Archivos Latinoamericanos de Producción Animal. 2023. 31 (4)
Soil fertility in silvopastoral systems integrating tree legumes with
signalgrass (Urochloa decumbens Stapf. R. Webster)
Recibido: 20221226. Revisado: 20230822. Aceptado: 20230930
1Corresponding author. Email address: aherrera@unet.edu.ve
2Animal Science Department, Universidade Federal Rural de Pernambuco. CNPq Fellow. Pernambuco, Brazil.
3Associated Professor I, Universidade Estadual do Maranhão. Maranhão, Brazil.
4North Florida Research & Education Center, University of Florida. Florida, United States.
5Animal Science Department. Facultad de Agronomía e Ingeniería Forestal. Pontificia Universidad Católica de Chile. Santiago de Chile. Chile.
6Instituto Agronômico de Pernambuco. Pernambuco, Brazil.
287
Ana María Herrera1
Abstract. Silvopastoral Systems (SPS) can increase overall productivity and income in order to stimulate the
simultaneous growth and development of trees, forage and livestock. Moreover, the SPS with tree legumes would
be important for adding nutrients to the system, mainly N, ensuring soil health and quality. Soil properties were
assessed in two SPS, implanted in 2011, using tree legumes (in double rows) intercropped with Urochloa decumbens
Stapf. R. Webster (Signalgrass). Treatments were Signalgrass + Mimosa caesalpiniifolia Benth (Sabiá) and Signalgrass
+ Gliricidia sepium (Jacq.) Kunth ex Walp. (Gliricidia), and they were allocated in a randomized complete block
design, with three replications. Soil was sampled in 2013, 2017, and 2018, at 0, 4, and 8 m along transects
perpendicular to tree double rows, from 0 to 20 and 20 to 40cm layers. Soil chemical properties evaluated
included pH, P, K+, Ca2+, Mg2+, Al3+, H++Al3+, cation exchange capacity (CEC), and base saturation. In addition,
light fraction of soil organic matter (LFSOM), soil basal respiration (SBR), and natural abundance of 13C of the
respired CO2 13CCO2) were analyzed. Soil pH (5.3, 5.2, 5.1), P (11.3, 7.2, 3.6 mg dm3), and CECeffective (5.8, 5.1, 5.0
cmolc dm3) decreased (P < 0.05) along the years 2013, 2017, and 2018, respectively. In 2018, the LFSOM and δ13C
CO2 were greater in Sabiá (1.1 g kg1 and 16.4 ‰) compared to Gliricidia (0.7 g kg1 and 18.2 ‰). Silvopastoral
systems reduced soil fertility regardless of the tree legume species used as a result of biomass nutrient stock,
without maintenance fertilization. Sabiá had greater deposition of LFSOM, without increasing SBR, providing
potential for microbial C use efficiency. Enriched CCO2 isotope composition had an efficient SOM oxidization in
SPS with Gliricidia or Sabiá. This information can contribute to the assessments related to CO2 balance and C
retention. Both SPS contribute to C sequestration.
Keywords: agroforestry systems; Gliricidia sepium; Mimosa caesalpiniifolia; soil chemical properties; C sequestration.
https://doi.org/10.53588/alpa.310401
Agricultural Research Department, Universidad Nacional Experimental del Táchira. Táchira, Venezuela.
