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Sugarcane (Saccharum officinarum L.) straw is a promising feedstock for bioelectricity and cellulosic ethanol in Brazil, but some straw is also needed to sustain nutrient cycling and crop yields. A literature review and two field studies were conducted to quantify above-ground macronutrient accumulation by sugarcane. Five straw removal scenarios using different amounts of biomass and nutrient composition data of top (green) and bottom (dry) leaves were constructed to estimate fertilizer requirements associated with straw removal in central southern Brazil. Calculated straw removal for five scenarios (S1 to S5) was 3.5, 7, 3, 6, and 12 Mg ha−1, respectively. By removing 12 Mg ha−1 of straw (S5), the potential N, P, K, Ca, Mg, and S removal was 69, 7, 92, 45, 16, and 14 kg ha−1, respectively. It represents a nutrient (NPK) replacement cost of US$ 90.00 ha−1 or US$ 7.60 per Mg of removed straw. The scenario analysis shows that less-impacting strategies are those that maintain top leaves in the field and harvesting only bottom leaves (S1 and S2), whereas total removal (S5) could double NPK-fertilizer consumption in sugarcane fields by 2050. Our findings provide stakeholder guidelines for improved straw management, establish an economic value for accumulated plant nutrients, and promote both socio-economic and environmental benefits of more sustainable bioenergy production in Brazil. [ABSTRACT FROM AUTHOR]

Global promotion of bioenergy for mitigating climate changes has arisen the interest of the Brazilian sugarcane industry to use crop residue (straw) as an important source of biomass for bioelectricity and cellulosic ethanol production. However, the sugarcane straw influences several soil properties, supporting soil quality and crop yields. Thus, defining an optimal removal rate would keep the benefits of the sugarcane straw in soil, and also maximize the bioenergy production. Shifts on soil bacterial structure have been used as a sensitive indicator of land management and could help to prescribe an optimal removal rate. We conducted a field study at two sites in São Paulo state to investigate how rates of sugarcane straw removal are associated with soil bacterial community changes over 1 year. Four sugarcane straw removal rates were evaluated: no removal (~ 14 Mg ha−1 of dry mass left) and 50% (~ 7.0 Mg ha−1), 75% (~ 3.5 Mg ha−1), and 100% of straw removal. The soil bacterial community structure was evaluated by the terminal restriction fragment length polymorphism (T-RFLP). Our results indicated that soil bacteria communities change over time, regardless of site conditions, and their changes are more strongly associated with changes on straw composition. A similar straw decomposition dynamics was observed under moderate (50%) and no removal treatments. Moderate straw removal induced the lowest modification of the bacterial niche occupancy and highest microbial interaction when compared with the no removal. Therefore, the identification of changes in soil bacterial structure community is useful to provide guidance for sugarcane straw removal. [ABSTRACT FROM AUTHOR]

Growing global demand for bioenergies has raised the interest in using sugarcane crop residues (straw) as feedstock to produce cellulosic ethanol and/or bioelectricity in Brazil. However, indiscriminate straw removal may deplete soil quality, particularly induced by its negative effects on soil microbial communities. A 2-year field study was conducted in soils classified as Oxisol (site 1) and Ultisol (site 2) in southeastern Brazil. The experiment started after plant cane cycle, establishing three straw removal rates (treatments), as follows: total removal, moderated removal, and no removal of sugarcane straw from the field. The amount of straw left on the soil surface and removed in the treatments varied according to the straw yield of each year and location. Soil samples were collected at 0–5- and 5–10-cm layers. The total abundance of bacteria, archaea, and fungi were analyzed by real-time quantitative polymerase chain reaction (qPCR). Bulk density, pH, base saturation, cation exchange capacity, phosphorus (P), and total organic C and soil microbial biomass C (MBC) were also measured. The soil chemical results indicate that the Oxisol presents higher inherent soil fertility compared with the Ultisol. In the first year, the straw had a different significant effect for bacterial and archaeal abundance in both soils and for fungi in the Oxisol site. In the second year, the numbers of gene copies of bacteria, archaea, and fungi in the 0–5-cm layer were higher under moderated and no removal when compared with those under total removal, regardless of site. The MBC decreased significantly under total removal of straw at the Ultisol site. Moderate straw removal has no significant effect on the abundance of soil microbes, but total straw removal may induce sharp reductions (from 23 to 54%) on microbial abundance. Soil microbes are a sensitive indicator to assess soil changes induced by crop residue management and should be taken into account for defining sugarcane straw management towards a sustainable bioenergy production. [ABSTRACT FROM AUTHOR]

Burning sugarcane (Saccharum officinarum) prior to manual harvest has been gradually replaced by a mechanized, green harvesting system that returns large amounts of crop residue (straw) to the soil surface in Brazil. A portion of the residue is required to protect soil against erosion, but some may be available as a feedstock for bioelectricity and cellulosic ethanol. Since excessive straw removal will degrade soil resources, it is imperative to determine the amount of straw needed for soil protection and to incorporate that information into decision-support tools so that straw management is sustainable. Our objective was to determine the amount of sugarcane straw needed to completely cover the soil surface. Photographic image analysis was used to quantify surface soil cover under 0 to 21 Mg ha−1 of straw. Photos of 1-m2 areas where various quantities of straw were homogeneously distributed were taken at a resolution of 8 megapixels (3264 × 2448 pixels) and then processed with ImageJ 1.52a software to obtain soil cover fraction. Straw layer thickness was also measured to the nearest millimeter using a ruler mounted in a rectangular acrylic box (0.5 m2, 0.15 m height) into which the equivalent of 1 to 21 Mg ha−1 of straw was placed. Soil cover increased exponentially, reaching more than 90% with 3 Mg ha−1 and full coverage with approximately 7 Mg ha−1. Straw layer thickness increased linearly by 0.5 cm per Mg of straw left on the soil surface. Our findings will lead to more sustainable straw management practices that balance soil conservation and provision of feedstock for bioenergy production. [ABSTRACT FROM AUTHOR]

