Tropical Grasslands-Forrajes Tropicales (2017) Vol. 5(3):143–152 143
Research Paper
Reduction of sward height in the fall and winter as a strategy to
improve the structure of marandu palisadegrass ( Urochloa
brizantha syn. Brachiaria brizantha cv. Marandu)
Reducción de la altura del pasto en otoño e invierno como estrategia para
mejorar la estructura de una pastura de Urochloa (sin. Brachiaria ) brizantha
cv. Marandu
MANOEL E.R. SANTOS1, MIRIÃ G. SIMPLÍCIO1, GUILHERME P. SILVA2, HERON A. DE OLIVEIRA1,
LUDIÊMILEM K.P. DA COSTA1 AND DIOGO O.C. DE SOUSA1
1 Faculty of Veterinary Medicine, Federal University of Uberlândia, Uberlândia, MG, Brazil. www.ufu.br
2 Animal Science Department, ESALQ, University of São Paulo, Piracicaba, SP, Brazil. www.esalq.usp.br
Abstract
The objective of this study was to identify defoliation strategies that might improve the structure of Urochloa brizantha (syn. Brachiaria brizantha) cv. Marandu (marandu palisadegrass). The following 3 defoliation strategies were compared in a plot study: sward kept at 15 cm in fall and winter (W) and 30 cm in spring (Sp) and summer (Su) (15W-30Sp-30Su); sward kept at 30 cm during the entire experimental period (30W-30Sp-30Su); and sward kept at 45 cm in fall and winter and 30 cm in spring and summer (45W-30Sp-30Su). The experimental design was completely randomized, with 4
replicates. Plots were cut with shears to the appropriate height weekly in winter and twice weekly in spring, summer and fall. Tiller density, mean tiller weight, leaf area index, forage mass, percentage of live leaf blades and percentage of stems were measured every 28 days. Forage mass in winter was directly related to pasture height (P<0.05) but differences had disappeared by summer (P>0.05). Mean tiller density was independent of cutting height but was higher in spring and summer than in winter (P<0.05). Mean tiller weight in winter was directly related to cutting height (P<0.05) but differences had disappeared by summer. The percentage of live leaf blades in the swards was affected by season with spring>summer>winter and by cutting height in fall/winter with leaf percentage inversely related to cutting height. Stem percentage in the swards in winter was directly related to cutting height. Grazing studies seem warranted to determine if these plot results are reflected under grazing conditions and what the impacts are on animal performance.
Keywords: Herbage mass, leaf area index, morphological composition, tillering.
Resumen
El objetivo del estudio, conducido en Uberlândia, Minas Gerais, Brasil, fue identificar estrategias de defoliación con el fin de mejorar la estructura de una pastura de Urochloa brizantha (sin. Brachiaria brizantha) cv. Marandu. Se compararon 3 estrategias: (1) mantener el pasto a una altura de 15 cm en otoño e invierno (W) y de 30 cm en primavera (Sp) y verano (Su) (15W-30Sp-30Su); (2) mantener el pasto a una altura de 30 cm durante todo el período experimental (30W-30Sp-30Su); y (3) mantener el pasto a una altura de 45 cm en otoño e invierno y de 30 cm en primavera y verano (45W-30Sp-30Su). El diseño experimental fue completamente al azar, con 4 repeticiones. Las parcelas se cortaron con tijeras a la altura respectiva semanalmente en invierno y 2 veces por semana en primavera, verano y otoño. Cada 28 días ___________
Correspondence: D.O.C. de Sousa, Faculty of Veterinary Medicine,
Federal University of Uberlândia, Campus Umuarama, Av. Pará
1720, Uberlândia CEP 38400-902, MG, Brazil.
Email: diogoolimpio@hotmail.com
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
144 M.E.R. Santos, M.G. Simplício, G.P. Silva, H.A. de Oliveira, L.K.P. da Costa and D.O.C. de Sousa se midieron la densidad de brotes, el peso medio de los brotes, el índice de área foliar, la masa de forraje, el porcentaje de hojas vivas y el porcentaje de tallos. La masa forrajera en invierno se relacionó directamente con la altura del pasto (P<0.05), pero las diferencias desaparecieron en verano (P>0.05). La densidad media de los brotes fue independiente de la altura de corte, pero fue mayor en primavera y verano que en invierno (P<0.05). El peso medio de los brotes en invierno estuvo directamente relacionado con la altura de corte (P <0.05), pero las diferencias desaparecieron en verano.