Alexandre Carneiro Leão de Mello2
Fertilidade do solo em sistemas silvipastoris integrando leguminosas arbóreas
com capimbraquiária (Urochloa decumbens Stapf. R. Webster)
Resumo. Os Sistemas Silvipastoris (SSP) podem aumentar a produtividade e gerar renda. Também, os SSP com
leguminosas arbóreas adicionam nutrientes ao sistema, principalmente N, garantindo a saúde e a qualidade do
solo. As propriedades do solo foram avaliadas em dois SSP utilizando leguminosas arbóreas em consorcio com
Urochloa decumbens Stapf. R. Webster (capimbraquiaria). Os tratamentos foram capimbraquiária + Mimosa
caesalpiniifolia Benth (Sabiá) e capimbraquiária + Gliricidia sepium (Jacq.) Kunth ex Walp. (Gliricídia), sendo
distribuídos em delineamento casualizado em blocos (três repetições). As coletas de solo foram realizadas nos anos
2013, 2017 e 2018, a 0, 4 e 8 m ao longo de transectos perpendiculares às fileiras duplas de árvores, nas
profundidades de 020 e 2040 cm. As propriedades químicas do solo avaliadas incluíram pH, P, K+, Ca2+, Mg2+,
Al3+, H++Al3+, capacidade de troca de cátions (CTC) e saturação por bases. Foram analisadas a fração leve da
matéria orgânica (FLMOS), a respiração basal (RBS) e a abundância natural do 13C do CO2 respirado 13CCO2). O
pH (5,3; 5,2; 5,1), P (11,3; 7,2; 3,6 mg dm3) e CTCefetiva (5,8; 5,1; 5,0 cmolc dm3) diminuíram (P < 0,05) ao longo dos
anos 2013, 2017 e 2018, respectivamente. Em 2018, a FLMOS e δ13CCO2 foi maior em Sabiá (1,1 g kg1 e 16,4 ‰) em
comparação com Gliricídia (0,7 g kg1 e 18,2 ‰). Os SSP reduziram a fertilidade do solo independentemente das
espécies arbóreas utilizadas em decorrência do estoque de nutrientes da biomassa, sem adubação de manutenção.
Sabiá teve maior deposição de FLMOS, sem aumentar a RBS, proporcionando potencial para a eficiência do uso do
Valéria Xavier de Oliveira Apolinário3José Carlos B. Dubeux Jr4
Robert Emilio MoraLuna5 Erinaldo Viana de Freitas6
288
Introduction
Herrera et al.
Silvopastoral systems (SPS), as an agroforestry
practice, can increase overall productivity and generate
income in order to stimulate the simultaneous growth
and development of trees, forage and livestock (Sarabia
et al., 2019; Watanabe et al., 2016). Moreover, SPS with
tree legumes enhance the delivery of ecosystem
services in livestock system (Dubeux Jr. et al., 2019),
including biological nitrogen fixation, shade and
fodder supply for ruminants, as well as production of
marketable timber, increase in producer income, and
stability of the soilplant system (Apolinário et al., 2015;
Dubeux Jr. et al., 2019). These combinations of SPS
would be important for stabilizing fertilization and
ensuring soil health and quality.
This stability of the soilplant system is possible from
beneficial interactions between biological components
(soil, water, air, plants, and animals) (Sheoran et al., 2017).
Tree legumes, for instance, can increase N input and
nutrient availability in the system, via Nfixation, litter
deposition and decomposition (Sarabia et al., 2019).
However, tree characteristics, such as canopy structure,
leaf deposition, and litter quality, may affect soil
chemical and biological properties (Alfaro et al., 2018).
The soil is considered a complex and fundamental
system for the dynamic of terrestrial ecosystems (Terra
et al., 2019); however, some livestock traditional
activities may contribute to the depletion of soil
productive capacity, leading vast grassland areas to
degradation (Santana et al., 2016). Soil chemical and
physical properties affect water and nutrient
availability for plants and soil microorganisms. The
most common soil properties used to assess nutrient
availability are pH, mineral content, cation exchange
capacity (CEC), soil organic matter (SOM), carbon and
mineralizable nitrogen content (Bünemann et al., 2018).
Regarding biological properties, microbial processes
have fundamental importance for the productivity and
sustainability of systems (Santos et al., 2014), being
C microbiano. A composição enriquecida de isótopos de CCO2 mostraram uma eficiente oxidação da MOS em SSP
com Gliricídia ou Sabiá. Essas informações podem contribuir para as avaliações relacionadas ao balanço de CO2 e
retenção de C. Ambos SSP contribuem para o sequestro de C.