In Brazilian sugarcane (Saccharum spp.) production systems, the practice of moving harvesting residue from row to inter‐row positions (i.e., raking) has increased in response to producer concerns over the potential negative effects of sugarcane straw on crop establishment and stalk yield. Despite increasing adoption among sugarcane farmers, the impacts of straw raking practices on plant growth and yield remain unclear. A 2‐yr experiment that included both dry and wet seasons was conducted at two sites in southeastern Brazil to evaluate straw management strategy effects on plant tillering, phytomass accumulation, plant nutritional status, and stalk yield. The experiments were established at the Bom Retiro mill and the Univalem mill. Experimental treatments included raking straw to inter‐rows (raked), total straw removal (bare soil), and no straw removal (straw cover). Raked and bare soil treatments improved plant tillering but did not influence final plant population. Straw management had a slight effect on phytomass accumulation. Reduction of phytomass yield was observed from the first to the second ratoon during both seasons at both sites. At Bom Retiro, phytomass yield decreased 37% for stands established during the dry season and 19% for stands established during the wet season. At Univalem, phytomass yield decreased 20% for stands established during the dry season and 30% for stands established during the wet season. Retaining straw in the field (regardless of treatment) increased leaf tissue P content but not stalk yield. Raking straw from row to inter‐row positions at these locations in southeastern Brazil had no benefit on sugarcane yield but may result in soil compaction and higher production costs over time. [ABSTRACT FROM AUTHOR]

Abstract Biofuels are fundamental for meeting societal energy needs within the next few decades, but the sustainability of large-scale land use conversions to supply feedstock crops remains unclear. Quantitative data documenting how biofuel crop expansion will affect ecosystem services (ES) is needed to develop sustainable energy policies. Using pairwise comparisons of published and novel environmental, social and economic indicators, we quantitatively assessed the provision of critical ES related to key aspects of the sustainability of pasture-to-sugarcane transitions in Brazil. We found that with the exception of maintaining biodiversity, conversion of pasturelands to sugarcane fields enhanced many ES. Based on the Sustainability index, aimed to capture changes on key sustainability aspects by considering multiple ES and properly integrating them, we concluded that pasture to sugarcane transitions would increase the sustainability by 78% in south-central Brazil. Our results provide science-based empirical evidence that the expansion of sugarcane into degraded pasturelands is a suitable strategy to enhance Brazil's biomass feedstock supplies for producing bioenergy. Moreover, facing the complex and multidimensional concept of sustainability, our study also illustrates the importance of considering holistically land use change effects rather than individual ESs when establishing sustainable land management practices and bioenergy policies. Graphical abstract Except for Maintenance of biodiversity, the expansion of sugarcane over pasturelands improve many ecosystem services in areas of biofuels expansion. As result, this LUC would increase the sustainability by 78% in south-central Brazil. SOC: soil organic C. FRT: Soil fertility index. H?: Shannon?s diversity index. CYC: C cycling index. STR: Soil structural quality index. SEC: Socioeconomic index. fx1 Highlights • In Brazil, most of the recent sugarcane expansion has been placed over extensive pastures. • Pasture (PA) to sugarcane (SG) transitions affects key ecosystem services (ES). • Except for Maintenance of biodiversity, this land use change improve the ESs evaluated. • As result, PA-SG transitions would increase the sustainability by 78% in south-central Brazil. • Our index provides a sensitive and science-based approach for sustainability assessments. [ABSTRACT FROM AUTHOR]

Highlights • SMAF is sanative to soil quality (SQ) assessment under sugarcane straw removal in the short-term. • Oxisol responds faster to sugarcane straw removal than Ultisol. • Indiscriminate straw removal for bioenergy production leads to Oxisol physical quality degradation even in the short term. • Straw and stalk yields are correlated to soil-physical attribute and SQ. • Actions should be taken to enhance soil-physical attribute and overall SQ. Abstract There is a growing interest by the Brazilian sugarcane (Saccharum sp.) industry in removing sugarcane straw from the field to use as raw material for increasing bioenergy production (e.g. , second generation and co-generation). In contrast, straw has an essential role in sustaining critical soil functions, so indiscriminate straw removal can jeopardize soil quality and consequently reduce crop yield. The objectives of this study were: (i) to apply the Soil Management Assessment Framework (SMAF) tool to investigate the short-term effects of sugarcane straw removal on a sandy clay loam Oxisol and on a sandy loam Ultisol, and (ii) to correlate soil quality attributes (i.e., chemical, physical and biological) and the overall Soil Quality Index (SQI) with plant yield (straw and stalk) in areas managed with straw removal. A 2-year experiment was conducted in a randomized block design replicated four times with three rates of straw removal: 0, 50 and 100% (i.e., no removal, moderate removal, and total removal, respectively). Soil samples were collected at the 0–5, 5–10, 10–20 and 20–30 cm layers and following indicators were analyzed: physical [bulk density (BD)], chemical [soil-pH, phosphorus (P) and potassium (K) content] and biological [soil organic carbon (C) and microbial biomass carbon (MBC)]. For the Oxisol, 100% straw removal decreased soil physical attribute scores (i.e. bulk density) in 5–10 and 10–20 cm depths and decreased SQI in the 0–20 cm depth, while the 0% and 50% straw removal rates enhanced SQIs in all depth increments. Furthermore, 50% straw removal sustained soil quality and increased feedstock availability for bioenergy production. Straw and stalk yields were correlated to soil physical attribute score and SQI for 0–10 cm soil depth in the Oxisol. For the Ultisol, straw removal did not influence SQI and there was no relationship between soil quality scores and phytomass. Our results highlight soil-specific responses to sugarcane straw removal and total straw removal in the Oxisol site leads to physical quality degradation even in the short term. Despite no short-term effect of straw management on Ultisol soil quality, the long-term benefits of the straw on the soil-plant system may be reduced with total removal, thus indiscriminate straw removal is not advocated. Based on our findings, partial straw removal can be a win-win scenario in Brazil, where a considerable volume of biomass can be used for bioenergy production with minimal impacts on soil quality. [ABSTRACT FROM AUTHOR]

