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Research, Society and Development, v. 10, n. 16, e78101623317, 2021
(CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23317
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Changes by use and management in alluvial plain soils in southern Brazil
Alterações por uso e manejo em solos de planície aluvial no sul do Brasil
Cambios por uso y manejo en suelos de llanuras aluviales en el sur de Brasil
Received: 11/15/2021 | Reviewed: 11/24/2021 | Accept: 11/25/2021| Published: 12/07/2021
Edsleine Ribeiro
ORCID: https://orcid.org/0000-0002-1184-9195
Universidade Federal do Rio Grande do Sul, Brazil
E-mail: edsleine@hotmail.com
Priscila Vogelei Ramos
ORCID: https://orcid.org/0000-0002-6232-3441
Universidad de Burgos, Espanha
E-mail: priscilav.ramos@yahoo.com.br
Tatiele Fruett
ORCID: https://orcid.org/0000-0003-2678-6374
Universidade Federal do Rio Grande do Sul, Brazil
E-mail: tatielefruett@yahoo.com.br
Paulo César do Nascimento
ORCID: https://orcid.org/0000-0003-1079-3748
Universidade Federal do Rio Grande do Sul, Brazil
E-mail: pcnasc@ufrgs.br
Estéfane Chaves
ORCID: https://orcid.org/0000-0001-9102-1429
Universidade Federal do Rio Grande do Sul, Brazil
E-mail: ecagronomia@gmail.com
Abstract
Agricultural land use causes changes in physical and chemical attributes of the soil, due to the management practices
employed the productive capacity of the soil can be compromised under different agricultural systems. The soils of
Porto Alegre are quite diverse reflecting the geology, topography and drainage network of the region, and include
lowland soils, like the alluvial plain of the Arroio Dilúvio. This study was carried out in four landscape units (Native
Forest, Agroforestry System, Horse Farm and Agricultural Crops), to assess changes in soil characteristics after
different types of land use and management on the plain of the Dilúvio Arroio. We sampled disturbed and undisturbed
soil samples for chemical (pH, EC, V, SOM, CEC, Al3+, H+Al) and physical analysis (porosity, microporosity and
macroporosity). These chemical and physical attributes of the soils, especially pH, V%, SOM, CEC and Al3+,
underwent changes under the different types of land use and management, with significant differences. Most changes
were detected in the cropland soils. Multivariate analysis demonstrated the influence of the different types of land use,
at the surface, land use and management had the greatest influence, while at depth, the proximity of the areas was the
predominant factor.
Keywords: Land use; Attributes of the soil; Soil quality.
Resumo
O uso do solo agrícola provoca alterações nos atributos físicos e químicos do solo, devido às práticas de manejo
empregadas a capacidade produtiva do solo pode ser comprometida sob diferentes sistemas agrícolas. O município de
Porto Alegre apresenta diversidade de solos, topografia e redes de drenagem superficial, em meio a esta diversidade
de ambientes é possível encontrar áreas de baixada como a planície aluvial do Arroio Dilúvio. Este estudo foi
realizado em quatro unidades de paisagem (Mata, Sistema Agroflorestal, Potreiro, Plantas de Lavoura) com o objetivo
de avaliar mudanças nas características dos solos após diferentes usos e manejos, na planície do Arroio Diluvio, em
Porto Alegre. Para o estudo foram realizadas coletas de amostras deformadas e indeformadas de solo, em
profundidades de 0-20 cm e 60-80 cm, para análises químicas (pH, CE, V, MOS, CTC, Al3+, H+Al) e físicas
(porosidade, microporosidade e macroporosidade). Os atributos químicos e físicos dos solos sofreram alterações nos
diferentes usos e manejos, destacando-se o pH, V%, MOS, CTC e Al3+, com diferenças significativas. O solo da área
cultivada com plantas de lavoura foi o solo que apresentou mais alterações. A análise multivariada evidenciou as
influências para as diferenças entre os tipos de uso do solo, pois em superfície o uso e manejo se mostrou o fator de
maior influência, enquanto em profundidade, a proximidade das áreas foi o fator predominante.
