Search

Abstract In the last decades, the use of biofuels as a mitigation measure for carbon emissions has led to land use and land cover changes in southeastern Brazil, especially in Paulista Peripheral Depression – Paraná Sedimentary Basin. Considering the human-landscape system associated with energy policy, these changes can affect landscape and natural resources over a range of temporal and special scales. Thus, the aim of study was on how human-landscape interactions have influenced the geomorphological dynamics in a São Paulo region that contains sugar cane crops associated with soils derived from sandstones and mudstones. The use of the Universal Soil Loss Equation (USLE) in three different scenarios from land use changes allowed verifying how they have affected soil loss: natural conditions (savannah), current land use and with the expansion of sugar cane crops. In addition, the total sediment transported, the sediment delivery ratio and the rate of soil removal were measured, considering the current land use. The land use scenarios pointed out that the land use change is directly related to increasing rates of soil loss, i.e. 0.03, 3.5 and 12.6 t ha−1 yr−1 for the natural conditions, current land use and with the expansion of sugar cane crops, respectively. These rates in the current land use and with continuous expansion of sugar cane crops are higher than the tolerable erosion limits in 17 and 57% of the study area, respectively. The suspended sediment concentration increases with increasing Cachoeirinha Stream discharge, with a specific daily flux of 88 kg km−2 day−1. The mean monthly flux in 2014 was 32 t month−1, with varying from 3.1 (August) to 144 (January) t month−1. The wet period was responsible for ca. 90% (436 t) of the total solids transported in 2014. The sediment delivery ratio was 9% of the total soil loss. The current rate of soil removal of 25.8 m Myr−1 is almost 3-fold higher than the long-term denudation rates suggested for the Peripheral Depression (9 m Myr−1). With the continuous expansion of sugar cane crops, the rate of soil removal probably will be higher than that obtained in the current scenario and, consequently, the current denudation rates should increase further. Thus, this study reinforce that the human-landscape systems in São Paulo State associated with energy policy are complex and increase the natural processes of soil removal and, consequently, affect the landscape evolution. Highlights • Human-landscape system associated with energy policies was study at São Paulo State. • Land use changes were directly related to increasing rates of soil loss. • The specific daily flux of suspended sediment was 88 kg km−2 day−1. • Approximately 90% of the total solids were transported in the wet period. • The current rate of soil removal was 3-fold higher than the long-term denudation rate. [ABSTRACT FROM AUTHOR]

Land-use/land-cover (LULC) pattern influences water quality, however, this relation may be different for various spatial scales. We evaluated the LULC effects on water quality of tropical low-order streams, comparing watershed and riparian zone models. Water quality parameters were analyzed separately and together using linear mixed and multivariate models. The results indicate that the forest cover plays a significant role in keeping water clean, while agriculture and urban areas lead to water quality degradation. Pasture land had mixed effects, but in general was not correlated with poor water quality. Dissolved oxygen, phosphorus, sediment, and fecal coliforms were influenced by LULC pattern at the watershed scale, while nitrogen and organic matter were more affected by the riparian zone composition. The water quality also varies with seasonal changes in streamflow and temperature. The overall water quality variation is explained better by the LULC composition within the watershed than in the riparian zone. [ABSTRACT FROM AUTHOR]

