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Research Article
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Cultivar and Nitrogen Splitting Effects on Amaranth Forage Yield and Weed Community |
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A. Aynehband
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ABSTRACT
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A 2 year field study was carried out at Agricultural Faculty of Shahid Chamran University of Ahvaz (Iran), in order to evaluate the response of Amaranth cultivars and weed dynamic to N splitting methods. Three Amaranth cultivars (i.e., Amont, Trigin and Plainsman) were grown in three N splitting methods (i.e., Commonly, Equal and Semi-equal) that being applied at planting, 12th leaf appearance and stem elongation. A split plot design replicated three times was used which Amaranth cultivars and N splitting methods were arranged in main and sub plots, respectively. Results showed that the highest forage yield was obtained for Trigin with Equal N splitting (i.e., 31.2 t ha-1) and Plainsman with Semi-equal N distribution (i.e., 3.8 t ha-1) the lowest. Also, the maximum and minimum protein content (%) were obtained for Trigin with Equal N splitting (16%) and Amont with commonly N splitting (11.9%), respectively. It was found that just Trigin with Equal N splitting treatment was the best treatment for both forage quality and quantity yield. Moreover, the weed communities and dominant species changed in response to various N splitting methods and Amaranth cultivars traits. Plainsman with Semi-equal N splitting treatment was the unfavorable treatment for both crop yield and weed infestation. Based on these results it is recommend that N splitting method be applied mainly as an Equal form in Trigin amaranth cultivar, to enhance crop forage yield and reduce weed infestation.
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INTRODUCTION
Amaranth (Amaranthus sp.) as a new crop is an
ancient pseudo-cereal originating in the Americas and can be used as a
high-protein grain and forage crop or a leafy vegetable. Amaranth is a
dicot, broadleaf, with C-4 photosynthesis and summer annual crop responding
well to high sunlight and warm temperature. The plant height ranges from
91 to 274 cm and soil temperature above 15°C is required to establish
a good plant stand. The two species of amaranth commonly grown are A.
cruentus L. (2n = 34) and A. hypochondriacus L. (2n = 32) that
can be used as a dual-purpose crop. The potential of amaranths as forage
has not been fully studied but highly prized as forage crops because of
their rapid growth rate, high protein content (the leaves, stem and head
have a 15-24% protein) and good forage yield (Myers, 1996). Several studies
have shown that yield differences of amaranth cultivars were due to nitrogen
availability (Myers, 1998; Pospisil et al., 2006; Schulte et
al., 2005) and individual cultivar traits (Henderson et al.,
2000; Sleugh et al., 2001; Stordahl et al., 1999). To grow
this alternative cereal efficiently, it is necessary to know the effect
of nitrogen fertilization on its yield because nitrogen was found to be
the primary limiting factor of amaranth production (Pospisil et al.,
2006). Varieties of different amaranth species respond differently to
the nitrogen amount applied. The author recorded low efficiency of nitrogen
use by amaranth with the increase of soil nitrogen content. Therefore,
higher nitrogen rate may have an adverse effect on the harvest due to
increased plant height, lodging and protracted seed ripening (Elbehri
et al., 1993). Also, some amaranth can have toxic levels of nitrate
and oxalates that can result from nitrates in forages, especially if drought
conditions accrue during a period of heavy nitrate uptake by plant (Sleugh
et al., 2001). Similarly it is reported that although amaranth
has some potential for use as forage, it is important to consider the
potential for accumulation of excessive NO3 in the leaves due
to high soil N. Leaf NO3 and certain other leaf properties
increased in response to fertilizer rate of 50 and 100 kg N ha-1.
But, the leaf NO3 levels fell rapidly as the season progressed
(Myers, 1998). Generally, nitrogen uptake seems to be very efficient in
amaranth. Without N fertilization, still 140 kg N ha-1 were
taken up; more than double the amount present in the soil at sowing. This
clearly exceeds comparable values for wheat and barley (Schulte et
al., 2005). Differences in N use have been reported as function of
genotype, N fertilizer timing and other factors, suggesting considerable
opportunities for improving NUE by managing cropping system components
(Lopez-Bellido et al., 2006). Report that the time of fertilizer
N applications has a significant effect on the uptake of fertilizer N
by the crop and the resulting partitioning of added N between soil and
plant (Limaux et al., 1999). Moreover, the efficiency of N fertilizer
use when applied as a topdressing in wheat is influenced by timing and
fertilizer rate. Perhaps even more important than the optimum rate to
use is the timing and splitting of nitrogen application. Splitting of
N fertilizer application has been suggested as a strategy to improve crop
N use efficiency (Lopez-Bellido et al., 2005).
