ABSTRACT Climate-smart agriculture (CSA) practices, mainly no-tillage (NT), cover cropping (CC), soil fertilization with organic amendments (OA), and crop-livestock (CL) and crop-livestock-forestry (CLF) systems, has been widely adopted in areas from Brazilian Cerrado. The CSA may partly offset former soil C losses and contribute to climate change mitigation. However, contradictory findings brought uncertainties about the effect of CSA on soil C. Here, by a systematic review of 87 papers and using 621 data pairs, we provided a pervasive biome-scale analysis of soil C stock changes associated with the adoption of CSA across Brazilian Cerrado. All CSA practices evaluated showed average positive rates of C stock change, indicating a general tendency of soil C accretion after its adoption. In areas under NT, CC and CLF, greater rates were estimated for the deeper soil profile evaluated (0.00-1.00 m) (1.24 ± 0.85, 0.54 ± 0.54 and 1.00 ± 1.47 Mg ha–1 yr–1, respectively), while OA and CL showed more soil C accretion when the assessment was limited down to 0.10 m depth (0.82 ± 0.60 and 0.59 ± 0.66 Mg ha–1 yr–1, respectively). Unfortunately, the lack of basic information precluded any attempt to statically compare our estimations. In this sense, we must be cautious in stating that soil C sequestration occurs at those rates after the adoption of CSA practices. Despite these limitations, the results clearly show that the diversification and intensification of agricultural areas in the Cerrado by the adoption of CSA is a promising pathway to increase soil C stocks, and consequently, contribute to climate change mitigation and adaptation. Finally, our findings emphasize the importance of efforts that stimulate farmers to adopt these practices on large scale, such as Brazil’s Low-Carbon Agriculture Plan, besides providing sound empirical evidence about the role of soil C sequestration in Brazil achieving its Nationally Determined Contributions commitments.

ABSTRACT To meet the growing demand for bioenergy such as ethanol, the area cultivated with sugarcane has expanded, especially in areas currently occupied by extensive pastures with low productivity. However, land-use change (LUC) from pasture to sugarcane implies changes in soil structure and variations in organic matter (SOM) stored in the soil. This study aimed to quantify the impact of LUC on organic matter fractions – particulate organic matter (POM) and mineral-associated organic matter (MAOM) – in soils with contrasting textures, and to explore the correlations between possible alterations in soil aggregation and the effects on carbon (C) stocks and SOM fractions. The study was conducted in two areas in Central-Southern Brazil, one with clayey soil and the other with sandy soil. In each area, a LUC chronosequence was evaluated: native vegetation (NV), pasture (PA), short-term sugarcane (SC1), the area analyzed during the sugarcane plant cycle; long-term sugarcane (SC2), area analyzed during the ratoon sugarcane cycle. In each use, undisturbed and disturbed samples were collected and macroaggregates and microaggregates were obtained by wet sieving and soil samples. In these samples, the physical fractionation of the SOM and the calculation of the C contained in each fraction of the SOM and C total stock of each use were performed. The conversion of NV to PA increased C stocks by more than 50 %, mainly in the MAOM fraction, and maintenance of macroaggregates (more than 80 %) in sandy site; and reduction of C stocks by more than 30 %, mainly MAOM in the clayey area. These benefits acquired from grazing on sandy area were lost with the expansion of sugarcane, a reduction of more than 20 % in macroagregation and C stocks. The sugarcane expansion into pasture with clayey site resulted in C accumulation (more than 2 Mg C ha-1 yr-1) and recovery of stocks on a SC2 basis. Expanding sugarcane areas into low-productivity pasture areas can be considered a sustainable strategy, especially in clayey soils, in which multiple gains occur through C sequestration and improved soil quality, as well as the reduction of CO2 emissions through the diversification of the energy matrix with the production of ethanol.

