Introduction
In Brazil, the direct seeding system is a production
model that soybean producers widely accept due to the minimum soil disturbance
and moderate use of pesticides and machinery. Thus, aiming to achieve maximum
yield in the same production area, the use of intercropping in the no-tillage
system in the crop rotation model has increased in the Cerrado, aiming to
diversify crops and reduce input costs (Ryan et al. 2012; Quintino et
al. 2016).
Thus, with the introduction of
forage species, the no-tillage system stands out due to its high dry matter production,
efficiency in recycling nutrients from the deeper layers, and nutrient
availability in the superficial layers through the straw (Crusciol et al.
2012). Thus, intercropping under no-tillage has become a promising option for
the model, as it influences the increase in the contribution of plant residues
and, consequently, the increase in organic matter and the speed of water
infiltration into
the soil, as in the use of forages from the genera Panicum and Urochloa
(Garcia et al. 2012).
To infer soil quality according
to the presence or absence of vegetation cover and, consequently, conversion to
straw, it is necessary to evaluate the biological attributes through microbial
biomass, basal soil respiration, and soil enzymatic activity. Soil microbial
biomass is the living fraction of organic matter responsible for soil
biological processes and is highly sensitive to external factors (Balota et
al. 1998; Dortzbach et al. 2013). Microbial respiration is the most
commonly used method to determine an indirect estimate of the rate of
decomposition of organic matter (Farias et al. 2018) and the enzymes β-glucosidase,
arylsulfatase, acid phosphatase, and urease are linked to the cycle of carbon
(C), sulfur (S), phosphorus (P), and nitrogen (N) and the fluorescein diacetate
(FDA) demonstrate the potential of a group of enzymes, aiming to infer
biologically more active soils (Mendes et al. 2021a).
Mendes et al. (2018)
evaluated the management systems with soybean in rotation with corn, brachiaria, and corn
intercropped with brachiaria and observed increases in the enzymes β-glucosidase
and arylsulfatase in treatments with the presence of brachiaria; thus, the
capacity of brachiaria was evident in maintaining a biologically healthier soil
under Cerrado conditions. Benetis (2014) observed in the same experiment an
increase in soybean yield in treatments with brachiaria, around 572 kg ha-1,
demonstrating the influence of biological attributes on crop yield.
Observing the sensitivity of
biological attributes and their impact on crop yield, after 21 years of studies
evaluating the state of the biological functioning of the soil, Embrapa launched the Soil
Bioanalysis (BioAS) technology, which consists of activity analysis of the
arylsulfatase and β-glucosidase enzymes associated with the S and C
cycles, respectively, as they are linked to the potential yield and
sustainability of land use (Mendes et al. 2021a).
Therefore, knowing the
importance of adopting conservation management systems based on the assumptions
that intercropping systems with brachiaria in no-tillage systems promote the
improvement of soil biological attributes, the present study aimed to evaluate
the biological attributes in soils under intercropping in two production areas
in Southwest of Goiás, Brazil.
Study areas
The study was conducted
during the 2017/2018, 2018/2019, and 2019/2020 crop seasons with soybean
cultivation in no-tillage after the cultivation of corn in monocropping and
corn and sorghum in intercropping in two locations in Southwest Goiano. One is
in Rio Verde, GO (17° 47' 53" latitude and 50° 55' 41" longitude,
altitude of 715 m), in the experimental farm of GAPES (Associated Research
Group of Southwest Goiano), and the other in the Boa Esperança farm in
Montividiu, GO (17° 26' 39" latitude and 51° 10' 29" longitude,
altitude of 821 m).
Sowing,
fertilization, handling with products (herbicides, insecticides, and
fungicides), and harvesting were carried out when necessary, adopting the same
criteria and conditions. Soil sample collections in both areas were carried out
on April 15 (the end of the rainy period) and September 18 (the end of the dry
period) in 2020.
