Renato Paiva de Lima

Soil compaction commonly occurs as compacted layers with reduced permeability, which can significantly affect water flow and retention throughout the soil profile, shortening drainage time and altering soil penetration resistance. The objective of this study was to investigate the impact of a compacted layer on soil water flow and penetration resistance using numerical modeling based on Richards’ equation implemented in COMSOL Multiphysics. A two-dimensional problem representing a soil profile was constructed with and without the presence of a compacted layer. The effect of compaction was examined by systematically increasing both the thickness of the compacted layer and the degree of compaction. Model parameterization was based on literature data for a clayey soil, including soil water retention curves, saturated hydraulic conductivity, and parameters describing soil penetration resistance. These parameters were used to numerically solve Richards’ equation for drainage from saturated conditions and to assess the influence of compacted layers on the temporal evolution of penetration resistance as a function of drainage time up to 10 days free drainage. The results showed that the presence of a compacted layer caused only minor changes in matric potential along the soil profile over time. The dominant factor controlling changes in penetration resistance in the simulations was the degree of compaction itself, as the lower permeability of more compacted layers promoted greater water retention in their vicinity, thereby alleviating soil penetration resistance. In conclusion, numerical simulations showed that compacted layers induced only minor changes in soil matric potential during drainage for actual compaction degree conditions. The degree of compaction was the primary factor controlling the temporal evolution of soil penetration resistance, outweighing the effect of layer thickness. Lower permeability in highly compacted layers promoted greater local water retention, which mitigated increases in penetration resistance over time. The scenario examined in this study should be extended to soils with varying textures and permeability in order to assess the broader applicability of these conclusions.

Soil structure can mitigate both mechanical impedance and water stress, thereby modulating root elongation and access to deep soil water. Although process-based root growth models represent soil–root interactions, they rarely account explicitly for structural conditions and their consequences for the combined effects of water and mechanical stresses on root growth. We quantify how soil structure under no-tillage influences soybean root elongation, effective rooting depth, and water-deficit mitigation, and we parameterize these effects in a biophysical root-growth model. A long-term field experiment established in 2016 compared three cropping systems preceding soybean (Glycine max): ruzigrass (Urochloa ruziziensis), maize (Zea mays), and fallow. Soybean root length density and soil physical attributes were measured in nine layers down to 210 cm. Effective rooting depth was defined as the depth containing 95% of total root length. Plant-available water was computed from soil water retention between −60 and −15,000 hPa, and readily available water was assumed as 50% of plant-available water within the rooted zone. Grain yield was determined at harvest. In addition, soybean root elongation rate was measured in the laboratory using core from field and repacked samples across gradients of degree of saturation and soil penetration resistance. The structural effect was incorporated as a parameter in a biophysical model that combines water and mechanical limitations to root elongation. Increasing soil penetration resistance from 1.0 to 3.5 MPa reduced relative root elongation by 46% in preserved structure, whereas reductions reached 76% in repacked soil. At 0.5 MPa and 60% degree of saturation, elongation in repacked soil was 29% higher than in preserved structure, but both structural conditions converged as soil penetration resistance increased to 1.0 MPa. Under 90% degree of saturation, elongation in preserved structure was nearly threefold that in repacked soil. In the field, effective soybean rooting depth (in a trench of 210 cm depth) differed among previous cropping systems, with ruzigrass promoting substantially deeper roots (154.7 cm at 95% cumulative distribution) compared with maize (127.9 cm) and fallow (121.0 cm). Root length density in the 0 to 10 cm layer was highest after ruzigrass (4.72 cm cm-3), followed by maize (3.33 cm cm-3) and fallow (2.48 cm cm-3). Cumulative root length in the soil profile from 0 to 210 cm reached 202.2 cm cm-2 after ruzigrass, compared with 128.4 cm cm-2 after maize and 94.3 cm cm-2 after fallow. Soybean yield was 2.9 (after ruzigrass), 2.6 (after maize), and 2.1 Mg ha-1 (after fallow). Plant-available water in the soybean root zone was 175 mm after ruzigrass, compared with 145 mm after maize and 140 mm after fallow, indicating a 25% increase relative to fallow. Assuming evapotranspiration of 7 mm d-1, this represents approximately 15 days of water supply after ruzigrass versus 12 days after fallow. Preserved soil structure improved soybean root performance under strong physical constraints and increased deep water access. Explicitly representing soil structural conditions in simulation models can improve predictions of rooting depth and drought mitigation under no-tillage.Acknowledgements: AGRISUS Foundation [PA 3534/23], CNPq [409621/2023-4] and FAPESP [23/10427-3 and 23/11945-8].

