151103-PD-2016 PLANTA DANINHA

SÃO MIGUEL, A.S.D.C. et al. Cover crops in the weed management in soybean culture
(9 páginas) PROVA GRÁFICA
1

SOCIEDADE BRASILEIRA DA
CIÊNCIA DAS PLANTAS DANINHAS ISSN 0100-8358 (print)
<http://www.sbcpd.org> 1806-9681 (online)

Article COVER CROPS IN THE WEED MANAGEMENT IN SOYBEAN

CULTURE
Culturas de Cobertura no Manejo de Plantas Daninhas na Cultura da Soja
SÃO MIGUEL, A.S.D.C.1*
PACHECO, L.P.1 ABSTRACT - The objective of this work was to evaluate the effect of cover crops on
SOUZA, E.D.1 weed suppression in no-tillage soybean production systems in Rondonopolis, Mato
Grosso. The experiment was carried out in an experimental area and consisted of the
SILVA, C.M.R.1 evaluation of nine cover treatments and soil management in a randomized complete
CARVALHO, Í.C.1 block design. The treatments were: NT fallow, CT fallow, Crotalaria spectabilis,
Crotalaria breviflora, maize + Crotalaria spectabilis, Pennisetum glaucum,
Urochloa ruziziensis, Cajanus cajan, sunflower + Urochloa ruziziensis, Stylosanthes,
Vigna unguiculata, Urochloa brizantha, maize + Urochloa ruziziensis. The
evaluations were carried out before the desiccation for soybean sowing in the crops
(10/23/2014) and (09/21/2015), before the post-emergence of soybean (09/12/2014)
and (12/11/2015) and in the second season (12/06/2015). The useful area was 5 x 5 m
and all weeds were counted and identified, but only the four species with the largest
population were collected. The weeds evaluated were: Digitaria horizontalis,
Digitaria insularis, Porophyllum ruderale and Tridax procumbens. Fallow treatments
presented higher weed populations in relation to the others, in all periods of
evaluation. Digitaria horizontalis presented the highest phytomass production in
most seasons. The production systems with Urochloa ruziziensis, Pennisetum
glaucum, Crotalaria spectabilis and intercropped with maize + Urochloa ruziziensis,
sunflower + Urochloa ruziziensis and maize + Crotalaria spectabilis were the best
alternatives for integrated weed management, reducing the incidence and increasing
control of the main species that were detected during the conduction of the experiment.

Keywords: Glycine max, no-till system, weed community, suppression.

RESUMO - O objetivo deste trabalho foi avaliar o efeito de culturas de cobertura

* Corresponding author: na supressão das plantas daninhas em sistemas de produção de soja sob plantio
<andressadallacort@hotmail.com> direto, em Rondonópolis, Mato Grosso. O experimento foi realizado em área
experimental e consistiu na avaliação de nove tratamentos de cobertura e manejo
Received: November 29, 2016 do solo em delineamento de blocos casualizados. Os tratamentos foram: pousio
Approved: April 26, 2017 PD, pousio PC, Crotalaria spectabilis, Crotalaria breviflora, milho + Crotalaria
spectabilis, Pennisetum glaucum, Urochloa ruziziensis, Cajanus cajan, girassol +
Planta Daninha 2018; v36:e18172534 Urochloa ruziziensis, Stylosanthes, Vigna unguiculata, Urochloa brizantha e milho
+ Urochloa ruziziensis. As avaliações foram realizadas antes da dessecação para
Copyright: This is an open-access semeadura da soja nas safras (23/10/2014 e 21/09/2015), antes da pós-emergência
article distributed under the terms of the da soja (09/12/2014 e 12/11/2015) e na safrinha (12/06/2015). A área útil foi de
Creative Commons Attribution License, 5 x 5 m, e foram contabilizadas e identificadas todas as plantas daninhas, porém
which permits unrestricted use, somente as quatro espécies com maior densidade populacional foram coletadas.
distribution, and reproduction in any As plantas daninhas avaliadas foram: Digitaria horizontalis, Digitaria insularis,
medium, provided that the original Porophyllum ruderale e Tridax procumbens. Os tratamentos com pousio
author and source are credited. apresentaram maior população de plantas daninhas em relação aos demais, em

1
Universidade Federal de Mato Grosso (UFMT), Rondonópolis-MT, Brasil.

Doi: 10.1590/S0100-83582018360100072
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SÃO MIGUEL, A.S.D.C. et al. Cover crops in the weed management in soybean culture 2

todas as épocas de avaliação. Digitaria horizontalis apresentou a maior produção de fitomassa na

maioria das épocas de avaliação. Os sistemas de produção com Urochloa ruziziensis, Pennisetum
glaucum, Crotalaria spectabilis e os consórcios com milho + Urochloa ruziziensis, girassol + Urochloa
ruziziensis e milho + Crotalaria spectabilis foram as melhores alternativas para o manejo integrado de
plantas daninhas, por reduzirem a incidência e aumentarem o controle das principais espécies que
foram detectadas durante a condução do experimento.