Regarding
the chemical characteristics of the soil at the beginning of the conduction in
the experimental farm of GAPES, Ca2+, Mg2+, H+Al, and K+
were 1.41, 0.54, 3.6, and 0.11 cmoLc dm-3, respectively,
P (mel) 3.2 mg dm-3, pH (CaCl2) 5.0, organic matter (OM)
18.7 g dm-3, and base saturation of 36% and particle-size of 52.0%
sand, 40.5% clay, and 7.5% silt. At Boa Esperança farm, the chemical
characteristics of the soil at the beginning of the experiment were as follows:
Ca2+, Mg2+, H+Al, and K+ of 1.31, 0.85, 2.7;
0.09 cmoLc dm-3, respectively, P (mel) 22.4 mg dm-3,
pH (CaCl2) 5.4; organic matter (OM) 15.8 g dm-3, and base
saturation of 54% and particle-size of 75.5% sand, 19.5% clay, and 5.0% silt.
Adopting the criteria
proposed by Köppen (1931), the climate is classified as tropical savanna with
dry winters and rainy summers (Aw-type), with average annual
precipitation above 1,000 mm in both areas (Fig. 1, 2).
Evaluated treatments
The 12 m x 37.5 m (450 m2)
strips were allocated in a randomized block design randomLy within the area.
The evaluated treatments were 1) corn in monocropping, 2) corn intercropped
with Urochloa ruziziensis, 3) corn intercropped with U. brizantha
cv. Marandu, 4) corn intercropped with U. brizantha cv. BRS Paiaguás,
and 5) sorghum intercropped with U. ruziziensis.
Soil
samples (0–10 cm) were taken from each treatment, where four composite samples
were collected. Each composite sample originated from three simple samples
collected randomLy in each plot. The samples were air-dried, grounded, and
sieved in a 2 mm mesh in the laboratory.
Laboratory analysis
Carbon (C-BM) and nitrogen
(N-BM) from microbial biomass: The
chloroform-fumigation-extraction (CFE) method proposed by Vance et al.
(1987), with the soil extractor ratio 1:2.5 (Tate et al. 1988), was used
to determine the carbon in the microbial biomass (C-BM). The analysis was
performed with three replicates of 20 g for each sample collected, three
fumigated with chloroform and three not fumigated, according to Brookes et
al. (1982) and Witt et al. (2000). The moisture content of the
samples was adjusted to 70% of field capacity. All replicates were subjected to
extraction with 50 mL of potassium sulfate solution (K2SO4)
0.5 moL L-1.
An aliquot of the extract (8 mL) was treated with a
potassium dichromate solution (K2Cr2O7) 0.4 N
in an acidic medium. Residual dichromate was measured by titration with an
ammoniacal ferrous sulfate solution [(NH4)2Fe(SO4)2.6H2O]
0.04 N using diphenylamine as an indicator. The extraction and quantification
were based on the Walkley
and Black (1934) methodology modified
according to Tedesco et al. (1995). The amount of C-BM was determined by
the difference between the organic carbon extracted from the fumigated and
non-fumigated soil samples, considering the correction factor (Kc) of 0.41
(Sparling and West 1988). The results of C-BM were expressed in mg C kg-1
soil.
The fumigation-extraction, the procedure described
by Brookes et al. (1985), was used to determine microbial biomass
nitrogen (N-BM). The extracts obtained using the CFE method of C-BM (Brookes et
al. 1982; Witt et al. 2000) were used to quantify N-BM. The extract
(10 mL) was removed and transferred to tubes with 2 g of catalyst mixture and 5
mL of sulfuric acid. The digestion was carried out in a digester block at 350ºC
for two hours, with steam distillation for N analysis (Kjeldahl) followed by
neutralization by acid-base volumetry (Alves et al. 1994). The amount of
BM-N was determined by the difference between the N extracted from fumigated
and non-fumigated soil samples, considering a Kc of 0.54 (Brookes et al.
1985). The N-BM results were expressed in mg N kg-1 soil.
Basal soil respiration (BSR)
The
assessment of microbial respiration was based on the methodology of Jenkinson and
Powlson (1976), starting with the weighing of two replicates of 20 g of soil
and transferred together with a flask with 10 mL of 1 M sodium hydroxide (NaOH)
to a 2 L hermetically closed flask, so that there is no entry of CO2
from outside air and leakage of internally produced CO2. After seven
days of incubation, the flask containing NaOH was removed, and barium chloride
(BaCl2) 10% (m/v) was added for total CO2 precipitation.