Palavraschave: sistemas agroflorestais; Gliricidia sepium, Mimosa caesalpiniifolia; propriedades químicas do solo;
sequestro de C.
Fertilidad del suelo en sistemas silvopastoriles que integran leguminosas
arbóreas con pasto señal (Urochloa decumbens Stapf. R. Webster)
Resumen. Los Sistemas Silvopastoriles (SSP) pueden aumentar la productividad general y generar ingresos.
Además, los SSP con leguminosas arbóreas adicionan nutrientes al sistema, principalmente N, asegurando la salud
y la calidad del suelo. Propiedades del suelo fueron evaluadas en dos SSP utilizando leguminosas arbóreas en
asociación con Urochloa decumbens Stapf. R. Webster (Barrera). Los tratamientos fueron Barrera + Mimosa
caesalpiniifolia Benth (Sabiá) y Barrera + Gliricidia sepium (Jacq.) Kunth ex Walp. (Gliricidia), distribuidos en un
diseño de bloques aleatorizados (tres repeticiones). Se realizaron colectas de suelo en los años 2013, 2017 y 2018, a 0,
4 y 8 m en transectos perpendiculares a las hileras de árboles, en las profundidades de 020 y 2040 cm. Las
propiedades químicas del suelo evaluadas incluyeron pH, P, K+, Ca2+, Mg2+, Al3+, H++Al3+, capacidad de
intercambio catiónico (CIC) y saturación de bases. Se analizaron la fracción activa de la materia orgánica (FAMOS),
respiración basal (RBS) y abundancia natural de 13C del CO2 respirado 13CCO2). El pH (5.3, 5.2, 5.1), P (11.3, 7.2,
3.6 mg dm3) y la CICefectiva (5.8, 5.1, 5.0 cmolc dm3) disminuyeron (P < 0.05) a través de los años 2013, 2017 y 2018,
respectivamente. En 2018, la FAMOS y δ13CCO2 fueron mayores en Sabiá (1,1 g kg1 y 16,4 ‰) comparada con
Gliricidia (0,7 g kg1 y 18,2 ‰). Los SSP redujeron la fertilidad del suelo independientemente de las especies
arbóreas utilizadas como resultado de la reserva de nutrientes de la biomasa, sin fertilización de mantenimiento.
Sabiá tuvo mayor deposición de FAMOS, sin aumentar RBS, favoreciendo potencialmente la eficiencia del uso de C
microbiano. La composición isotópica de CCO2 enriquecida muestra una oxidación eficiente de la MOS en SSP con
Gliricidia o Sabiá. Esta información puede contribuir a las evaluaciones relacionadas con el balance de CO2 y
retención de C. Ambos SSP contribuyen al secuestro de C.
Palabras clave: sistemas agroforestales; Gliricidia sepium; Mimosa caesalpiniifolia; propiedades químicas del suelo;
secuestro de C.
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289
Soil fertility in silvopastoral systems
Location, procedures and experimental design
The research was conducted at the Experimental
Station of the Agronomic Institute of Pernambuco
(IPA), located in Itambé, Pernambuco, Brazil. The
station is located at 7°23’ S and 35°10’ W. Average
annual rainfall is 1253 mm (APAC, 2022), and the
average annual temperature is 25°C (RIMA, 2014), with
KöppenGeiger climate classified as hot and humid
tropical (As). The predominant soil is dystrophic
Ultisol (Silva et al., 2001).