Palavras-chave: Uso da terra; Atributos dos solos; Qualidade do solo.
Research, Society and Development, v. 10, n. 16, e78101623317, 2021
(CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23317
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Resumen
El uso de suelos agrícolas provoca cambios en los atributos físicos y químicos del suelo, debido a las prácticas de
manejo empleadas la capacidad productiva del suelo puede verse comprometida bajo diferentes sistemas agrícolas. El
municipio de Porto Alegre cuenta con diversidad de suelos, topografía y redes de drenaje superficial, en medio de esta
diversidad de ambientes es posible encontrar zonas de tierras bajas como la llanura aluvial del Arroio Dilúvio. Este
estudio se realizó en cuatro unidades de paisaje (Bosque, Sistema Agroforestal, Potrero, Plantas de Cultivo) con el
objetivo de evaluar cambios en las características del suelo después de diferentes usos y manejos, en la llanura Arroio
Diluvio, en Porto Alegre. Para el estudio, se recolectaron muestras de suelo deformado y no perturbado a
profundidades de 0-20 cm y 60-80 cm, para análisis químicas (pH, CE, V, MOS, CTC, Al3+, H + Al) y físicos
(porosidad, microporosidad y macroporosidad). Los atributos químicos y físicos de los suelos sufrieron cambios en
los diferentes usos y manejos, destacando el pH, V%, MOS, CTC y Al3+, con diferencias significativas. El suelo de la
zona cultivada con plantas de cultivo fue el suelo que presentó más alteraciones. El análisis multivariado evidenció las
influencias para las diferencias entre los tipos de uso del suelo, ya que en superficie el uso y manejo fue el factor más
influyente, mientras que en profundidad, la proximidad de las áreas fue el factor predominante.
Palabras clave: Uso de la tierra; Atributos del suelo; Calidad del suelo.
1. Introduction
Unlike air or water quality concepts, there are no unique standards or normatization to assess soil quality, currently
various concepts to define soil quality or degradation are considered (Araujo et al., 2012). Nevertheless, most definitions
empahsize the need to adopt a series of properties, especially the context of land use and land cover. Soil quality indicators are
measurable properties (quantitative or qualitative) of the soil or plant involved in a process or activity and allow the changes in
each ecosystem to be characterised, evaluated and monitored (Karlen et al., 1997).
Agricultural land use causes changes in physical and chemical attributes of the soil. Which could lead to a decrease in
quality as a result of the removal of plant cover and the excessive use of mechanisation or turning, among others. Due to the
management practices employed, the productive capacity of the soil can be compromised under different agricultural systems
(Rheinheimer et al., 2007).
Reis et al. (2021) attests that in an Ultisol with pasture and silvopasture area, there were changes in the chemical
attributes of the soil and that when the system is well managed it is possible to maintain the quality of the soil. Chaves et. al
(2021) in a study of changes in soil and clay fraction after cultivation with viticulture showed that there is change in chemical
attributes, mineralogy and soil fertility over the years, especially where the soil is managed for a longer time with the input of
chemical fertilizers. Santos et al. (2021), they concluded that soil management caused changes in soil structure and organic
matter content, especially in the first 30 cm, when subjected to tractor weight in the planting line. And changing the ground
cover for planting vines leads to a reduction in carbon stock, compared to native pastures, for example. Rodrigues et al. (2017)
evaluated changes in Amazonian soils under different uses and managements, with forest, native pasture, areas prepared by
minimum tillage system and conventional tillage. They concluded that soil fertility was altered. Nutrient availability was
reduced with the use of conventional tillage compared to the system with minimal soil disturbance.
From studies on soils with different uses, such as perennial crops, forestry and pasture that point to changes in soil
quality, we hypothesize that these land uses have changed soil quality in this environment. The aims of this study were: to
evaluate a series of physical and chemical attributes of soils under different types of land use and management, on the alluvial
plain of the Arroio Dilúvio in Porto Alegre and to compare these types of land-use and management in relation to the amount
of change caused in these attributes.