Titration was carried out with two drops of 1% phenolphthalein (m/v) and
titrated under stirring with 0.5 M hydrochloric acid (HCl). The color will go
from pink to colorless, estimating the amount of CO2 released from
the unfumigated soil. The results of microbial respiration were expressed in mg
C-CO2 kg-1 soil h-1.
Metabolic
(qCO2) and microbial (qMic)
quotient
The
qCO2 was calculated by the ratio between the respiration rate
and the C-BM (Anderson and Domsch 1993), expressed in mg C-CO2 g-1
BMS-C h-1. The qMic was calculated by the ratio between C-BM
and organic carbon (OC), expressed as a percentage.
Sample soil (1 g) was weighed and transferred to a
polyethylene beaker (blank) to carry out the OC determination. Sodium dichromate
digester solution (10 mL) (Na2Cr2O7).2H2O
4N + sulfuric acid (H2SO4) 10 N was added. Then, it was shaken on a horizontal shaker for 10
min. After stirring, it was left to stand for one hour. After, 50 mL of
distilled water was added and left to settle overnight. For determination,
reading was performed in a moLecular absorption spectrophotometer at a
wavelength of 650 nm (transmittance), hitting zero with the blank test.
β-glucosidase
The
β-glucosidase enzyme activity was based on the methodology of
Tabatabai (1994). Soil samples (1 g) were weighed and placed in a 50 mL
Erlenmeyer flask, then 0.25 mL of toluene, 4 mL of MUB pH 6, and, except for
the blank, 1 mL of 0.025 M PNG were added. They were incubated for one hour at
37°C, then 1 mL of CaCl2 0.5 M and 4 mL of THAM pH 12, and only in the blank, 1
mL of PNG 0.025 M were added. They were shaken and filtered through Whatman nº
2 filter paper, and the yellow color was read in a molecular absorption
spectrophotometer at 410 nm. The activity of the β-glucosidase
enzyme will be expressed in mg p-nitrophenol kg-1 soil h-1.
Arylsulfatase
The
activity of the arylsulfatase enzyme was based on the methodology of Tabatabai
(1994). 1 g was weighed and placed in a 50 mL Erlenmeyer flask, then 0.25 mL of
toluene, 4 mL of acetate buffer pH 5.8, and, except for the blank, 1 mL of 0.05
M PNS were added. It was incubated for one hour at 37°C, then 1 mL of 0.5 M
CaCl2, 4 mL of 0.5 M NaOH, and only in the blank, 1 mL of 0.05 M PNS
were added and filtered through Whatman nº 2 filter paper, and the yellow color
was read in a molecular absorption spectrophotometer at 410 nm. The activity of
the arylsulfatase enzyme will be expressed in mg p-nitrophenol kg-1
soil h-1.
Acid phosphatase
The
acid phosphatase enzyme activity was based on the methodology of Tabatabai
(1994). 1 g was weighed and placed in a 50 mL Erlenmeyer flask, then 0.25 mL of
toluene, 4 mL of MUB pH 6.5, and except for the blank, 1 mL of 0.05 M PNF were
added. It was incubated for one hour at 37°C, then 1 mL of CaCl2 0.5
M, 4 mL of NaOH 0.5 M, and only in blank, 1 mL of PNF 0.05 M was added. This
was shaken and filtered through Whatman nº 2 filter paper, and the yellow color
was read in a molecular absorption spectrophotometer at 410 nm. The acid
phosphatase enzyme activity will be expressed in mg p-nitrophenol kg-1
soil h-1.
The
urease enzyme activity was based on the methodology of Tabatabai and Bremner
(1972). 5 g of soil was weighed, adding 0.2 mL of toluene, 9 mL of buffer (pH
9), and 1 mL of solution with urea (0.2 mol L-1), and incubated for
2 hours in an oven with a temperature of 37°C. After this period, 35 mL of
KCI-Ag2SO4 was added to stop the reaction, stirred for a
few minutes, and left for about 5 minutes at room temperature. After this
period, the solution was completed with KCI-Ag2SO4 to 50 mL
and stirred for a few minutes.
