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Agroecosystems in the upper Mississippi River Basin are highly productive but often contribute to deterioration of water quality and greenhouse gas emissions. Cover cropping and no-till are conservation strategies implemented to reduce the environmental impact of these agroecosystems. However, using multiple strategies can lead to systemwide interactions that are not fully understood. These interactions can affect not only environmental quality metrics, such as subsurface drainage nitrate losses or nitrous oxide (NBoth subsurface nitrate losses and nitrous oxide emissions were linked with weather. Subsurface nitrate losses were linked with cumulative annual drainage. Nitrous oxide emissions were linked with fertilizer N applications. Rye cover crop with no-till reduced nitrate losses with no yield declines.

Tillage and no-tillage result in different soil mechanical responses which in turn may affect crop growth. Better understanding of soil compressive behavior, therefore, is relevant for the assessment of tillage practices in agricultural systems. We studied the change in soil compressive properties and their relationship with soil physical attributes and plant growth through a chisel tillage chronosequence in a Nitisol where soil was untilled after chiseling for 24 months, 18 months, 12 months, 6 months, and zero months, and was under continuous (12-year) NT. The effects were measured for three soil depth layers: 0 to 7-cm, 7 to 17-cm and 20 to 30-cm. Mechanical chiseling was found to reduce both the degree of compactness and the pre-compression pressure compared to continuous NT, but made the soil more susceptible to new compaction. The effects of chisel tillage generally persisted for a period of 12–24 months. The degree of compactness and soil pre-compression pressure were found to be strongly correlated, and were strongly correlated with other soil physical attributes (soil penetration resistance, soil macroporosity, and soil aggregate stability). They were negatively correlated with root length, root density, and root volume, as well as stalk diameter, linking soil structure indicators to plant growth. Our results also showed that soil compressive parameter values can be estimated based on other soil physical properties that influence plant growth. These findings have potential for studies of crop response to soil structure and soil compaction and could be used to aid in choosing optimal soil management practices, in order to reduce the risk of soil compaction, linking soil compressive behavior and soil physical conditions to plant growth.

Soil health changes induced by prairie reconstruction (cultivated fields to tallgrass prairie) were assessed in Central Missouri within sites representing a chronosequence of 0, 2, 3, 4, 6, 9, 10, 11, 12, and 13-yr postreconstruction. In addition, a nearby remnant native prairie, two long-term reconstructed prairies (-25 and -57-yr post-reconstruction), and a biofuel prairie 9-yr post-reconstruction were evaluated for comparative purposes. From 0 to 8-yr, prairie reconstruction increased soil aggregation, total soil organic carbon (SOC), total nitrogen (TN), active C and N (permanganate oxidizable C and total protein), and mineralizable C and N (soil respiration and potentially mineralizable nitrogen), becoming more similar to levels in the remnant prairie. Further, four enzymes involved in the cycling of C (13-glucosidase), N (13-glucosaminidase), P (acid phosphatase), and S (arylsulfatase) demonstrated amplified activities within samples collected to a depth of 15-cm. Over time, the ratios of active C to SOC and active N to TN declined, reflecting the conversion of active C/N pools into more stable C/N pools due to continued organic inputs and increased microbial activity. In contrast, from 8- to 13-yr post-reconstruction, the number of these same soil health indicators declined, which may be attributed to historical land use, the improvement of prairie reconstruction and management strategies, and ecological processes related to succession. Overall, prairie reconstruction holds great potential for soil health restoration in degraded agricultural landscapes, and further study is needed to understand how historical land use and prairie reconstruction practices affect soil health and ecological resilience. Missouri EPSCoR program - National Science Foundation [IIA1355406, IIA1430427] Published version Support for this research came from the Missouri EPSCoR program, funded by the National Science Foundation under Award #IIA1355406 and #IIA1430427. We would like to thank the Missouri Department of Conservation, Prairie Fork Conservation Area (PCFA) , and University of Missouri Biological Sciences Department (Tucker Prairie) staff, and specifically Jeff Demand and Melody Kroll, for permission to soil sample. We thank Jill Souliere Staples of the USDAARS, Seth Roberts of the University of Missouri, and student workers for laboratory assistance. Public domain – authored by a U.S. government employee