The treatments were defined by two SPS: Gliricidia
+ signalgrass (Gliricidia) and Sabiá + signalgrass
(Sabiá). The experimental area consisted of six
paddocks of 1.0 ha each. Tree legumes were established
in double rows spaced by 15.0 m (between double
rows) x 1.0 m (between rows) x 0.5 m (within rows)
(Fig. 1). Establishment of signalgrass occurred in open
pits (approx. 5 cm deep) and seeds were placed
manually (10 kg of commercial seed ha1 with 40 %
cultural value). Signalgrass was previously established
in one of the blocks since 1969. In the other two blocks
were established along with the tree legumes, between
the double rows. Legume seeds were planted in a
greenhouse and inoculated with specific
Bradyrhizobium strains obtained from the Soil
Microbiology Laboratory at Universidade Federal
Rural de Pernambuco (UFRPE). All paddocks were
fertilized in July 2011 with 44 kg ha1 of P (as single
superphosphate) and 100 kg ha1 of K (as potassium
chloride) on the entire area. Legume seedlings were
transplanted to the field in June 2011 at approximately
30cm height and planted in 20cm deep furrows.
Paddocks were fully established in October 2011.
Material and Methods
highly related to SOM decomposition derived from
plant and animal waste, as well as its recycling. Basal
soil respiration, microbial biomass, and C:N ratio are the
most valuable variables in the interpretation of SOM
dynamics (Alfaro et al., 2018; Santos et al., 2014), as those
are considered indicators of soil organic matter cycling.
Gliricidia sepium (Jacq.) Kunth ex Walp. (Gliricidia)
and Mimosa caesalpiniifolia Benth. (Sabiá) are tree
legumes, introduced and native, respectively, with
potential for use in SPS. These species are drought
tolerant and nitrogen fixers (Apolinário et al., 2015).
Recently, SPS integrating those legumes with the grass
Urochloa decumbens Stapf. R. Webster (signalgrass) have
been evaluated in Northeastern Brazil, in terms of
biomass production, chemical composition, litter
quality, deposition and decomposition, as well as
animal performance (Apolinário et al., 2016, 2015;
Oliveira et al., 2018; Santos et al., 2020). However, there
are few assessments of changes in soil chemical and
biological properties in SPS, including those tree
legumes. The hypothesis of this study was that the
inclusion of those tree legumes in SPS would improve
soil fertility differently with time. The aim of the
experiment was to evaluate the changes along a time
sequence in soil chemical and biological properties in
two SPS, integrating tree legumes, Gliricidia or Sabiá,
with signalgrass.
Fig. 1. Tree spacing in the double row silvopastoral system and soil sampling area. Each oneha plot had 14 double rows.
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Soil chemical properties
Interaction between treatment × distances for H+
+Al3+ (P = 0.04) and TEB (P = 0.02), year × distances for
K+ (P = 0.05) and year × treatment × distances for Mg2+
(P = 0.04) and base saturation (P = 0.004) were
observed. Soil pH, P, CECeffective and CECpotential (Tables
1 and 2) were different (P < 0.05) among years, with no
treatment differences (P > 0.05) in any of the variables
considered in soil chemical properties.
Soil pH significantly reduced from 2013 to 2018
(Table 1), showing increased acidity of soil reflecting
the activity of nitrifying bacteria as they release NO3
and H+ during oxidizing the ammonium NH4+N
(Neina, 2019). Further, this is favored by the presence
of nitrogenfixing species (e.g., Gliricidia and Sabiá)
and nitrate concentrations (Mathesius, 2022).
Moreover, these species deposited Nrich litter that
will further add H+ during nitrification of the
decomposing litter. According to Johan et al. (2021)
soils with elevated acidity, usually have low base
Results and Discussion
290
Initial soil physical characteristics (2011) from 0 to
20cm depth were loamclaysandy texture with
proportions of coarse sand (0.22 mm), fine sand (0.05
0.2 mm), silt (0.0020.05 mm), and clay (< 0.002 mm) of
44, 17, 16, and 22 %, respectively, and soil and particle
density of 1.33 and 2.52 g cm3, respectively. Average
monthly rainfall for the experimental years is shown as
supplementary material.