Increasing global demand for biofuel has accelerated land-use change (LUC) in Brazil, primarily through the planting of sugarcane ( Saccharum officinarum ) to replace degraded pastures. The intensive mechanization associated with this LUC has increased concerns regarding structural quality of Brazilian tropical soils. Through decades of research focusing on identifying sensitive indicators of soil degradation due to land use and management, the Visual Evaluation of Soil Structure (VESS) method has emerged as a simple, fast, reliable and accurate semi-quantitative approach for assessing soil structure changes. VESS integrates soil properties related to size, strength and porosity of aggregates, and root characteristics into a single score (Sq – structural quality) that ranges from 1 (good structural quality) to 5 (poor structural quality). Although the VESS method was developed for temperate soils, it has been used successfully as an indicator of soil and crop management practice effects on structural quality of tropical and subtropical soils. Our objectives were to evaluate soil structural quality changes associated with a LUC sequence ( i.e ., native vegetation to pasture to sugarcane) at three sites under Oxisols, Alfisols and Ultisols across central-southern Brazil using the VESS; and to correlate VESS scores with quantitative measurements of soil physical properties. Average VESS scores were 2.0, 2.7, and 3.1 for native vegetation, pasture, and sugarcane, respectively. Overall the VESS method was able to detect soil structural quality changes under LUC for sugarcane cultivation, indicating a decrease in soil quality from native vegetation through pasture to sugarcane. The VESS scores were significantly correlated with quantitative soil physical property measurements, suggesting VESS is a reliable indicator of soil structural quality in tropical soils. A VESS score Sq = 3.0 seems to be suitable as a guide for management decisions. We conclude that VESS scores provide an efficient method to identify impacts of sugarcane expansion on soil structural quality, and recommend that VESS assessment be incorporated into monitoring protocols for evaluating not only sugarcane expansion areas, but also overall soil quality/health in Brazil. [ABSTRACT FROM AUTHOR]

Globally, the rate of land-use change (LUC) is increasing rapidly to support biofuel feedstock production. In Brazil, sugarcane ( Saccharum officinarum ) expansion to produce ethanol is displacing degraded pastures. Intensive mechanization for sugarcane production, could impact soil physical quality in these areas. We evaluated a typical LUC sequence (i.e., native vegetation–pasture–sugarcane) on soil physical quality at three sites in the central-southern region of Brazil. The soil physical properties evaluated through on-farm and laboratory soil analyses were: bulk density, degree of compactness, macroporosity, microporosity and total porosity, water-filled pore space, indexes of soil water storage and aeration capacity, soil resistance to penetration, field-saturated hydraulic conductivity and stability structural index. Calculations of mean weight diameter for the soil aggregates and soil physical quality ratings from a visual evaluation of soil structure (VESS) were also included in this study. From those data we defined a minimum dataset for calculating an additive soil physical quality index (SPQI). Long-term conversion from native ecosystems to pasture increased soil compaction (i.e., higher bulk density, degree of compactness and resistance to penetration values), decreased aeration porosity and water hydraulic conductivity, and consequently, created an unbalanced ratio between water- and air-filled pore space in the soil. Based on our SPQI, the soil's capacity to perform its physical functions decreased from 90% under native vegetation to 73% under pasture. Land-use change from pasture to sugarcane induced slight soil physical quality degradation, in which soil function was 68 and 56% of capacity. Overall, soil physical quality decreased under sugarcane fields, due to decreases in soil porosity, aeration and water hydraulic conductivity as well as increases in soil penetration resistance, structural degradation and erosion risk. Tillage operations performed during the sugarcane replanting (~ 5 years) had a short-term positive effect on soil physical quality, although over time it further decreased the resistance to erosion and structural degradation. Therefore, to convert degraded pasture to sugarcane in a sustainable manner, the soils should be managed in ways that increase the soil organic matter and minimize compaction. These actions are needed to prevent further soil physical quality degradation and to improve both economic and environmental sustainability of sugarcane ethanol production. [ABSTRACT FROM AUTHOR]

Increasing demand for biofuel has intensified land-use change (LUC) for sugarcane (Saccharum officinarum) expansion in Brazil. Assessments of soil quality (SQ) response to this LUC are essential for quantifying and monitoring sustainability of sugarcane production over time. Since there is not a universal methodology for assessing SQ, we conducted a field-study at three sites within the largest sugarcane-producing region of Brazil to develop a SQ index (SQI). The most common LUC scenario (i.e., native vegetation to pasture to sugarcane) was evaluated using six SQI strategies with varying complexities. Thirty eight soil indicators were included in the total dataset. Two minimum datasets were selected: one using principal component analysis (7 indicators) and the other based on expert opinion (5 indicators). Non-linear scoring curves were used to interpret the indicator values. Weighted and non-weighted additive methods were used to combine individual indicator scores into an overall SQI. Long-term conversion from native vegetation to extensive pasture significantly decreased overall SQ. In contrast, conversion from pasture to sugarcane had no significant impact on overall SQ at the regional scale, but site-specific responses were found. In general, sugarcane production improved chemical attributes (i.e., higher macronutrient levels and lower soil acidity); however it has negative effects on physical and biological attributes (i.e., higher soil compaction and structural degradation as well as lower soil organic carbon (SOC), abundance and diversity of macrofauna and microbial activity). Overall, we found that simple, user-friendly strategies were as effective as more complex ones for identifying SQ changes. Therefore, as a protocol for SQ assessments in Brazilian sugarcane areas, we recommend using a small number of indicators (e.g., pH, P, K, Visual Evaluation of Soil Structure -VESS scores and SOC concentration) and proportional weighting to reflect chemical, physical and biological processes within the soil. Our SQ evaluations also suggest that current approaches for expanding Brazilian sugarcane production by converting degraded pasture land to cropland can be a sustainable strategy for meeting increasing biofuel demand. However, management practices that alleviate negative impacts on soil physical and biological indicators must be prioritized within sugarcane producing areas to prevent unintentional SQ degradation over time. [ABSTRACT FROM AUTHOR]