• Irrigation and long-term cultivation (26 years) did not affect SOC stock. • SOC dynamics in the subsoil is particularly vulnerable to irrigated agriculture. • Land use favors large amounts of aliphatics products along the soil profile. • Management changes microbiological parameters, especially bacterial communities. • Changes in the bacterial community suggests alterations in groups of subsoil C. Changes in the global water cycle affect irrigation requirements and soil processes as well as the structure of soil microbial communities and function and the carbon (C) balance. The microbial structure and C sequestration under land use changing scenarios are rarely studied in the semi-arid region of Brazil. Here, we assessed the effects of land-use changes (irrigation and cultivation) on C storage in the soil and the structure of total bacteria (16S rRNA gene profile) and fungus (18S rRNA gene profile) at soil depth. We evaluated two soil profiles in the semi-arid region in northeastern Brazil. Profile P1 in an area with long-term irrigation (1,500 mm of water per year) and cultivation (small-scale farming systems, mainly with subsistence crops, which is a frequent land use system in the region of irrigated soil) for about 26 years. Profile P2 under natural conditions with 400 mm of water per year of rainfall (rain-fed hyperxerophilic Caatinga). Land-use changes showed a small influence on C storage; however, the changes strongly affected the soil organic matter (SOM) quality as well as the bacterial and fungal community structure, indicated by higher contents of labile-C and microbial biomass along with lower C-CO 2 emission. The relatively large amounts of aliphatic groups in the soil surface and subsurface in the cropped system (P1) suggested enrichment of methylene structures and probable increase of microbial-derived compounds. Methoxylic and aromatic groups tend to increase at depth (Bt horizon) indicating that the subsoil C responds to soil management changes. The structures of the bacterial community are distinct at depth in P1 and more similar at depth in P2. On the other hand, the structures of the fungal communities are more similar at depth in P1 than in P2. Furthermore, the irrigated agriculture also presented a carbon management index greater than 140% in most horizons, indicating that the soil management system did not cause soil degradation. [ABSTRACT FROM AUTHOR]

Abstract: Native Indians (Macuxi, Ingarikó and Uapishana) in the Raposa–Serra do Sol Indian Reserve have been cultivating forest soils since the early XIX century, especially those derived from dolerite sills, scattered within the quartzitic dominated landscape. Representative soils developed from mafic rocks under Indian shifting cultivation in northeastern Roraima, were submitted to physical, chemical and mineralogical analyses to characterize their pedogenetic characteristics and infer on their status under native Indian shifting cultivation. The soil profiles were classified as: Orthic Ebanic Chernosol (USDA Mollisol), vertic Orthic Ebanic Chernosol (USDA Mollisol), Eutrophic Haplic Cambisol (USDA mollic Inceptisol) and Eutrophic Red Nitosol (USDA Red Alfisol), which occupy, respectively, lower slopes and less dissected terrains (Mollisols) and steeper slopes (Alfisols). The first two are eutrophic, and not typical of the Amazon region. Their mineralogies range from kaolinite/goethite rich upland, deeply weathered Nitosol, to 2:1 clay rich downslope Chernosols. The latter has primary minerals in the silt fraction and high CEC resulting in high fertility. The Nitosols reveal a process of severe topsoil loss, due to widespread sheet erosion from deforestation and shifting cultivation. Chemical analyses showed varied soil fertility, ranging from high levels in the Chernosols to a low level in the non-cultivated Nitosol. Phosphorus levels are limited in all soils, despite the high fertility. The Chernosols located in lowland, flat areas close to the valley floor are more suitable environments for the slash-and-burn native farming system. In the Chernosols and Cambisols, the clay activity below the value limit for this class indicates a current natural process of increasing leaching. The more weathered and eroded Nitosol showed low Fe-oxalate and Si-oxalate levels. Micronutrients such as total zinc and copper, decreased with depth and weathering. The Nitosols showed the highest phosphate adsorption levels (1.574mg g−1 of soil) which can be attributed to its clayey texture. Chernosols showed overall lower P adsorption values, increasing with depth. All soils under native Indian cultivation display signs of physical and chemical degradation due to shortened fallow under intense land use pressure in the Raposa–Serra do Sol Reserve. [Copyright &y& Elsevier]