Palavras-chave: Glycine max, sistema plantio direto, comunidade infestante, supressão.

INTRODUCTION

Soybean is one of the oleaginous plants of major interest in the world and its development is
often affected by various factors, among them weeds, which compete with soybean for water,
light and nutrients, causing reduced grain yields and difficulties in harvesting (Pittelkow et al.,
2009). The species known as Jamaican crabgrass (Digitaria horizontalis), sourgrass (Digitaria
insularis), couvinha (Porophyllum ruderale) and coatbuttons (Tridax procumbens) are difficult to
control in soybean, maize and millet crops (Pittelkow et al., 2009; Meschede et al., 2007; Martins
et al., 2016). As a result, there is a need for techniques that can be used to assist in the chemical
control of integrated weeds management.
The no-tillage cropping system (NT) is an effective soil management alternative for weeds
suppression by means of the phytomass produced by cover plants. The species of cover plants
used in the production systems need to establish quickly and produce adequate amounts of
phytomass to cover the soil. Maize growing systems intercropped with U. ruziziensis P. glaucum
and Cajanus cajan have a phytomass production capacity of 10,000 to 16,000 kg ha-1 (Carneiro
et al., 2008; Pacheco et al., 2013; Queiroz et al., 2016). Single crops with Pennisetum glaucum,
Urochloa ruziziensis and Crotalaria spectabilis or intercropped with annual cultures can be effective
in suppressing the infesting community.
In the NT system, weeds control is achieved by the phytomass of cover plants, which acts as
a physical barrier to the passage of sunlight and makes weeds’ seed germination and seedlings
growth difficult (Borges et al., 2013). Cover crops also have allelopathic effects on weeds, in their
seeds or seedlings, through root exudation or during phytomass decomposition, interfering
with the plants growth and development (Borges et al., 2013). Some studies with sorghum
identified allelopathic action of this species, which has high phytotoxic activity as photosystem
II inhibitors, acting similarly to the triazine group of herbicides (Czarnota et al., 2003; Santos
et al., 2012).
Furthermore, an even bed of plant cover on the soil is capable of diminishing weeds
infestations and improving the soil structure and fertility (Cosdta et al., 2015). To promote these
improvements, the cover species in cerrado lands need to adapt to the biome edaphoclimatic
conditions and produce large amounts of phytomass. Therefore, knowing the behavior of each
cover plants species is necessary for an optimal production in monocropping, crop rotation or
intercropping farming systems (Meschede et al., 2007) as well as for weeds control. This study
aimed to evaluate the cover plants’ effectiveness in suppressing weeds in no-till soybean
production system.

MATERIAL AND METHODS

The experiment was carried out in 2013/2014, 2014/2015 and 2015/2016 crop years at the
Federal University of Mato Grosso - UFMT, Campus of Rondonópolis (16o27’75" S and 54o34’55" O
and altitude of 292 meters). The soil in the area is Dystrophic Oxisol (Embrapa, 2006),
whose chemical and physical attributes are described on Table 1. The climate, according to
Köppen classification, is Cwa, with well-defined dry and rainy seasons, the rainy season
beginning in October and ending in May (Souza et al., 2013). Precipitation rates and mean
maximum and minimum air temperatures during the experiment conduction are described in
Figure 1.

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SÃO MIGUEL, A.S.D.C. et al. Cover crops in the weed management in soybean culture 3

Table 1 - Physicochemical attributes of Dystrophic Oxisol prior to the experiment’s establishment

pH O.M. P K Ca Mg Al H+Al CEC V

Depth
(CaCl2) (g kg-1) -3
(mg dm ) 3
(cmolc dm ) (%)
00-10 cm 4.1 17.6 5.4 55 0.5 0.2 1.2 6.8 7.6 11.0
10-20 cm 4.0 19.9 1.4 49 0.2 0.1 1.4 7.2 7.6 5.6
20-40 cm 4.1 13.7 0.2 31 0.3 0.1 1.3 6.2 6.7 7.2
P = available phosphorus; exchangeable K+, Ca2+ and Mg2+; H+Al = potential acidity; CEC = cation exchange capacity at a pH value of 7.0;
V = base saturation; O.M. = organic matter. P: extraction method of Mehlich-1.

Figure 1 - Monthly and accumulated precipitation and minimum and maximum average air temperatures during the conduction of
the experiment in Rondonópolis-MT.

