DOSES
AND SOURCES OF NITROGEN ON YIELD AND BROMATOLOGICAL COMPOSITION OF XARAÉS
GRASS
Kátia
Aparecida de Pinho Costa1, Eduardo da Costa Severiano1,
Fabiano Guimarães Silva1, Elenildo Ferreira Borges2,
Patrícia Soares Epifânio3, Kátia Cylene Guimarães1
1Professores
dos Programas de Pós-Graduação em Zootecnia e Ciências Agrárias do
Instituto Federal Goiano, Campus Rio Verde, Rio Verde, GO, Brasil.
katiazoo@hotmail.com.
2 Engenheiro
Agrônomo, Universidade de Rio Verde, Rio Verde, GO, Brasil
3Pós-graduanda
do Instituto
Federal
Goiano, Campus Rio Verde, Rio Verde, GO, Brasil.
ABSTRACT
This study
evaluated the effect of nitrogen sources and doses on dry matter yield
and bromatological composition of xaraés
grass throughout the year. The experiment was carried out at the
Agronomy Faculty of Rio Verde University from October 2008 to January
2010. The experiment consisted of a randomized complete block design in
a 2 x 4 factorial arrangement with measures repeated in time, and four
replications. We tested two nitrogen sources (ammonium sulfate and urea)
and four nitrogen levels (0, 200, 400 and 600 kg ha-1). The
evaluations were conducted on the same plots throughout the year and
during all four seasons (autumn, winter, spring, and summer). The
results demonstrated that the maximum grass
production of dry matter and crude protein of xaraés
grass for the sources of urea and ammonium sulfate were estimated at
doses of 500 and 472 kg ha-1 and 407 and 396 kg N ha-1,
respectively. And for TDN level the maximum dose was 404.74 kg ha-1
N, for the source of ammonium sulfate. This result indicates that, regardless of the source, the application of increasing
doses of up to 400 kg ha-1 of nitrogen in xaraés
grass is sufficient to maintain a high dry matter production, associated
with the nutritional value of the forage. The source ammonium sulfate
demonstrated higher efficacy for xaraés
grass dry matter production in the seasons evaluated, however additional
studies are needed to evaluate the economical feasibility of its use.
--------------------
KEYWORDS:
Ammonium sulphate; Brachiaria brizantha; urea; year season.
DOSES E FONTES DE NITROGÊNIO NA PRODUÇÃO
E COMPOSIÇÃO BROMATOLÓGICA DO CAPIM-XARAÉS
RESUMO
O
objetivo do trabalho foi avaliar o efeito de doses e fontes de
nitrogênio na produção de massa seca e composição bromatológica do
capim-xaraés em diferentes estações do ano. O experimento foi conduzido
no Campus da Faculdade de Agronomia da Universidade de Rio Verde, no
período de outubro de 2008 a janeiro de 2010. O delineamento
experimental utilizado foi em blocos completos ao acaso, em esquema
fatorial 2 x 4, com
medidas repetidas no tempo, com quatro
repetições. Foram testadas duas fontes de nitrogênio
(sulfato de amônio e uréia) e quatro doses de nitrogênio (0, 200, 400 e
600 kg ha-1). As avaliações foram
realizadas durante o ano, nas estações de outono, inverno,
primavera e verão, nas mesmas parcelas. Os resultados demonstraram que
a máxima produção de massa seca e teores de PB do capim-xaraés nas
fontes de ureia e sulfato de amônio foram estimados nas doses de 500 e
472 kg ha-1 e de 407 e 396 kg ha-1 de N,
respectivamente. E para os teores de NDT a dose máxima foi de 404,74
kg ha-1 de N, na fonte de sulfato de amônio. Esse resultado
indica que independente
da fonte nitrogenada, a aplicação de doses crescentes de até 400 kg ha-1
de nitrogênio no capim-xaraés é suficiente para manter uma alta produção
de massa seca, associada ao valor nutritivo da forragem. A
fonte de sulfato de amônio mostrou maior eficiência na produção de
massa seca do capim-xaraés nas estações analisadas.