2. Methodology
The municipality of Porto Alegre has a great diversity of landscapes, due to variations in geology and geomorphology
that are reflected in different soils (Hasenack et al., 2008). The Arroio Dilúvio (stream) cuts through almost the whole
Research, Society and Development, v. 10, n. 16, e78101623317, 2021
(CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23317
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municipality, in an east-west direction, with an alluvial plain that has mostly been urbanised. Despite these changes caused by
urbanization, this geomorphologic feature has great environmental importance in areas where natural landscape is maintained,
like the presence of riparian forest, and others ecosystem functions. However, these lowlands are occupied by different types of
land use at Agronomy Faculty of Rio Grande do Sul Federal University (FAGRO - UFRGS) campus, because of teaching,
research and extension activities. Factors like the relief, and parent material of soils, make this environment representative of
several areas in Porto Alegre municipality, that have been used in agricultural and non-agricultural activities.
The study was carried out in Porto Alegre, state of Rio Grande do Sul. Porto Alegre is inserted in the Pampa Biome,
and is also influenced by the Atlantic Forest Biome. The climate in the region is classified as humid subtropical (EMBRAPA,
2014). Porto Alegre is located in the South Riograndense Shield, where the vast majority of the rocky substratum is occupied
by granite rocks. Hills and mounds stand out in the landscape and there are also areas of flatlands composed of sediments of
alluvial and colluvial origin (Hasenack, 2008).
Four landscape units (LU), also known as land-use types or treatments, were chosen for the study on the campus of
the School of Agronomy at UFRGS, located on the alluvial plain of the Arroio Dilúvio. These comprise an area of Native
Forest (NF), an area under an Agroforestry System (AFS), an area of Horse Farming (HF) and a demonstration area for
Agricultural Crops (AC). The landscape units, or land-use types, are employed as an aid in teaching, research and extension
activities, and each has a different history of land use and plant cover (Figure 1).
Figure 1 - Area of the FAGRO campus located on the plain of the Arroio Dilúvio, with emphasis on areas of interest to this
study (Native forest; Agroforestry System; Horse Farm; Agricultural Crops).
Source: Authors.
The NF is of flat relief, 30-40 years of age, occupied by recovered vegetation following deforestation, and maintained
as a preservation area of soil and litter, without agricultural use and management. The AFS has flat relief and a system,
introduced 10 years ago, of diverse vegetation with tree-like, shrubby and creeping species with the presence of plant ground
cover, and is used for experimental agriculture. There were records of ground cover employing plant residue from pruning, and
the use of cover crops and green manure (legumes and grasses), like common vetch (Vicia sp) and crotalaria (Crotalaria sp).
The HF has flat relief, with a system of pasture planted 38 years ago, a vegetation of low grasses, with no fertiliser or liming.
The AC landscape unit is of flat relief, used as a demonstration unit, including the cultivation of agricultural crops (oats,
cassava, beans, maize, velvet beans, and soybeans), desiccated by the use of herbicides, with manual weeding, and is fallow or
cultivated during the winter. Conventional soil tillage including ploughing and harrowing is employed, with exposure and
Research, Society and Development, v. 10, n. 16, e78101623317, 2021
(CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23317
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turning of the surface soil. There are records that fertiliser and liming have not been used in this area in the last five years.
The soils of the Arroio Dilúvio alluvial plain have taxonomic classifications as “Cambissolo Flúvico” e “Gleissolo
Háplico” (EMBRAPA, 2018) and all profiles are classified as “Gleyic Fluvic Cambisols” according to FAO (2015). In fact, the
main difference between them is the depth of gleyic horizon, that occurs between 25 and 70 cm.
The experimental design consisted of four replications per treatment or land use (LU). Undisturbed samples were
collected from the surface layer using a steel cylinder (10 cm in thickness), representing an approximate depth of 0 to 20 cm.
Disturbed soil samples were taken from the same points on and below the surface (at depths 0-20 and 60-80 cm respectively).
