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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.

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.

A manifestacao do potencial produtivo das culturas depende de fatores geneticos e de condicoes favoraveis de ambiente e de manejo. A epoca de semeadura pode afetar significativamente a produtividade de graos do feijao comum. O objetivo do trabalho foi de estudar o comportamento de cultivares brasileiras e epocas de semeadura nos componentes de producao e produtividade de graos do feijao comum cultivado nas condicoes ambientais de Lichinga, Provincia de Niassa, Mocambique. O experimento de campo foi conduzido em duas safras agricolas, utilizando-se o delineamento experimental de blocos casualisados em esquema fatorial 5x3x2, com quatro repeticoes. Os tratamentos constaram da combinacao de cinco cultivares de feijao comum (BRS Pontal, BRS Agreste, BRS Perola e BRS Requinte, desenvolvidas pela Embrapa e uma variedade local, Encarnada) com tres epocas de semeadura (inicio do periodo chuvoso, 15 e 30 dias apos) e duas safras agricolas. A cultivar brasileira de feijao comum BRS Pontal foi a mais produtiva em todas as epocas de semeadura, seguidas da BRS Agreste, que nao foi a mais produtiva, somente na segunda epoca de semeadura da safra 2013/2014. A cultivar Encarnada de Mocambique foi a cultivar menos produtiva em todas as epocas de semeadura e em todas as estacoes de crescimento. A melhor epoca de semeadura para as cultivares de feijoeiro-comum e no inicio do periodo chuvoso. O uso de tecnologias como o uso de sementes de novas cultivares, epoca de semeadura adequada, adubacao e controle de plantas daninhas permitem aumentar significativamente a producao de graos do feijoeiro-comum em Lichinga, Mocambique.

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.

Recent studies have shown harmful effects of soil compaction in no-tillage system (NTS), but there are indications that soil structure improves with time of NTS adoption. We formulated the hypothesis that topsoils of NTS initially have worse soil physical conditions than those under conventional systems, but these conditions gradually improve with time also down to deeper depth, even when the soil is wheeled by farm machinery. Our objective was to evaluate the effect of a long-term no-tillage system and machine traffic on soil mechanical and hydraulic properties. The treatments and soil conditions consisted of five periods since the last conventional tillage (or age of NTS) in a Hapludox: 0.2,1.5, 3.5, 5 and 14 years, with and without traffic; named recent tillage, and initial, intermediate, transition and stabilized NTS phases. Soil samples were collected from soil layers 0-7, 7-14 and 14-21 cm depth to determine soil porosity, precompression stress, compressibility coefficient, saturated hydraulic conductivity, air permeability, water retention curve, bulk density and organic carbon. Conventional tillage of soil previously under no tillage significantly affected soil capacity properties, resulting in high macroporosity and deformation susceptibility, low bulk density and precompression stress. Intensity properties were affected initially by an increased soil pore obstruction, negatively affecting air permeability and saturated hydraulic conductivity, from 0 to 21 cm soil depth. However, after five years of no-tillage there was an increase in microporosity and, although small, in soil organic carbon, especially in the 0-7 cm soil layer; thus, soil water retention and soil intensity properties (like soil water and air permeability) were also improved, regardless of farm machinery traffic. Over time, soil reconsolidation occurred, which resulted in reduction of the compressibility coefficient and degree of compactness, mainly in the upper layers (07 and 7-14 cm). However, in the deepest layer with the least disturbance, the degree-of-compactness and bulk density increased. The evolution of physical properties and processes (from recent tillage to stabilized NTS phase) for no-tilled soil is proposed for controlled and uncontrolled traffic systems as a framework based on field data for capacity and intensity soil properties. The process of creating aggregates is represented, at first, by an increased number of contact points before they are re-loosened and strengthened at the same time by a rearrangement of particles, reducing aggregate bulk density but increasing soil strength at the same time. The framework is divided into 4 phases: initial (1.5 years), intermediary (3.5 years), transitional (5 years), and stabilized (14 years) conditions. (C) 2015 Elsevier B.V. All rights reserved.

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.

Resumo: O objetivo deste trabalho foi determinar o tempo de duração do efeito da descompactação do solo, por escarificação mecânica, por meio de indicadores físico-hídricos de Latossolo argiloso, manejado em sistema plantio direto (SPD). Os tratamentos consistiram em meses (0, 6, 12, 18, 24, 30 e 36) transcorridos após escarificação mecânica em SPD e em testemunha sem escarificação em SPD há 27 anos. Foram avaliadas as variáveis: resistência mecânica à penetração, taxa de infiltração de água no solo, densidade e densidade relativa do solo, distribuição do tamanho de poros e condutividade hidráulica do solo saturado. A duração dos efeitos da escarificação mecânica variou com a propriedade do solo, tendo se mantido por 6 meses na densidade e na densidade relativa, na porosidade total e na macroporosidade; 18 meses na resistência à penetração; e 24 meses na condutividade hidráulica e na taxa de infiltração de água no solo. Propriedades do solo relacionadas ao transporte de água, como condutividade hidráulica e taxa de infiltração estável de água no solo, mantêm o efeito da escarificação por mais tempo e, portanto, são mais adequadas para avaliar a duração da descompactação mecânica. Abstract: The objective of this work was to determine the duration of the effects of soil decompaction, by mechanical chiseling, through physical and hydraulic indicators of a clayey Oxisol under no-tillage (NT). The treatments consisted of months (0, 6, 12, 18, 24, 30, and 36) after chiseling under NT and of a control treatment without chiseling under NT during 27 years. The following variables were evaluated: penetration resistance, infiltration rate, bulk density and relative density, pore size distribution, and saturated hydraulic conductivity. The duration of the effects of mechanical chiseling varied according to the evaluated soil property, lasting six months for bulk density and relative density, total porosity, and macroporosity; 18 months for penetration resistance; and 24 months for hydraulic conductivity and infiltration rate. Soil properties related to water transport, such as hydraulic conductivity and steady infiltration rate, maintain the effect of mechanical chiseling for a longer time and, therefore, are more suitable to measure the duration of mechanical decompaction.

