Accumulated biomass and nutritional quality indicators in chaco

Transcripción

4
ARTICLES
RIA / Vol. 38 / N.º3
Accumulated biomass and nutritional
quality indicators in chaco bromegrass
(Bromus auleticus Trinius ex Nees)
BUSTAMANTE, E.G.R.¹; RUIZ, M.A.1,²; MORICI, E.1,³; BABINEC, F.J.2,3; PORDOMINGO, A.B.1,2
ABSTRACT
Bromus auleticus (chaqueña bromegrass) may be considered as one of the most valuable forage species
for the Southern Cone. This species shows variation among populations, determined in diverse vegetative
characters, which could result in differences in production and forage quality. The objective of this study was to
evaluate two origins of Bromus auleticus (Argentina and Uruguay) for characters of biomass accumulated and
quality in two periods of the year (Summer-Autumn and Autumn-Spring). Five Uruguayan (U) and Argentine
(A) clones were compared, randomly arranged in rows spaced one meter from each other, with 10 plants each
one. Biomass accumulated per plant (B) and biomass quality were determined in two times of the year measuring neutral detergent fiber (NDF), crude protein (CP) and dry mater digestibility (DMD). In general, quality of
biomass was poor due to time cuttings, limiting the scope of the results. However, differences between the clones in this stage of development could be indicating the presence of variation among genotypes of “chaqueña”
prairie grass U and A in biomass and nutritional quality. Significant effect of origin for B was not observed. In all
biomass quality variables evaluated in Summer-Autumn, significant differences between origins were found.
In Autumn-Spring, differences between origins were significant in DMD. U clones showed more CP, less NDF
and higher DMD. Within each origin, A showed less differences than U both in B and quality. Concerning A or
U clones, no coincidence between high biomass and high quality was found.
Keywords: winter grasses, biomass accumulated, fiber, crude protein.
INTRODUCTION
Chaqueña bromegrass (Bromus auleticus Trin. Ex Nees)
is considered one of the most valuable forages in the Southern Cone (Traverso, 2001; Millot, 2001), and thus its incorporation to pastures is recommended due to its significant
growth during Autumn-Winter and its high persistence (Olmos, 1993, Costa et al., 1995; Saenz et al., 1995; Mombelli
and Spada, 1996; Romero and Ruiz 1997, Ruiz et al., 2004).
In Argentina its distribution extends over a vast meadow
area that comprises the provinces of La Pampa, Buenos
Aires, Cordoba, Santa Fe, Entre Rios and Corrientes.
Chaqueña bromegrass also grows in Uruguay and the
Brazilian states of Rio Grande do Sul and Santa Catarina
(Steibel et al., 1997, Gutierrez and Pensiero, 1998; Millot,
2001). The acceptability and preference by livestock is evidenced by its decline in natural community due to the intensive and continuous grazing (Ragonese, 1985). Chaqueña
bromegrass forage has been defined from “good” to “excellent” (Berreta et al., 1990; Olmos, 1993, Gasser et al.,
1996). In the livestock-farming area (Argentina, coastline
area of Uruguay and southern Brazil) it has almost disappeared as a result of continuous tillage (Millot, 2001).
Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Uruguay 151, (6300) Santa Rosa, La Pampa.
²INTA EEA Anguil “Ing. Agr. Guillermo Covas”, CC11, (6326) Anguil, La Pampa.
³Facultad de Agronomía, Universidad Nacional de La Pampa, Ruta 25, Santa Rosa, La Pampa
1
Received January 7th 2011 // Accepted May 18th 2012 // Published online June 13th 2012
Accumulated biomass and nutritional quality indicators in chaqueña bromegrass (Bromus auleticus Trinius ex Nees)
December 2012, Argentina
This species shows variation among populations for features such as seed production (Millot et al., 1990; Ruiz and
Covas, 2007, Pinget et al., 2007), seedling vigour (Ré et
al., 2006), and different vegetative characteristics including
pilosity, length and width of leaves and growth habits (Millot et al., 1990). In the accessions of the Germplasm Bank
at EEA INTA Anguil differences were observed in the width
and color of the leaves (Traverso, 2001). These characters may result in forage production and quality differences
(Methol and Freire, 1990), which has also been suggested
by De Battista and Costa (1998).