Prior to the experiment installation, the area was cleared, followed by plowing and harrowing
and manual roots removal. On Oct 08, 2013, liming was applied to the area (4,000 kg ha-1) with
Filler lime (PRNT: 99.02%), incorporated with a plow and harrow. The experiment was implemented
in a randomized block design with nine treatments (Table 2) and four replications. Each
experimental plot was 7 m wide x 9 m long.
In all production systems, soy was cultivated in two crop seasons. After being harvested, the
second season began, when annual cereal crops were grown (60,000 maize plants ha-1, 55,000
sunflower plants ha-1, 160,000 Vigna unguiculata plants ha-1) and the following cover plants:
Pennisetum glaucum (18 kg ha-1), Urochloa ruziziensis and Urochloa brizantha (15 kg ha-1 with 60%
of cultural value), Crotalaria breviflora (17 kg ha-1), Crotalaria spectabilis (15 kg ha-1), Cajanus cajan
(40 kg ha-1) and Stylosanthes capitata + S. macrocephala (8 kg ha-1), as described in Table 2. The
systems with single cover crops were implemented with spacing of 0.45 m between rows; in the
intercropping systems, annual crops (maize and sunflower) were implemented with spacings of
0.45 m, and the intercropped cover crops were sowed in between rows. All systems during the
second season were sowed and fertilized manually. As can be seen in Table 2, some treatments
(S4, S7, S8 and S9) had rotation of species sowed between the 2014 and 2015 second seasons, for
systems diversification. Fallow treatments (S1 and S2) are the controls.

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Table 2 - Characterization of production systems for sowing second season soybean seeds and after 2014/15 and 2015/16 harvests

Systems 2014 Second season 2015 Second season

S1: NT fallow NT fallow
S2: CT fallow CT fallow
S3: Crotalaria spectabilis Crotalaria spectabilis
S4: Crotalaria breviflora Maize + C. spectabilis
S5: Pennisetum glaucum ADR 8010 Pennisetum glaucum ADR 300
S6: Urochloa ruziziensis Urochloa ruziziensis
S7: Cajanus cajan Sunflower + U. ruziziensis
S8: Stylosanthes capitata + S. macrocephala Vigna unguiculata
S9: Urochloa brizantha cv. Marandu Maize + U. ruziziensis
NT - No-till system; CT- Conventional till system with plow + harrow.

The soybean cultivar TMG 132 RR was sowed in November 2013, with spacing of 0.45 m
between rows and density of 12 plants m-1. After the soybean harvest, the cover crops of the
2013/2014 crop year were sowed. In the beginning of the 2014/2015 crop, in October, all cover
crops were desiccated using glyphosate herbicides (5 L ha-1) and 2.4-D (1.5 L ha-1). Afterwards,
the soybean cultivar ANTA 82 RR was sowed on the remaining plant residues deposited on the
soil, with a distribution of 29 plants m-1 and spacing of 0.45 m between rows. Soybean was
harvested in February 2015, and again cover crops were sowed manually. The soybean cultivar
used in 2015/16 was TMG 1175 RR, with a density of 25 plants m-1. In 2015/16 crop, soybean
was sowed on Oct. 29, 2015 and harvested on Feb. 16, 2016.
The fertilization used in soybean in both crop seasons was 120 kg ha-1 of P2O5 and 22 kg ha-1
of N, via monoammonium phosphate in the sowing grooves, and 100 kg ha-1 of K2O via potassium
chloride, half of it scattered over during pre-sowing and the rest when the soybean was in the V4
phenological stage. For all soybean plantations, the seeds were inoculated with liquid inoculant
(Cell Tech HC® Nitragin) at a dosage of 150 mL of inoculant per 50 kg of seeds, exhibiting a
bacterial concentration of 3x109 CFU per mL, with Bradyrhizobium japonicum bacteria (SEMIA
5079 and 5080). In the annual crops sowed during the second season (maize, V. unguiculata and
sunflower), fertilizations were made as recommended by Souza and Lobato (2004), while in the
parcels of land where single crops of cover plants were grown, no fertilizers were used.
The evaluations were carried out before desiccation for soybean sowing in the 2014/2015
(Oct. 23, 2014) and 2015/2016 crop years (Sept. 21, 2015), prior to application of the selective
herbicide in post-emergence of soybean in 2014/2015 (Dec. 09, 2014) and 2015/2016 (Nov. 12,
2015) and in the second season (June 12, 2015). In each parcel, a 5 x 5 m of useful area was
assessed, where all weed species were counted and identified, but only the four species with the
largest population amount were collected for phytomass determination. The four species were
cut close to the ground and dried in a forced-circulation oven at 65 oC during 72 hours;
subsequently, manual cleaning of residues was made to remove adhered soil and obtain dry
phytomass. Soybean grains yield was assessed by harvesting the plants in two 2 meter long
rows, expressed in kg ha-1 (standardized at 13% moisture).
The main weeds evaluated in the experimental area were Jamaican crabgrass (Digitaria
horizontalis), sourgrass (Digitaria insularis), couvinha (Porophyllum ruderale) and coatbuttons (Tridax
procumbens). The parameters used for the main weeds were density (plants m-2), phytomass
(kg ha-1), incidence:
Population of evaluated species
x 100 , expressed in percentage, and control effect:
Total population

Population of evaluated species x 100

− 100 , also expressed in percentage.
Average of treatement with the highest population

The results were subjected to analysis of variance, with data transformed by equation “X+1,
except for the control treatment; means were compared by Scott-Knott’s test at 5%, using SISVAR
5.4 software (Ferreira, 2008).