---------------------
INTRODUCTION
The genus Brachiaria
lies among the most important tropical forages in Brazil. Brachiaria brizantha is one of the most important species for forage
production, and within this species, xaraés
presents several advantages in relation to other cultivars, such as
greater sprouting velocity, and greater yield, assuring a high support
capacity and higher yield per area (FLORES et al., 2008). However,
because it is a recently released cultivar, little information is
available about its soil fertility requirements.
FAGUNDES
et al. (2006) reported that low nutrient availability certainly is one
of the factors that seriously affect forage yield and quality. Thus,
nutrient supply, in adequate amounts and proportions, especially
nitrogen, takes a fundamental role in the production process of forage
grasses, since soil nitrogen, from organic matter mineralization, is not
sufficient to meet the requirements of high yield potential grasses.
The nutrient state of plants is evaluated primarily by
chemical analysis of leaf tissue, especially for identification of
nutrient deficiencies and estimation of nutrient demand. Nitrogen
application increases the protein content in plant dry matter (DM).
Since proteins are synthesized from amino acids, increases in nitrogen
supply reduce soluble carbohydrates. Large accumulation of nitrogen
products and proteins cause a dilution in the cell wall fraction,
increasing digestibility (COSTA et al., 2008). Studies indicate that the
use of nitrogen fertilizers in forage grasses, besides increasing dry
matter production (RODRIGUES et al., 2005), also improves forage
quality, increasing crude protein (CP) and total digestible nutrients
(TDN) contents, and decreasing neutral
detergent fiber (NDF), acid detergent fiber (ADF) and lignin contents,
thus improving digestibility (CECATO et al., 2004; MISTURA et al., 2007;
BENETT et al., 2008; MARANHÃO et al., 2009 e COSTA et al., 2010).
Therefore,
this study evaluated the effect of nitrogen sources and doses on dry
matter yield and chemical-bromatological composition of xaraés
grasses throughout the year stations.
MATERIAL AND METHODS
The
experiment was carried out at the Agronomy Faculty of Rio Verde
University, located in the farm Fontes do Saber, at 748 m above sea
level, 17° 48’ S and 50o 55’ W, from October 2008
to January 2010. The forage grass area used was about 500 m2,
each experimental unit measured 16 m2 and the evaluated area
6 m2.
The
experiment consisted of a randomized complete block design in a 2 x 4
factorial arrangement with measures repeated in time, with four
replications. We tested two nitrogen sources (ammonium sulfate and urea)
and four nitrogen levels (0, 200, 400 and 600 kg ha-1). The
evaluations were conducted on the same plots throughout the year and
during all four seasons (autumn, winter, spring
and summer).
The
soil was classified as a distroferric Red Latosol (EMBRAPA, 2006), and
its average chemical and physical attributes, before treatments, are
shown in Table
1.
The area was prepared by eliminating
competing plants with glyphosate and, subsequently, by harrowing. Before
sowing the grass, 910 kg ha-1 lime was applied to increase
base saturation to 45%, 80 kg ha-1 P2O5,
60 kg ha-1 K2O and 20 kg ha-1 FTE
BR-12, using the sources super simple phosphate, potassium chloride, and
fritted micronutrients, respectively. Sowing of Brachiaria
brizantha cv. xaraés
was done with 9 kg of pure viable seeds per hectare.
Nitrogen
fertilization (treatments) was done 45 days after sowing, after a
standardized cut at the height of 20 cm in all plots. Nitrogen
fertilization was split in four seasons, after each evaluation cut of
the forage grass. The fertilizations were done in December, January,
February and March, considering an interval of 30 days.
The
evaluations of dry matter yield and nutritional value were done in the
rainy and dry seasons. Two 1 m2 samples were randomly
collected in each plot, using a harvesting knife. Harvest was done in
the Summer (January/2009; February/2009 and March/2009); Autumn
(April/2009 and May/2009); Winter (July/2009 and September/2009) and
Spring (October/2009 and December/2009).
After
each evaluation harvest, a standardized cut was done in the whole
experimental area, at the same height of the evaluated plants (20 cm),
and the material was removed from the area.