Soil organic carbon (SOC) influences several soil functions, making it one of the most important soil health indicators. Its quantity is determined by anthropogenic and inherent factors that must be understood to improve SOC management and interpretation. Topsoil (&le, 15 cm) SOC response to tillage depth and intensity, cover crops, stover removal, manure addition, and various cropping systems was assessed using 7610 observations from eight U.S. regions. Overall, including cover crops, reducing tillage depth and intensity increased SOC. The positive effects of cover crops were more noticeable in South Central, Northwest, and Midwest regions. Removing high rates (&gt, 65%) of crop residue decreased SOC in Midwestern and Southeastern soils. Depending on region, applying manure increased SOC by 21 to 41%, compared to non-manured soils. Diversified cropping systems (e.g., those utilizing small mixed vegetables, perennials, or dairy-based systems) had the highest topsoil SOC content, while more intensive annual row crops and large-scale single vegetable production systems, had the lowest. Among inherent factors, SOC increased as precipitation increased, but decreased as mean annual temperature increased. Texture influenced SOC, showing higher values in fine-texture than coarse-texture soils. Finally, this assessment confirmed that SOC can be a sensitive soil health indicator for evaluating conservation practices.

The performance of no-till (NT) in temperate regions may be enhanced through the integration of additional conservation practices such as cover cropping and crop rotations. This study assessed the long-term impacts of continuous (20+ years) NT in comparison to plow-till (PT) management on soil properties and corn (Zea mays L.) yields in New York. The effects of tillage were assessed in combination with different cropping systems (24 years corn monoculture vs. 12 years corn monoculture; and with or without interseeded cover crops) on three soil textures: clay loam, loamy sand and silt loam. We measured four soil biological indicators - organic matter (OM), active carbon (ActC), respiration (Resp) and protein (Prot); four soil physical indicators - available water capacity (AWC), water stable aggregation (WSA), penetration resistance (PR) and water infiltration rate (InfRate); soil chemical indicators (plant available nutrients, pH and total N), and corn yield. Soil managed under long-term NT showed the most favorable soil biological, physical and chemical conditions for plant development, with higher levels of OM, Prot, Resp, WAS, total N, P and Zn, and InfRate. Benefits of introducing a grass-legume cover crop mixture into the cropping system were evident after 4 years for OM, Prot, Resp, AWC, Fe and Zn. Cover crop effects were greater under NT than PT, and additive to the NT benefits. On the clay loam soil, the effects of a 6-year interruption of continuous corn production with a perennial grass crop were still discernable with several soil health indicators 12 years after resuming corn production under NT. The better soil conditions under NT resulted in higher corn yields in both the loamy sand and silt loam soils, but not the clay loam. Our study shows that long-term NT can be viable in temperate regions, promoting significant improvement in soil health and crop yield and that these benefits are enhanced when NT is combined with crop rotation (perennial grass) and cover crops.

We assessed long-term cultivation effects on several structural stability indicators within the 0- to 5- and 10- to 15-cm depth increments of different Oxisols. Comparisons were made between native and cultivated soils managed using no-till (NT) practices for 12+ years. Overall, conversion significantly decreased structure stability due to machinery traffic, high fertilizer and lime applications, soil organic matter (SOM) depletion, and reduced input of organic material (roots and crop residues). The magnitude of change varied depending on inherent (mineralogy) and dynamic (cropping system) factors, as well as soil depth. Kaolinitic Oxisols were much more susceptible to degradation than Gibbsitic Oxisols. Combining more diversified cropping systems with NT can mitigate the negative effects of cultivation by increasing living vegetation and crop residue additions throughout the entire year. Increased quantity and quality of SOM input improves soil biological activity and improves topsoil structural stability. Those changes also reduce eluviation of dispersed clay (primarily kaolinite) with percolating water and prevent concentration of the clay at the 10 to 15 cm depth, which further degrades the soil by contributing to formation of the dense subsurface layers beneath either NT or conventional production systems.