• Successful prediction of weathering indices with MIR spectroscopy. • Land use explains minor part of variations in soil thickness and weathering degree. • Soil thickness and weathering degree mainly determined by slope gradient. • Locally high erosion does not necessarily result in changes at landscape-scale. Land use and land cover changes (LUCC) can drastically alter various components of the critical zone, including soil thickness and soil chemical weathering processes. Often these studies, however, tend to focus on extreme cases, not representing what actually happens on average at larger, regional scales. Here, we evaluate the impact of LUCC on soil thickness and soil weathering degree at the regional scale, where we use soil spectroscopy to derive weathering indices. In a subtropical region in Southern Brazil, we collected calibration/validation soil samples (n = 49) from 4 different locations for which we measured the mid-infrared (MIR) spectral reflectance and 3 soil chemical weathering indices: chemical index of alteration (CIA), the total reserve in bases (TRB), and the iron ratio (Fe d /Fe t). We used partial least square regressions on this calibration/validation dataset to relate the MIR spectra of the soil samples to these weathering indices, resulting in good calibration relationships with R2 values of 0.97, 0.91 and 0.84 for CIA, TRB and Fe d /Fe t , respectively. Applying these relations to MIR spectra of regionally collected soil samples allowed us to calculate soil weathering degrees for a large number of soil samples (n = 229), without requiring costly and time-consuming chemical analyses. We collected these soil samples at 100 mid-slope positions: 50 under forest and 50 under agricultural land use. Land use explained only a minor part of the variation in soil thickness and weathering degree. Thus, while local water and tillage erosion rates might be considerable after deforestation, this has not led to significant reductions in average soil thickness and has not affected soil weathering degree. Slope gradient is the main factor influencing the spatial variability in soil thickness and weathering degree on mid-slope sections in our study area. Human activities over the last century did not fundamentally alter these patterns. [ABSTRACT FROM AUTHOR]

• The measured attributes contributed significantly to discriminate between land use systems; • Agroforestry systems contribute to the reduction of the cohesive layers of soils; • Agroforestry systems therefore have the ability to improve the physical soil quality. • Land use, management and physical attributes of dense Ferralsols in tropical northeastern Brazil. In Brazil, Haplic Ferralsols (Densic) are commonly known to have physical limitations, including higher bulk density and less drainable porosity, less water infiltration and greater resistance to root growth. However, there are extensive areas with these soils in Brazil that are important for agricultural production. Because maintaining and/or recovering the physical quality of these soils is an important task to maintain agricultural sustainability, the objective of this study was to evaluate the impact of different use and management systems on the physical quality and total organic carbon content of Haplic Ferralsols (Densic) in northeastern Brazil. The evaluated systems were: conventional planting (CC), pasture (PP) and two agroforestry systems: one 7 years (AF7) and the other 12 years old (AF12). An area of secondary forest with remnants of the Atlantic Forest Biome (SF) was selected and sampled as a reference. The total organic carbon content (TOC), flocculation index (FI) and particle density (Dp) were determined. Saturated hydraulic conductivity (Ko), macroporosity (MaP), microporosity (MiP), total porosity (TP), soil bulk density (Ds) and aggregate stability were also determined in samples collected in the 0– to 0.10, 0.10 to 0.20 and 0.20– to 0.40 m soil layers. The variables that best distinguished the agroforestry systems from the other systems were GMD, MaA, WMD and TOC. Correlations of these variables, all related to the soil structure in the AF7 and AF12 systems, contribute to maintaining or regenerating soil aggregation. None of the soil management systems were grouped with the forest area, although areas in the agroforestry systems had lower impact on the physical soil quality parameters compared to the CC and PP systems. [ABSTRACT FROM AUTHOR]