Each plot had 14 double rows with a tree density of
approximately 2500 plants ha1. Treatments were
allocated in a randomized complete block design, with
three replications. Yearling crossbred Holstein × Zebu
steers, with approximately 200 kg of body weight (BW)
were used as experimental animals, under continuous
stocking with variable stocking rate (Mott and Lucas,
1952). Stocking rate was adjusted every 28 days
following the recommendation of Sollenberger et al.
(2005). The target herbage allowance was 3 kg DM d1
of green herbage mass per kilogram of BW. Water and
a mineral mixture (Ca: 107 g kg1, P: 88 g kg1, S: 12 g
kg1, Na: 126 g kg1, Co: 55 mg kg1, Cu: 1530 mg kg1,
Fe: 1800 mg kg1, I: 75 mg kg1, Mn: 1300 mg kg1, Zn:
3630 mg kg1, F: 880 mg kg1) were offered ad libitum on
each paddock.
Soil chemical properties
Soil chemical properties were evaluated in 2013, 2017
and 2018, at 0 to 20cm depth. Three soil samples
(sampling units) were analyzed per paddock
(experimental unit), at two distances within each
paddock, in between the double rows and at 8 m from
them in a perpendicular transect to the tree row (Fig. 1),
resulting in a composite sample for each distance per
plot. Soil variables included pH, P, K+, Ca2+, Mg2+, Al3+,
and H++Al3+, obtained from the Soil Chemical
Laboratory at UFRPE. Subsequently, the total
exchangeable bases (TEB), effective (TEB + Al3+) and
potential (TEB + H++Al3+) CEC and base saturation
were estimated following EMBRAPA (2017) procedures.
Indicators of soil organic matter cycling
Indicators of soil organic matter cycling were
evaluated for two years (2017 and 2018) at 0 to 20 and
20 to 40cm depth (Fig. 1). The sampling protocol was
similar to the one used for soil chemical properties.
Indicators of soil organic matter cycling included the
light fraction of SOM (LFSOM), soil basal respiration
(SBR), and natural abundance of 13C of the respired
CO213CCO2).
The light fraction of SOM was estimated using the
SOM fractionation methodology proposed by Meijboom
et al. (1995) and adapted by Dubeux Jr. et al. (2006). Soil
basal respiration was determined by CO2 emission from
soil samples incubated for 21 d, with soil humidity at
around 60 % of field capacity, without light and
temperature between 25 to 28 °C, quantified and
estimated by titration (Harris et al., 1997; Silva et al.,
2007). After titration, the suspension was processed
following the method of Ramnarine et al. (2012), and
subsequently dried in a forcedair oven (65±2 °C) to
constant weight for storage. Samples were sent to the
University of Florida, to determine the δ13CCO2 using a
CHNS analyzer through the Dumas dry combustion
method (Vario Micro Cube, Elementar) coupled to an
isotope ratio mass spectrometer (IsoPrime 100,
IsoPrime). The δ13CCO2 estimate was performed
according to Unkovich et al. (2008) and Fry (2006).
Statistical analysis
Variance analyses were performed using the PROC
MIXED procedure of the SAS (SAS University Edition
software), using the Tukey test, when the F test was
significant (P < 0.05). For chemical and biological
properties, SPS, distance from the double rows of
legumes, soil depth, and year (as appropriate), were
considered fixed effects, and blocks were the random
effect. The year effect was analyzed using the repeated
measurement procedure.
Herrera et al.
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291
concentration, elevated Al3+ and high P fixation. The
lower soil pH values observed in 2018 compared to
2013 may also be explained by the extractions of
cations by trees and the pasture. This result is probably
associated with decreased P, Mg2+ K2, TEB and
CECeffective over the years (P < 0.05).