El porcentaje de hojas vivas en la pastura se vio afectado por la estación del año, con primavera>verano>invierno y por la altura de corte en otoño/invierno cuando el porcentaje de hojas estuvo inversamente relacionado con la altura de corte.
El porcentaje de tallos en invierno estuvo directamente relacionado con la altura de corte. Estudios de pastoreo parecen justificados para determinar si estos resultados, obtenidos a nivel de parcela de corte, se reflejan bajo condiciones de pastoreo, y cuáles son los impactos en la producción animal.
Palabras clave: Composición morfológica, índice de área foliar, masa forrajera, rebrotes.
Introduction
could result in lower maintenance respiration by the
plants, which would provide greater energy and carbon
Pasture structure is a function of how the organs of the
balance in the sward (Taiz and Zeiger 2012). In contrast,
aerial parts of forage plants are distributed in the pasture,
keeping pasture tall in winter would increase the energy
both vertically (Zanini et al. 2012) and horizontally
needs for survival of individual plants, precisely when
(Barthram et al. 2005). Some parameters used to describe
photosynthesis is at its lowest point.
pasture structure are: sward height, forage mass, volume
Moreover, Santana et al. (2014) suggested that the
and density (Carvalho et al. 2009).
greater shading at the plant base, inherent in taller
Pasture height is highly correlated with forage mass
pastures, would lead to greater leaf senescence at the
and morphological composition (Paula et al. 2012; Nantes
lower canopy stratum, which might inhibit tillering in
et al. 2013), in addition to being a cheap, easy and quick
early spring. On the other hand, pasture grazed short in
measurement. For this reason, average pasture height has
winter would permit greater incidence of light at the base
been recommended as a management criterion for when
of the sward in spring, which should stimulate the
to commence and cease grazing (Silva and Nascimento
appearance of young tillers (Paiva et al. 2012) with better
Júnior 2007). Studies on grazing management strategies,
structural traits (Barbosa et al. 2012).
based on pasture height, enable the understanding of
We therefore hypothesize that, by varying sward
variations in pasture structure, as well as the responses of
height during fall and winter, it may be possible to modify
animals and plants to these variations (Trindade et al.
physiological processes such as photosynthesis and
2007; Fonseca et al. 2012, 2013).
respiration as well as plant development, e.g. tillering and
Sbrissia et al. (2010) suggested that the optimal height
leaf senescence. All these processes, in turn, may change
range for management of marandu palisadegrass
sward structure not only in fall and winter, the seasons in
( Urochloa brizantha syn. Brachiaria brizantha cv.
which plant height is changed, but also in subsequent
Marandu) under continuous grazing during the rainy
ones.
season was 20‒40 cm. However, Santos et al. (2013)
This study was conducted to characterize the structural
suggested that pasture height should be adjusted
changes of a marandu palisadegrass sward maintained at
according to the season of the year to optimize the
various sward heights in fall and winter, and kept at a
productivity of the pasture. Other studies, e.g. Sbrissia
constant height in spring and summer. This knowledge
and Silva (2008) and Giacomini et al. (2009), indicated
should prove beneficial in formulating recommendations
that plant development is often affected by interactions
regarding defoliation strategies for this forage plant
between defoliation management strategies and season of
throughout the year.
the year, which suggests that the success of a particular
management strategy might differ between seasons. On
Materials and Methods
the basis of these findings, we conclude that grazing
management strategies should be flexible over the year
The experiment was conducted from March 2013 to
and vary with seasonal conditions.