The infield transport of harvested sugarcane stalks (transshipment operation) during mechanized harvesting is widely recognized as the operation with the greatest potential to induce soil compaction. Nevertheless, there is still a lack of experimental data on the effect of compaction resulting from transshipment vehicles on soil physical functionality. We assessed the effects of realistic infield traffic from different transshipment configurations on soil structural and functional properties and their effects on crop yield. Three transshipment systems under controlled traffic farming system were evaluated: a tractor pulling one four-axle trailer unit with 21 Mg carrying capacity (1T/21), a tractor pulling two axle trailer units with 10 Mg carrying capacity (2T/10), and an autonomous truck with four axles and one trailer with 20 Mg carrying capacity (1TT/20). Several analyses were conducted, including degree of compaction (DC), macroporosity (MaP), air-filled porosity (ε_a10), soil air permeability (k_a10), and saturated hydraulic conductivity (Ks). Soil samplings were performed in surface and subsurface layers of an Oxisol in southeastern Brazil at the planting row and inter-row, and at the midpoint between these positions, over two consecutive sugarcane harvests. Although machine traffic occurred at low soil water content, all transshipment configurations promoted soil compaction during the first harvest, with the greatest changes in soil physical attributes in the 0–10 and 10–20 cm layers in the inter-row center and, in some cases, at the midpoint. However, all treatments preserved soil conditions in the planting row. The 1TT/20 transshipment induced the greatest compaction, with significant effects on DC, MaP, and ε_a10 in the inter-row and midpoint positions. Despite structural alterations, no significant differences were observed among treatments for k_a10 and Ks. However, after the first harvest, k_a10 frequently reached critical thresholds of low permeability in trafficked areas, indicating functional degradation of soil aeration. Sugarcane yield was not affected by the transshipment configurations. The absence of productivity differences reflects the effectiveness of controlled traffic in confining compaction to the inter-row center and midpoint while preserving the planting row. Although short-term yield was not affected, structural degradation in trafficked areas and the persistence of high subsoil compaction indicate the potential for cumulative long-term impacts. Continuous monitoring and integrated soil management strategies remain essential to mitigate progressive compaction under mechanized sugarcane harvesting.

Soil respiration, the exchange of gases between soil and the atmosphere (O₂ consumption and CO₂ production), plays a key role in ecosystem functioning and climate regulation. This study investigated the short-term temporal variability of soil CO₂ emissions and O₂ influx and their relationship with tropical climate conditions and soil attributes in the Cerrado region, Selvíria, MS, Brazil. Soil CO₂ emissions were measured using the LI-8100 portable system, while soil O₂ influx was estimated by linear interpolation of O₂ variation inside the chamber using a UV Flux 25% (ultraviolet light) sensor. Soil temperature and moisture were measured simultaneously in three land use types: pasture (~11 years) and reforested areas with native species and eucalyptus (~35 years). Soils were classified as Oxisoils according to Soil Taxonomy. Significant short-term temporal variability was observed in CO₂ emissions (mean 3.2 ± 0.5 µmol m⁻² s⁻¹), O₂ influx (mean 1.8 ± 0.3 mg O₂ m⁻² s⁻¹), soil temperature and moisture across the land use types. Pasture areas exhibited the lowest CO₂ emission rates, associated with improved soil attributes (soil organic matter, sum of bases and pH) due to management practices, while reforested areas showed overlapping soil respiration patterns and higher temporal variability. Principal component analysis revealed strong coupling between O₂ influx and CO₂ emission in reforested soils. These findings highlight the influence of land use on short-term soil respiration dynamics and underscore the importance of sustainable pasture management and reforestation in the Brazilian Cerrado. The results also support public policies aimed at restoring degraded pastures, reducing deforestation and burning, and enhancing soil carbon sequestration to mitigate climate change.