Table 1. Soil chemical properties between 0 to 20cm depth in silvopastoral systems intercropped with signalgrass in Itambé,
Pernambuco state, Brazil.
pH P Ca2+ Mg2+ K+ Al3+
Factor (water, 1: 2.5) mg dm3 cmolc dm3
Year (Y)
2013 5.3A 11.3A2.5 2.7A 0.23A0.23A
2017 5.2AB 7.2B3.0 1.1C0.17AB 0.17AB
2018 5.1B 3.6C2.9 1.5B0.12B0.12B
Standard error 0.05 0.07 0.29 0.08 0.06 0.06
Pvalue 0.0061 <0.0001 0.1864 <0.0001 0.0122 0.0122
Treatment (T)
Gliricidia + Signalgrass 5.3 6.1 3.1 1.8 0.21 0.21
Sabiá + Signalgrass 5.1 7.3 2.5 1.6 0.14 0.14
Standard error 0.05 0.07 0.33 0.07 0.06 0.06
Pvalue 0.1239 0.4993 0.3070 0.3514 0.1038 0.1038
Distance (D)
0 m 5.2 6.5 2.7 1.7 0.19 0.19
8 m 5.2 6.8 2.9 1.8 0.15 0.15
Standard error 0.04 0.06 0.26 0.07 0.05 0.05
Pvalue 0.2074 0.8010 0.2563 0.4255 0.1857 0.1857
Y × D
Standard error 0.06 0.08 0.35 0.10 0.09 0,11
Pvalue 0.0974 0.1084 0.8288 0.3055 0.2246 0,0493
Y × T × D
Standard error 0.09 0.11 0.50 0.15 0.13 0.11
Pvalue 0.4229 0.6171 0.4893 0.0017 0.2464 0.3893
P: phosphorus (MehlichI); Ca2+: calcium; Mg2+: magnesium; K+: potassium; Al3+: exchangeable aluminum.
Different uppercase letters in the column, within each factor, differ significantly (P < 0.05). Other interactions were not significant (P > 0.05).
Both legume species, Gliricidia and Sabiá, had an
average biomass accumulation during the initial 5.5
years of approximately 10 Mg ha1 year1 (Apolinário et
al., 2015). Biomass fractions included thin,
intermediate, and thick branches and total leaves (19,
22, 54, and 5 %, respectively). During these years,
nutrient absorption increased exponentially with
growth (mainly due to woody tissue production) until
it reached its maximum growth (between 7 to 10 years,
depending on the species). The order of nutrient
concentrations for all components of the aboveground
biomass, in general, follows this sequence: N> Ca2+>
K+> Mg2+> P (Moura et al., 2006). This could result in
nutrient depletion in the soil over time (Alvarado,
2015), especially when maintenance fertilization is not
considered. Nutrients associated with the residues, as
litter, represent 50 % of total nutrients associated with
aerial biomass, contributing to chemical soil properties
with 40–45 % of the N, 54 % of the K+, 56 % of the Mg2+,
and 28 % of the P (Montagnini, 2000).
Soil P also decreased over the years (P < 0.05), being
considered as medium level in the years 2013 and 2017
and as low in 2018 (Table 1). This decrease may be
associated with the concentration of the element in the
aboveground biomass. For Sabiá with 8 years of
establishment and diameter at breast height (DBH)
between 34 cm, P concentrations of 0.88 g kg DM1
were determined in the aerial biomass (Moura et al.,
2006). Considering the biomass accumulation of 50 Mg
ha1 reported by Apolinário et al. (2015), it is estimated
that approximately 44 kg ha1 of P were stocked in the
arboreal biomass, not to mention the root system.