March 2014, on the Capim Branco farm, belonging to the
Maintaining the sward shorter during winter, the
Faculty of Veterinary Medicine of the Federal University
season with adverse climate and in which the plant has the
of Uberlândia, in Uberlândia, MG, Brazil (18º53’19” S,
lowest rate of photosynthesis (Lara and Pedreira 2011a),
48°20’57” W; 776 masl). The climate in the region of
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Sward height and yield of palisadegrass 145
Uberlândia, according to the Köppen (1948) classifi-
Before the experiment commenced, soil samples from
cation, is a Cwa altitude tropical type, with mild and dry
the 0‒10 cm layer were collected and analyzed, revealing
winters and well defined dry and rainy seasons. The aver-
the following chemical properties: pH in H2O - 6.1; P -
age annual temperature is 22.3 ºC, with mean maximum
9.4 mg/dm3 (Mehlich-1); K+ - 156 mg/dm3; Ca2+ - 5.5
and minimum values of 23.9 and 19.3 ºC, respectively.
cmolc/dm3; Mg2+ - 1.7 cmolc/dm3; Al3+ - 0.0 cmolc/
Average annual precipitation is 1,584 mm.
dm3 (KCl 1 mol/L); effective CEC - 7.6; CEC at pH 7.0 -
The experiment was developed on a pasture of
10.3; and base saturation - 74%. Based on these results,
Urochloa brizantha syn. Brachiaria brizantha cv.
35.5 kg P/ha as single superphosphate, 50 kg N/ha as urea
Marandu (palisadegrass), established in the year 2000,
and 41.5 kg K/ha as KCl were broadcast on the plots in
and well managed with cattle. Twelve plots (experimental
February 2013. These same amounts were applied again
units) with an area of 12 m2 each were used. A border area
in January 2014.
of 0.25 m wide was discarded leaving a usable area of
Three defoliation strategies were evaluated, charac-
8.75 m2 on each plot for data collection.
terized by the heights at which the marandu palisadegrass
Climatic conditions during the experimental period
sward was maintained during fall and winter (15, 30 and
were monitored at the meteorological station, located
45 cm), with a standard height of 30 cm during spring and
approximately 200 m from the experimental area (Figures
summer. To maintain the grass at these heights, the
1 and 2).
swards were cut with pruning shears once a week in
winter and twice a week during spring, summer and fall.
This approach aimed to ensure that the actual heights of
the canopies remained within 100‒110% of the desired
values. The first strategy, with marandu palisadegrass
maintained at 15 cm in fall and winter and 30 cm in spring
and summer, equated with heavy defoliation during
winter and moderate defoliation subsequently. For the
second strategy the pasture was maintained at 30 cm
during the entire experimental period, according to the
recommendations of Sbrissia and Silva (2008), i.e.
moderate defoliation throughout. The third strategy
consisted of maintaining the grass at 45 cm in fall and
winter, i.e. only light defoliation, and at 30 cm in spring
and summer.
Figure 1. Monthly mean minimum and maximum temperatures
The experimental period during which pasture
and precipitation from March 2013 to March 2014. The seasons
measurements occurred was divided into winter (July‒
are: winter, July‒September 2013; spring, October‒December
September 2013), spring (October‒December 2013) and
2013; and summer, January‒March 2014.
summer (January‒March 2014). The experimental design
was completely randomized, with 4 replicates.
The fall (March‒June 2013) was considered the period
of acclimation of the plants to the particular sward heights.
From June 2013, at 28-day intervals, tiller density was
evaluated by counting the live tillers within two 50 × 25 cm
metal frames randomly located in each experimental unit.
The data were grouped according to season.
Monthly, in each season of the year and on each plot,
a sample of 50 tillers with average length similar to the
sward height was chosen. These tillers were harvested at
ground level and divided into live leaf blade, dead leaf
blade and live stem (stem + leaf sheath). Parts of the leaf
Figure 2. Summary of the water balance in the soil from
blade that did not show signs of senescence (green
January 2013 to April 2014. Arrows indicate the time when
organ) were incorporated into the live leaf blade
fertilizer was applied. The seasons are: winter, July‒September
fraction. Any part of the leaf blade with a yellowish tone
2013; spring, October‒December 2013; and summer, January‒
and or necrosis was considered dead leaf blade. Each
March 2014. DEF (-1) = Deficit; EXC = Excess.