From another point of view, for many producers, weed
control is their biggest problem, because herbicides are not presently
available for weed control in amaranth, weed control is accomplished with
change in agronomic practices. For example, manipulation of crop fertilization
is a promising cultural practice to reduce weed interference in crop (Angonin
et al., 1996). Although nutrients clearly promote crop growth,
in some cases, fertilizers benefit weeds more than crops. The increase
in weed competition at higher N rate has been suggested to be related
to an increase in the efficiency of nutrient accumulation and use by weed
(Di Tomaso, 1995). Moreover, N application may influence the composition
of the weed flora, suggesting that the effect of N fertilizer is not direct
but depends on the density and competitiveness of the crop (Scursoni and
Arnold, 2002).
There is only limited information about amaranth agronomic
characters in Asia. However, sensitivity of Amaranth cultivars to high
N availability, absent of specific herbicide and different response of
amaranth and weed to N fertilizer are some of the most important agronomic
problems for this crop. Therefore, the objective of this study was to
evaluate of how N splitting methods influence on Amaranth cultivars yield,
as well as its effects on weed community.
MATERIALS AND METHODS
This field experiment was carried out during the two
successive summer seasons of 2005 and 2006 at the experimental farm of
Agricultural Faculty of Shahid Chamran University, Ahvaz, Iran (31°N,
48°E, with elevation at 20 m). The soil texture of the experimental
site was clay loam. Mean air temperature from June to September was 40°C,
with no precipitation in this period. The experimental design was a randomized
complete block with a split plot arrangement with three replications and
nine plots per replication. The main plots were devoted to amaranth cultivars
while the sub-plots were devoted to N splitting. The area of the sub plot
was 13.5 m2 consisting of six rows 75 cm width and 3 m length.
Plant population was 130000 plants ha-1. The amaranth cultivars
used were A. cruentus cv. A mont and Trigin-G6 and A. hypochondriacus
cv. Plainsman that were planted and harvested on 23 July and 2 October,
respectively. N splitting was applied in various proportions among planting,
12th leaf appearance and stem elongation including: 25-0-75% (Common);
33-33-33% (Equal) and 25-50-25% (Semi-equal) distribution. Nitrogen fertilizer
was applied at rate of 110 kg N ha-1. The normal agricultural
practices for growing amaranth were followed as recommended by Thomas
Jefferson Agricultural Institute, Columbia, MO. Plant harvest carried
out manually at the flowering stage. Samples were dried before weighing.
Above ground biomass yield, leaf and stem weight, protein content (%)
and plant height were determined for each plot. Weeds were sampled at
two weeks after each N splitting treatment. All the weeds in 1 m2
quadrate per plot were removed by hand, sorted by species, counted, dried
and weighed. Total weed density and biomass (i.e., weed m2),
total density and biomass of broadleaf and annual grass weed species and
weed dominant species were determined. Data were processed by the analysis
of variance the MSTAT-C program and treatment means were separated with
Duncan test at p<0.05 (average means of two years data was used in
tables).
RESULTS AND DISCUSSION
Forage yield: All forage yield parameters significantly changed
depending on cultivars and N splitting application (Table
1). Trigin and plainsman cultivars with commonly and semi-equal
N splitting had the highest and lowest plant height, respectively. In
addition to the effect of amaranth cultivars, the plant height value
had the lowest response to the two-part N splitting than the three parts
N splitting. Trigin had the greatest plant height in all N splitting
methods. In contrast, plainsman was less sensitive to N splitting for
this factor. The stem and leaf weight were found highest for Trigin
with equal N splitting than other treatments. It`s indicated that more
than genotype effect (i.e., amaranth cultivars), the equal distribution
of N topdressing had a clear influence on better nutrient absorption
and vegetative growth in amaranth. Response of Plainsman to N splitting
was very lower than Amont and Trigin cultivars that were similar behavior
to the plant height for those cultivars. Elbehri et al. (1993)
indicated that plant height proved to be very responsive to N fertilization.
Similarly, Myers (1998) cited Amaranthus cruentus L. was the
tallest cultivar, followed by Plainsman and its plant height was particularly
responsible to N. Also, in many cases, stem weight was higher than leaf
weight, the exception being Amont and Plainsman with semi-equal N distribution.