ABSTRACT Soils are the largest terrestrial carbon (C) reservoir, and most of this C is retained as soil organic matter (SOM). Due to its ability to capture, stabilize, and store C for extended periods, soils are considered important allies in decarbonizing the atmosphere. The term ‘C stabilization’ includes a series of mechanisms or processes by which soil C is protected within soils and its losses are reduced through microbial decomposition or leaching. Due to their relevance in the global C cycle, C stabilization mechanisms have received intensive attention from the scientific community. As new analytic technologies push the boundaries of what was previously possible to know, new paradigms emerge. This literature review summarizes the current knowledge of the main mechanisms that may promote SOM stabilization. Factors that govern accumulation of SOM are also addressed. We highlight the role of organo-mineral associations and spatial inaccessibility of SOM due to occlusion within soil aggregates to understand the relative contribution of these mechanisms in different soil conditions (e.g., soil texture, mineralogy, and land- use). In addition, the contribution of cutting-edge approaches and analytical techniques to advance the understanding of SOM protection is presented. Modern techniques to evaluate SOM on a micro, nano, and molecular scale can contribute to the mechanistic understanding of SOM stabilization and the study and adoption of management strategies that maintain and increase C stocks in soils.

ABSTRACT: Crop residues left in the field cover and protect the soil surface, and regulate key processes and functions, such as gas and water exchanges. However, the Brazilian sugarcane (Saccharum officinarum L.) sector has begun to use straw as feedstock to produce bioenergy. We conducted a field study to evaluate the effects of sugarcane straw removal in soil temperature and moisture changes at three sites (with different soil textures: Site 1 - clayey Oxisol, Site 2 - medium texture Oxisol, and Site 3 - sandy Ultisol) in the state of São Paulo, Brazil. The experimental design was randomized blocks with four rates of straw removal: i) no removal (NR); ii) moderate removal (MR); iii) substantial removal (SR), and iv) total removal (TR). Soil temperature was measured by sensors in the 0- to 5- and 5- to 10-cm soil layers. Undisturbed soil samples were collected from the 0- to 20- and 20- to 40-cm layers to determine soil moisture. Intensive straw removal (HR and TR) increased the soil temperature between 2 and 3 °C and the thermal amplitude between 5 and 9 °C in the 0- to 5-cm layer, compared to MR and NR. Soil moisture decreased between 0.03 and 0.07 g g–1 in the 0- to 20-cm layer with intensive straw removal. The sandy soil was more susceptible to straw removal. Therefore, straw maintenance on the soil surface plays an essential role in temperature regulation and preservation of higher soil moisture, especially in regions with severe water deficits and long periods of water stress.

ABSTRACT Brazilian soil scientists have increased the use of the term “soil quality” in their scientific publications in the last decade. However, it remains unclear if those publications only mention “soil quality” in a broad context, or the studies are focused on soil quality assessments, integrating soil chemical, physical and biological indicators. The objective of this systematic review was to carry out a critical analysis of the conception in using the term “soil quality” in recent publications derived from studies performed in Brazil. For this purpose, the terms [(“soil health” or “soil quality” or “qualidade do solo”) and (“Brazil*” or “Brasil*”)] were searched in databases of Web of Science, Scopus, and Scielo from 2014 to 2021. Initially, 1,284 peer-reviewed papers were found, subsequently selected according to the criteria established in two filters: (i) First filter - studies carried out in Brazil, which mentioned at least one of the terms of interest (“soil health” or “soil quality” or “qualidade do solo”) and that evaluated soil biological, physical or chemical indicators, assessing at least one of them; (ii) Second filter - studies in which all three groups of soil indicators were assessed and integrated, and presented a specific discussion about soil quality. According to the results, 36 % of the papers met the first criteria (n = 464), and only 2 % (n = 30) attended the second filter. The terms “soil health” or “soil quality” or “qualidade do solo” were mentioned 7 and 37 times per paper for those papers selected in the first and second filter, respectively. We evidenced in our study that the term soil quality in agricultural science papers has been predominantly used in a broad context, mostly to refer to the suitable soil conditions for plant growth. Thus, we concluded that even if the use of soil quality term is increasing in Brazilian literature, there are still very few researchers working specifically with soil quality assessments, in its full conception (i.e., integrating chemical, physical and biological indicators). Therefore, there is a promising research field to be explored to promote scientific advances in the soil quality area (e.g., new concepts, assessment frameworks, on-farm monitoring protocols), as well as disseminate the soil quality assessment among the Brazilian farmers, environmentalists, and other stakeholders.