The specific role of each fraction of soil C (i.e., particulate [POC] or mineral‐associated organic carbon [MAOC]) in each soil strength mechanism remains unexplored. We investigated the relationships of total organic C and its physical fractions with soil strength of two tropical soils (sandy clay loam [SCL _soil ] and sandy clay [SC _soil ]). We measured soil strength indicators from oven‐dry aggregates [tensile strength ( σ _t )] and some related to soil compaction [precompression stress ( σ _p ), compression index ( λ ), and penetration resistance (SPR) at constant matric potential (−100 hPa)]. These soil strength indicators were used as response variables in path analyses to determine direct effects of C, MAOC, and POC mediated by key physical strength inducers (bulk density or water content). Results suggest a C role conferring soil strength verified by positive correlation with tensile strength and SPR increase, positively influenced by MAOC in SCL _soil and C/POC/MAOC in SC _soil . For SPR, the C effect was mediated by water content or bulk density (i.e., indirect contribution for correlation). Organic C, in turn, showed limited effect on soil compressibility. These findings indicate that increases in soil carbon that enhance aggregate mechanical strength and penetration resistance do not result in reduced soil compressibility (i.e., resistance to compaction). In sandy clay loam soils, MAOC plays a key role in increasing soil strength, whereas all carbon fractions contribute to strength gains with increasing clay content. Thus, while organic carbon can promote beneficial structural stability in the long term, it may also increase SPR, which affects root growth.

Livestock production systems can negatively affect soil structure, resulting in negative changes in physical–hydraulic properties, compromising soil functioning and productivity. This research aimed to evaluate the effects of rotational silvopastoral systems on soil physical–hydraulic functioning in their second year of implementation. The study was performed under Oxisol soil with a loamy sand texture in Southeast Brazil. We considered four grazing systems: an intensive silvopastoral system with Panicum maximum in consortium with Leucaena leucocephala (ISPS + L), an intensive silvopastoral system with Panicum maximum in consortium with Tithonia diversifolia (ISPS + T), an silvopastoral system with Panicum maximum (SPS) with tree row (TRs), and open pasture under a rotational grazing system with Panicum maximum (OP). The treatments ISPS + L, ISPS + T, and SPS had tree rows (TRs) every 20 m composed of Khaya ivorenses, Leucaena leucocephala, Eucalyptus urograndis, Acacia mangium, and Gliricidia sepium. Nine physical–hydraulic indicators were evaluated in the first 0.40 m of depth: bulk density (Bd), total porosity (TP), macroporosity (MaP), microporosity (MiP), field capacity (FC), permanent wilting point (PWP), available water content (AWC), total soil aeration capacity (ACt), and S-index. The soil physical–hydraulic properties were sensitive to the effects of the livestock systems. The use of silvopastoral systems in consortium with grass (ISPS + L and ISPS + T) allowed for better soil water retention, resulting in higher FC and AWC than the OP, SPS, and TR. The indicators Bd, ACt, MaP, FC, MiP, and S-index presented the greatest variance; however, FC, ACt, MaP, and MiP enabled the greatest differentiation among systems. Therefore, these properties are important in studies on soil physical quality since they provide information about the soil porous status and its ability to retain water and exchange soil air and gases. Therefore, enhancing the physical–hydraulic attributes of the soil in silvopastoral systems with shrub species is crucial for ensuring long-term productive sustainability and strengthening environmental resilience against future climate challenges.

Sugarcane crops have a long cycle with successive harvests before re-planting, and row gaps are one of the main problems associated with the yield. The objective of this study was to establish an alternative methodology for measuring the planting and regrowth of sugarcane rows using UAV (Unmanned Aerial Vehicle) images and to compare it with manual measurements. This study was conducted in a 1 ha experimental area under mechanized harvesting. The reference methodology consists of measuring the continuous distances without regrowth between two plants along a planting row, considering distances greater than 0.50 m as gaps and the following gaps classes: >0.5–1.0 m, >1.0–1.5 m, >1.5–2.0 m, >2.0–3.5 m, and >3.5 m. Images were collected from a UAV equipped with a 12-megapixel RGB camera. The number of regrowth gaps measured through imaging for the class of gaps with a length between 0.5 and 1.0 m was eight times higher than field measurement. In the class of gaps with a length between 1.0 and 1.5 m, the result is the opposite, as the field measurement was approximately three times higher than the UAV measurement, with a significant difference in both classes. In the other length classes analyzed, the number of gaps did not show significant differences. Our results suggest that regrowth gaps can be quickly estimated with the proposed methodology for gaps greater than 1.5 m. For gaps smaller than <1 m, the methodology using a UAV is not accurate.