Crop production guidelines in Brazil currently focus on soil fertility or chemical indicators (i.e., soil pH and nutrient availability) but often neglect physical and biological aspects of soil health. No-tillage (NT) practices have been widely adopted in Brazil primarily to mitigate erosion, but chemical-based guidelines associated with those practices may be contributing to nutrient stratification and a concentration of crop roots within the top few centimeters of the soil profile. Our objective was to quantify relationships between soil physical and chemical attributes and root growth in soils with a long-term NT history (>10-yr). Crop root development and several soil health indicators were measured within the 0 to 7-, 7- to 17- and 20- to 30-cm depth increments of two long-term NT studies on Rhodic Hapludox soils in Brazil. Data from both experiments showed strong organic carbon (OC) stratification, significant differences in soil physical and chemical attributes, and root systems that were concentrated within the surface layer. Soil compaction below 7-cm appeared to be the dominant factor limiting root growth. Soil-test phosphorus (P) and OC were also correlated to root growth. Based on these analyses and other on-farm observations, we concluded that it is important to recognize that despite its benefits, NT practices can result in plant root stratification. Therefore, it is important to not only monitor soil fertility/chemical conditions, but also soil structure and biological indicators of soil health when developing NT guidelines for Brazil.

Applying lime is a fundamental practice for abating acidity in highly weathered soil, but better management strategies for no-till systems are needed to prevent surface pH elevation with little to no subsurface effects. This study was conducted to quantify chemical changes within the soil profile in response to lime and straw applications under both greenhouse and field conditions. Four controlled environment experiments (soil columns) and one field study were conducted on soils classified as Rhodic Hapludox and Rhodic Eutrodox. The soil column experiments evaluated four lime rates (0, 3.9, 7.8, or 15.6 Mg ha−1) and four straw rates (0, 4, 12 and 16 Mg ha−1) either individually or in combination. Lime treatments were surface applied or incorporated in the top 5-cm, while straw treatments were incorporated in the top 5-cm. In the field, lime rates of 0, 8.3 and 33.2 Mg ha−1 were incorporated into the 0 to 10-cm depth in both a soybean [Glycine max] monoculture and diversified cropping system with white oat (Avena sativa), soybean, black oats (Avena strigosa), corn (Zea mays) and wheat (Triticum aestivum). Both field and soil columns studies showed minimal lime movement into the soil profile with chemical changes being limited to 2.5-cm below where it was applied or incorporated regardless of cropping system. Surface application of high lime rates promoted chemical stratification resulting in dramatic increases in topsoil pH and exchangeable Ca and Mg levels with minimal mitigation of subsurface soil acidity. Other studies also suggest that lime movement into the soil profile can vary depending on the experimental condition. Therefore, additional investigations across a wider geographic area, greater range of weather and climatic conditions, methods and rates of lime application need to be conducted to improve lime recommendation for high weathered soil managed using no-till practices.

Tillage intensity can affect chemical soil health indicators either positively or negatively depending on inherent soil properties and management practices. Soil chemical data (total N, P, K, Ca, Mg, and pH) from four depth increments within 196 published studies were compiled and subjected to a meta‐analysis comparing chisel plow (CP), no‐till (NT), and perennial systems (PER) with moldboard plowing (MP). Overall, CP did not affect soil chemical indicators when compared to MP, but converting from MP to NT increased total N, P, and K concentrations within the top 15 cm. Below that depth, Ca and Mg concentrations were lower under NT than MP but total N, P, and K were not significantly different. Topsoil total N response to NT was moderated by soil order and cropping system, with the largest increase in total N found in Ultisols, Inceptisols, Alfisols, and Mollisols under more diversified cropping systems including those with cover crops. The greatest topsoil P increase in response to NT was found under long‐term experiments (>5‐yr) and on fine‐textured soils. Phosphorus changes in studies on coarse‐textured soils, with short‐term duration, and manure applications were generally neutral. Perennial systems had lower soil P and K but higher total N content in the surface layer as compared to MP. The positive response to PER systems was most notable in Alfisols, Mollisols, and Ultisols and under long‐term PER management. Finally, we demonstrate that these chemical indicators respond to tillage and cropping systems over a wide range of conditions, showing utility for soil health assessment.