The aim of this work was to evaluate chaqueña bromegrass from two sources, Argentina (A) and Uruguay (U) for
accumulated biomass and nutritional quality indicators in two
periods of the year (Summer-Autumn and Autumn-Spring),
to determine its possible use in future plans for forage improvement, in particular for its use as deferred forage in associated pastures and its reintroduction into natural fields.
5
Determinations:
Accumulated material was determined in four plants per
clone. Plants were hand-cut using a sickle at ground level.
The cuts were performed twice after the made on two occasions after the trimming on December 28th, 2007: on April
11th (1631 ° Cd) and October 29th (1466 ° Cd). Thereafter,
both “cut dates” will be referred as Summer-Fall and FallSpring. The collected material was dried in oven at 60° C
for 48 hours and weighed to determine the accumulated
biomass per plant (g DM/plant-1).
An aliquot of the obtained dry material was grinded
using a Wiley Mill (mesh: 1 mm) to perform nutritional quality analysis: Crude Protein (CP, Kjeldahl method, AOAC,
1990), NDF and ADF (Goering and Van Soest, 1970). DM
digestibility (DMD) was calculated using the formula DMD
= 88.9 x (0.779 x %ADF), (Moore and Undersander, 2002).
Statistical analysis:
MATERIALS AND METHODS
We worked with five Uruguayan and five Argentine clones of chaqueña bromegrass, obtained from a collection
of 200 clones previously characterized based on leaf traits.
We chose those considered more representatives of each
group: glaucous green leaves, 2-6 mm width in Argentine
specimens, and dark green leaves, 6-10 mm, in the specimens from Uruguay (Traverso, 2001). Plants were obtained from regenerating patches at the INTA EEA Anguil
Germplasm Bank. These plants were transplanted (2001)
in unreplicated rows, spaced 1 m, randomly arranged. Each
clone included ten plants spaced 0.50 m. Clones were trimmed on December 28th 2007.
Average temperature during the first period of biomass
accumulation was 20.6 ºC and 12.9 ºC during the second.
Rainfall during the trial was 475 mm. Monthly rainfall is
shown in Figure 1 along with historical averages. Although
the annual total was similar to historical (2008= 623 mm;
historical average= 664 mm) in 2008 rainfalls were more
abundant during January and February and lower during
March and April. Soil was Haplustol Entish type, 41.86
ppm of phosphorus and 0.12% nitrogen, a field capacity of
15.7% and permanent wilting point 11.6%.
As clones were not replicated, we used a methodology
derived from the one recommended for augmented design
tests (Wolfinger et al., 1997). Results were analyzed using
a mixed model with fixed effects of origin, Argentine (A) and
Uruguayan (U), and random clones within each source,
using the PROC MIXED of SAS (1997). We used the mean
square of clones within provenance to prove the existence
of differences between sources (Singer, 1998). Means were
obtained from sources and compared by F test. Predictors
were obtained for clones (BLUPs: Best Linear Unbiased
Predictor) and confidence intervals (α = 0.10), which were
used in the respective comparisons (Panter y Allen, 1995a,
1995b, Littell et al., 1996).
RESULTS
When cuts were performed senescent material was present next to the green material. No trace of inflorescences
was observed in Autumn, while in Spring the plants were
in early panicle (panicle not fully emerged). No significant
differences were detected between accumulated biomass
depending on the origin of the plant in any of the cuts. Argentine clones accumulated a similar amount of biomass
during the Summer-Autumn cut. U102 was the Uruguayan clone that accumulated most biomass, unlike U191.
No differences were observed in Argentine clones in the
Autumns-Spring cut. Among the Uruguayan clones, U102
displayed higher biomass, differing from the rest (Table 1).
The quality of accumulated biomass (Table 1) in the Summer-Autumn cut differed between origins in all variables.
However, in the Autumn-Spring cut differences were only
observed among origins in regards with DMD.
Figure 1. Rainfall at Anguil (La Pampa) during 2008 and historical
average 1921-2006.
Differences among origins for crude protein were significant in Summer-Autumn, and we observed that Uruguayans clones displayed the higher protein content, whereas
Argentine clones presented 1.37% less protein. Among
origins, significant differences were observed in Autumn-
6
ARTICLES
Clon
B (g/pl.)