From the solution, 20 mL was pipetted and taken to
nitrogen still, adding 0.2 g of MgO. In the nitrogen distiller, the distillate
is collected in a beaker with a boric acid solution (H3BO3)
containing methyl red (C15H15N3O2)
and bromocresol green (C21H14Br4O5S)
as indicators, titrated with a standardized solution of H2SO4
(0.005 mol L-1). A control sample was performed for each sample,
with urea being added only after the KCl-Ag2SO4. The
urease activity is expressed in ug N-NH4+ g dry soil -1
h-1.
The urease enzyme
activity was based on the methodology of Diack (1997). 3 g of soil was weighed,
and 30 mL of a buffer solution with fluorescein was added. The tube was %20301-311_files/image002.png)
Fig. 1:
Monthly temperature and rainfall
data (during the experiment, 2020) in the Experimental farm of the Associated
Group of Producers of Southwest of Goiás (GAPES) in Rio Verde, GO, Brazil. Source: Authors, 2022
%20301-311_files/image004.png)
Fig. 2:
Monthly
temperature and rainfall data (during the experiment, 2020) in the Boa
Esperança farm in Montividiu, GO, Brazil. Source: Authors, 2022
capped and incubated in rotation at 35ºC. After
this period, 2 mL of acetone was added to stop the reaction. The suspended soil
was stirred for 5 min; the supernatant was filtered with Whatman nº 42 filter
paper and determined with a molecular absorption spectrophotometer at 490 nm.
The fluorescein concentration is expressed in mg F g dry soil-1 day-1.
Data were analyzed using analysis of variance, and
means were compared using the Tukey test (5%). The data analysis was performed
with the Sisvar 5.8 software (Ferreira 2019). For the principal component
analysis, the Paleontological Statistics Software Package – PAST4 software
(Hammer et al. 2013) was used.
Farm
of associated group of southwest goiano producers (Rio Verde, GO)
The C-BM showed a statistical difference for corn +
U. brizantha cv. Paiaguás in the
rainy period, differing from the other treatments. In the dry period,
treatments with Corn + U. ruziziensis,
Corn + U. brizantha cv. Marandu, and
Corn + U. brizantha cv. Paiaguás
exhibited a difference when compared to conventional corn treatment (Table 1).
In the N-BM component,
both in the rainy and dry periods, with Corn + U. ruziziensis and Corn + U.
brizantha cv. Marandu showed differences between the other treatments with
higher Nitrogen efficiency in the soil (Table 1).
No differences were
observed for the qCO2 attribute in either collection period.
In the rainy period, the intercropping of corn with U. brizantha cv.
Paiaguás showed the highest contents for C-BM and qMic, the
intercropping of corn with U. ruziziensis showed the highest content of
N-BM, and the intercropping did not show differences for BSR compared to
monoculture. In the dry period, the
intercrops were superior to monoculture. In the attributes C-BM and qMic,
the intercropping of corn with U. ruziziensis showed superiority to
monoculture and similarity with sorghum with U. ruziziensis with N-BM,
and the intercropping did not show a difference compared to BSR with monocropping
(Table 1).
No differences were observed in
the rainy period for the attributes β-glucosidase, acid
phosphatase, arylsulfatase, urease, and FDA, and in the dry period for the
attributes β-glucosidase, acid phosphatase, urease, and FDA. For
the arylsulfatase enzyme, the intercropping of corn with U. brizantha
cv. Paiaguás showed superiority to corn and sorghum intercropping with U.
ruziziensis, with no difference from monocropping (Table 2).