Tillage intensity affects soil microbiological activity in many ways, often driven by changes in soil organic C (SOC) content. The magnitude and direction of those changes, however, depends on inherent (e.g., soil type and texture), experimental (e.g., study duration and sampling depth) and agronomic factors (e.g., cropping system and crop residue management). This nationwide meta-analysis examines published effects of chisel plowing (CP), no-tillage (NT), and perennial cropping systems (PER) relative to moldboard plow (MP) on seven soil health indicators: SOC, microbial biomass C (MBC), microbial biomass N (MBN), soil respiration (Resp), active-C (AC), beta-glucosidase activity (BG) and soil protein (Prot) within four soil depth increments in 302 studies from throughout the United States (U.S.). Overall, converting from MP to CP primarily affected topsoil (0 to ≤ 15 cm) SOC, MBC, and Resp, whereas converting from MP to NT significantly increased all seven soil health indicators in the topsoil. Below the topsoil, NT had greater MBC, MBN, Resp, and BG relative to MP (i.e., 15 to 25-cm). The impact of NT was affected by latitude, soil order, time under NT, and cropping system. Among soil orders, management practices had the largest positive effects in Ultisols, Inceptisols, Alfisols, and Mollisols. Those effects were most noticeable at lower latitudes, in systems that included cover crops or residue retention, and in experiments conducted for at least three years. Perennial systems had a positive effect on all soil health indicators at all soil depths (0 to >40-cm). The positive response of PER systems compared to MP was enhanced at lower latitudes and in Alfisols, Inceptisols, Entisols, and Mollisols. Based on this meta-analysis, reducing tillage intensity, planting cover crop and/or minimizing crop residue removal within annual cropping systems can significantly improve soil biological health in the U.S. Finally, we demonstrate that SOC and many other biological indicators are sensitive to management practices, confirming their utility in soil health assessment.

Tillage intensity affects soil structure in many ways but the magnitude and type (+/&minus, ) of change depends on site-specific (e.g., soil type) and experimental details (crop rotation, study length, sampling depth, etc.). This meta-analysis examines published effects of chisel plowing (CP), no-tillage (NT) and perennial cropping systems (PER) relative to moldboard plowing (MP) on three soil structure indicators: wet aggregate stability (AS), bulk density (BD) and soil penetration resistance (PR). The data represents four depth increments (from 0 to &gt, 40-cm) in 295 studies from throughout the continental U.S. Overall, converting from MP to CP did not affect those soil structure indicators but reducing tillage intensity from MP to NT increased AS in the surface (&lt, 15-cm) and slightly decreased BD and PR below 25-cm. The largest positive effect of NT on AS was observed within Inceptisols and Entisols after a minimum of three years. Compared to MP, NT had a minimal effect on soil compaction indicators (BD and PR) but as expected, converting from MP to PER systems improved soil structure at all soil depths (0 to &gt, 40-cm). Among those three soil structure indicators, AS was the most sensitive to management practices, thus, it should be used as a physical indicator for overall soil health assessment. In addition, based on this national meta-analysis, we conclude that reducing tillage intensity improves soil structure, thus offering producers assurance those practices are feasible for crop production and that they will also help sustain soil resources.

Soil chiseling under no-tillage (NT) promotes root growth in depth. This practice, however, might affect soil aggregation. This study evaluated the chiseling effects on the aggregation of a Ferralic Nitisol (Rhodic), under NT, in humid subtropical climate region. The treatments carried out consisted of the time that soil was kept under NT after chiseling: continuous NT for 24 months after chiseling in September 2009; continuous NT for 18 months after chiseling in March 2010; continuous NT for 12 months after chiseling in September 2010; continuous NT for 6 months after chiseling in March 2011; NT in newly chiseling soil in September 2011; continuous NT without chiseling (control). The species cultivated in the area were: corn in 2009/2010 growing season; wheat in 2010; soybean in 2010/2011 growing season; rye in 2011; and corn in 2011/2012 growing season. Treatment effects were evaluated through the following determinations: soil organic carbon, aggregates stability, mean weight diameter, aggregates larger than 2 mm, and soil macroaggregates and microaggregates. The corn root density was correlated to the soil aggregation parameters. The effect of soil chiseling, in a clayey humid subtropical soil under NT, reduced the size of soil aggregates, in the layer 0.07 to 0.17 m, in the first six months after this practice. However, 12 months after the soil chiseling, the aggregates returned to the original size. Root growth was favored in the layer between 0.07 and 0.20 m, due to the chisel action, and did not influence soil aggregation in relation to the control treatment. The soil chiseling practice, therefore, did not promote persistent improvement in the structure of a clayey soil under NT, in humid subtropical climate region.