ABSTRACT Although numerous studies have been conducted with common bean regarding nitrogen (N) dose, time of application, and source in no-till (NT) soils in Brazil, the heterogeneity of the results makes it difficult to establish technical recommendations based on individualized studies. This meta-analysis aimed to rank the main factors influencing common bean response to N management in NT areas. The database consisted of 99 scientific papers that encompassed 160 trials and 2394 observations. In general, the probability of obtaining a positive response to N application in common bean productivity was 77 %, with an average 18 % increment (358 kg ha-1). The main factors that affect the response of common bean grain yield to N fertilization and the choice of the applied N dose are soil organic matter (OM) content and the preceding crop. In soils with OM content >20 g kg-1, the N dose that determines the highest economic return is 50 kg ha-1. For soils with OM content <20 g kg-1, the N dose to be applied is 70 and 100 kg ha-1 for crops preceded by legumes and grasses, respectively. The timing of the N application did not result in a significant difference in common bean yield in 62 % of the trials. However, the results showed that the average yield increase in the common bean went from 15 % (293 kg ha-1) with a single application to 32 % (622 kg ha-1) with split N applications. All N sources tested showed similar gains to those obtained with N application through urea. Excluding situations with high doses of N application (>100 kg ha-1), inoculating common bean seeds increased grain yields by 6 % on average (118 kg ha-1). The combined analysis of the available results demonstrated that the crop recommendations used in Brazilian soils under NT could be refined considering the soil OM concentration and preceding crop. Additionally, seed inoculation and N dose splitting in the form of common urea should be recommended.

ABSTRACT Conventional tillage and intensive machinery traffic are the major causes of physical soil degradation in sugarcane fields. This study evaluates the impact of adopting conservation management practices during sugarcane planting on soil physical properties and stalk yield of sugarcane in the municipality of Ibitinga, state of São Paulo, Brazil. The experimental design (split-block) included four cover crops and three soil tillage systems, with three repetitions. For comparison purposes, a control treatment was also included (without cover crop and under conventional tillage). Sampling for soil physical analysis was performed in three layers that coincide with soil horizons A (0.00-0.20 m), AB (0.20-0.30 m), and Bt (0.30-0.70 m), during cane-plant and first sugarcane ratoon cycles. The results showed that cultivation of sunn hemp associated with deep subsoiling induced high stalk yield of sugarcane in both production cycles, cane plant (116 Mg ha -1 ) and first ratoon (114 Mg ha -1 ), with a net gain of 11 and 9 Mg ha -1 compared with the control treatment, respectively. However, these results were not sufficient to induce significant differences in sugarcane yield. Nonetheless, the use of sunn hemp and millet, associated with subsoiling (at 0.40 or 0.70 m depth) during sugarcane planting, are promising management strategies to sustain better soil’s physical quality when compared to traditional management, conventional soil tillage without cover crops and/or cash crop, as peanuts, that increase the risks of soil compaction and physical degradation.

RESUMO O monitoramento da influência dos sistemas de produção pecuária na qualidade do solo (QS) na região amazônica colombiana é importante para garantir a sustentabilidade desses agroecossistemas. Neste trabalho foi utilizado o Soil Management Assessment Framework (SMAF) para avaliar as respostas da QS às mudanças no uso do solo associadas à adoção de sistemas silvipastoris (SPS) em duas localidades da Amazônia Colombiana. Em cada local de estudo foi estabelecida uma cronossequência conformada por três sistemas de uso da terra que refletem a transição no uso da terra típica da região: i) vegetação nativa (VN), ii) pastagem (PAST) e iii) SPS. Amostras de solo foram coletadas a cada 10 cm de profundidade até atingir 30 cm de profundidade. Em seguida, o pH do solo, potássio, fósforo disponível, carbono microbiano, carbono orgânico do solo e densidade aparente foram medidos. Dados da Avaliação Visual da Estrutura do Solo (VESS) foram também correlacionados. Os resultados foram interpretados usando os algoritmos do SMAF e o Índice de Qualidade do Solo (IQS) foi calculado. Nossos dados mostraram uma degradação da QS devido à mudança de uso da terra de VN para PAST, com uma redução na capacidade de funcionamento dos solos de 0.72 para 0.62. O estabelecimento de SPS sobre PAST restaura a QS (SQI = 0.69) quando comparado com a PAST (ambos locais), alcançando valores de IQS semelhantes aos observados em VN no local 1. O SMAF mostrou ser uma ferramenta potencial para monitorar a QS em solos de baixa fertilidade da região amazônica Colombiana. As pontuações do VESS foram também correlacionadas com as pontuações do SMAF, demonstrando ser uma ferramenta complementar e simples para os produtores monitorar a qualidade do solo na região amazônica.