Without proper management, land-use change (LUC) associated with producing sugarcane ( Saccharum officinarum ) for bioenergy in Brazil can lead to soil degradation and have negative implications on ecosystem functions. Phosphorus (P) depletion is one of the most frequent causes of land degradation in tropical environments, and as such, soil P pools have been identified as potential indicators of negative environmental impacts. We quantified soil P dynamics for the most common LUC sequence in sugarcane expansion areas [i.e., native vegetation (NV) to pasture (PA) to sugarcane (SC)], to determine if and how these changes could be used to evaluate environmental impacts of LUC in weathered Brazilian soils. Soil samples were collected from three areas in central-southern Brazil, representing the primary sugarcane-producing region of the world. Soil P fractionation was performed, and P stocks were calculated for the surface 30 cm. Soil chemical attributes and macrofauna data were correlated with P pools. Long-term conversions from natural ecosystems (Cerrado and Atlantic forest biome) to extensive PA decreased total P stocks by 31.2% indicating progressive soil degradation in these areas. In contrast, the LUC from PA to SC increased total P stocks by 35.6%; nevertheless, fertilization management altered the soil P-cycle, causing P accumulation in less plant-available forms. Available P increases to support adequate SC growth are still needed. Applying P using organic residues increased labile organic P and may be a complementary strategy for increasing nutrient supplies in SC fields. Phosphorus availability showed significant positive correlations with other soil chemical properties and clay content, while the functional diversity of soil macrofauna was strongly correlated with labile and biological P. We conclude that P pools can be useful indicators for assessing LUC modifications on soil quality in the tropics, and recommend they be used to assess land degradation and environmental sustainability within SC expansion areas in Brazil. [ABSTRACT FROM AUTHOR]

The Soil Management Assessment Framework (SMAF) was developed to evaluate impacts of land use and management practices on soil quality (SQ), but its suitability for Brazilian tropical soils was unknown. We hypothesized that SMAF would be sensitive enough to detect SQ changes associated with sugarcane (Saccharum officinarum L.) expansion for ethanol production. Field studies were performed at three sites across the south-central region of Brazil, aiming to quantify the impacts of a land use change sequence (i.e., native vegetation-pasture-sugarcane) on SQ. Eight soil indicators were individually scored using SMAF curves developed primarily for North American soils and integrated into an overall Soil Quality Index (SQI) and its chemical, physical, and biological sectors. The SMAF scores were correlated with two other approaches used to assess SQ changes, soil organic C (SOC) stocks and Visual Evaluation of Soil Structure (VESS) scores. Our findings showed that the SMAF was an efficient tool for assessing land use change effects on the SQ of Brazilian tropical soils. The SMAF scoring curves developed using robust algorithms allowed proper assignment of scores for the soil chemical, physical, and biological indicators assessed. The SQI scores were significantly correlated with SOC stocks and VESS scores. Long-term transition from native vegetation to extensive pasture promoted significant decreases in soil chemical, physical, and biological indicators. Overall SQI suggested that soils under native vegetation were functioning at 87% of their potential capacity, while pasture soils were functioning at 70%. Conversions of pasture to sugarcane induced slight improvements in SQ, primarily because of improved soil fertility. Sugarcane soils are functioning at 74% of their potential capacity. Based on this study, management strategies were developed to improve SQ and the sustainability of sugarcane production in Brazil. [ABSTRACT FROM AUTHOR]

Historical data of land use change (LUC) indicated that the sugarcane expansion has mainly displaced pasture areas in Central–Southern Brazil, globally the largest producer, and that those pastures were prior established over native forests in the Cerrado biome. We sampled 3 chronosequences of land use comprising native vegetation (NV), pasture (PA), and sugarcane crop (SC) in the sugarcane expansion region to assess the effects of LUC on soil carbon, nitrogen, and labile phosphorus pools. Thirty years after conversion of NV to PA, we found significant losses of original soil organic matter (SOM) from NV, while insufficient new organic matter was introduced from tropical grasses into soil to offset the losses, reflecting in a net C emission of 0.4 Mg ha − 1 yr − 1 . These findings added to decreases in 15 N signal indicated that labile portions of SOM are preserved under PA. Afterwards, in the firsts five years after LUC from PA to SC, sparse variations were found in SOM levels. After more than 20 years of sugarcane crop, however, there were losses of 40 and 35% of C and N stocks, respectively, resulting in a rate of C emission of 1.3 Mg ha − 1 yr − 1 totally caused by the respiration of SOM from C4-cycle plants. In addition, conversion of pastures to sugarcane mostly increased 15 N signal, indicating an accumulation of more recalcitrant SOM under sugarcane. The microbe- and plant-available P showed site-specific responses to LUC as a function of different P-input managements, with the biological pool mostly accounting for more than 50% of the labile P in both anthropic land uses. With the projections of 6.4 Mha of land required by 2021 for sugarcane expansion in Brazil to achieve ethanol's demand, this explanatory approach to the responses of SOM to LUC will contribute for an accurate assessment of the CO 2 balance of sugarcane ethanol. [ABSTRACT FROM AUTHOR]