sub-sample (live leaf blade, dead leaf blade and live
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
146 M.E.R. Santos, M.G. Simplício, G.P. Silva, H.A. de Oliveira, L.K.P. da Costa and D.O.C. de Sousa
stem) from the 50 tillers was collected in a single paper
bag, dried in an oven at 65 ºC for 72 h and then weighed
together, in order to obtain the masses of the morpho-
logical components, and the mean weight of tillers was
calculated. The masses of the sward morphological
components were obtained by the following formula:
FM = NT × TM, in which FM is the forage mass or the
mass of the plant morphological component (kg DM/ha);
NT is the number of tillers/10,000 m2; and TM is the
mass of the morphological component of the tiller (kg
DM/tiller). The masses of the plant morphological
components were expressed as percentages of the total
forage mass.
After harvesting the tillers in each plot, 50 live leaf
Figure 3. Effects of time of year on mean tiller density in
blades were also collected at random and placed in plastic
palisadegrass swards.
bags. A small portion of the extremities of the leaf blades
Means followed by the same letter do not differ (P>0.05).
(apex and base) was cut and discarded, so as to generate
an approximately rectangular leaf blade segment. The
Mean tiller weight was influenced by defoliation
width and length of each segment were measured, and the
strategy (P = 0.016) and by the interaction between this
leaf area of the leaf blade segments was calculated as the
factor and season of the year (P = 0.024). In winter, tiller
product of these dimensions. These segments were placed
weight was greater in the sward maintained at 45 cm in
in a forced-ventilation oven at 65 ºC for 72 h and then
fall/winter than in that at 15 cm, while in spring, the sward
weighed. With these data, the specific leaf area (cm² leaf
kept at 45 cm in fall/winter produced heavier tillers than
blade/g dry leaf blade) was calculated. The leaf area index
that at 30 cm in fall/winter. However, by summer, mean
of each tiller was calculated as the product of the specific
tiller weight was similar for all defoliation strategies in
leaf area and the live leaf blade mass of the tiller. The
fall/winter (Figure 4). The sward maintained at 45 cm in
pasture leaf area index, however, was obtained by
fall/winter produced similar sized tillers throughout
multiplying the leaf area of the tiller by the number of
(P>0.05), while the 30 cm sward in winter produced its
tillers per ha.
smallest tillers in spring (P<0.05) and the 15 cm sward in
For the data analysis, the results were grouped
winter produced progressively bigger tillers from winter
according to the season of the year (winter, spring and
to summer (P<0.05).
summer). Initially, the dataset was analyzed to check if it
Forage mass in the marandu palisadegrass was
met the assumptions of the analysis of variance (normality
influenced by season of the year (P = 0.013) and by the
and homogeneity). The data were then analyzed using the
interaction between this factor and defoliation strategy (P
MIXED procedure (mixed models) of the SAS®
= 0.009). In winter, forage mass was greatest in the sward
(Statistical Analysis System) statistical package, version
maintained at 45 cm, intermediate in the sward
9.2. The variance and covariance matrix was chosen using
maintained at 30 cm, and lowest in the sward maintained
Akaike’s Information Criterion (Wolfinger 1993). The
at 15 cm in fall/winter. In spring, forage mass in the sward
treatment means were estimated using the “LSMEANS”
maintained at 45 cm in fall/winter was greater than in that
option, and compared with each other by Student’s t test
kept at 30 cm in fall/winter. However, forage mass in
at 5% probability.
summer was independent of defoliation strategy in
fall/winter (Figure 5).
Results
The percentage of live leaf blades (PLLB) in the forage
mass was influenced by both season of the year (P<0.0001)
Tiller density in the palisadegrass was influenced only by
and defoliation strategy (P = 0.010). Overall PLLB
season of the year (P = 0.035), with fewer tillers in winter
followed the order: spring>summer>winter (Figure 6A),
than in spring and summer (Figure 3).
and was inversely related to height in winter (Figure 6B).
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Sward height and yield of palisadegrass 147
Figure 4. Effects of time of year and defoliation management on mean tiller weight in palisadegrass swards.