In Gliricidia, Barreto and Fernandes (2001) reported
P concentrations of 1.7 g kg1 for 4yearold trees,
resulting in an estimated P stock of 85 kg ha1 of P, not
considering the roots. In addition to the element
depletion generated by the absorption of the plant
throughout its growth, according to Larsen (2017) the
total P content of the soils is relatively low (between
500 and 10,000 kg ha1 P up to 50cm deep) and a
portion is usually in forms unavailable for plants
absorption. These assumptions indicate the need to
supply this element. The availability and absorption of
this element stimulate the root growth of crops,
increasing the area of soil explored by vegetation and
greater absorption of other nutrients. Consequently, P
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Soil fertility in silvopastoral systems
Factor H++Al3+ TEB CECeffective CECpotential Base Saturation
cmolc dm3 %
Year (Y)
2013 5.0B5.3A 5.8A10.3B53A
2017 9.6A4.6B 5.1B14.2A32B
2018 9.8A4.6B 5.0B14.4A32B
Standard error 0.4 0.3 0.3 0.5 2.1
Pvalue <0.0001 0.0446 0.0404 <0.0001 <0.0001
Treatment (T)
Gliricidia + Signalgrass 7.5 5.3 5.6 12.7 43
Sabiá + Signalgrass 8.7 4.4 5.0 13.2 35
Standard error 0.6 0.4 0.3 0.6 2.60
Pvalue 0.1842 0.2175 0.2508 0.6464 0.1027
Distance (D)
0 m 8.4A4.7 5.2 13.2 37B
8 m 7.8B5.0 5.4 12.8 41A
Standard error 0.4 0.3 0.3 0.5 2.0
Pvalue 0.0216 0.2904 0.5455 0.3013 0.0440
T × D
Standard error 0.5 0.5 0.4 0.7 2.8
Pvalue 0.0438 0.0240 0.0666 0.8775 0.0008
Y × T × D
Standard error 0.7 0.6 0.4 0.9 3.4
Pvalue 0.0510 0.1975 0.3802 0.5867 0.0039
292
Fig. 2. Interaction between treatment × year × distances for soil Mg2+ (A) and base saturation (B), in silvopastoral systems
intercropped with signalgrass in Itambé, Pernambuco state, Brazil.
The same uppercase letters for treatments and lowercase for distance, across years, do not differ significantly (P > 0.05).
deficiency could affect plant growth, seed formation,
crop maturation, and nitrogenfixing capacity of legume
species (Dubeux Jr et al., 201SanzSaez et al., 2017).
In the interaction between treatment × year ×
distances (P < 0.05) for Mg+2, values were greater in
2013 for both SPS and distances (Fig. 2A). This
response is possibly associated with the lower
requirement of trees because of younger age (2 years),
enabling greater Mg2+ concentration from the
deposited arboreal components.
Table 2. Potential acidity, total exchangeable bases, cation exchange capacity and base saturation between 0 to 20cm depth, in
silvopastoral systems intercropped with signalgrass in Itambé, Pernambuco state, Brazil.
H++Al3+: potential acidity; TEB: total exchangeable bases; CEC: cation exchange capacity
Different uppercase letters in the column, within each factor, differ significantly (P < 0.05). Other interactions were not significant (P > 0.05).
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Herrera et al.
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Soil fertility in silvopastoral systems
In 2017 and 2018, the average soil Mg2+ was lower
than in 2013; however, soil Mg2+ concentration was still
adequate for plant growth. According to Karley and
White (2009), Mg2+ concentrations in the soil solution
should be between 0.0125 0.85 cmolc dm3 to support
plant growth. This reduction observed between 2013
and 2017, may be related to the increase in tree nutrient
requirement along 7 years of growth, promoting
depletion of the element into the soil. Barreto and
Fernandes (2001) and Moura et al. (2006), respectively,
reported aboveground biomass Mg2+ concentrations in
Gliricidia (6.6 g kg1) and Sabiá (2.8 g kg1). Considering
these values, and biomass accumulation of 50 Mg ha1
for both species during the initial 5.5 years of tree
development (Apolinário et al., 2015), it is estimated
that approximately 330 and 140 kg ha1 were stocked in
the biomass of Gliricidia and Sabiá, respectively.
Magnesium is often stored in root cells and released to
the xylem if shoots become Mg2+ deficient (Karley and
White,