The samples were air dried, grounded and sieved through 2mm mesh. The undisturbed samples were saturated by capillary
action for 48 hours, weighed and submitted to a tension equal to a 60 cm water column on a tension table for 72 hours. After
balancing, the samples were drained and weighed. Finally, they were dried in an oven (105°C) and again weighed, to calculate
the volume of micropores, macropores and total pores, the latter by subtraction (EMBRAPA, 2011). Bulk density (BD) was
calculated from the following formula: BD (g cm-3) = Dry soil weight (Wds)/Total volume (Vt). Particle size was determined
using the pipette method, with prior separation of the sand by sifting, and the silt calculated by subtraction (EMBRAPA, 2011).
The pH of the samples was obtained in a 1:1 soil solution with water, as per Tedesco et al. (1995). The Ca2+, Mg2+ and
Al3+ content was obtained by atomic absorption spectrophotometry after extraction with 1.0 mol L-1 KCl. The potential acidity
(H+Al content) was estimated using the SMP method. The organic carbon content of the soil was obtained by organic-matter
carbon oxidation, with potassium dichromate reduction in acid medium under high temperature. The P, K and Na content was
extracted by the Mehlich method (EMBRAPA, 2011), with P determined by colourimetry and K and Na by spectrophotometry
(EMBRAPA, 2011). The S content was determined by colourimetry after extraction with CaHPO4 at 500 mg L-1 P. With the
data from the analysis, it was possible to calculate the cation exchange capacity (CECpH 7.0), sum of bases (Sb) and base
saturation (V%).
The data were analysed using the SPSS v20.0 statistical package. The attributes were compared for land use by
ANOVA at each depth, at 10% significance level. Data from some attributes required transformation (square root or
logarithmic) because lack of homogeneity of variance. In some cases, non-parametric methods (the Kruskall-Wallis and Mann-
Whitney tests) were applied. Additionally, a discriminant analysis was performed using principal discriminant functions and
calculating the distances of each sample in relation to the centroid of the treatment for each depth sampled.
3. Results and Discussion
Clay content has a wide distribution, between 20 and 38 percent. Despite this, all samples could be included in classes
3 and 4, according Wietholther et al. (2004). This attribute wasn’t analysed with respect to comparations between LUs, but is
used to explanation of results involving other attributes, because clay contents are directly related to them. Bulk density can be
used as a quality parameter that is related to soil compaction and to other attributes, such as porosity and soil moisture (Costa
et al., 2007). This attribute showed significant statistical differences between the types of land use (treatments), with the
highest density in HF of 1.90 m-3 m-3 (Table 1).
Research, Society and Development, v. 10, n. 16, e78101623317, 2021
(CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23317
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Table 1 - Mean values and standard deviations of the physical attributes of soils under different types of land use and
management, analysed at a depth of 0 to 20 cm.
Land use
Density
Macroporosity
Microporosity
Total porosity
mn
sd
Mn
sd
Mdn
Sd
Mn
Sd
g/cm3
----------------------------- m3 m-3 -----------------------------
Native Forest
1.41 B
0.13
0.08 ns
0.04
0.49 ns
0.08
0.57 ns
0.05
Agroforestry System
1.53 B
0.22
0.08
0.01
0.47
0.15
0.55
0.15
Horse Farm
1.90 A
0.14
0.07
0.42
0.41
0.04
0.48
0.06
Agricultural Crops
1.71 AB
0.18
0.09
0.14
0.42
0.09
0.51
0.10
mn = mean; sd = standard deviation. Uppercase letters indicate a significant difference at 10%. ns = no significant difference. Source:
Authors.
The critical density for root development is not the same for all soils, but some authors establish values of between 1.7
and 1.8 g cm-3 (Silva et al., 2015). The higher bulk density in HF is attributed to the compaction caused by the weight of the
animals on the ground, and to the lack of management of the pastures in the area. This result is accompanied by lower values
for macroporosity, microporosity and total porosity; however, these attributes, showed no significant differences between
treatments. These results are in accordance with Vzzotto et al. (2000), where the study shows a reduction in total porosity and
an increase in soil density, in the first five centimeters of depth of a flat soil. The study also shows that the roots of the pastures
were not efficient in unpacking the soil in a period of six months after occupation of the area with cattle. Other studies also
confirm the effect of animal trampling on soil compaction, such as Marchezan et al. (1998) who proved that there is an
increase in soil density and a reduction in total porosity after a period of grazing on the soil. Considering the history of the HF,
similar results were obtained by Correa & Reichardt (1995), evaluating the influence of the time of 4, 6 and 10 years of grazing
on physical characteristics of a soil, concluded that there was an increase in the resistance to penetration with over the years of
grazing, in the 0-10 cm layer of soil.