The
collected material was placed in plastic bags and sent to the
laboratory, where a 500 g sample was removed and dried in a forced air
oven at 58 to 65ºC until constant weight was achieved. Subsequently, the
samples were ground through a 1 mm screen in a Wiley mill and stored in
plastic bags until laboratory analysis.
The bromatological analyses were done in
the Bromatological Lab of the Animal Science Department of
Rio Verde University, to determine dry matter (DM), crude
protein (CP), neutral detergent fiber (NDF) and acid detergent fiber
(ADF), using the method described by SILVA & QUEIROZ (2002). The
total digestible nutrient (TDN) was obtained using the formula: TDN =
105.2 - 0.68 * (% NDF), proposed by CHANDLER (1990).
Temperature
and rainfall were monitored daily during the experimental period, and
their averages are presented in Figure
1.
The
data were subjected to analysis of variance with significance level of
5% probability and depending on the significance of the variables were
adjusted by regression equations. Analyses were performed by a
split-plot model in time, as the adequacy of linear models of
Gauss-Markov, using the software SISVAR (FERREIRA, 2000).
RESULTS AND DISCUSSION
Dry
matter production by xaraés grass was affected (P<0.05) by the interaction of nitrogen
sources and doses in all seasons of the year. A quadratic regression
adjustment (P<0.05) for yield as a function of nitrogen doses for
both sources can be observed in Figure
2. In general the production increased until the dose of
400 kg ha-1 in all seasons, with sharp responses in relation
to the lack of nitrogen (control). MARTUSCELLO et al. (2009) reported
that nitrogen supply is one of the major management factors that control
different growth processes in plants.
Xaraés
grass was quite responsive to nitrogen fertilization. However, decreases
in dry matter production were observed after the maximum responses
estimated as 500 and 472 kg ha-1 N as urea and ammonium
sulfate, respectively, in the summer and 511 and 497 kg ha-1
N as urea and ammonium sulfate, respectively, in the autumn. Similar
results were obtained by BENETT et al. (2008) for marandu grass, with yield decrease at the dose 600 kg ha-1.
Ammonium
sulfate was a better nitrogen source for increasing yield, in all
seasons. The lower yield obtained with urea can be explained as a
function of its transformations in the soil, since nitrogen
fertilization was done by spreading over the grass, which resulted in
greater nitrogen losses by ammonia volatilization (OLIVEIRA et al.,
2007), thus limiting the grass responses to nitrogen, impairing dry
matter production. MARTHA JÚNIOR et al. (2004) explained that under high
temperatures, lack of rainfall immediately after fertilization and high
water evaporation rates from the soil, volatilization losses can reach
up to 80% of the nitrogen applied as urea, compromising the yield of the
forage plant. Another factor that could have contributed for greater dry
matter yield of the sulfate source would be the presence of sulfur.
BONFIM-DA-SILVA & MONTEIRO (2006) reported that areas that received
large amounts of nitrogen fertilizers demand the supply of sulfur to
maximize the forage response, especially in degraded areas, with low
levels of organic matter, where, usually, the levels of sulfur-sulfate
have low availability in the soil.
Yield
evaluation throughout the year indicated that higher dry matter yields
were obtained in the summer, followed by the autumn (Figure
2). Weather conditions (rainfall and
temperature) were more favorable for grass growth in these seasons (Figure
1), affecting the forage grass development. PEDREIRA et
al. (2009) explained that environment variables, such as lighting,
temperature, and water status, can affect forage tillering and be as
important as hormone factors for the development of buds and tiller
stimulation to maintain yield.
COSTA
et al. (2010), studied different sources and doses of nitrogen for
recovery of marandu grass,
and found that the dry matter yield under ammonium sulfate at the dose
of 300 kg ha-1 was 18% greater than under urea. PRIMAVESI et
al. (2006), analyzing two sources (ammonium nitrate and urea) and four
doses of nitrogen (0, 200, 400 and 800 kg ha-1) in marandu
grass, found that the forage grass yield under ammonium nitrate was
greater than under urea, reaching values of 13.070 and 12.328 kg ha-1,
respectively, in the maximum doses.