Ethanol derived from sugarcane (Saccharum officinarum) could replace a substantial amount of fossil fuel in Brazil, provided the greenhouse gas (GHG) budget is balanced. Green harvest systems have significantly increased the potential amount of sugarcane residue (straw) available for harvest and bioenergy production, but several questions about how those practices will affect field GHG fluxes. In this sense, we quantified GHG emissions associated with four straw harvest rates (12 [no removal]; 6 [moderate removal]; 3 [high removal] and 0 Mg ha−1 [total removal] of dry matter of straw left on the soil), with and without 100 L ha−1 vinasse + N-fertilizer [80 kg ha−1 (NH 4) 2 SO 4 ]. GHG fluxes were measured for 60 days using static chambers. Our results showed that total straw removal reduced CO 2 and N 2 O emissions by 15% and 25%, respectively. After vinasse and fertilizer additions, CO 2 emissions were 2.5-fold higher, and N 2 O were 5-fold higher, regardless of straw rates. In additional, synergic effect of vinasse + fertilizer and straw removal decreased 60% CH 4 uptakes. Direct N2O emission factor was estimated at 0.32%. Net GHG emissions induced by vinasse + fertilizer applied in the sugarcane plantation were 220 g m−2 CO 2 e (or 60 g m−2 C-equivalent), disregarding straw harvest rate. Therefore, we conclude that maintaining at least 6 Mg ha-1 of sugarcane straw in the field will result in a 'win-win situation' by mitigating GHG emissions, sustaining soil, and still saving part of the raw-material for bioenergy production. • Total removal reduced emissions associated with CO2 by 15% and N2O, by 15%. • Vinasse + fertilizer increase CO2 emissions in 2.5 times and N2O, 5 times, regardless of straw harvest rates. • Direct N2O emission factor was estimated at 0.32%. • Net GHG emissions induced by vinasse + N-fertilizer were 220 g m-2 CO2e disregarding straw harvest rate. • Straw harvest rate did not alter the GHG emission. [ABSTRACT FROM AUTHOR]

• The Soil Management Assessment Framework (SMAF) detected soil health changes induced by straw removal in sugarcane areas. • Sandy and clayey soils were functioning at 41–56% and 67–86% of their full potential, respectively. • Intensive straw removal rates induced soil health degradation. • Healthier soils were associated with higher sugarcane stalk yields. • Soil health assessments are crucial to design sustainable straw management in Brazil. Sugarcane straw removal is a promising strategy to increase bioenergy production in Brazil. However, if straw removal is not properly managed, it may lead to soil health degradation, thus threatening sustainability of the entire bioenergy production system. In this context, a comprehensive assessment was conducted in 12 field experiments located in central-southern Brazil, the world's largest sugarcane-producing region, to investigate the impacts of straw removal scenarios on soil health, using the Soil Management Assessment Framework (SMAF). Two groups of experiments were arranged in this study, consisting of three (no–NR; moderate–MR; and total removal–TR) and four straw removal treatments (NR; low–LR; high–HR; and TR). Soil samples were collected (0–10 and 10−20 cm) to evaluate a selected set of soil health indicators (i.e., pH, available phosphorus, exchangeable potassium, bulk density and soil organic carbon). Indicators were individually scored and then integrated into an overall Soil Health Index (SHI) and its chemical, physical, and biological components. Datasets were analyzed by site, experiment groups and soil texture (clayey and sandy soils) and the relationships among straw removal, soil health, and sugarcane yield were also investigated. Our findings showed that soil health responses to straw removal were properly detected by SMAF scoring curves. Based on SHI, sandy and clayey soils were functioning at 41–56% and 67–86% of their full potential, respectively. Soil health degradation was mostly induced by TR and HR, while LR and MR resulted in minimal detrimental effects on a short-term basis compared with NR. However, sandy soils were more prone to soil health degradation, indicating that straw removal should be avoided on those soils. For clayey soils, decline in soil health was driven by physical degradation. Healthier soils were associated with higher sugarcane stalk yields, and physical degradation was the main driver for crop yield losses. Conclusions drawn from this study suggest that comprehensive soil health assessments by integrating chemical, physical and biological indicators are fundamental to design more sustainable straw management and bioenergy production systems in Brazil. [ABSTRACT FROM AUTHOR]

Land use changes (LUC) for the expansion of bioenergy cropping have caused consistent reductions in soil organic carbon (SOC) stocks in tropical soils. This study addresses the mechanisms underlying such SOC losses by assessing LUC effects on, and relationships between, soil engineering invertebrate fauna, soil structural stability, and C allocation and sequestration within soil aggregates. We sampled three sites with sets of land use types varying in the level of anthropogenic stress in sandy loam, sand clay loam, and clay soils along a 1000-km-long transect in central Brazil, where bioenergy cropping expands across pasturelands. We quantified the effects of LUC on soil engineer fauna (i.e., termites, earthworms, coleopterans, and ants), soil structural stability, and C allocation and fitted structural equation models (SEM) to elucidate mechanistic links between the measured variables. We found that reductions in SOC stocks following LUC were concomitant with reductions in the abundance of soil engineers (log abundance of soil engineers, −1.17 ± 0.54; P = 0.0322), destabilization of soil structure (normalized stability index, −0.16 ± 0.04; P < 0.0001), and soil depth-dependent decreases in the amounts and increases in the humification degree of aggregate-occluded SOC. Our SEMsupported the predicted relationships among these responses, and indicated that soil engineering by invertebrates indirectly mediated changes in SOC stocks across land uses by controlling the physical protection of low-humified, aggregate-occluded SOC, a C fraction that accounted for over 90% of the change in total SOC stocks following LUC. When analysing the influence of the different invertebrate groups separately, we found stronger support for the role of termites in this process compared to that of earthworms, coleopterans, and ants. Hence, negative LUC effects on populations of soil engineers weaken soil functioning and its C storage. These results highlight the need for land-use strategies that maintain soil fauna in order to sustain key ecosystem processes like soil structural formation and soil C stabilization. • Soil engineering by invertebrates indirectly mediated changes in SOC stocks following land-use change (LUC). • Invertebrates control the physical protection of low-humified, aggregate-occluded SOC. • Microaggregate-occluded SOC can account for over 90% of the change in total SOC stocks following LUC. • Termites can have a more prominent role in this process compared to earthworms, coleopterans, and ants. • Negative LUC effects on populations of soil engineers weaken soil functioning and its C storage. [ABSTRACT FROM AUTHOR]