ABSTRACT Monitoring the influence of livestock systems’ on soil quality (SQ) in the Colombian Amazon region is important to ensure the sustainability of those agroecosystems. Here we used the Soil Management Assessment Framework (SMAF) to assess the SQ responses to land-use change associated with the adoption of silvopastoral systems (SPS) at two study sites in the Colombian Amazon region. A chronosequence formed by three land-use systems, reflecting the typical land transition performed in the region, was established at each study site: i) native vegetation (NV), ii) pasture (PAST), and iii) SPS. Soil samples were collected at 10 cm deep increments until reaching 30 cm deep. Then soil pH, potassium, available phosphorus, microbial carbon, soil organic carbon, and bulk density were measured. In addition, data from Visual Evaluation of Soil Structure (VESS) were correlated. Data were interpretated using SMAF algorithms, and a Soil Quality Index (SQI) was calculated. Our data showed an SQ degradation due to land-use change from NV to PAST, with soils reducing their capacity of soils function from 0.72 to 0.62. The establishment of SPS over extensive PAST restored soil quality (SQI = 0.69) compared to PAST (both sites), even reaching similar SQI values to those observed in NV at site 1. The SMAF showed to be a potential tool to monitor the SQ in low-fertility soils from the Colombian Amazon region. The VESS scores were also correlated with SMAF - scores, proving to be a simple and complementary tool for farmers to monitor SQ in the Amazon region.

ABSTRACT: Knowledge of the distribution of total phosphorus (P) content in native soils provides information on the management of ecosystem, land capability for agriculture, environmental quality, and biodiversity conservation. We mapped the spatial distribution of total P concentrations in topsoils (0-30 cm) of uncultivated (native) areas in Brazil. We obtained data on native total P of the southern, south-eastern, and north-eastern regions from reports of exploratory projects developed between 1960s and 1970s by EMBRAPA and by the RADAM Brazil Project. We estimated data from the central-western and northern regions from the relationship between total P and soil properties (Fe, Al, C and clay content), based on the RADAM Brazil Project. Soil total P varied widely (< 25 to > 500 mg kg–1) in all regions in Brazil. Higher concentrations (> 500 mg kg–1) were observed in southern region compared to most of the rest of the country (< 200 mg kg–1), while the Cerrado (Central), Amazon (North) and Caatinga (Northeast) biomes are very poor in total P. This first national native soil total P map provides a valuable baseline for understanding the historical patterns of agriculture expansion in Brazil. It allows quantifying the effect of agriculture expansion and future cropping systems on soil available P content and legacy P, targeting regional soil-crop specific strategies for optimization of ecosystem services, and mitigating potential environmental risk due to P transference to water bodies.

ABSTRACT: In tropical regions, climate conditions favor fast decomposition of soil organic matter (SOM), releasing into the soil organic composts in solid, liquid, and gaseous forms with variable compositions. Dissolved organic matter (DOM), a complex mixture of thousands of organic compounds, is only a small fraction of the decomposition products; however, it is highly mobile and reactive to the soil. Therefore, DOM play a key role in soil aggregation (formation of organometallic complexes), energy source for microorganisms, as well as C storage, cycling, and provision of plant-available nutrients. DOM multifunctionality to sustain soil functions and important ecosystem services have raised global scientific interest in studies on DOM fractions. However, previous studies were conducted predominantly under temperate soil conditions in natural ecosystems. Therefore, there is paucity of information on tropical soil conditions under agricultural systems, where DOM turnover is intensified by management practices. This review synthesized information in the literature to identify and discuss the main sources, transformations, and future of DOM in soils. We also discussed the importance of this fraction in C cycling and other soil properties and processes, emphasizing agricultural systems in tropical soils. Gaps and opportunities were identified to guide future studies on DOM in tropical soils.