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RESULTS AND DISCUSSION

The studied cover crops had an influence on weeds development (Table 3). D. horizontalis
was the species that exhibited the highest population density among the assessed weed species.
Edaphoclimatic conditions with rising temperature and rains are ideal conditions for breaking
the dormancy of this seed and, consequently, its development, suppressing other species (Andrade
et al., 2000).
In the evaluation prior to the desiccation of the area in 2015 (Sept 21, 2015), D. horizonthalis
plants were not counted because they had already senesced due to water stress occurred in this
period (Figure 1) and for not actually representing the situation of the species. These results are
confirmed in the evaluation conducted during the 2015/2016 crop (Nov.12, 2015), so that after
the rains, D. horizonthalis was present in the area. The other species did not appear in the
evaluations, probably because of the production systems, which, by means of the cover crops
phytomass control or the characteristics of each species, they may have been dormant for a
while, awaiting better conditions for germination.
P. ruderale and T. procumbens weeds were more numerous in the fallow area than in the
treatments with cover crops (Table 3), which indicates that there is a greater proliferation of
these species when there is no control by the cover crops phytomass. Rizzardi and Silva (2014)
studied management strategies to prevent the emergence of weeds in soybean crop, and Martins
et al. (2016) in maize crop, reported that in fallow areas, managed with or without chemical
control, contribute to the proliferation and a more difficult control of weeds. T. procumbens was
found in fallow areas at all times, and in the evaluation at the time of desiccation for planting
soybean, it was found in the area with P. glaucum. Cover crops phytomass exerts interspecific
inhibition on weeds species (Meschede et al., 2007), either by the physical suppression effect or
by the allelochemicals released by the plant matter in decomposition or produced by the roots of
photosynthetically active crops.
In the conventional till (CT) fallow system, incorporation of plant residues reduced the density
of infesting species in most of the soybean pre- and post-emergence evaluations, when compared
to the NT fallow treatments (Table 3). Results obtained by Pacheco et al. (2016) in rice production
system in the state of Piauí corroborate the temporary effectiveness of this management practice
in the early stage of crop development.
It is worth noting that in the off-season evaluation, the CT fallow system exhibited higher
counts of the species studied, except for D. insularis, which has a slower cycle and, therefore, did
not exhibit a great number of individuals of this species (Table 3). It is known that weeds control
by conventional tillage, when soil is turned over, is temporary, only by the time that soybean is
sowed. In addition, with soil mechanical agitation, the seeds bank has more stimulus to germinate
and emerge, resulting in a greater density of weeds in the off-season. So, the use of this technique
is not recommended because it causes an increased infestation and increased seeds bank in
the area over time.
The use of U. ruziziensis as cover crop promoted a lower incidence of weeds in most of
the times and species evaluated (Table 3). These results were obtained because this cover
species is able to produce a great amount of phytomass. Pacheco et al. (2016) obtained, in dry
rice cultivation systems with U. ruziziensis, amounts between 10,800 and 12,500 kg ha-1 of
phytomass for weeds control. Cover crops with this characteristic are vitally important for
the integrated management of weeds, because it reduces weed infestations and the use of
herbicides.
Gomes Jr. And Christoffoleti (2008) and Monquero et al. (2009) reported that the amount of
phytomass produced by cover crops can interfere with the process of germination of weed seeds
by reducing the soil temperature. This favors proliferation of soil micro- and mesofauna, which
feeds on the seeds or colonizes them, and can also prevent the passage of light that is required
for cellular histodifferentiation of positive photoblastic species. Mondo et al. (2010) examined
four species of the genus Digitaria and found that D. horizontalis has positive photoblastism,
differently from D. insularis, which exhibited negative photoblastism, which explains the high
density of D. horizontalis in the area.