Boa esperança farm (Montividiu, GO)
In the rainy period, the intercropping of sorghum with U.
ruziziensis, corn with U. ruziziensis, and corn with U. brizantha
cv. Paiaguás showed higher levels of C-BM than monocropping. The intercropping
showed no difference in Table 1: Soil biological
attributes (0-10 cm deep) in two periods (rainy and dry) after three years of
cover crop cultivation in a no-tillage system on the experimental farm of the
Associated Group of Producers of Southwest of Goiás (GAPES), Rio Verde, GO,
Brazil
|
Crops |
C-BM |
N-BM |
BSR |
qCO2 |
qMic |
|
|
mg C kg-1 soil |
mg N kg-1 soil |
mg C-CO2 kg-1 soil h-1 |
mg
C-CO2 g-1 BMS-C h-1 |
% |
|
|
Rainy
Period |
||||
|
Corn |
165.68 c |
127.31 b |
1.69 ab |
0.11
a |
1.09
b |
|
Corn + U. ruziziensis |
171.25 c |
173.95 a |
1.59 ab |
0.12
a |
1.30
b |
|
Corn + U. brizantha cv. Marandu |
233.30 bc |
206.28 a |
1.35 b |
0.09
a |
1.70
b |
|
Corn + U. brizantha
cv. Paiaguas |
359.15 a |
119.56 b |
1.56 ab |
0.13
a |
3.04
a |
|
Sorghum + U. ruziziensis |
269.26 b |
131.66 b |
1.89 a |
0.12
a |
1.84
b |
|
CV (%) |
12.98 |
10.47 |
11.39 |
17.59 |
23.02 |
|
|
Dry
Period |
||||
|
Corn |
271.43 b |
37.23 bc |
5.47 ab |
0.46
a |
2.31
b |
|
Corn + U. ruziziensis |
416.70 a |
60.92 a |
4.66 b |
0.41
a |
3.70
a |
|
Corn + U. brizantha cv. Marandu |
498.12 a |
26.75 bc |
5.77 ab |
0.47
a |
4.10
a |
|
Corn + U. brizantha
cv. Paiaguas |
457.07 a |
22.80 c |
6.74 a |
0.53
a |
3.63
a |
|
Sorghum + U. ruziziensis |
521.55 a |
45.41 ab |
5.18 ab |
0.39
a |
4.00
a |
|
CV (%) |
12.51 |
22.23 |
14.52 |
16.62 |
13.06 |
Means followed by the same letter in the column do not
differ by Tukey's test (p < 0.05)
%20301-311_files/image006.jpg)
Fig. 3: Principal component analysis of the biological
attributes of the soil (0-10 cm deep) during the rainy period after three years
of cover crop cultivation in the no-tillage system on the experimental
farm of the Associated Group of Producers of Southwest of Goiás (GAPES), Rio
Verde, GO, Brazil
%20301-311_files/image008.jpg)
Fig. 4: Principal component analysis of the biological
attributes of the soil (0-10 cm deep) during the dry period after three years
of cover crop cultivation in the no-tillage system on the experimental
farm of the Associated Group of Producers of Southwest of Goiás (GAPES), Rio
Verde, GO, Brazil
monocropping with N-BM. The intercropping of corn with U.
brizantha cv. Marandu demonstrated superiority to the other intercropping
systems and monocropping systems with BSR and qCO2 and corn
and sorghum with U. ruziziensis with qMic. In the dry period, the
intercropping, except for sorghum with U. ruziziensis, did not differ
from the monocropping in C-BM. About N-BM, corn in monocropping and
intercropped with U. brizantha cv. Paiaguás and qMic with corn
intercropping with U. ruziziensis had the highest contents. The BSR
showed no difference between the intercropping and monocropping and only the
intercropping of U. brizantha cv. Marandu showed inferiority to other
intercropping and monocropping with qCO2 (Table 3).
No differences were observed for
the acid phosphatase, arylsulfatase, urease, and FDA attributes in the rainy
period. The intercropping of corn and sorghum with U. ruziziensis was
superior to monocropping and similar to the intercropping of corn with U.
brizantha cv. Paiaguás concerning to β-glucosidase. In the dry
period, no differences were observed for β-glucosidase, acid
phosphatase, urease, or FDA. The arylsulfatase enzyme showed the superiority of
corn intercropping with U. ruziziensis with other intercrops, with no
difference from monocropping (Table 4).
