2013) suggested that the risk of dung P reaching groundwater in bahiagrass pastures established

Figure 2. Soil P, K, and Mg concentration changes from June 2001 to October 2003 on Pensacola bahiagrass pastures that were rota-tionally stocked with 1- and 7-d grazing periods or that were continuously stocked. Positive numbers indicate nutrient enrichment and negative numbers indicate nutrient depletion from 2001 to 2003. Data presented are averaged across replications.


on Smyrna sandy soils is low due to P retention capacity within the rooting zone. Phosphorus and Mg are excreted mainly in dung, and greater density of dung deposition in Zone 1 in the 21-d rotational stocking and continuous treatments may explain the greater soil nutrient concen-tration in those zones. Similar results were obtained by West et al. (1989) and Mathews et al. (1994a). Schnyder et al. (2010) also observed a close correlation between topsoil stocks of N and P and excreta density.

There are few studies in warm climates that have eval-uated the effect of stocking method on soil nutrient con-centration. Mathews et al. (1999) compared short (3–3.5 d) and long (20–22 d) grazing periods of rotational stock-ing on soil nutrient distribution using a zonal sampling

approach. They did not find differences between grazing periods in terms of soil nutrient distribution. In another study, Mathews et al. (1994a) compared rotational stock-ing with short and long grazing periods vs. continuous stocking and again did not observe differences in terms of soil nutrient distribution among stocking methods. In that research, shade and water locations were moved the same distance every 2 d on all treatments to avoid confound-ing of water and shade locations and stocking method. In the current study, nitrate N and total-extractable N concentrations were greater as length of grazing period of rotational stocking increased, but there were no effects of stocking method on soil P, K, and Mg concentrations, nor were there stocking method × zone interactions for any

Table 7. Effect of pasture zones on soil N concentration at different soil depths in bahiagrass pastures grazed using different stocking methods for 3 yr. Data are means across three treatments and two replicates.

Zone

Nitrate N NH4 N Total extractable N

0–8 cm 8–23 cm P† 0–8 cm 8–23 cm P 0–8 cm 8–23 cm P

mg kg-1 soil mg kg-1 soil mg kg-1 soil mg kg-1 soil mg kg-1 soil mg kg-1 soil

1 5.4a‡ 1.9a 0.14 8.2a 2.2a <0.01 13.7a 4.1a <0.01

2 2.5b 2.3a 0.89 2.6b 4.0a 0.35 5.1b 6.3a 0.07

3 4.3a 0.9a 0.07 6.0a 1.7a <0.01 10.3b 2.7a <0.01† Level of P for comparison of the two soil depths within a nutrient and zone.‡ Within columns, means followed by the same letter are not significantly different (P > 0.10).

Table 8. Effect of pasture zone on soil P, K, and Mg concentration at different soil depths in bahiagrass pastures grazed using different stocking methods for 3 yr. Data are means across three treatments and two replicates.

Zone

P K Mg



1 17a‡ 16a 0.70 181a 107a 0.07 171a 118a 0.48

2 8b 14a 0.07 77b 74a 0.95 127ab 124a 0.97

3 6b 13a 0.03 67b 77a 0.80 95b 141a 0.54† Level of P for comparison of the two soil depths within a nutrient and zone.‡ Within columns, means followed by the same letter are not significantly different (P > 0.10).

Table 6. Soil N concentration at different soil depths of rotationally and continuously stocked bahiagrass pastures after 3 yr of grazing. Data are means across three zones and two replicates.

Treatment

Nitrate N NH4 N Total extractable N



Rotational

1 d 0.7 0.2 0.93 5.6 3.4 0.05 6.3 3.6 0.02

3 d 2.8 0.5 0.39 3.4 2.4 0.09 6.1 2.8 0.01

7 d 3.9 2.4 0.42 2.5 1.3 0.09 6.4 3.7 0.02

21 d 7.7 3.4 0.15 7.2 4.0 0.02 14.9 7.4 <0.01

Effect (P value) linear‡ (<0.01) linear (0.04) NS§ quadratic (0.09) linear (<0.01) linear (0.07)

Continuous 5.3 2.1 0.10 9.4 2.2 <0.01 14.7 4.3 <0.01

R otational vs. cont (P value)

0.09 0.61 0.07 0.69 0.07 0.81

† Level of P for comparison of the two soil depths within a nutrient and a treatment.‡ Polynomial contrast for effect of length of grazing period of rotational treatments.§ Not significant (P > 0.10).


soil nutrient. All soil nutrients accumulated in the zone closest to shade and water relative to other zones, suggest-ing that in warm climates the positioning of shade and water points plays a major role in soil nutrient redistri-bution. Moving shades to improve excreta distribution is a recommended practice (Ellington and Wallace, 1991); however, it may not be adopted by farmers.

SUMMARY AND CONCLUSIONSThe responses measured suggest a role of stocking method in animal behavior and nutrient distribution, but the mag-nitude of that role in warm climate grasslands is subject to debate. Supporting the importance of stocking method, 24-h measures of dung distribution and end-of-experi-ment soil nutrient concentrations were more homogeneous across pastures with a 1- than a 7-d grazing period or for continuous stocking. In addition, indices of dung and urine deposition and total time spent in pasture zones (zones based on distance from shade and water), weighted accord-ing to the area of these zones, showed greater uniformity for pastures with short than long grazing periods. On the other hand, actual time spent by cattle and number of dung and urine events in each pasture zone during daylight hours did not differ among stocking methods. Additionally, after 3 yr of imposing treatments there was no stocking method × zone interaction for soil N, P, K, or Mg concentrations. This indicates that the zonal pattern of nutrient redistribu-tion was similar across stocking methods. In fact, the data show that for all nutrients, regardless of stocking method, soil concentrations after 3 yr of grazing were greatest in Zone 1, closest to shade and water.

These findings lead to conclusions that within a warm-climate context (i) animal behavior measured during day-light hours was little affected by stocking method, prob-ably due to the overriding attraction of animals to shade and water locations during hot, humid conditions and (ii) structural features of stocking method (e.g., positioning of shade and water points) have a greater effect on animal behavior and soil nutrient redistribution than stocking density–mediated effects on competition among cattle for forage. These conclusions are supported by the finding that day time air temperature, wind speed, and tempera-ture–humidity index explained 49% of the variation in time cattle spent under shade. It is quite possible, however, that shade and water positioning may have less impact on animal behavior in cooler environments, increasing the potential role of other stocking method factors in deter-mining animal behavior and nutrient distribution.

AcknowledgmentsThis research was sponsored in part by USDA CSREES Tropi-cal and Subtropical Agricultural Research Program Grant 34135-12348.

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Stocking Method, Animal Behavior, and Soil Nutrient Redistribution: How are They Linked?