DM (%)
NDF (%)
DMD (%)
CP (%)
Summer-Fall
Argentina
Uruguay
Fall-Spring
Argentina
Uruguay
167
71,48
69,56
78,03
47,68
6,28
176
77,55
74,35
78,45
47,70
5,07
184
71,81
68,03
76,58
48,87
6,19
192
82,79
70,19
76,45
49,49
6,06
196
90,85
70,71
78,55
48,02
5,61
102
126,43
61,39
74,45
52,41
6,93
128
94,67
61,74
75,56
51,98
7,03
130
94,83
61,04
74,19
53,07
7,46
189
89,29
66,64
77,01
50,92
6,66
191
71,30
66,13
73,42
52,28
8,02
11,12
167
22,15
41,96
75,40
54,96
176
17,28
43,67
75,04
53,49
8,94
184
21,84
45,38
74,97
56,40
10,38
192
26,02
44,59
78,01
57,42
11,00
196
17,38
42,51
76,44
56,45
10,61
102
67,13
42,38
72,96
57,90
10,19
128
44,23
42,16
73,71
59,00
11,23
130
38,18
43,48
73,47
56,60
9,52
189
24,22
43,92
77,08
58,06
11,86
191
21,44
42,79
75,19
60,14
12,07
Table 1. Predictors (BLUPs) for accumulated biomass (B), crude protein (CP), neutral detergent fiber (NDF) and dry matter digestibility
(DMD) in chaqueña bromegrass clones from two different origins.
Spring. In Summer-Autumn, the highest percentage of protein among Argentine clones was presented by clone A167,
which differed from A176. Among Uruguayan cloned, U191
presented the highest protein contents and differed from
U167 (Table 1). In Autumn-Spring, the Argentine clones displaying the highest protein content were A167 and A192,
and differed from A176. Among the Uruguayans, U189 and
U191 displayed the highest values of CP, and differed from
U130.
We analyzed the ratio between biomass and CP, considering that the protein content of plant covers dilutes as accumulated biomass increases (Gastal and Lemaire, 2002),
and to a greater degree if dead material or inflorescences
are present. This dilution is due to the increase in the proportion of structural tissue in detriment of tissues containing
the highest N proportion.
Figure 2 shows the relationship between the biomass
per plant and CP for the clones of the two origins, in both
cuts. We observed that the ratio followed approximately
the same trend, except during the Autumn-Spring period in
Argentine clones, as a result of low accumulated biomass
variability that induces an erratic relationship.
The negative relationship between biomass and protein is significant only if both cuts are considered together.
Analyzed Uruguayan genotypes presented higher %CP
(and %N) that Argentine, compared to similar biomass.
The difference seems to reduce at lower biomass values.
However, this type of comparisons should be made comparing similar live accumulated biomass, and in this work, in
both courts, the N content observed is typical of advanced
development pastured, with low sheets proportion, where
most of the plant N is located (Evans, 1983).
Significant differences were detected in regards to NDF
among origins in the Summer-Autumn cut, where Argentine
clones presented higher NDF than Uruguayan clones. No
differences among origins were detected in the AutumnSpring cut. Although Argentine cloned were similar in the
Summer-Autumn cut, Uruguayan clone U191 presented
lower NDF, as opposite to U189. No differences were observed among the Argentine clones in the Autumn-Spring
cut, whereas among the Uruguayan clones U198 displayed
the higher NDF and differed from 102, 128 and 130.
Both in the Summer-Autumn cut, as in the Autumn-Spring
cut, DMD was significantly higher in clones from Uruguay.
In the first case, no differences were observed among Argentine clones, whereas among the Uruguayans U130
presented the higherst DMD, and differed from U189. In
the second, Argentine clones with higher DMD were A184,
A192 and A196, which differed from A176. Among the Uruguayans, U191 presented the higher DMD and differed
from U130.
7
Figure 2. Relationship between biomass and crude protein in Uruguayan and Argentine clones.
DISCUSSION
The temperate forages commonly used in the country
have a foliar half-life of 500 to 600 °Cd (Agnusdei et al.,
1998). This indicates that when the interval between harvests exceeds that period, the net accumulation will tend to
reach a ceiling as a result of the death of older leaves. Considering that accumulation periodios during this experience
lasted between 1631 and 1466 °Cd, accumulated biomass
values should not be taken as accurate productivity estimators of materials. In this work we have observed differences
in accumulated biomass in Uruguayans clones, not among
Argentines.