Some researcher had found that higher dry matter content
Table 1: |
Forage yield and yield components of
amaranth cultivars as affected by N splitting methods |
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Means with the same letter(s) within
the column are not significantly different at 5% probability level |
in the flowering stage (especially higher stem weight) indicates the
ability of plants to produce higher total dry matter (Pospisil et al.,
2006). However the data here indicated that the highest and
lowest leaf weight and leaf number were not obtained from similar treatments
(Table 1), so, leaf thick change in response to these
differences (data not shown). These data underlines the need to take into
account interaction between genotype x agronomic methods and showed that
some agronomic methods (i.e., N splitting) have different effects on crop
genotype (i.e., amaranth cultivars) and vice versa.
Forage yield of amaranth cultivars showed a different response to N splitting
(Table 1). The highest yield quantity (i.e., 31 t ha-1)
was obtained by Trigin with equal distribution of N topdressing, but it`s
reduced by change in N splitting methods (i.e., 32 to 15 t ha-1).
So, Trigin cultivar was very sensitive to N splitting pattern. In contrast,
forage yield of Plainsman was unaffected by N splitting methods (i.e.,
the lowest among the three cultivars). In the present experiment, Trigin
with the equal N splitting had the greatest forage yield. This periphery
can be attributed to both higher stem weight (i.e., 1671 g m-2)
and leaf weight (i.e., 1132 g m-2) compared to other yield
parameters. These results are in general agreement with other studies
that emphasize on the effect of genotype and agronomic practices on crop
yield (Henderson et al., 2000; Myers, 1996; Stordahl et al.,
1999), but also studies amaranth in tropical regions have shown inconsistent
yield responses to N availability, reflecting the diversity of environments
and conditions under which the studies have been conducted (Myers, 1998).
Although, Trigin with equal N splitting had the highest
protein content (similar to its forage yield), Plainsman with semi-equal
N distribution also had protein content (%) just as much as Trigin with
equal N splitting, in spite of its lowest forage yield. It seemed that
leaf weight was more effective than leaf number in protein content (%).
However, it is reported that protein content (%) of amaranth cultivars
was affected by both leaf weight and number (Sleugh et al., 2001).
In fact, Trigin with equal N splitting was the best treatment for yield
quantity; Trigin with both common and equal along with Plainsman with
semi-equal N splitting were the best treatments for yield quality; but
it was just Trigin with equal N splitting that proved significantly superior
for both yield quality and quantity. Some of these differences were due
to individual genotype effects and others associated with N splitting
methods. In other words, with managing of N application in time, forage
quality could be improved not only in high yielding cultivar (i.e., Trigin)
but also in lower yielding cultivar (i.e., Plainsman). Similarly, it is
reported that the forage nutritive value of amaranth is equal to or better
than commonly used forages, but quality parameters of amaranth cultivars
(i.e., protein content and dry matter digestibility) were different (Pospisil
et al., 2006; Schulte et al., 2005). Walters et al.
(1988) showed that forage quality of several amaranth accessions declined
linearly with changing in nitrogen availability levels. This suggested
that nitrogen management could be an option in improving the forage quality
of amaranth. The positive effect of splitting N fertilizer was also reported
by Limaux et al. (1999) and Lopez-Bellido et al. (2006).
Weed dynamic: Amaranth cultivars and N splitting had a significant
effect on weed community (Table 2). Maximum broadleaf
weed density was obtained in Plainsman with semi-equal N splitting. Also,
semi-equal N distribution method provided the highest broadleaf weed biomass
in all amaranth cultivars. For each cultivar, the greatest broadleaf weed
biomass was achieved in the highest broadleaf weed density treatment.
Total weed density and biomass were greatest in Plainsman with semi-equal
N treatment that may be related to agronomic traits of individual amaranth
cultivar. Because this cultivar (i.e., Plainsman) had the lowest plant
height, leaf number, leaf weight and also its canopy was closed later
than the others. Therefore, poor establishment of Plainsman associated
with semi-equal distribution of N, thus probably contributed most to increase
in emergence of total weed species at this treatment. It appears that
the
Table 2: |
Effect of N splitting methods on the
weed density and biomass in amaranth cultivars |
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Means with the same letter(s) within
the column are not significantly different at 5% probability level |
earlier N is available, the more beneficial it is for
crop`s competitive ability. In contrast, if N is available at late crop
stage, the weed`s growth is favored (Scursoni and Arnold, 2002). This
situation will exceed for crop like amaranth which grows slowly during
the first few weeks and plant growth is not vigorous early in the season
(Myers, 1998). Similarly, split application of N fertilizer may be a useful
practice for managing weed in sweet corn. Early-season soil N levels are
kept intentionally lower in a split application management system because
sweet corn demand for N at this time is low, whereas the potential for
loss of excess N from the system is high (Davis and Liebman, 2001). In
another study, it was reported that the split application of nitrogen
caused slightly higher increases of sterile oat dry weight and total nitrogen
and greater grain yield reduction of wheat grown with oat, compared to
that of a single application (Dhima and Eleftherohorinos, 2001).