Exploiting native soil phosphorus (P) and the large reservoirs of residual P accumulated over decades of cultivation, namely "legacy P", has great potential to overcome the high demand of P fertilisers in Brazilian cropping systems. Long-term field experiments have shown that a large proportion (> 70%) of the surplus P added via fertilisers remains in the soil, mainly in forms not readily available to crops. An important issue is if the amount of legacy P mobilized from soil is sufficient for the crop nutritional demand and over how long this stored soil P can be effectively 'mined' by crops in a profitable way. Here we mapped the spatial–temporal distribution of legacy P over the past 50 years, and discussed possible agricultural practices that could increase soil legacy P usage by plants in Brazil. Mineral fertiliser and manure applications have resulted in ~ 33.4 Tg of legacy P accumulated in the agricultural soils from 1967 to 2016, with a current annual surplus rate of 1.6 Tg. Following this same rate, soil legacy P may reach up to 106.5 Tg by 2050. Agricultural management practices to enhance soil legacy P usage by crops includes increasing soil pH by liming, crop rotation, double-cropping, inter-season cover crops, no-tillage system and use of modern fertilisers, in addition to more efficient crop varieties and inoculation with P solubilising microorganisms. The adoption of these practices could increase the use efficiency of P, substantially reducing the new input of fertilisers and thus save up to 31.8 Tg of P fertiliser use (US$ 20.8 billion) in the coming decades. Therefore, exploring soil legacy P is imperative to reduce the demand for mineral fertilisers while promoting long-term P sustainability in Brazil. [ABSTRACT FROM AUTHOR]

Land use changes (LUC) from pasture to sugarcane ( Saccharum spp.) crop are expected to add 6.4 Mha of new sugarcane land by 2021 in the Brazilian Cerrado and Atlantic Forest biomes. We assessed the effects of these LUC on the abundance and community structure of animals that inhabit soils belowground through a field survey using chronosequences of land uses comprising native vegetation, pasture, and sugarcane along a 1000-km-long transect across these two major tropical biomes in Brazil. Macrofauna community composition differed among land uses. While most groups were associated with samples taken in native vegetation, high abundance of termites and earthworms appeared associated with pasture soils. Linear mixed effects analysis showed that LUC affected total abundance ( X 2 (1) = 6.79, p = 0.03) and taxa richness ( X 2 (1) = 6.08, p = 0.04) of soil macrofauna. Abundance increased from 411 ± 70 individuals m − 2 in native vegetation to 1111 ± 202 individuals m − 2 in pasture, but decreased sharply to 106 ± 24 individuals m − 2 in sugarcane soils. Diversity decreased 24% from native vegetation to pasture, and 39% from pasture to sugarcane. Thus, a reduction of ~ 90% in soil macrofauna abundance, besides a loss of ~ 40% in the diversity of macrofauna groups, can be expected when sugarcane crops replace pasture in Brazilian tropical soils. In general, higher abundances of major macrofauna groups (ants, coleopterans, earthworms, and termites) were associated with higher acidity and low contents of macronutrients and organic matter in soil. This study draws attention for a significant biodiversity loss belowground due to tropical LUC in sugarcane expansion areas. Given that many groups of soil macrofauna are recognized as key mediators of ecosystem processes such as soil aggregation, nutrients cycling and soil carbon storage, our results warrant further efforts to understand the impacts of altering belowground biodiversity and composition on soil functioning and agriculture performance across LUC in the tropics. [ABSTRACT FROM AUTHOR]

• Soil physical properties and soil functions were assessed in the MATOPIBA region. • No improvements on soil structure indicators were observed after LUC. • Agricultural expansion in the MATOPIBA region reduced the SPQI. • Water flux and air diffusion functions were the most affected by LUC. In the so-called MATOPIBA region in northeastern Brazil, large areas of the Brazilian savannah (Cerrado biome) were converted to agricultural areas (e.g., soybean and cotton production) in recent years. However, little is known about the long-term impacts of this land-use change on soil physical properties and related soil functions. We carried out a field experiment in three consolidated agricultural areas (~23 years old) across a 1000-km transect within the MATOPIBA region to quantify land-use change effects from native vegetation (NV) to agricultural areas under no-tillage (NT) on soil physical properties and associated functions; and compare the obtained results with critical values from literature considered as thresholds for soil degradation. Soil samples were collected from paired plots (NV and NT) in each location at 0–5, 5–10, 10–20, and 20–30 cm soil depth to determine key soil physical properties related to soil texture, compaction, porosity, water storage, and structural stability. Additionally, a set of soil physical indicators was added into a soil physical quality index (SPQI) as an integrated and quantitative approach for evaluating changes in soil functions. Our results indicated that conversion from NV to agriculture under NT increased the compaction process and reduced total soil porosity, unbalancing the proportion between soil water and air storage to critical levels. Besides, water infiltration within the soil profile was strongly decreased. The land-use conversion further induced changes on soil aggregate stability, decreasing large macroaggregates (>2000 µm) and increasing small macroaggregates (250–2000 µm) and the silt/clay-sized fraction (<53 µm). The SPQI was reduced by ~33% in NT, indicating detrimental effects of agriculture expansion on soil functionality. Based on the SPQI, water availability and air diffusion were the soil functions most affected by land-use change. Our results provide a quantitative assessment of soil physical properties and soil function changes as a consequence of agricultural expansion in the MATOPIBA region, indicating the need to improve NT practices towards alleviating soil compaction and improving soil structure. Best management practices are fundamental to restore soil functionality, ensuring crop yields and other ecosystem services. [ABSTRACT FROM AUTHOR]