In the analysis of principal
components for the biological attributes of the soil, they represent 77.44 and
73.94% of the total variance in the rainy and dry periods, respectively. In the
rainy period, the intercropping of corn and sorghum with U. ruziziensis
correlated with C-BM, qMic, β-glucosidase, urease, and FDA.
The intercropping of corn with U. brizantha cv. Marandu correlated with
BSR and qCO2. The monocropping correlated with acid
phosphatase and arylsulfatase (Fig. 5). The intercropping of sorghum with U.
ruziziensis correlated with urease and FDA, corn with U. ruziziensis
with C-BM, qMic, and arylsulfatase, corn with U. brizantha cv.
Paiaguás and Marandu with acid phosphatase and β-glucosidase. The
monocropping correlated with N-BM, BSR, and qCO2 (Fig. 6).
About C-BM, in the rainy period, the intercropping of
corn with U. brizantha cv. Paiaguás showed superiority concerning the other
intercropping and monocropping systems, and in the dry period, the
intercropping system was superior to the monocropping (Table 1). In the absence
of a cover crop, only spontaneous vegetation reduces the C-BM content (Carneiro
et al. 2008). Duarte et al. (2014) noted the superiority of the
intercropping Mucuna pruriens and millet regarding C-BM contents,
validating this attribute's management difference. There is a quick influence
on biological attributes due to the plant cycle and the addition of plant
residues (Hoffmann et al. 2018, Miranda et al. 2020).
Regarding N-BM, the
intercropping of corn with U. ruziziensis showed superiority to monocropping
in both periods. In the dry period, there was similarity between sorghum and U.
ruziziensis (Table 1). According to Souza et al. (2010), low forage
height or absence can cause a reduction in N-BM under water stress conditions,
which may be correlated with the chemical composition of the residues (Tian et
al. 1992).
The intercropping systems did
not differ from monocrop in both periods for BSR (Table 1). In a study by
Duarte et al. (2014), basal soil respiration was not different in one of
the analyzed experiments evaluating the management of millet, Canavalia
ensiformis, M. pruriens, Cajanus cajan, and Crotalaria juncea.
No differences were observed for
the qCO2 in both periods (Table 1). Despite the superiority
of the two intercropping systems in the rainy period and the intercropping
system in the dry period, there was no impact on qCO2.
According to Cunha et al. (2011), the more effective the C-BM, due to
the assimilation of C from the soil, the lower the value of qCO2.
Concerning qMic, in the rainy period, the
intercropping of corn with U. brizantha cv. Paiaguás was superior to the
other intercropping systems and monocrop, and in the dry period, the
intercropping system was superior to the monocropping (Table 1). The lowest qMic
content observed was 1.09% in corn monocropping. In a study by Jakelaitis et
al. (2008), the qMic values ranged between 0.9 and 1.8% when
assessing corn monocropping, intercropped corn, and native vegetation. They
stated that values less than 1% indicate that there is some limiting factor to the
microbiological activity in the soil, which did not occur in this work.
In both periods, no differences
were observed for the β-glucosidase, acid phosphatase, urease, and
FDA, in addition to the absence of a difference for the arylsulfatase enzyme in
the rainy period (Table 2). According to Green et al. (2007) and
Ferreira et al. (2017), the sowing system can increase the enzymatic
activity values in the superficial layer. As we observed in this work, the
differences between the evaluated managements may be in deeper layers.
For the arylsulfatase enzyme in
the dry period, the intercropping of corn with U. brizantha cv. Paiaguás
showed superiority to corn and sorghum intercropping with U. ruziziensis,
with no difference from the monocropping (Table 2). According to Rodrigues et
al. (2022), arylsulfatase was the most sensitive indicator to detect
changes in the soil with evaluated crops, responding to the water regime and
the presence of brachiaria. Mendes et al. (2005), in Rio Verde, Goiás,
Brazil, observed significant increases in the activity of this enzyme just one
year after the adoption of the no-tillage system, showing the enzyme's ability
to show minimal changes, even before the carbon of microbial biomass and
organic matter from the soil.