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Table 3 - Density and phytomass of four weeds at different times and cropping systems for growing soybean. Mato Grosso,
2014/2015 and 2015/2016

Oct 23, 2014 Dec 09, 2014 June 12, 2015 Sept 21, 2015 Nov 12, 2015
System Density Phytomass Density Phytomass Density Phytomass Density Phytomass Density Phytomass
(m-²) (kg ha-1) (m-²) (kg ha-1) (m-²) (kg ha-1) (m-²) (kg ha-1) (m-²) (kg ha-1)
Digitaria horizontalis
S1 : 11.55 a 136.64 a 8.72 a 15.63 a 17.44 a 1171.21 a -- -- 91.53 a 183.66 a
S2 : 11.49 a 150.13 a 4.31 a 5.56 a 22.13 a 1454.44 a -- -- 56.50 b 142.82 a
S3 : 0.00 b 0.00 b 3.92 a 4.12 a 0.05 b 1.07 b -- -- 28.75 c 71.39 b
S4 : 0.27 b 12.18 b 4.39 a 8.63 a 0.05 b 3.38 b -- -- 8.65 d 21.79 b
S5 : 0.44 b 10.01 b 0.97 a 1.26 a 0.00 b 0.00 b -- -- 8.85 d 17.37 b
S6 : 0.00 b 0.00 b 0.64 a 0.41 a 0.00 b 0.00 b -- -- 14.45 d 32.49 b
S7 : 0.00 b 0.00 b 2.10 a 8.73 a 3.07 b 93.25 b -- -- 43.90 b 170.91 a
S8 : 0.00 b 0.00 b 0.24 a 0.07 a 0.00 b 0.00 b -- -- 29.75 c 69.57 b
S9 : 0.19 b 0.97 b 6.36 a 7.58 a 0.00 b 0.00 b -- -- 10.19 d 25.31 b
VC (%) 17.4 43.78 45.98 61.99 31.6 61.09 -- -- 29.77 35.92
Digitaria insularis
S1 : -- -- -- -- 0.16 a 16.67 a 0.57 a 31.81 a -- --
S2 : -- -- -- -- 0.09 a 18.05 a 0.37 a 16.98 a -- --
S3 : -- -- -- -- 0.08 a 6.92 a 0.42 a 2.87 b -- --
S4 : -- -- -- -- 0.00 a 0.00 a 0.05 b 0.89 b -- --
S5 : -- -- -- -- 0.00 a 0.00 a 0.11 b 2.74 b -- --
S6 : -- -- -- -- 0.00 a 0.00 a 0.00 b 0.00 b -- --
S7 : -- -- -- -- 0.00 a 0.00 a 0.00 b 0.00 b -- --
S8 : -- -- -- -- 0.00 a 0.00 a 0.03 b 0.83 b -- --
S9 : -- -- -- -- 0.00 a 0.00 a 0.00 b 0.00 b -- --
VC (%) -- -- -- -- 4.8 92.5 10.64 66.43 -- --
Porophyllum ruderale
S1 : 1.52 a 18.87 a -- -- 0.51 b 47.41 b 0.14 a 2.31 a -- --
S2 : 0.89 b 13.95 a -- -- 0.88 a 106.48 a 0.32 a 13.05 a -- --
S3 : 0.07 c 0.38 b -- -- 0.22 c 5.43 c 0.01 a 0.21 a -- --
S4 : 0.00 c 0.00 b -- -- 0.00 c 0.00 c 0.00 a 0.00 a -- --
S5 : 0.60 b 22.61 a -- -- 0.06 c 0.43 c 0.09 a 0.55 a -- --
S6 : 0.00 c 0.00 b -- -- 0.00 c 0.00 c 0.00 a 0.00 a -- --
S7 : 0.00 c 0.00 b -- -- 0.03 c 0.35 c 0.00 a 0.00 a -- --
S8 : 0.00 c 0.00 b -- -- 0.02 c 0.35 c 0.00 a 0.00 a -- --
S9 : 0.00 c 0.00 b -- -- 0.00 c 0.00 c 0.00 a 0.00 a -- --
VC (%) 12.6 45.76 -- -- 5.25 60.59 7.12 72.32 -- --
Tridax procumbens
S1 : 0.53 a 4.05 a -- -- 0.14 a 31.73 a 0.24 a 11.65 a -- --
S2 : 2.51 a 51.70 a -- -- 0.15 a 32.98 a 0.16 a 11.15 a -- --
S3 : 0.00 a 0.00 a -- -- 0.00 b 0.00 b 0.00 b 0.00 b -- --
S4 : 0.00 a 0.00 a -- -- 0.00 b 0.00 b 0.00 b 0.00 b -- --
S5 : 0.00 a 0.00 a -- -- 0.00 b 0.00 b 0.03 b 0.57 b -- --
S6 : 0.00 a 0.00 a -- -- 0.00 b 0.00 b 0.00 b 0.00 b -- --
S7 : 0.00 a 0.00 a -- -- 0.00 b 0.00 b 0.00 b 0.00 b -- --
S8 : 0.00 a 0.00 a -- -- 0.00 b 0.00 b 0.00 b 0.00 b -- --
S9 : 0.00 a 0.00 a -- -- 0.00 b 0.00 b 0.00 b 0.00 b -- --
VC (%) 36.83 153.38 -- -- 3.88 105.71 5.1 73.51 -- --
Systems: S1- NT fallow; S2- CT fallow; S3- Crotalaria spectabilis; S4- C. breviflora (2014) and maize + C. spectabilis (2015); S5 P. glaucum
ADR 8010 (2014) and ADR 9010 (2015); S6- U. ruziziensis, S7- Pigeon beans (2014) and sunflower + U. ruziziensis (2015); S8- Stylosanthes
Campo Grande (2014) and cowpea bean (2015); S9- U. brizantha (2014) and maize + U. ruziziensis (2015). Evaluations: Oct 23, 2014 –
Prior to desiccation for growing soybean in 2014/15; Dec 09, 2014 – Prior to application of selective herbicide at soybean post-emergence
in 2014/15; June 12, 2015 – Second season; Sept 21, 2015 – Prior to desiccation for growing soybean in 2015/16; Nov 12, 2015 – Prior
to application of selective herbicide at soybean post-emergence in 2015/16. Means followed by same letters in column do not differ
statistically from each other by the Scott-Knott’s test (P<0.05).