Liming represents a common agricultural practice for abating soil acidity. Nevertheless, elevated amounts of agricultural lime in Oxisols, with or without cultural residue addition, could alter soil physicochemical properties and impact soil structure. In this context, the physical, chemical, and structural behaviors of an Oxisol under the addition of lime and straw were assessed. Lime doses (0, 3.9, 7.8, and 15.6 Mg ha–¹) were either applied on the surface or incorporated into the 0- to 5-cm soil layer. Straw applications followed the same procedure with quantities of 0, 4, 12, or 16 Mg ha–¹. The effects on the soil profile were evaluated through physicochemical (specific surface area, ζ potential, and pH), physical (density, penetration resistance, water dispersible clay, and total porosity), and micromorphological properties (surface area, volume, connectivity, size, and pore anisotropy) 1 yr after soil incubation in polyvinyl chloride cylinders 30 cm long and 14.5 cm in diameter. Lime application on the surface or into the 0- to 5-cm layer increased soil pH to values above 7.0 and the electronegative potential of soil colloid surface, promoting clay dispersion. Water-dispersed clay migrated in the soil profile, causing pore obstruction, and higher soil density and penetration resistance. In addition, excessive lime decreased specific surface area, anisotropy degree and the connectivity of the soil pore system. Straw addition promoted a slight increase of colloids electronegative potential but did not alter soil physical properties.

O objetivo deste trabalho foi avaliar a persistência dos efeitos da escarificação sobre a compactação de Nitossolo Vermelho, manejado sob plantio direto (PD), na região subtropical úmida do Brasil. O experimento foi realizado em blocos ao acaso, com quatro repetições e seis tratamentos, constituídos pelo tempo de manutenção do solo sob PD após escarificação: PD contínuo por 24 meses após escarificação, realizada em setembro de 2009; PD contínuo por 18 meses após escarificação, realizada em março de 2010; PD contínuo por 12 meses após escarificação, realizada em setembro de 2010; PD contínuo por seis meses após escarificação, realizada em março de 2011; plantio realizado em solo recém escarificado, em setembro de 2011; e PD contínuo e sem escarificação (testemunha). As espécies cultivadas na área foram: milho, safra 2009/2010; trigo, em 2010; soja, safra 2010/2011; centeio, em 2011; e milho, safra 2011/2012. Os efeitos dos tratamentos foram avaliados a partir de parâmetros físicos do solo e de parâmetros morfológicos e produtivos da cultura do milho, na safra 2011/2012. A escarificação do Nitossolo sob plantio direto, em região de clima subtropical úmido, não aumenta a produtividade de grãos de milho, e os seus efeitos sobre a estrutura do solo não persistem por mais de 18 meses. The objective of this work was to evaluate the persistence of chiseling effects on the compaction of a Ferralic Nitisol (Rhodic), under no-till (NT), in the Brazilian humid subtropical region. The experiment was carried out in randomized complete blocks, with four replicates and six treatments, consisting of the time that the soil was kept under NT after chiseling: continuous NT for 24 months, after chiseling in September 2009; continuous NT for 18 months, after chiseling in March 2010; continuous NT for 12 months, after chiseling in September 2010; continuous NT for six months, after chiseling in March 2011; crop planted right after soil chiseling, in September 2011; and continuous NT, without chiseling (control). The species cultivated in the area were: corn in the 2009/2010 growing season; wheat in 2010; soybean in the 2010/2011 growing season; rye in 2011; and corn in the 2011/2012 growing season. Treatment effects were assessed by soil physical parameters and by morphological and productive parameters of the corn crop in the 2011/2012 growing season. The chiseling of Nitisol under no-till in a humid subtropical region does not increase corn grain yield, and its effects on soil structure do not last longer than 18 months.

Global interest in soil health has increased exponentially during the past decade, with many different government, non-government, and private sector groups striving to develop monitoring and assessment protocols. This brief review focuses on developments in the United States (U.S.) with some references to activities in other countries. It also documents how the soil health concept evolved and projects what is needed to scientifically advance monitoring and assessment with a particular focus on activities in the U.S. Recommendations emphasize improving the Soil Management Assessment Framework (SMAF) and/or Comprehensive Assessment of Soil Health (CASH) assessment tools, developing protocols for national soil health monitoring, identifying and calibrating better indicators of soil biological, chemical, and physical health, and developing sensors and other tools for more rapid and in-situ assessments. Collectively, these and other research and technology transfer activities will help achieve what we suggest should be a universal goal – striving for healthy soils, healthy landscapes, and vibrant economies.