ABSTRACT: Chemical and physical properties of soil can be altered with the successive application of liquid swine manure (LSM), also known as slurry. Therefore, monitoring the impact of LSM is essential to an assessment of the potential agronomic and environmental benefits and risks associated with management practices. The aim of this study was to evaluate the effects of LSM on the chemical and physical attributes of soil under pasture (Cynodon spp.), located in southern Brazil. Four areas were sampled: three areas cultivated with Cynodon spp. pasture with successive applications of 200 m3 ha–1 y–1 of LSM for three, eight and 15 years; and untreated native forest as a reference. The soil attributes evaluated were: organic carbon (OC), active (pH water) and potential acidity (H + Al+ 3), nutrient availability (i.e., P, K, Ca, Mg, Cu and Zn), soil bulk density, macro, micro and total porosity. Successive applications of LSM on pasture reduced soil active acidity, and increased the soil organic C and plant-available N, P, Ca, Mg, Cu and Zn contents. These effects were more intense with time and in the shallowest layers, i.e. 0-10 cm. Excessive increases in P, Cu and Zn in the soil should be carefully monitored to minimize the contamination risks to soil, ground and surface waters. Soil physical attribute changes were more associated with land use (pasture versus native forest) than LSM use, and LSM applications induced slight improvements in the soil structural quality over time.

ABSTRACT: The utilization of Normalized Difference Vegetation Index (NDVI) data obtained through satellite images can technically improve the process of delimiting management zones (MZ) for annual crops, resulting in socio-economic and environmental benefits. The aim of this study was to compare delimited MZ, using crop productivity data, with delimited MZ using the NDVI obtained from satellite images in areas under a no-tillage system. The study was carried out in three areas located in the state of Rio Grande do Sul, Brazil. Three crop productivity maps, from 2009 to 2015, were used for each area, whereby the NDVI was calculated for each crop productivity map using images from the Landsat series of satellites. Descriptive and geostatistical analysis were conducted to determine the productivity and NDVI data. The MZ were then delimited using the fuzzy c-means algorithm. Spearman's correlation matrix was used to compare the methodologies used for delimiting the MZ. The MZ based on NDVI calculated from the satellite images correlated with the MZ based on crop productivity data (0.48 < r < 0.61), suggesting that the NDVI can replace or be complementary to productivity data in delimiting MZ for annual cropping systems.

ABSTRACT Sulfur (S) fertilization recommendations for grain crops in Brazil were formerly established from studies on crops with a low yield potential grown on soils under conventional tillage (CT). However, the subsequent adoption of no-tillage (NT) altered S dynamics in the soil, making it necessary to carefully evaluate the applicability of these S fertilizer recommendations. In addition, the emergence of modern high-yield-potential genotypes, the successive application of concentrated low-sulfur fertilizers, and reduction in S atmospheric deposition have raised the likelihood of positive responses of crops to S fertilization. Available literature reports contrasting crop responses to S fertilization in Brazilian soils, ranging from substantial gains to slight yield losses depending on the particular crop, soil, and climate. The primary aim of this study was to examine available data for crop grain responses to S application in NT soils in order to ascertain whether existing recommendations established for Brazilian CT soils also hold for NT soils. A systematic review of data from 35 scientific publications spanning 58 crop harvests revealed a positive yield response to S fertilization in 31 % of the crop harvests, with an average yield increase of 16 %. Crops on soils with available SO42–-S contents above the critical level (viz., 7.5 mg dm-3) exhibited no positive response to S fertilization in any crop harvest (n = 18). Dry edible bean and corn were the most responsive crops, and canola and wheat, the least. For the trials with positive crop responses, a fertilizer rate of 26 kg ha-1 S sufficed to obtain at least 95 % of the maximum possible yield. In general, the S fertilization recommendations previously established for CT soil proved effective with grain crops on NT soils as a result of the critical levels of soil available SO42--S and the fact that the recommended S rates are similar to those found in this study considering trials conducted under NT conditions only. However, existing recommendations could be improved by using additional criteria for soils with available SO42--S contents below the critical level since a positive response was observed in 22 % (n = 18) and 92 % (n = 12) of the crop harvests under a subtropical and a tropical climate, respectively. Our results suggest that S fertilization must be prioritized in NT soils with available SO42--S contents below 7.5 mg dm-3 in the 0.00-0.20 m layer, especially in tropical climate zones. In addition, regional fertilizer recommendation guidelines should consider crop type and yield expectation in order to facilitate more sustainable S management and increased crop yields in Brazil.