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D. horizontalis exhibited a higher phytomass production compared to the other species in

most of the evaluation periods in all treatments (Table 3). The fast growth and development of
this species makes it capable of accumulating phytomass very quickly to cover the soil surface,
which results in more competition with other species and soybean plants if there is no proper
control. Pittelkow et al. (2009) observed that high weed infestations affect the number of pods per
plant, grain yield and reduced accumulation of dry matter during the soybean cycle, and the
damages were higher as the weeds infestation levels increased.
P. ruderale, T. procumbens and D. insularis exhibited lower accumulation of phytomass because
of lower population density (Table 3). These weeds have low individual weights and a slow
development stage, which results in more time to accumulate phytomass, propagate and increase
their populations. The highest weeds phytomass amount was found in the fallow area, due to the
lack of phytomass of cover crops to exert control on the development of these species. In a study
conducted in Cáceres-MT, Meschede et al. (2007) found similar results for fallow, obtaining high
weeds phytomass values.
With respect to incidence, the highest value found was 11.1% for D. insularis in the evaluation
that preceded desiccation for soybean sowing (2015/2016) in the area with C. spectabilis. In the
other evaluations, the highest incidences were found for D. horizontalis (Table 4), which exhibited
the highest infestation rate in all treatments for having a high seeds germination rate and fast
establishment, which becomes a control problem.
Machado et al. (2006) reported that D. insularis has slow initial growth and this can diminish
its competition with the other weed species, but it may become the dominant species if the
herbicide dosage is not sufficient to control it. This trait of the species is confirmed by the data
found in the evaluation conducted before management desiccation (Sept 21, 2015), when chemical
control had not been used yet, and D. insularis exhibited high incidence and dominance over the
other species.
Concerning the control variable, the treatments that influenced most in the reduction of
weeds germination or growth were single U. ruziziensis and maize + U. ruziziensis intercropping
with 100% of control in most of the periods and species investigated (Table 4). The high amounts
of phytomass and slow decomposition of U. ruziziensis exerted a suppressive effect on the weeds
in the off-season and part of the growing season, contributing to the integrated management of
weeds in the cerrado by reducing the use of herbicides. Pacheco et al. (2011) stated that grasses
like U. ruziziensis and U. brizantha are potential cover crops to be grown in the second season
cropping systems in the cerrado, due to their high phytomass production, with values over
8,000 kg ha-1.
The treatments with P. glaucum, C. spectabilis and V. unguiculata also exhibited high rates of
control, reaching 100% in some evaluations. In the off-season evaluation, it was possible to
observe D. horizonthalis phytomass reduction and population density in these treatments
compared to the previous evaluations (Table 4). Results obtained by Meschede et al. (2007)
corroborate the results of the present study, in which P. glaucum and C. spectabilis exhibited the
smallest number of weeds per m2, which indicates a greater control of these cover crops on
weeds. These cover crops release secondary metabolites, also called phytotoxins, which are able
to prevent the seeds germination, cause a suppressive effect on the seedlings and, finally, develop
injuries in the plants’ structure and physiology, which may cause the weeds death (Golisz et al.,
2008).
With respect to the sunflower + U. ruziziensis and maize + C. spectabilis intercropping, high
rates of control of weeds were also found at the dates of evaluation (Table 4). These data indicate
the importance of intercropping in NT management systems, as well the diversity of species to
be used as cover crops, so that the spectrum of suppressive effects on weeds may be enlarged,
thus contributing to the integrated management of weeds with reduced applications of chemicals.
Alsaadawi et al. (2011), in experiment conducted in southern Bagdad, Iraq, extracted various
allelopathic substances from sunflower, which were able to control weeds and also add nutrients
to the soil, improving its fertility. Erasmo et al. (2009), in a study carried out in Jaboticabal-SP,
observed a reduction of 60% of dry matter of D. horizontalis’ roots by incorporating 30 g dm-3 of
C. spectabilis biomass to the soil.