The various land-use types under study showed significant differences in pH (Table 2). The highest value for pH at
the surface was found in AFS (pH 5.3), showing no significant difference to HF.
The practice of incorporating pruning residue, together with the use of green manure, contributes to recycling and the
increase of base cations in the soil. The lack of any difference with HF demonstrates the efficiency for nutrient cycling of the
vegetation and animal waste. According to Vendramini et al. (2007) and Souza et al. (2018) animal waste deposited on pasture
soil is the main source of nutrient return to the system. For this reason, there is a great importance of the manure to maintain
soil fertility in the pasture, in which the animal excreta are responsible for the return of approximately 70 to 95% of the
nutrients ingested by the animals, both in the form of urine and feces (Balbinot et al., 2009).
The lowest value for pH was found in NF (pH 4.4), with no significant difference to AC. The higher acidity found in
the soil of NF, extremely acidic, can be explained by the existence of a large accumulation of plant residue, but only those with
natural occurrence in the area, with a lack of turning of the surface soil creating an acidification front (Silva et al., 2015).
Research, Society and Development, v. 10, n. 16, e78101623317, 2021
(CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i16.23317
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Table 2 - Mean values for the chemical attributes of soils showing a significant difference between treatments (land use and
management).
Land use
pH
V%
SOM
CE
Al
%
%
cmolcdm-3
cmolcdm-3
00 - 20 cm deep
Native Forest
4.4 C
34.3 B
2.88 A
17.93 A
0.70 AB
Agroforestry System
5.3 A
64.8 A
1.78 B
11.20 BC
0.10 B
Horse Farm
5.2 AB
61.5 AB
1.85 B
12.85 B
0.30 AB
Agricultural Crops
4.6 BC
35.5 B
1.15 B
9.13 C
0.78 A
60 - 80 cm deep
Native Forest
4.3 B
16.3 B
0.50ns
14.10 A
1.85 A
Agroforestry System
4.6 A
31.5 AB
0.40
11.55 A
1.65 AB
Horse Farm
4.6 A
36.5 AB
0.28
10.60 AB
1.83 A
Agricultural Crops
4.7A
42.2 A
0.23
6.57 B
0.55 B
V%: base saturation; SOM: soil organic matter; CEC: cation exchange capacity; Al: Aluminium. Uppercase letters indicate
significant differences between treatments within each depth. ns = no significant difference
Source: Authors.
The lowest value for pH in NF was repeated at a depth of 60-80cm, with no significant differences between the other
types of land-use or management. AC was the only LU type where pH and base saturation increased with depth, with a
significant difference at 60 to 80 cm in relation to all the other treatments. We evaluate that a little greater restriction on
drainage in this LU appear to contribute to cation retention, resulting in a value for V% significantly higher than in the other
treatments.
Soil organic matter (SOM) is a good indicator of soil quality, since according to Mielnickzuk (1999), it is susceptible
to changes due to management practices and may be related to most soil properties. At a depth of 0 to 20 cm, NF presented the
highest value for SOM (2.88%), differing from the other treatments, with values ranging from 1.15% in AC to 1.85% in HF.
With exception of NF, all LU have SOM contents considered low (Wietholter et al., 2004). The greater value for SOM in NF
shows that the use and management of the other soils under study reduced the C content of the soil, with a trend towards faster
processes of mineralisation and lower input of organic materials in managed systems (Houghton et al., 1991). At a depth of 60-
80 cm, there were no significant differences between treatments, with measured values varying less than 0.5%, which agrees
with reports from other studies that the impact of land use and management occurs mostly in surface layer (Portugal et al.,
2010).