ABSTRACT: The use of crop residues as a bioenergy feedstock is considered a potential strategy to mitigate greenhouse gas (GHG) emissions. However, indiscriminate harvesting of crop residues can induce deleterious effects on soil functioning, plant growth and other ecosystem services. Here, we have summarized the information available in the literature to identify and discuss the main trade-offs and synergisms involved in crop residue management for bioenergy production. The data consistently showed that crop residue harvest and the consequent lower input of organic matter into the soil led to C storage depletions over time, reducing cycling, supply and availability of soil nutrients, directly affecting the soil biota. Although the biota regulates key functions in the soil, crop residue can also cause proliferation of some important agricultural pests. In addition, crop residues act as physical barriers that protect the soil against raindrop impact and temperature variations. Therefore, intensive crop residue harvest can cause soil structure degradation, leading to soil compaction and increased risks of erosion. With regard to GHG emissions, there is no consensus about the potential impact of management of crop residue harvest. In general, residue harvest decreases CO2 and N2O emissions from the decomposition process, but it has no significant effect on CH4 emissions. Plant growth responses to soil and microclimate changes due to crop residue harvest are site and crop specific. Adoption of the best management practices can mitigate the adverse impacts of crop residue harvest. Longterm experiments within strategic production regions are essential to understand and monitor the impact of integrated agricultural systems and propose customized solutions for sustainable crop residue management in each region or landscape. Furthermore, private and public investments/cooperations are necessary for a better understanding of the potential environmental, economic and social implications of crop residue use for bioenergy production.

RESUMO. Não existe consenso na literatura sob qual é o número de subamostras necessário para realizar o mapeamento da resistência do solo à penetração (RSP) de modo acurado. Dessa forma, o objetivo deste estudo foi definir o número de subamostras por ponto amostral para quantificar a RSP. O experimento foi realizado em uma área de 4,7 ha seguindo uma malha amostral de 50 × 50 m (18 pontos amostrais). A RSP foi avaliada com auxílio de um penetrômetro digital em dois anos seguidos utilizando-se 1, 2, 3, 4, 5, 6, 9, 12 e 15 subamostras por ponto amostral. Os mapas de RSP gerados com diferente número de subamostras foram comparados com o mapa referência (15 subamostras) utilizando o coeficiente de desvio relativo e de correlação linear de Pearson. A redução do número de subamostras por ponto amostral promove aumento da variabilidade da RSP. De maneira geral, esse estudo sugere o uso de pelo menos quatro subamostras por ponto amostral para atingir mapas de RSP com coeficiente de desvio relativo inferior a 10% (erro máximo de 30% em torno da média por ponto amostral) e correlação significativa com os mapas referência (15 subamostras).

ABSTRACT. There is no consensus in the literature regarding how many subsamples are needed to perform accurate on-farm soil penetration resistance (SPR) mapping. Therefore, the objective of this study was to define the number of subsamples per sampling point needed to quantify the SPR. The experiment was performed in a 4.7 ha area and employed a 50 × 50 m grid system (18 sampling points). The SPR was evaluated using a digital penetrometer in two different years with 1, 2, 3, 4, 5, 6, 9, 12, and 15 subsamples per sampling point. The SPR maps produced with increasing numbers of subsamples were compared to the reference maps (15 subsamples) using the relative deviation coefficient and Pearson´s linear correlation. A reduction in the number of subsamples promoted an increase in the variability of the SPR data. Generally, the results from this study suggest the use of at least four subsamples per sampling point to achieve SPR maps with a coefficient of relative deviation less than 10% (30% maximum error per point around the mean) and significant correlation with the reference maps (15 subsamples).