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SÃO MIGUEL, A.S.D.C. et al. Cover crops in the weed management in soybean culture 8

Table 4 - Incidence and control of four weed species at different times and cropping systems for growing soybean. Mato Grosso,
2014/2015 and 2015/2016

Oct 23. 2014 Dec 09. 2014 June 12. 2015 Sept 21. 2015 Nov 12. 2015
System Incidence Control Incidence Control Incidence Control Incidence Control Incidence Control
(%) (%) (%) (%) (%) (%) (%) (%) (%) (%)
Digitaria horizontalis
S1: 17.81 a 76.41 b 22.54 a 0.00 b 14.81 a 80.30 b -- -- 21.85 a 0.00 d
S2: 13.45 a 0.00 c 16.57 a 87.64 a 17.55 a 0.00 c -- -- 16.95 a 84.56 c
S3: 0.00 b 100.00 a 20.48 a 88.76 a 1.47 b 99.94 a -- -- 18.95 a 92.14 b
S4: 10.38 a 99.44 a 15.31 a 87.41 a 5.00 b 99.94 a -- -- 18.86 a 97.63 a
S5: 3.50 b 99.10 a 20.52 a 97.22 a 0.00 b 100.00 a -- -- 17.14 a 97.58 a
S6: 0.00 b 100.00 a 9.00 a 98.16 a 0.00 b 100.00 a -- -- 23.85 a 96.05 a
S7: 0.00 b 100.00 a 11.65 a 93.98 a 16.44 a 96.53 a -- -- 21.10 a 88.00 c
S8: 0.00 b 100.00 a 10.00 a 99.31 a 0.00 b 100.00 a -- -- 13.60 a 91.87 b
S9: 14.71 a 99.61 a 19.47 a 81.76 a 0.00 b 100.00 a -- -- 18.00 a 97.21 a
VC (%) 56.33 1.80 46.7 12.19 44.81 4.57 -- -- 16.79 5.06
Digitaria insularis
S1: -- -- -- -- 0.13 a 0.00 b 5.23 a 0.00 c -- --
S2: -- -- -- -- 0.07 a 85.93 a 3.58 a 83.77 b -- --
S3: -- -- -- -- 2.35 a 87.50 a 11.10 a 81.58 b -- --
S4: -- -- -- -- 0.00 a 100.00 a 6.66 a 97.80 a -- --
S5: -- -- -- -- 0.00 a 100.00 a 5.00 a 95.17 a -- --
S6: -- -- -- -- 0.00 a 100.00 a 0.00 a 100.00 a -- --
S7: -- -- -- -- 0.00 a 100.00 a 0.00 a 100.00 a -- --
S8: -- -- -- -- 0.00 a 100.00 a 5.00 a 98.68 a -- --
S9: -- -- -- -- 0.00 a 100.00 a 0.00 a 100.00 a -- --
VC (%) -- -- -- -- 34.14 12.62 63.03 11.91 -- --
Porophyllum ruderale
S1: 0.02 b 0.00 d -- -- 0.00 b 85.51 c 0.02 a 88.67 c -- --
S2: 0.01 b 84.95 c -- -- 0.00 b 0.00 d 0.02 a 0.00 d -- --
S3: 0.02 b 98.84 a -- -- 0.14 a 93.75 b 0.05 a 99.22 a -- --
S4: 0.00 c 100.00 a -- -- 0.00 b 100.00 a 0.00 a 100.00 a -- --
S5: 0.05 a 90.13 b -- -- 0.03 b 98.29 a 0.05 a 92.97 b -- --
S6: 0.00 c 100.00 a -- -- 0.00 b 100.00 a 0.00 a 100.00 a -- --
S7: 0.00 c 100.00 a -- -- 0.00 b 99.14 a 0.00 a 100.00 a -- --
S8: 0.00 c 100.00 a -- -- 0.02 b 99.43 a 0.00 a 100.00 a -- --
S9: 0.00 c 100.00 a -- -- 0.00 b 100.00 a 0.00 a 100.00 a -- --
VC (%) 0.73 2.35 -- -- 1.74 3.53 1.86 1.74 -- --
Tridax procumbens
S1: 1.04 a 94.44 b -- -- 0.10 a 76.66 b 2.80 a 0.00 d -- --
S2: 2.78 a 0.00 c -- -- 0.11 a 0.00 c 1.65 a 84.11 c -- --
S3: 0.00 a 100.00 a -- -- 0.00 b 100.00 a 0.00 b 100.00 a -- --
S4: 0.00 a 100.00 a -- -- 0.00 b 100.00 a 0.00 b 100.00 a -- --
S5: 0.00 a 100.00 a -- -- 0.00 b 100.00 a 1.34 a 96.61 b -- --
S6: 0.00 a 100.00 a -- -- 0.00 b 100.00 a 0.00 b 100.00 a -- --
S7: 0.00 a 100.00 a -- -- 0.00 b 100.00 a 0.00 b 100.00 a -- --
S8: 0.00 a 100.00 a -- -- 0.00 b 100.00 a 0.00 b 100.00 a -- --
S9: 0.00 a 100.00 a -- -- 0.00 b 100.00 a 0.00 b 100.00 a -- --
VC (%) 40.99 0.77 -- -- 3.11 1.05 34.99 1.08 -- --
Systems: S1- NT fallow; S2- CT fallow; S3- Crotalaria spectabilis; S4- C. breviflora (2014) and maize + C. spectabilis (2015); S5 P. glaucum
ADR 8010 (2014) and ADR 9010 (2015); S6- U. ruziziensis, S7- Pigeon beans (2014) and sunflower + U. ruziziensis (2015); S8- Stylosanthes
Campo Grande (2014) and cowpea bean (2015); S9- U. brizantha (2014) and maize + U. ruziziensis (2015). Evaluations: Oct 23, 2014 –
Prior to desiccation for growing soybean in 2014/15; Dec 09, 2014 – Prior to application of selective herbicide at soybean post-emergence
in 2014/15; June 12, 2015 – Second season; Sept 21, 2015 – Prior to desiccation for growing soybean in 2015/16; Nov 12, 2015 – Prior
to application of selective herbicide at soybean post-emergence in 2015/16. Means followed by same letters in column do not differ
statistically from each other by the Scott-Knott’s test (P<0.05).