45W-30Sp-30Su: sward kept at 45 cm in winter and 30 cm in spring and summer; 30W-30Sp-30Su: sward kept at 30 cm in winter, spring and summer; and 15W-30Sp-30Su: sward kept at 15 cm in winter and 30 cm in spring and summer. Lowercase letters compare defoliation strategies within seasons of the year, and uppercase letters compare seasons of the year within each defoliation strategy.
Means followed by the same letter do not differ (P>0.05).
Figure 5. Effects of time of year and defoliation strategy on forage mass in palisadegrass swards.
45W-30Sp-30Su: sward kept at 45 cm in winter and 30 cm in spring and summer; 30W-30Sp-30Su: sward kept at 30 cm in winter, spring and summer; 15W-30Sp-30Su: sward kept at 15 cm in winter and 30 cm in spring and summer. Lowercase letters compare defoliation strategies within each season of the year, and uppercase letters compare seasons of the year within each defoliation strategy. Means followed by the same letter do not differ (P>0.05).
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
148 M.E.R. Santos, M.G. Simplício, G.P. Silva, H.A. de Oliveira, L.K.P. da Costa and D.O.C. de Sousa
Figure 6. Percentage of live leaf blades in the forage mass of palisadegrass according to season of the year (A) and defoliation management strategy (B).
45W-30Sp-30Su: sward kept at 45 cm in winter and 30 cm in spring and summer; 30W-30Sp-30Su: sward kept at 30 cm in winter, spring and summer; and 15W-30Sp-30Su: sward kept at 15 cm in winter and 30 cm in spring and summer. In each graph, means followed by the same letter do not differ (P>0.05).
The percentage of stems (PS) was influenced by
The percentage of dead material was not influenced by
season of the year (P<0.0001), defoliation strategy (P =
season of the year (P = 0.191), defoliation strategy
0.0002) and the interaction of these factors (P = 0.007). In
(P = 0.575) or by the interaction of these factors
winter, the sward kept at 15 cm in fall and winter dis-
(P = 0.305), averaging 23%.
played a lower PS than those kept at 45 and 30 cm. During
Season of the year affected leaf area index (LAI)
spring and summer, PS was independent of the sward
(P<0.0001), with a lower value in winter than in spring
height during the fall/winter period (Figure 7).
and summer (Figure 8).
Figure 7. Percentage of live stems in the forage mass of palisadegrass according to time of year and defoliation strategy.
45W-30Sp-30Su: sward kept at 45 cm in winter and 30 cm in spring and summer; 30W-30Sp-30Su: sward kept at 30 cm in winter, spring and summer; 15W-30Sp-30Su: sward kept at 15 cm in winter and 30 cm in spring and summer. Lowercase letters compare defoliation strategies within each season of the year, and uppercase letters compare seasons of the year within each defoliation strategy. Means followed by the same letter do not differ (P>0.05).
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Sward height and yield of palisadegrass 149
The adverse climatic conditions for plant growth in
winter (Figure 1) might also have resulted in a lower
percentage of live leaf in the forage mass in this season as
compared with spring and summer (Figure 6A). Low
temperatures and water deficit, typical of winter conditions,
decrease leaf appearance and elongation rates (Lara and
Pedreira 2011b), which would reduce the percentage of live
leaves in the forage mass. A similar lower percentage of live
leaves during winter was observed by Paula et al. (2012) in
palisadegrass pastures continuously grazed at 15, 30 and 45
cm throughout the year.
The low tiller density in winter (Figure 3) was partially
responsible for the low forage mass in swards maintained
at 15 and 30 cm in fall/winter (Figure 5), as well as for the
lower leaf area index (LAI) in all swards (Figure 8) in
winter. Three structural traits could potentially change the
Figure 8. Leaf area index of palisadegrass according to
sward LAI: tiller density, number of leaves per tiller and
season of the year.
leaf blade size. Of these, tiller density has the greatest
Means followed by the same letter do not differ (P>0.05).
potential to change the LAI (Matthew et al. 2000).