• Soil compaction parameters were examined at around field capacity. • Operations for straw removal intensify soil compaction in sugarcane fields. • Baling operation may transmit stress greater than 400 kPa near the soil surface. • Initial soil bulk density govern the magnitude of impact by straw removal traffic. Straw removal requires a complex set of mechanized operations, including machines for raking, baling, and transporting the straw, which may intensify soil physical degradation in sugarcane fields. A field experiment was conducted to estimate the stress transmitted caused by a set of machines used for sugarcane straw removal and to quantify the impact of these stresses on soil physical indicators. The treatments consisted of reproducing the field traffic of individual and sequential operations used for straw removal, including raking; raking + baling; and raking + baling + transporting operations. Soil bulk density (BD), soil penetration resistance (SPR), macroporosity (MaP) and microporosity (MiP) at the depths of 2.5, 5, 15, and 30 cm were measured before and after the field operations. Contact area of the tires and stress transmitted into the soil induced by the straw removal operations were simulated by SoilFlex model and then used to assess the magnitude of the changes in soil physical indicators. Results showed that baling operation transmitted the highest stress (∼400 kPa), followed by straw raking and transporting, whose transmitted stress level exceed 300 kPa near the soil surface. The sum of sequential operations (i.e., raking + bale + transporting) showed the highest negative impact on soil physical quality. The magnitude of the changes in soil physical indicators occurred according to initial conditions of BD and transmitted stress. Our results show that operations for straw removal intensify soil compaction, which can be detrimental to sustain soil health and plant growth. Therefore, we advocate that traffic control strategies should be adopted during the straw removal operations to improve soil quality towards greater sustainability of sugarcane production in Brazil. [ABSTRACT FROM AUTHOR]

The expansion of sugarcane (Saccharum spp.) over extensive pasture areas has been one of the primary land-use change (LUC) scenarios in central-southern Brazil. However, LUC could negatively affect soil fauna along with the multiple functions and services associated with these organisms. Numerous groups of macroinvertebrates inhabiting the soil surface (i.e., epigeic) or the soil profile (i.e., edaphic) are fundamental for litter fragmentation, soil structuring and stabilization, water infiltration, biogeochemical cycling. In this study, both the edaphic and epigeic macrofauna communities were surveyed simultaneously to assess responses induced by the expansion of sugarcane cultivation over extensive pastures and to investigate whether the magnitude of such responses to LUC differs according to the community niche (i.e., soil profile versus surface). We hypothesized that LUC to a semi-perennial crop such as sugarcane would increase the density and diversity of the edaphic macrofauna, while the epigeic community would be negatively affected by LUC due to drastic changes in surface litter. The studied areas were two sites varying in soil texture (i.e., clay versus sandy soils) each including the following land uses: i) native vegetation, ii) extensive pasture, iii) newly planted sugarcane crop (sugarcane); and iv) established sugarcane (sugarcane ratoon). To evaluate edaphic macrofauna the TSBF methodology was adopted, while pitfall traps were installed at the same sampling points to collected epigeic macrofauna. The evaluated community attributes were density, Shannon diversity index, evenness index, richness of soil macrofauna taxa, as well as the chemical and physical attributes of the soil. Linear mixed effects analysis showed that LUC affected the relative abundance of edaphic (Land use p = 0.1191 r2 marginal = 0.28, r2 conditional = 0.33) and epigeic (Land use p = 0.0176; r2 marginal = 0.22, r2 conditional = 0.32) macroinvertebrates. Both groups showed the greatest density of organisms under native vegetation. Coleoptera and earthworms were associated with pasture areas, especially in clayey soil. Response ratios of LUC effects on macrofauna showed stronger responses of the epigeic compared to edaphic macrofauna, indicating a greater sensitivity of surface-dwelling organisms and their functions to disturbances such as those caused by LUC. In general, the density and diversity of macrofauna exhibited a positive correlation with soil organic matter, microbial carbon and nitrogen, macroporosity, and total porosity, and a negative correlation with soil density (p < 0.05). Also, the conversion of pasture to sugarcane cultivation (planting) causes significant macrofauna losses, particularly, in the clay soil. The cultivation of ratoon sugarcane led to a reduction of the density, taxonomic richness, diversity, and evenness of macrofauna. Given the importance of epigeic macroinvertebrates for litter fragmentation and decomposition, these results may indicate a rapid loss of key soil functions related to decomposition and carbon and nutrient cycling following LUC. [Display omitted] [ABSTRACT FROM AUTHOR]