Even
in the winter, with little rainfall, we observed xaraés
grass development. Dry matter yield obtained in this season at the dose
of 400 kg ha-1, with the source ammonium sulfate, was
equivalent to 59, 44 and 26% of the yield obtained in summer, autumn and
spring, respectively. One of the factors that favored the best xaraés
grass development in this period was splitting nitrogen fertilization,
with the last one applied at the end of March. These results
demonstrated the importance of fertilization at the end of the rainy
season, thus minimizing the seasonality effect of forage production.
Another factor favoring forage development in this period was the
greatest sprouting ability of xaraés
grass, demonstrating that even under water deficit, this forage grass
can grow. FLORES et al. (2008) reported that xaraés
grass have advantages over other Brachiaria
cultivars, such as greater sprouting velocity and forage yield.
A
significant effect of the interaction (P<0.05) of nitrogen sources
and doses was observed in the summer and autumn, for the CP contents (Figure
3), with quadratic equation adjustments. The greatest
contents obtained in the summer were found for the doses 407 and 396 kg
ha-1 N from urea and ammonium sulfate, respectively.
At the dose of 400 kg ha-1 N, the CP content under
the source ammonium sulfate was 6.6% greater than under urea in the
summer and 5.2% in the autumn. A study of nitrogen sources and doses on
forage yield and quality of marandu
grass, by BENETT et al. (2008),
indicated that the average of CP contents varied from 10.6% in
the control treatment to 17.6% at the greatest nitrogen dose (600 kg ha-1).
In
winter and spring only the nitrogen doses had effect on CP. In these
seasons, the CP contents, as a function of nitrogen doses adjusted by a
quadratic equation, with maximum estimated at 443.98 and 427.65 kg ha-1
N for winter and spring, respectively (Figure
3). A study of nitrogen and phosphorus doses in
signalgrass, by MAGALHÃES et al. (2007), showed that only nitrogen
affected the contents of CP, with an increase of 22.5% at the dose 100
kg ha-1 nitrogen, in comparison to the non fertilized
control. An increase of CP contents under nitrogen doses was also
observed by CECATO et al. (2004), MISTURA et al. (2007) and MARANHÃO et
al. (2009).
An
important aspect to be considered in this study is the response ability
of xaraés grass to nitrogen
fertilization, increasing the CP content to adequate values for the
development of the forage plant. Excepting winter, even in the treatment
with no nitrogen fertilization, the CP contents were above the critical
level of 7% (COSTA et al., 2010), which is limiting for cattle
consumption, in different periods. In the summer, the CP contents at the
dose 400 kg ha-1 reached 16.3% under the source ammonium
sulfate and 15.3% under urea.
The
CP content varied through the seasons of the year. The highest levels
were found in the summer, followed by autumn and spring. These greater
contents can be explained due to the favorable climate conditions for xaraés
grass growth and development. In contrast, in winter, the conditions of
temperature and rainfall (Figure
1) were limiting for plant development, slowing growth
and the formation of new tillers, which led to pasture aging, thus
decreasing nutritional quality, since harvest was done in 64-days cycle,
and not 32-days, such as in the other seasons, as a response to forage
production seasonality. MITCHELL et al. (1998) reported that grazing can
be used as a tool to open the forage canopy and stimulate the appearance
of new tillers, with greater quality, if environment factors, such as
temperature, humidity and lighting are adequate.
Another
important variable expressing forage quality is NDF, comprising
structural carbohydrates, which are largely used by ruminants,
especially cellulose and hemicellulose (VAN SOEST, 1994). Nitrogen
sources and doses affected (P<0.05) NDF contents only in the autumn.
There was a decrease in NDF contents until the dose 400 kg ha-1,
with subsequent increases in both sources, but greater with ammonium
sulfate (Figure
4). Studies of
nitrogen sources and doses for the recovery of marandu
grass, by COSTA et al. (2010), indicated that only the doses affected
NDF contents, reducing contents as nitrogen levels increased. Similar
results were also obtained by MISTURA et al. (2007) and BENETT et al. (2008).