According to Fagundes et al. (2005), the low LAI of the
Discussion
pastures in winter would be a result of the lower number
of live leaves per tiller and the shorter final length of the
This study has provided further valuable information on
leaves at that time.
how the height, at which a marandu palisadegrass pasture
On the other hand, in spring and summer, the increase
is maintained in winter, spring and summer, affects the
in temperature and occurrence of rainfall (Figure 1)
structure and composition of the pasture. This will be of
provided favorable conditions for tillering, resulting in
use in explaining why pastures behave differently and
increased numbers of tillers (Figure 3), a typical response
have different levels of production under differing
pattern observed in other research studies with forage
grazing strategies, especially in winter.
grasses of the genus Brachiaria (Sbrissia and Silva 2008;
We hypothesized that keeping pasture short in winter
Calvano et al. 2011). Lara and Pedreira (2011b) recorded
would allow greater light penetration to the base of the
twice as many tillers in summer as in winter in cvv.
sward, which might stimulate greater tiller development
Marandu, Xaraés, Arapoty and Capiporã of Urochloa
brizantha (syn. Brachiaria brizantha) and cv. Basilisk of
in spring as reported by Matthew et al. (2000) and Sbrissia
U. decumbens (syn. B. decumbens).
et al. (2010). However, the defoliation strategy in
The greater number of tillers in spring and summer
fall/winter did not influence the number of tillers in the
(Figure 3) resulted in a higher LAI of the swards in these
sward in spring and summer, which demonstrates the
seasons (Figure 8). Since increased LAI increases
flexibility of marandu palisadegrass to variations in
interception of light by the sward (Pedreira et al. 2007),
height in the fall and winter. During fall/winter tiller
which is a premise for the occurrence of photosynthesis
density was similar on all pastures regardless of sward
(Taiz and Zeiger 2012), this results in increased growth
height and increased following the onset of better
rate of the pasture.
conditions for growth in spring. Climatic conditions
As a consequence of the accumulated effects of
seemed to be the overriding factor. There was very little
rainfall, temperature and solar radiation as the seasons
precipitation in June and no rain in July and August, with
progressed, a larger number of tillers was expected in
mean minimum temperature below 15 ºC (Figure 1).
summer than in spring. This response pattern did not
When the temperature is below 15 ºC, the lower threshold
occur, possibly due to the lower than normal rainfall
temperature for marandu palisadegrass (Mendonça and
experienced in January and February 2014 (Figure 2).
Rassini 2006), the rate of photosynthesis is impaired,
Additionally, the similar LAI in spring and summer
which compromises tillering in the pasture. Sbrissia and
(Figure 8) might also have contributed to tiller density
Silva (2008), in a study with marandu palisadegrass under
remaining stable in these seasons (Figure 3). The LAI
continuous stocking, also observed lower tiller density in
controls, in part, the amount of solar radiation that reaches
winter than in spring and summer.
the soil surface, such that a larger LAI is associated with
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
150 M.E.R. Santos, M.G. Simplício, G.P. Silva, H.A. de Oliveira, L.K.P. da Costa and D.O.C. de Sousa higher light interception by the sward (Giacomini et al.
greater stem elongation and consequently a greater tiller
2009) and in fact, with lower penetration of light to the
weight (Figure 4), as well as a higher percentage of live
soil. Since the amount of light received at the base of
stems in the forage mass (Figure 7). This high relative
plants has a significant influence on degree of tillering
contribution of live stem in winter resulted in a reduction
(Martuscello et al. 2009), the constancy of LAI in spring
in the percentage of live leaves during the entire
and summer might have provided similar levels of
experimental period in the sward kept at 45 cm in
luminosity close to the soil surface, resulting in similar
fall/winter as compared with that kept at 15 cm (Figure
numbers of basal buds developing into new tillers. The
6B). Nevertheless, in spring, when all swards were kept
maintenance of marandu palisadegrass at a constant
at the same height (30 cm), the highest one (45 cm) in fall
height in spring and summer also resulted in similar tiller
and winter continued to present a greater tiller weight.
weight in these seasons to the swards managed at 15 and
Thus, a residual effect of the management employed in
45 cm in fall/winter (Figure 4).
fall and winter was detected in the subsequent season.