Soil compaction has always been a problem to the agricultural productivity, mainly in clayey soils under the no-tillage (NT). Alternatives to mitigate this problem are necessary. The aim of this study was to evaluate the effect of seeder equipped with fixed shanks openers, working at three depths, in a Ferralic Nitisol (Rhodic), under NT on the mitigation of soil compaction and corn ( Zea mays L.) plant development. The test comprised three treatments regarding the depth at which the shank openers of a seeder used to sow corn worked: openers reaching up to 0.05 m; openers reaching up to 0.07 m; and openers reaching up to 0.17 m. The effect of these treatments was evaluated in relation to the determination of soil physical parameters, and corn plant parameters. The use of a seeder equipped with fixed shanks openers up to 0.17 m depth caused an increase in soil macroporosity and total porosity, and a decrease in soil bulk density, soil resistance to penetration and degree of compactness in the layer between 0.07 and 0.17 m. The improved physical conditions of the soil in this layer led to a further development of the root system of plants in greater depth, and consequently to a better development of corn plants with higher stalk diameter, root density and root length. The use of a seeder equipped with fixed shanks openers working up to 0.17 m depth, therefore, promoted physical improvement to the soil, favoring the development of corn plants, and presenting potential to mitigate the compaction of clayey soils under NT.

Horizontes subsuperficiais escuros com características morfológicas similares aos solos com caráter sômbrico são encontrados nas áreas mais elevadas da porção leste do Escudo sul-rio-grandense, desenvolvidos nos horizontes A2, AB (ou AC) e BA de Argissolos, Luvissolos e Neossolos Regolíticos, respectivamente. Os mecanismos responsáveis pela sua gênese são ainda pouco compreendidos, apesar de a maioria dos autores concordar com a origem iluvial do húmus e de constituir horizonte diagnóstico. Os objetivos deste trabalho foram caracterizar e analisar o enquadramento de nove perfis de solos com horizontes subsuperficiais escuros do Escudo sul-rio-grandense nos critérios do SiBCS, WRB e Soil Taxonomy, sendo sete deles com características morfológicas de sômbrico. A observação de campo (continuidade lateral na paisagem) e a morfologia (ausência de horizonte E, cores mais escuras que os horizontes sobrejacentes e presença de cutans) apóiam o caráter sômbrico para a maioria dos perfis estudados, com a inserção do caráter sômbrico em nível de subgrupo nas classes de Argissolos Bruno-Acinzentados, Amarelos e Vermelho-Amarelos, bem como em Luvissolos e Neossolos Regolíticos, além da inclusão de eutrófico no nível de grande grupo na classe dos Argissolos Bruno-Acinzentados. Os dados sugeriram a revisão da definição de dessaturação na determinação do caráter sômbrico (distrófico) no SiBCS, com a adoção do valor V de 65 %, adequando essa à definição do Soil Taxonomy e WRB, bem como uma investigação mais aprofundada quanto à não associação do húmus com Al; e a consideração da retirada da capacidade de troca de cátions da matéria orgânica no cálculo da atividade da argila, para os horizontes subsuperficiais escuros. Dark subsurface horizons with morphological characteristics similar to sombric horizons are found in higher altitude areas of the eastern portion of the Sul-Rio-Grandense Shield, Brazil. They developed in the A2, AB (or AC), and BA horizons of Ultisols, Alfisols, and Entisols. The mechanisms responsible for their genesis are still poorly understood, although most authors agree on the illuvial origin of the humus horizon and on its diagnostic character. The objective of this study was to characterize and analyze nine soil profiles with dark subsurface horizons from the Sul-Rio-Grandense Shield within the current criteria of the Brazilian Soil Classification System (SiBCS), the WRB, and Soil Taxonomy, seven of these soils having morphological characteristics of the sombric horizon. Field observation (lateral continuity in the landscape) and soil morphology (absence of E horizon, darker color than the overlying horizons, and the presence of cutans) support the sombric character for most of the soils studied, adding the sombric trait to the subgroup level in the Gray-Brown Argisol (Argissolo Bruno-Acinzentado), Yellow Argisol (Argissolo Amarelo), and Red-Yellow Argisol (Argissolo Vermelho-Amarelo), as well as to the Luvisol (Luvissolo) and Regolitic Neosol (Neossolo Regolítico) classes, in addition to including eutrophic in the Great Group level of the Gray-Brown Argisol (Argissolo Bruno-Acinzentado) class. The data suggest revising the definition of base desaturation (dystrophic) for the sombric character in the SiBCS, with adoption of the base saturation value of 65 %, fitting it to the Soil Taxonomy and WRB definition, as well as a deeper investigation of the lack of association of humus with Al and disregard of cation exchange capacity of organic matter in calculating clay activity for the dark subsurface horizons.