The epigeic fauna, ground surface-dwelling invertebrates that inhabit leaf-litter, acts on multiple soil processes and key ecosystem services and is threatened by global land-use change (LUC). In Brazil, LUC for sugarcane expansion over extensive pasture has been taking place for promoting bioenergy production; however, conventional sugarcane cultivation includes monoculture, periodic soil tillage and agrochemicals may alter the quantity and quality of crop residue inputs, soil habitats and communities of soil fauna. Thus, a field study at three sites in central southern Brazil was conducted to evaluate if the expansion of sugarcane cultivation affects soil epigeic fauna. In each site, we sampled epigeic fauna in areas under LUC from native vegetation to extensive pasture, and from that to sugarcane. The epigeic fauna was collected using pitfall traps and then quantified and classified in taxonomic groups (Order, Class, Family). In addition, as a focal organism group, ants were classified at the species level. Overall, 13 taxonomic groups were identified, in which the Formicidae family was the most abundant group (i.e., 67% of individuals), followed by Diptera (13%), Araneae (5%) and Coleoptera (4%). Land transition from native vegetation to pasture increased fauna abundance by 27% but reduced the diversity of epigeic fauna community by 43%. In contrast, sugarcane expansion over extensive pasture reduced fauna abundance (−22%), did not alter the diversity of the invertebrate community at a broad taxonomic level, but decreased species richness of the dominant taxa (ants) by 55%. Ant individuals were classified into 37 species, allowing to verify that sugarcane cultivation over pastures decreased both the abundance and richness of ants and altered community composition. Ant species Ectatomma brunneum were more sensitive to LUC and, therefore, could be characterized as potential indicators of disturbed environments. We demonstrate that sugarcane expansion over pasturelands reduces the total abundance of the soil epigeic fauna, and that effects on fauna diversity vary from broad to fine taxonomic resolutions. Further studies are needed to evaluate if the declines in fauna abundance and ant species richness impair specific soil functions and soil-related ecosystem services. • The sugarcane expansion over pasturelands reduced the total abundance of epigeic fauna by 30%. • The conversion from pasture to sugarcane reduced taxonomic richness of ant community by 55%. • The ant species Ectatomma brunneum can be a potential bioindicator for monitoring habitat disturbances. • Fine taxonomic resolution (species level) was fundamental for detecting biodiversity changes induced by land transitions. [ABSTRACT FROM AUTHOR]

• Sugarcane cultivation reduced soil porosity, C and aggregate stability. • Soil structural benefits are declined during tillage for sugarcane replanting. • Soil tillage for sugarcane replanting alleviates soil hardening. • Sugarcane cultivation declines performance of soil physical functions. In northeastern Brazil, the sugarcane expansion has occurred historically over the Atlantic Forest biome. However, little is known about the physical process and changes induced by sugarcane cultivation in this biome. Thus, a field study was conducted to evaluate changes induced by sugarcane cultivation on soil physical properties, processes and functions in the Atlantic Forest biome. For that, soil samples were collected at three sites in northeastern Brazil: AF – Atlantic Forest, SC ratoon – successive sugarcane ratoon cultivation and SC till – tilled soil for sugarcane replanting. Quantitative and semi-quantitative soil properties [i.e. bulk density, soil penetration resistance (SPR), water-stable aggregates, soil organic carbon (C), pore size distribution and Visual Evaluation of Soil Structure (VESS) scores] were examined. In addition, four critical soil functions were evaluated by a soil physical quality index (SPQI). Atlantic Forest soil presented the greatest soil physical quality (i.e. lower bulk density, higher porosity, soil C and soil aggregate stability), functioning, according to SPQI, at 88% of its full capacity. However, SPR under AF was significantly higher than SC ratoon and SC till. Soil tillage reduced SPR in SC till compared to the area under successive sugarcane cultivation (SC ratoon). The results revealed that the high SPR in AF and SC ratoon areas occurred without soil volume variation (i.e. no compaction) in relation to the SC till , indicating that these soils are susceptible to hardening induced by C bonds and thixotropy processes. Soil tillage for sugarcane replanting resulted in immediate improvements on physical conditions for root growth by decreasing SPR; however, soil disturbance increases its susceptibility to degradation by reducing water-stable soil aggregate, organic C and aeration pores. Thus, sugarcane cultivation declined the performance of soil physical functions to 72 and 67% of its full capacity in SC till and SC ratoon , respectively. Finally, best management practices to reduce soil disturbance and increase C should be prioritised, as well as minimising the mechanisms responsible by soil hardening in order to reduce soil physical degradation and improve the environment for root growth in sugarcane fields. [ABSTRACT FROM AUTHOR]

Coastal wetlands are known for their diverse ecosystems, yet their soil characteristics are often misunderstood and thought to be monotonous. These soils are frequently subjected to saline water saturation, leading to unique soil processes. However, the combination and intensity of these processes can vary considerably across different ecosystems. In this study, we hypothesize that these diverse soil processes not only govern the geochemical conditions in coastal ecosystems but also influence their ability to deliver ecosystem services. To test this hypothesis, we conducted soil analyses in mangroves, seagrass meadows, and hypersaline tidal flats along the Brazilian coast. We used key soil properties as indicators of soil processes and developed a conceptual model linking soil processes and soil-related ecosystem services in these environments. Under more anoxic conditions, the intense soil organic matter accumulation and sulfidization processes in mangroves evidence their significance in terms of climate regulation through organic carbon sequestration and contaminants immobilization. Similarly, pronounced sulfidization in seagrasses underscores their ability to immobilize contaminants. In contrast, hypersaline tidal flats soils exhibit increased intensities of salinization and calcification processes, leading to a high capacity for accumulating inorganic carbon as secondary carbonates (CaCO 3 ), underscoring their role in climate regulation through inorganic carbon sequestration. Our findings show that contrary to previously thought coastal wetlands are far from monotonous, exhibiting significant variations in the types and intensities of soil processes, which in turn influence their capacity to deliver ecosystem services. This understanding is pivotal for guiding effective management strategies to enhance ecosystem services in coastal wetlands., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)