Weed dominant species: More scrutiny evaluation of weed communities
showed that cultural approaches (amaranth cultivars and N splitting) also
had a significant effect on diversity of dominant weed species. In most
N splitting methods, Plainsman had the greatest density and frequency
of broadleaf weed dominate species (Table 3). Also, this
amaranth cultivar with semi-equal N treatment had a higher density and
biomass of weed dominate species than other treatments. Evidently, the
presence of unfavorable amaranth cultivar (Plainsman), in spite of N splitting
methods, resulted in just one weed species (Chenopodium album L.)
became dominant in broadleaf weed community with the same phenological
stage (i.e., in the budding stage). Conversely, in more favorable amaranth
cultivars (i.e., Amont and Trigin), agronomic traits with a concomitant
N splitting methods resulted in diversification of dominant broadleaf
species depending on density, biomass and phonological stage. Therefore,
it`s remarkable that the influence of N splitting methods on dominant
broadleaf community was higher in good amaranth cultivar stands in comparison
with the poor ones. These results are in general agreement with other
studies indicating that changes in weed community composition are the
result of selection pressures imposed by agronomic practices (Derksen
et al., 2002). For example, the ability of a species to better
utilize available nutrients can also provide an advantage in competition
for water and light. Therefore, its can be dominant (Di Tomaso, 1995).
Also, it is reported that crop cultivars vary in a number of developmental
characteristics, including stature, canopy development and leaf parameters.
These qualities can have a dramatic effect on competitiveness in the presence
of weed species (Angonin et al., 1996; Di Tomaso, 1995). Other
research has shown that the level of N availability, through its effect
on weed growth and the resultant seed rain, potentially could influence
the species composition of weed community. Therefore, agronomic practices
that influence the competitive ability of a crop also can select against
less competitive weed species (Stevenson et al., 1997).
Dominant annual grass weed species was also affected by amaranth cultivars
and N splitting treatments (Table 4). Under such conditions,
the highest density and biomass of weed dominant species with frequency
of 70.9 and 84.62% were obtained in Plainsman cultivar with semi-equal
N treatment, respectively. Data showed that annual grass dominant species
was more affected by amaranth cultivars than N splitting methods, because
each amaranth cultivar had a specific weed dominant species (Sorghum
halepense L. in Amont, Cyperus rotundus L. Trigin and Echinochloa
crus-galli (L.) Beauv. in Plainsman). Although each amaranth cultivar
had an individual dominant weed species, their phenological stages were
different. These kinds of responses could be attributed to the effect
of N splitting method on pattern of N availability to weeds. In other
words, varying in N availability led to different weed phenology. These
results are in the same line of the finding reported that weed communities
are constantly evolving in response to crop management practices. Fertilization
alters soil fertility,
Table 3: |
Dominant broadleaf weed species parameters
in amaranth cultivars as affected by N splitting methods |
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Means with the same letter(s) within
the column are not significantly different at 5% probability level |
Table 4: |
Dominant annual grass weed species parameters
in amaranth cultivars as affected by N splitting methods |
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Means with the same letter(s) within
the column are not significantly different at 5% probability level |
which affects not only crop growth but also composition
and growth of associated weeds. Therefore, understanding the shifts in
weed community composition under different fertilization availability
would help in designing effective crop management program (Yin et al.,
2005). Other studies suggested that since seed production is correlated
with individual biomass, the species adapted to a form of N availability
would produce more offspring than other weeds and increase in abundance
in the weed community (Angonin et al., 1996).
CONCLUSION
The results of this research indicated that amaranth
with production of high quality and quantity of forage yield can be established
as a prominent and profitable alternative forage crop in our cropping
systems. Amaranth cultivars with different agronomic traits were affected
by N splitting methods. Trigin cultivar and Equal N splitting produced
highest forage yield (i.e., 31.2 t ha-1) and protein content
(i.e., 16%), respectively. Also, it was observed that weed flora was changed
depending on amaranth cultivars and N splitting methods. Commonly and
Semi-equal N distribution, were more favorable for weeds than crops growth,
respectively. In addition, weed phenology was very responsive to N splitting
methods. These findings indicate that some common agronomic practices
although obviously useful for crop yield will also stimulate weed infestation,
too. Therefore, crop production efficiencies can be gained through appropriate
fertilizer timing methods and support this concept that producers could
enhance crop yield and concomitantly reduce weed problem by choosing more
conscious agronomic practices.
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