The highest value for CEC was found in the soil of NF, with intermediate values in AFS and HF. AC had the lowest
value for CEC. NF has a high value for CEC in 0-20 cm; and all the others have medium values. The high CEC found in NF
can be explained by the natural addition of plant residue to the system, with no rotation or exposure of the soil. For the study in
question, CEC and SOM had a correlation coefficient of r = 0.69 (p<0.05), at a depth of 0 to 20 cm. SOM, with a large
quantity of loadings in the functional groups, can contribute from 20% to 90% of soil CEC (Fontes et al., 2001). At depth (60-
80 cm), there were significant differences between land-use types, especially between NF and AC, establishing a significant
correlation with clay (r = 0.90, p <0.05). As such, a change can be seen in the origin of the CEC dependent on land use and
depth (Khaledian et al., 2017).
Research, Society and Development, v. 10, n. 16, e78101623317, 2021
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AC presented the highest levels of soil Al at the surface, which can be explained by the low soil pH. At this depth, the
correlation coefficient between pH and exchangeable aluminium was -0.90 (p<0.05), confirming the close relationship between
the variables (Portugal et al., 2010). According to Silva et al. (2008), the organic acids present in the SOM can reduce Al
toxicity, since they participate in the complexation process, changing the mobility and solubility. At a depth of 60 to 80 cm, the
area of AC stands out with the lowest values for Al. In this case, the influence of the water regime is evaluated, the water
remaining longer in the soil, increasing the pH (Minasny et al., 2016). The pH to Al ratio had a coefficient of -0.71 (p<0.05),
while clay and Al had a correlation coefficient of r = 0.61, also significant at 5%.
The phosphorus content showed no significant differences between treatments in both depths, despite the values
having presented marked differences at the surface, similar to NF and HF (Table 3).
Table 3 - Mean values and standard deviations of the chemical attributes, phosphorus and sulphur under different types of land
use and management.
Land use
Phosphorus
Sulphur
Mn
Sd
Mn
Sd
mg kg-1
mg kg-1
00-20 cm deep
Native Forest
32.7ns
22.7
30.3 A
10.8
Agroforestry System
23.2
15.00
14.0 B
2.8
Horse Farm
17.1
19.1
17.3 B
7.9
Agricultural Crops
18.5
13.9
18.0 AB
1.8
00-60 cm deep
Native Forest
5.6ns
02.0
33.5ns
5.5
Agroforestry System
3.5
0.8
29.0
16.7
Horse Farm
4.6
0.9
25.5
14.5
Agricultural Crops
5.1
01.3
16.7
8.5
ns = no significant difference. Source: Authors.
Great variability in the LUs, expressed by high standard deviation values, resulted in absence of sensible diferences
between them. The fact that there are no treatments with intensive applications of phosphorus also contributes to this lack of
difference, but is importante to note that, mainly in NF, phosphorus content is generally high. According to Selle (2007), plant
residues from the forest are the main means of transferring carbon, nitrogen and phosphorus to the soil and the greatest
contribution to nutrient cycling is offered by the leaves, being responsible for about 67.5 to 75% of total nutrients transferred.
This trend in distribution was repeated for sulphur, but with significant differences for NF in relation to HF and AFS
in layer 0 – 20 cm, once again demonstrating the importance of native forest in cycling and maintaining sulphur in the surface
layers (Toledo et al., 2002; Cunha et al., 2013). At a depth of 60 to 80 cm, no difference was detected between land-use type,
the greater values at depth being highlighted due to the dynamics of the element itself (Rheinheimer et al., 2007). The elements
Cu and Zn showed significant differences only for Cu at a depth of 0 to 20 cm (not shown). AFS had significantly higher
values than AC and NF, and although it wasn’t stated in the interviews, we evaluate that some composts used in diseases
treatments had an important influence (Brunetto et al., 2018).
The samples were analysed relative to a set of determined attributes, to compare their attributes in relation to the mean
values for each land-use type. Discriminant functions within the multivariate analysis were used for this, with attributes that
presented a significant difference between treatments. Thus, for both depths, pH, CEC, and the levels of clay, organic matter,
phosphorus and sulphur were used. Soil density was used in 0-20 cm depth.
At 0 to 20 cm, the two principal discriminant functions expressed approximately 92% of the variation, with function 1
showing a greater relationship to CEC and organic matter, while function 2 was mainly related to pH and sulphur (Figure 2).