In the rainy period, the
intercropping of sorghum with U. ruziziensis, corn with U.
ruziziensis, and corn with U. brizantha cv. Paiaguás had higher
levels than monocropping for C-BM (Table 3). Notably, the C-BM levels found in
this work only with intercropping with corn indicate positive responses of the
management adopted with microbial diversity (Duarte et al. 2014). Gallo et
al. (2019), evaluating the C-BM contents in monocropping and intercropped
corn, observed higher contents in corn intercropped with C. juncea and C.
cajan than in corn monocropping.
In the dry period, the
intercropping, except for %20301-311_files/image011.png)
sorghum with U. ruziziensis, did not differ from the
monocropping for C-BM (Table 3). Hoffmann et al. (2018) observed
differences in the transition of collection periods. According to Mendes et
al. (2009), stressful soil conditions, such as the collection period, can
increase C-BM values. In the rainy period, the intercropping showed no
difference in monocropping compared to N-BM, and in the dry period, corn
monocropping and intercropping with U. brizantha cv. Paiaguás did not
differ (Table 3). Brandão Junior (2005) and Fernandes Junior (2021), evaluating
different types of management, did not observe significant differences.
%20301-311_files/image012.png)
In the rainy period, the intercropping of corn with U.
brizantha cv. Marandu showed superiority to the other intercropping systems
and monocropping concerning BSR, and in the dry period, there was no difference
between the intercropping and monocropping (Table 3). The behavior of the rainy
period was also observed by Cunha et al. (2011), where intercropping
provided higher levels of soil respiration, which provided a greater amount of
labile C in the soil. In their second experiment, Duarte et al. (2014)
observed the superiority of the intercropping of millet and M. pruriens
to the cultivation of millet alone, as observed in the rainy period. In a study by Gallo et al.
(2019), greater releases of microbial respiration were observed in corn alone
and intercropped with M. pruriens, C. cajan, and C. juncea, with this
behavior observed in the dry period. For the BSR, the variable behavior of the
tests is evident, mainly according to the collection period, not presenting
conclusive indications. According to Gonçalves et al. (2019), the BSR
does not allow conclusions to be drawn, as the high values may be related to an
efficient production system or some disturbance.
In the rainy period, the
intercropping of corn with U. brizantha cv. Marandu showed the
superiority of qCO2 to the other intercropping systems and
the monocropping, and in the dry period, the intercropping system, except for
corn of U. brizantha cv. Marandu showed no difference (Table 3). The qCO2
contents tend to be higher when the C-BM is lower. Duarte et al. (2014)
observed no difference between the soil coverages evaluated. In Gallo et al.
(2019), single corn had the highest values compared to intercropping.
In the rainy period,
intercropping corn and sorghum with U. ruziziensis was superior to the
other intercropping systems and monocropping. In the dry period, corn with U.
ruziziensis had the
highest values of qMic (Table 3). Cunha et al. (2011) found the
influence of cover crops on this attribute, using C. juncea, C. cajan,
M. pruriens, and sorghum, and in work by Gallo et al. (2019), with corn
intercropped with C. cajan and C. juncea.
No differences were observed for
β-glucosidase, acid phosphatase, urease, and FDA in the rainy and
dry periods. There was no difference in the arylsulfatase enzyme in the rainy
period (Table 4). Note the lack of response to intercropping systems and monocropping for urease,
acid phosphatase, and FDA, validating the lack of sensitivity of the parameter.
The study by Mendes et al. (2005) observed variable behaviors in the
properties evaluated regarding β-glucosidase enzymes and the
absence of a difference for acid phosphatase with no-tillage with sorghum and
off-season corn. Mendes et al. (2018) showed high levels of activity of β-glucosidase and arylsulfatase enzymes in
treatments with the presence of brachiaria (intercropped and not), in addition
to the equivalence of monocropping of corn and brachiaria and corn intercropped
with brachiaria.