On swards maintained at 15 and 30 cm in fall/winter,
Contrastingly, maintaining the sward lower (15 cm) in fall
the greater forage mass in summer than in the other
and winter resulted in lower tiller weight in winter (Figure
seasons of the year (Figure 5) might have been a
4), as well as a lower percentage of live stems in the
consequence of the onset of flowering of the palisadegrass
forage mass during winter (Figure 7). These results allow
in this season (Calvano et al. 2011). With flowering, the
us to infer that the structure of the marandu palisadegrass
leaf:stem ratio in the plant is reduced (Santos et al. 2009),
kept shorter in winter would be more favorable for forage
which explains the lower percentage of live leaves in the
intake by grazing animals.
forage mass in summer as compared with spring (Figure
The effect of a particular defoliation strategy in a
6A). Since stem is a denser organ than leaf (Pereira et al.
particular season of the year on tiller growth in the
2010), its greater proportion in the sward should result in
following season is partially due to the phenotypic
a larger forage mass. Furthermore, with flowering,
plasticity of the forage plant, i.e. to the change in the
compounds from root reserves are translocated to the
morphogenetic and structural traits of the plant in
aerial parts of the forage plant (Silva et al. 2015), which
response to environmental variations, including the
also contributes to increasing the sward forage mass.
defoliation environment (Silva and Nascimento Júnior
It should be noted that we might have overestimated
2007). This is a gradual process, and, therefore, does not
the forage mass values (Figure 5) in this study. To obtain
occur in the short term; when the defoliation manage-
this response variable, we multiplied average tiller weight
ment in a sward is changed, there is a carry-over effect
by the number of tillers. It is possible that some young
and effects of the previous management are displayed in
tillers, shorter than the average sward height, were
counted along with the taller ones. However, to determine
the subsequent periods.
mean tiller weight, we harvested only those with height
similar to the sward height, so the average tiller weight
Conclusions
would have been overestimated, with an equal effect on
forage mass.
This study has shown that: 1) Urochloa brizantha (syn.
Considering that the tiller is the basic growth unit of
Brachiaria brizantha) cv. Marandu (marandu palisade-
forage grasses (Hodgson 1990), the stability of tiller
grass) shows limiting structural traits in winter as compared
density in the swards subjected to variable defoliation
with spring and summer; 2) both pasture height and season
regimes in fall and winter indicates that their perenniality
affect pasture structure of Marandu; and 3) managing
was not compromised and that the growth potential of the
Marandu at 15 cm in fall and winter and 30 cm in spring
pasture was probably not impaired.
and summer will result in a leafier pasture with lower
In winter, variations in mean weight of tillers (Figure
percentage stems than keeping it at 30 or 45 cm in winter.
4) and forage mass (Figure 5) were a consequence of the
Grazing studies seem warranted to determine whether
modification of the sward height in this season. When the
the effects demonstrated in this experiment hold under
sward heights were similar (30 cm) in all swards,
grazing and how varying pasture height in different
differences in tiller weight and forage mass between the
seasons compares with maintaining a fixed grazing
swards declined and had disappeared by summer (Figure
height. Furthermore, how the sward height variation
4). Moreover, in the sward kept at 45 cm in fall and
affects pasture yield and quality and translates into animal
winter, there might have been more competition for light
performance should be monitored before recommen-
among the tillers (Sbrissia et al. 2010), which can lead to
dations should be made.
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Sward height and yield of palisadegrass 151
Acknowledgments
Köppen W. 1948. Climatologia. Gráfica Panamericana, Buenos
Aires, Argentina.
We thank Fundação de Amparo à Pesquisa do Estado de
Lara MAS; Pedreira CGS. 2011a. Estimativa da assimilação
Minas Gerais for financial support, and the interns of
potencial de carbono em dosséis de espécies de braquiária.
Grupo de Estudo e Pesquisa em Forragicultura of the
Pesquisa Agropecuária Brasileira 46:743‒750. DOI:
Federal University of Uberlândia for their endeavors in
10.1590/s0100-204x2011000700010
Lara MAS; Pedreira CGS. 2011b. Respostas morfogênicas e
conducting the activities of this project.
estruturais de dosséis de espécies de Braquiária à
intensidade de desfolhação. Pesquisa Agropecuária
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DOI: 10.1590/s0103-84782012000500020
(Received for publication 30 September 2016; accepted 11 June 2017; published 30 September 2017)
© 2017
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