A adoção do plantio direto na região subtropical úmida do Brasil, fundamentada apenas em dois preceitos da agricultura conservacionista - mobilização de solo restrita à linha de semeadura e manutenção de resíduos culturais na superfície do solo -, tem induzido à estratificação de atributos químicos do solo na camada de 0-20 cm profundidade e degradação física da camada subsuperficial (entre aproximadamente 5-20 cm de profundidade), que podem contribuir para frustrações de safras agrícolas, quando da ocorrência de estiagens. O objetivo deste trabalho foi avaliar o efeito residual de uma semeadora/adubadora, equipada com elemento rompedor de solo tipo haste sulcadora, atuando em quatro profundidades para a semeadura de milho (Zea mays L.), na mitigação de problemas de ordem física e química, em um Latossolo Vermelho distrófico húmico, manejado em plantio direto há mais de 10 anos. Os tratamentos avaliados foram: T1 = hastes sulcadoras atuando até 5 cm de profundidade; T2 = hastes sulcadoras atuando até 10 cm de profundidade; T3 = hastes sulcadoras atuando até 15 cm de profundidade; e T4 = hastes sulcadoras atuando até 17 cm de profundidade. O efeito desses tratamentos sobre os atributos físicos do solo foi avaliado pela técnica do perfil cultural associada à determinação da densidade, porosidade total, macroporosidade e resistência do solo à penetração, aos oito e 12 meses, após a semeadura da cultura de milho. Sobre os atributos químicos, esses efeitos foram avaliados pela determinação de pH em H2O, P e K disponíveis, Ca, Mg e Al trocáveis, acidez potencial e matéria orgânica, em amostras de solo coletadas em camadas de 2,5 cm de espessura, de 0-22,5 cm de profundidade. A utilização da semeadora/adubadora, equipada com elemento rompedor de solo tipo haste sulcadora, evidenciou-se eficaz em mitigar os problemas físicos e químicos do solo, tanto aos oito como aos 12 meses após a operação de semeadura.

Physical degradation of the subsurface layer of soils reduces the effectiveness of no-till (NT) as a sustainable soil management approach in crop production. Chemical factors may reduce the structural stability of Oxisols and thereby exacerbate compaction from machinery traffic. We studied the relationship between chemical management and structural degradation in Oxisols cultivated under NT at three sites in southern Brazil. The surface and subsurface layers of the soils were characterised chemically and mineralogically and three physical attributes related to soil structural stability (readily dispersible clay in water, mechanically dispersible clay in water, and water percolation) were quantified for each layer. The same characterisations were performed on Oxisols collected from adjacent non-cultivated areas, to provide reference data for non-degraded soil. The levels of dispersed clay in the cultivated soil from the surface layer matched those of the non-cultivated soil, but for the subsurface layer higher dispersed clay levels in the cultivated soil showed that it was physically degraded relative to the non-cultivated soil. Water percolation was found to be slower through the Oxisols cultivated under NT, irrespective of the soil layer. The relationships between the three indicators of soil structural stability and the measured chemical and mineralogical variables of the soils were explored through an analysis of canonical correlation. The principal variables associated with the lower stability of the cultivated vs non-cultivated Oxisols were the lower concentrations of organic carbon and exchangeable aluminium and, for the surface layer, the higher pH. It is argued that structural degradation of Oxisols cultivated under NT, observed predominantly in the subsurface layer, has been aggravated by the accumulation of amendments and fertilisers in the surface soil and reduced levels of organic matter, especially in the subsurface layer.