Research, Society and Development, v. 10, n. 16, e78101623317, 2021
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Figure 2 - Values assumed by centroids for the land-use types and samples under analysis from discriminant functions, at a
depth of 0 to 20 cm. 1 – Agricultural crops (AC); 2 - Agroforestry System (AFS); 3 – Horse Farm (HF); 4 - Native Forest
(NF).
Source: Authors.
Each of the 16 samples was classified as to treatment or original land-use type, with no sample being reclassified; NF
presented greater differentiation between the types of land use, while HF and AFS showed the smallest distance between each
other, followed by AFS and AC. It can be seen from the position of the representative centroids for land-use type, that the
intensity of the land use and management was a defining factor in the behaviour of the treatments, with more intensive uses
gradually assuming lower values for function 1 (Benites et al. 2010). Consolidation of these different land-use types of marked
installation time and with very clear differences between management practices, resulted in well-defined behaviour for the
types of land use and management under analysis. Whereas, at 60 to 80 cm, two groups were clearly formed, AFS and NF, and
HF and AC respectively (Figure 3).
Figure 3 - Values assumed by centroids for the land-use types and samples under analysis from discriminant functions, at a
depth of 60 to 80 cm. 1 – Agricultural crops (AC); 2 - Agroforestry System (AFS); 3 – Horse Farm (HF); 4 - Native Forest
(NF).
Source: Authors.
Research, Society and Development, v. 10, n. 16, e78101623317, 2021
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In this case, there seems to be an influence from the spatial positioning of the area of each treatment, which is
reinforced by the fact that a sample of NF was reclassified as an area of AFS, which in turn had a sample reclassified as NF;
one sample of AC was reclassified as HF. In this way, thirteen samples had their initial classifications confirmed. These
results, examined from a pedologic perspective, suggests that this soil, formed from alluvial deposits, may have some
variations in depth and thickness of the deposition layers. These are expressed in the areas of the treatments showing the
greatest distance between each other (Santos et al., 2012). So, it was possible conclude that, in surficial layer, land use and
management intensities was the main factor responsible for similarities and differences between LUs. For example, the more
likelihood occurred between AFS and HF may be interpreted like a result related with relatively similar degree of intensity and
environmental impact. On the other hand, at 60 to 80 cm. depth, physical proximity seems to be the main factor, grouping HF
and AC, and NF and AFS.
4. Conclusion
Changes were detected in chemical and physical attributes of the soils under the different types of land-use and
management. Among the physical attributes, only bulk density showed significant differences between treatments.
Chemical soil indicators displayed significant differences, such as pH, base saturation (V%), SOM, CEC, and Al, with
NF having the lowest values for pH at the surface, and the highest for CEC and SOM, consistent with an unused landscape unit
and agriculture use.
There appears to be different causes for the behaviour of each land-use type according to depth. At the surface, the
treatment with the lowest use intensity (NF) showed greater differentiation compared to the other treatments, whereas HF
assumed intermediate values between this and the other treatments (AFS and AC). At this depth, the influence of land-use type
and management was more marked. At 60 to 80 cm, the greatest cause of the differences was spatial distance, emphasising the
spatial variability of these soils.
Finally, some attributes indicated processes of alteration that are reflected in soil degradation, at least in its initial
stages. This is the case of HF, with high bulk density, and AC, with low levels of organic matter, together with the extremely
acidic pH and higher aluminum content. These results highlight the susceptibility to impacts generated from land uses and
management changes, and the importance of sustainable use in this environment.
To complement this research, new studies with other chemical and physical attributes of these soils, in the four
Landscape Units, are important. Thus, it will be possible to obtain new indices and soil quality parameters.
With the maintenance and preservation of these Landscape Units, it will be possible to generate data on changes due
to use and long-term management in this plain, creating important reference data.
Acknowledgments
The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the
Master’s scholarship. The authors further wish to thank the departments of Agriculture, Zootechnics and Plant Health of the
School of Agronomy at UFRGS. Thanks are also due to the UVAIA group and to the administration of the School of
Agronomy at UFRGS.
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