• Thermal techniques are robust and rapid methods for determining changes in SOC. • SOC of our sites was mainly represents polysaccharides and aliphatic structures. • PA + SM and NV showed higher contribution of microbial-derived in the SOC. • The application of SM increases SOC content. • SM application combined to no-tillage practices may lead to SOC stabilization. The pool of carbon (C) present in soil systems is larger than the amount of organic C stored in living biomass and the atmosphere. Soil degradation has increased soil C emissions at the expense of C accumulation. Climate-smart management practices may be adapted to increase C sequestration as soil organic carbon (SOC). To avoid the SOC loss, different strategies have been applied, including no-tillage and organic fertilizer. Here, we investigated thermal stability of SOC after long-term manure application across land uses and tillage systems in weathered soils of Brazil. We chose five commercial areas with different land uses: pasture with swine manure (SM) application (PA + SM), conventional tillage (CT) with SM application (CT + SM), natural vegetation (NV), no-tillage with SM application (NT + SM), and no-tillage (NT). Thermal analysis revealed that SOC oxidation and CO 2 emission started around 240 °C, close to gibbsite and goethite structural collapse, suggesting preferential adsorption of SOC onto these minerals. Approximately 50% of SOC for all sites was oxidizable at lower temperature (~315 °C) which suggests the prevalence of polysaccharides, decarboxylation of acidic groups and dehydration of hydroxylate aliphatic structures, regardless of land-use. The energy content of SOC for NV (6.5) and PA + SM (10.6) were in average, 46% lower than other treatments which suggest a higher necromass contribution to SOC in these systems. However, the higher energy content in CT + SM (14.9), NT + SM (16.5), and NT (15.8), suggests a higher contribution of plant-derived compounds in SOC. Our results showed that SM application on pastureland reached similar SOC accumulation to NV and increment of ~33% when applied to no-till system. We conclude that SM could a drive higher C accumulation and stabilization if preferentially associated to soil conservative system. [ABSTRACT FROM AUTHOR]

• Capacitive probes calibration showed good results under different land uses. • Changes in land use influence the spatial and temporal variability of θv. • The deforestation of the caatinga reduces the θv in 47%. • Converting the Caatinga for forage cactus decreases the reduction of θv for 26%. • It is recommended to establish forage cactus in already deforested areas. The semiarid region of Brazil undergoes constant changes in land use due to the process of deforestation and high water seasonality, represented among other variables by a decline in the soil moisture content. In this study, the influence of land use on the soil moisture dynamics is analysed. For this purpose, three experimental sites were evaluated, characterised by different types of land use: an agroecosystem of forage cactus, a deforested environment and an area of Caatinga vegetation, located in the semiarid central hinterlands of Brazil. Calibration of the Diviner2000® capacitive probes was carried out using the relationship between the soil volumetric moisture content (θv), obtained by the gravimetric method, and the relative frequency readings of the probes. Weekly measurements of the moisture content were taken at 22 points at depths of 0.00–0.60 m from November 2014 to October 2017, providing 157 sampled days. The mean values and standard deviations of the θv variable for the three surfaces were analysed over twelve periods, and grouped according to the local water regime into rainy, dry and transitional. To analyse the temporal stability of θv, the relative difference and the Spearman correlation matrix were calculated. Finally, multivariate principal component analysis (PCA) was used to identify associations between the mean values of θv and physical properties in the different soil layers. Based on the results, the local calibration curves presented significant coefficients of determination, showing that the equations can be used for reliable estimates of θv. The θv was higher in the Caatinga (0.086 m3 m−3), intermediate in the forage cactus (0.064 m3 m−3) and lower in the deforested area (0.045 m3 m−3). Changes in land use influence the spatial variability of θv in the soil layers, which responded to the local rainfall regime, especially in the upper layers (0.05–0.25 m). Significant differences in θv between soil surface coverage occurred during the dry sub-periods and the transition periods, when the Caatinga was superior to the other areas. The temporal stability analysis identified the forage cactus area as the most representative location for θv estimates, while the Spearman correlation matrix detected the more-unstable areas of moisture, with persistent moisture patterns between the dry sub-periods and transition periods only. Associations between moisture and different soil properties were affected by soil surface coverage and soil layer depth. All the proprieties explained moisture distribution along the profile. It can be concluded that converting the Caatinga vegetation into other soil surface coverages changes soil-moisture distribution patterns, resulting in a reduction in θv of 26% and 47% for forage cactus and deforested areas, respectively. Therefore, the establishment of forage cactus in current deforested areas of the Brazilian semiarid may attenuate the temporal variability and reduction of soil moisture compared to bare soil surfaces. [ABSTRACT FROM AUTHOR]