Greater
contents of NDF were observed in winter. This increase is a consequence
of cell wall constituents increase, which occurs with the advance of
plant age (64 days), possibly due to the reduction in leaf blades and
increase in stem proportion, thus increasing the fiber components (COSTA
et al., 2007). This fact is associated to unfavorable climate conditions
in winter, with low rainfall (Figure
1).
Only
the nitrogen doses affected NDF contents in the summer, winter and
spring. Similarly to what happened in the autumn, a sharp decrease in
NDF contents was observed with increasing nitrogen doses, until 506,
560, and 548 kg ha-1, respectively. This NDF reduction is relevant to
improve forage nutritional value and the increased consumption of dry
matter by the animals, since NDF content is an important parameter for
defining forage quality, as well as for limiting the intake ability of
the animals (COSTA et al., 2010). CECATO et al. (2004) reported that the
increase of nitrogen components demands a compensating decrease in cell
wall, thus reducing NDF and ADF contents.
Only
the nitrogen doses affected ADF contents, in all periods analyzed,
showing a linear decrease (P<0.05) in the autumn and a quadratic
decrease (P<0.05) in the summer, winter and spring, with increasing
nitrogen doses (Figure
5). This decrease is considered important, since the ADF
content is used to evaluate feed digestibility. High ADF contents in the
forage decrease dry matter digestibility, compromising animal yield. No
significant decrease in ADF contents was observed beyond the dose 400 kg
ha-1, which was similar to the dose 600 kg ha-1, in winter and spring.
In
an evaluation of marandu grass bromatological composition, under
nitrogen doses, CECATO et al. (2004), found ADF contents of 37.0 and
39.0% in the non fertilized treatment and 35.5 and 35.0% under 600 kg
ha-1, in the summer and winter, respectively. Such results were greater
than those found in this study. However, MARANHÃO et al. (2009),
studying nitrogen doses (0, 75, 150 and 225 mg dm-3) in marandu grass,
found lower NDF contents, varying from 34.5 and 25.0% for the control
and maximum nitrogen dose, respectively. These authors also explain that
nitrogen fertilization favors ADF reduction by the greater participation
of soluble constituents and CP.
Interaction
(P<0.05) between nitrogen sources and doses for TDN contents was
observed only in the autumn. TDN contents for the source ammonium
sulfate reached the maximum point at 404.74 kg ha-1 N (Figure
6). Subsequently, a decrease in TDN content was observed.
CAPPELLE et al. (2001) reported that estimates of feed and diet
energy values are important for high yield animals, especially dairy
cattle, which require a large amount of energy. Diets deficient in
energy reduce milk production, cause excessive weight loss, reproduction
problems and can decrease resistance against diseases. In contrast,
during summer, winter and spring, only the nitrogen doses affected TDN
contents. A quadratic effect (P<0.05) was observed for the nitrogen
doses, and the greatest contents obtained were at 400 kg ha-1.
No significant differences were observed above this dose for TDN
contents.
VAN
SOEST (1994) explained that several factors, such as plant species,
temperature, light intensity, water availability, latitude, maturity,
type of harvest and associated forages affect the chemical composition
and, consequently, feed energy availability.
BENET
et al. (2008) found that as nitrogen doses increased, considerable
increases were observed in the average TDN contents from the first to
the third harvest, with average values varying from 54.63% for the
control to 56.72% for the dose 600 kg ha-1 nitrogen. The TDN
results obtained in that study were lower than those found in the
present study for all evaluated seasons.
CONCLUSIONS
The
sources of urea and ammonium sulfate were estimated at doses of 500 and
472 kg ha-1 and 407 and 396 kg N ha-1,
respectively, for the maximum production of dry
matter and crude
protein of xaraés grass. And for TDN level the maximum dose was 404.74 kg ha-1
N, for the ammonium sulfate source. This result indicates that
regardless of the source, the application of increasing doses of up to
400 kg ha-1 of nitrogen to xaraés
grass is sufficient to maintain a high dry matter production, associated
with the nutritional value of the forage.
The
source ammonium sulfate demonstrated higher efficacy for xaraés grass dry matter production in the seasons evaluated, however
additional studies are needed to evaluate the economical feasibility of
its use.
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em: 9 maio 2013.