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SÃO MIGUEL, A.S.D.C. et al. Cover crops in the weed management in soybean culture 9

The lowest rates of weeds suppression were found in the fallow treatments (Table 4). This
was due to the absence of cover crops to exert control on weeds, which, without the inhibitory
effect of cover crops, proliferate in fallow treatments, and therefore increases the seeds bank for
the next crops, which makes control more difficult.
With regard to soybean yields, there was as a significant effect of the systems only in 2015/
2016 (Table 5). The system with Crotalaria spectabilis exhibited better results compared to the
other systems, with high control of weeds, among other factors. This weeds control minimized
interspecific competition for resources and contributed to higher yields of soybeans. In the fallow
systems, the absence of cover crops associated with the management system resulted in lower
soybeans yields. Management with spontaneous plant species and mechanical agitation of soil
showed, since the early stages of soybean growth, a high density of weeds and, consequently,
more competition between the crop and the infesting community.

Table 5 - Yields of soybean grown in rotation with annual crops and cover crops sown in second season in nine different
cropping systems in 2014/2015 and 2015/2016

Soybeans yield (kg ha-1)

Cropping 2014/2015 2015/2016
systems Crop year Crop year
2014/2015 2015/2016
S1: Soybean-NT Fallow Soybean-NT Fallow 2763ns 1889 C
S2: Soybean-CT Fallow Soybean-CT Fallow 2837 2276 B
S3: Soybean-C. spectabilis Soybean-C. spectabilis 4059 2686 A
S4: Soybean-C. breviflora Soybean-Maize + C. spectabilis 4054 2155 B
S5: Soybean-P. glaucum Soybean-P. glaucum 3349 2347 B
S6: Soybean-U. ruziziensis Soybean-U. ruziziensis 3373 2273 B
S7: Soybean-Cajanus cajan Soybean-Sunflower + U. ruziziensis 3660 2301 B
S8: Soybean-Stylosanthes capitata + S. macrocephala Soybean-V. unguiculata 3170 2425 B
S9: Soybean-U. brizantha Soybean-Maize + U. ruziziensis 2560 2051 C
VC (%) 24.26 7.67
Means followed by same letters in column do not differ from each other by the Scott-Knott’s test at 5% probability level. ns
not
significant by the F test at 5% probability.

The cropping systems with U. ruziziensis, P. glaucum, C. spectabilis and intercropping with
maize + U. ruziziensis, sunflower + U. ruziziensis and maize + C. spectabilis are good alternatives
to assist integrated weeds management, by reducing the incidence and increasing the control
of D. horizonthalis, D. insularis, P. ruderale and T. procumbens, detected in soybean growing systems
during the conduction of the experiment in the cerrado region in Rondonópolis-MT. The system
with C. spectabilis results in higher soybeans yield. With this integrated management, costs
with herbicides applications, use of implements and fuel are reduced, besides incorporating
phytomass to the system, making NT farming system an efficient method in managing
agricultural farming systems.

ACKNOWLEDGEMENTS

The authors are thankful to the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
(CAPES) for the MD scholarship granted to the first and fourth authors. To the Conselho Nacional
de Desenvolvimento Científico e Tecnológico (CNPq) for the financial support (Universal Call no.
14/2012 – Project no. 484801/2012-0) and for the productivity scholarships granted to the second
and third authors. To the Fundação AGRISUS – Agricultura Sustentável (Project no. 1604/15) for
the financial support.

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