Variations in fiber content and digestibility between and within a cultivar have been reported in other species such as
alfalfa, suggesting the possibility of improving species using
such characters (Julier et al., 2000). For chaqueña bromegrass populations, both from Argentina and Uruguay, the existence of a significant variation in leaf traits has been indicated,
including length, width of leaf, pilosity and plant size (Methol
and Freire, 1990 ; Millot et al., 1990; Traverso, 2001).
All these characters suggest the existence of differences
between populations for biomass and nutritional quality.
However, evaluations have been generally conducted out
only in improved cultivars and/or populations (Olmos, 1993,
Costa et al., 1995, Saenz et al., 1995; Mombelli and Spada,
1996; Romero and Ruiz 1997, Ruiz et al., 2004).
Results show the negative impact of excessive biomass
accumulation on the nutritional quality of the forage. For
example, the highest NDF content was detected in Argentine
clones, with a rank between 73 and almost 79%. These are
very high levels, typically associated with forages in an advanced state of maturity, with high contents of senescent material and structural fractions. Similar considerations apply to
DMD parameters (less than 58%) and CP (range 5-12%).
This would explain the high proportion of NDF, low DMD
and the low values of CP, which are associated to pastures with high content of senescent material. In adult leaves,
after their growth period, an export of soluble compounds
may have occured, which would increase of NDF (Avila et
al., 2010), which may even have worsened by water deficit
(Fulkerson et al., 2007). In fact, NDF values found in this
work are higher than those reported for other winter grasses as Bromus inermis Leyss, and even higher than those
reported for C4 species (Buxton and Redfeam, 1997).
Protein values and DMD in both periods were also high
when compared to other assessments in C3 grasses including Festuca arundinacea, Dactylis glomerata and Bromus
wildenowii (Fulkerson et al., 2007). This may be attributed
in Summer–Autumn to the long period of biomass accumulation and drought, whereas in Autumn-Spring, these factors add to reproductive development, since the forage was
in early panicle.
Different studies conducted in Argentina and Uruguay
found a wide range of values of CP including levels ranging
from below the requirements for a functioning rumen (8%)
to high levels (21%), although always relate to a single cultivar or native population (Costa et al., 1995; De Battista and
Costa, 1998, Romero and Ruiz, 1997; Olmos, 2003, Ruiz
et al., 2004). One of the causes of the observed variability is that sometimes trials were fertilized. Although certain
differenced in the anatomy and proportion of leaf tissue in
chaqueña bromegrass genotypes have beenindicated, in
those investigations CP was not analyzed (Methol and Freire, 1990; Millot et al., 1990; Gasser et al., 2005).
As in Argentina, in Uruguay’s natural fields protein values
range from 9% to 15% (Olmos, 1993), whereas in fertilized
cultivated pasture, values range between 10% and 21%
(Costa et al., 1995; Olmos, 1993). The % of CP in chaqueña bromegrass Pampera INTA in three regions of the
8
ARTICLES
Pampean caldenal ranged from 7 to 11% CP (Ruiz et al.,
2004). These latter values are closer to those found in the
present study, where the soil was not fertilized nor received
irrigation. The higher values in Uruguayan clones SummerAutumn can be possibly explained by the foliar morphology,
wider and greener leaves. This should be confirmed in further investigations, where green biomass should be solely
evaluated.
Some authors suggested the possible existence of variation in digestibility and protein (Methol and Freire, 1990;
De Battista and Costa, 1998) for Chaco bromegrass. In this
work we found that Uruguayan genotypes had higher DMD
that Argentines, which would be related to leaf morphology,
as the Argentine clones presented narrower and pubescent
leaves (Methol and Freire, 1990; Gasser et al., 2005).
CONCLUSION
Forage nutritional quality was very low in all cases, due
to prolonged accumulation periods, with NDF values above
72%, DMD values lower than 58% DMS and CP 5-12%. Differences were detected between clones from Uruguay and
Argentina that suggest the existence of genotypic variation
in the evaluated chaqueña bromegrass materials. Uruguayan clones presented more PB, lower NDF, and increased
DMS. Within each source, Argentine clones were more similar to each other than the Uruguayans.
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Accumulated biomass and nutritional quality indicators in chaco

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