The intercropping of corn and
sorghum with U. ruziziensis was superior to monocropping and similar to
the intercropping of corn with U. brizantha cv. Paiaguás in the rainy
period for β-glucosidase activity. In the dry period, the enzyme
arylsulfatase showed the superiority of corn and U. ruziziensis
intercropping concerning other intercropping systems, with no difference in
monocropping (Table 4). According to Mendes et al. (2021b), in 20 years
of studies with bioindicators in the Cerrado region, the enzymes arylsulfatase
and β-glucosidase were the most efficient indicators of soil
quality due to the management system. Rodrigues et al. (2022), with
samples obtained in March during the rainy period, observed that the activity
of β-glucosidase and arylsulfatase responded positively and
significantly to the management system.
In the analysis of the main components for the
biological attributes of the soil, two main components were used, which
together represented 75.45, 77.06, 77.44 and 73.94% of the total variance of
the rainy and dry periods in Rio Verde and Montividiu, respectively. According
to Regazzi (2000), the amount of principal components that explain 70% or more
of the proportion of the total variance is used so that your assessment can be
validated.
In Rio Verde, intercropping
correlated with all biological attributes in the rainy period, and the
monocropping showed similarity with corn and U. ruziziensis
intercropping for acid phosphatase and arylsulfatase enzymes (Fig. 3). In the
dry period, it maintained the same behavior except for β-glucosidase,
which was associated with monocropping (Fig. 4). The response of the
intercropping regarding the biological attributes was evidenced, where the
enzymes arylsulfatase > β-glucosidase > acid phosphatase,
following this order, according to Rodrigues et al. (2022), are the most
sensitive to detect changes in the soil. According to Mendes et al. (2018),
brachiaria can keep the soil biologically more active, and the β-glucosidase
and arylsulfatase enzymes are the most sensitive to minor differences. Carneiro
et al. (2013) studied an integrated crop-livestock system that promoted
improvements in the carbon contents of microbial biomass and soil carbon
stocks.
In Montividiu, intercropping is
correlated with biological attributes in the rainy period, except acid
phosphatase and arylsulfatase, which are associated with monocropping (Fig. 5).
In the dry period, the intercropping system correlated with biological
attributes except for N-BM, basal soil respiration, and qCO2,
which were associated with monocropping (Fig. 6). For Mendes et al. (2018),
the superiority of soybean/brachiaria rotation in relation to soybean/fallow is
evidenced, as for C-BM and the enzymes β-glucosidase,
arylsulfatase, and acid phosphatase, but higher levels of β-glucosidase
from the soybean/ U. ruziziensis rotation compared to soybean/corn and
soybean/corn + U. ruziziensis.
Despite the variable behavior,
the presence of cover crops reinforces the importance of agrobiodiversity for
soil health, and the best way to transform the soil into a biologically active
and productive land is to offer diversified cover crops in an adequate quantity
for microbial communities that reside in it (Mendes et al. 2021a).
It is concluded that the management influenced the biological
attributes and enzymatic activity. The carbon and nitrogen of the microbial
biomass, and qMic, got the best response in the intercroppings in the study
area in Rio Verde, GO, Brazil.
The results of carbon of the
microbial biomass, basal soil respiration, qCO2, and qMic were
better in intercropping than monocropping in the rainy period in the area
evaluated in Montividiu, GO, Brazil.
The β-glucosidase
and arylsulfatase enzymes showed high sensitivity to management. The β-glucosidase
enzyme in the rainy period in Rio Verde, GO, showed high efficiency on U.
ruziziensis for soil biological components.
Acknowledgments
To the Goiano Federal Institute – Campus Rio Verde, the
Federal University of Lavras, the Associated Research Group of Southwest Goiano
(GAPES), Boa Esperança Farm, Center of Excellence in Bioinputs (CEBIO), Coordination for the Improvement of
Higher Education Personnel (CAPES), and the National Council for Scientific and Technological
Development (CNPq), for their funding and contribution to the execution of this
study.
Author Contributions
MVAV, HRFB, ELS, MACC, and DCS planned the experiments; MVAV
and HRFB collected samples in
the field; MVAV and HRFB performed the
analysis; MVAV, HRFB, ELS, and MACC interpreted and discussed the
results; MVAV and HRFB statistically analyzed the data; MVAV and ELS wrote and revised the text.
Conflicts of Interest
All other authors declare no conflicts of interest.
Data Availability
Not applicable.
Ethics Approval
Not applicable.
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