A compactação tornou-se uma das principais causas de degradação do solo em áreas agrícolas, estando diretamente relacionada ao sistema de manejo do solo adotado e, muitas vezes, demandando práticas de descompactação para mitigar esse problema. Este trabalho objetivou avaliar a duração do efeito de intervenções mecânicas, como a aração e escarificação do solo associadas à ação de semeadora de plantio direto equipada com mecanismos rompedores de solo tipo discos e discos + facão, como práticas mitigadoras da compactação de um solo manejado sob o Sistema Plantio Direto (SPD), por meio da avaliação de atributos físicos do solo e do esforço de tração. O estudo foi realizado no município de Coxilha, na região Norte do Rio Grande do Sul, localizado nas coordenadas geográficas de 28°10'18,7" S e 52°22'39,89" O, sobre um Latossolo Vermelho, em experimento instalado no ano de 2001 em área com histórico de oito anos sob SPD. Nessa área foram realizadas intervenções mecânicas anuais, mediante a aração e escarificação do solo, anteriores à implantação da cultura de verão. Os tratamentos de manejo do solo constituíram- se da testemunha, com manutenção ininterrupta do SPD por 16 anos e por seis períodos de tempo de condução desse sistema (7,5; 6,5; 5,5; 4,5; 3,5; e 2,5 anos) após a escarificação ou aração, aplicados nas parcelas principais. Nas subparcelas foram aplicados dois tratamentos de dispositivo de aplicação do adubo no sulco de semeadura (discos duplos defasados e facão + discos). O delineamento experimental adotado foi de blocos completos casualizados com parcelas subdivididas e três repetições. Os resultados indicaram a existência de compactação na camada subsuperficial do solo, situada entre 7 e 15 cm, evidenciada por aumentos na densidade e redução na porosidade total e macroporosidade do solo em todos os tratamentos avaliados. Observou-se que a intervenção mecânica apresenta potencial efêmero para mitigar a compactação e melhorar a estrutura do solo, com duração de até dois anos e meio dos atributos porosidade total e macroporosidade após a escarificação, e a densidade do solo depois da aração. Nos demais atributos avaliados, tais benefícios deixaram de ser perceptíveis em período inferior a dois anos e meio após a intervenção mecânica, o que não provocou alterações na força exercida na barra de tração do trator agrícola, comparativamente à testemunha. Contudo, o mecanismo facão + discos de rompimento do solo na semeadora foi efetivo em alterar os atributos avaliados, aumentando a macroporosidade, diminuindo a microporosidade, a densidade do solo e o esforço de tração e auxiliando, assim, na mitigação da compactação do solo. Compaction has become one of the main causes of soil degradation in agricultural areas. It is directly related to the soil management system, often requiring decompaction practices to mitigate the problem. This study aimed to determine the duration of the effects of mechanical soil decompaction, e.g., by plowing and chiseling, associated with soil breaking devices on the seeders, for example disks and disk-ripper, to mitigate the compaction of soil under no tillage; soil physical properties and the force exerted by the traction bar were evaluated. The study was carried out in Coxilha, in the north region of Rio Grande do Sul (Brazil) (28°10'18.7" S, 52°22'39.89" W), on a Red Oxisol. The experiment was installed in 2001, in an area for eight years under no-tillage (NT). In this area, mechanical interventions of soil plowing and chiseling were annually performed, prior to summer crop planting. The treatments consisted of one control (uninterrupted NT for 16 years) and six NT periods (7.5; 6.5; 5.5; 4.5; 3.5, and 2.5 years) after chiseling and plowing in the main plots. In the subplots, two fertilizer treatments were applied in the sowing furrow (disks or disk-ripper). The experiment was evaluated in a randomized block design in split plots and three replications. Results indicated the existence of soil compaction in the subsurface layer (7-15 cm), evidenced by increases in soil density and reduction in soil total porosity and macroporosity in all treatments. It was observed that the effects of mechanical intervention to mitigate compaction and improve the soil structure were ephemeral, with a durability of up to two and a half years after chiseling for total porosity and macroporosity and for soil density in the plowing treatments. For the other parameters, these benefits were no longer detectable less than two and a half years after intervention. Mechanical intervention caused no alterations in the force exerted by the traction bar, in comparison with the control. However, the soil breaking mechanism of the disk-ripper on the seeder was effective in altering the appraised parameters, increasing soil macroporosity and reducing microporosity, soil density and traction force, thus mitigating soil compaction.

Conservation agriculture can provide a low-cost competitive option to mitigate global warming with reduction or elimination of soil tillage and increase soil organic carbon (SOC). Most studies have evaluated the impact of zero till (ZT) only on surface soil layers (down to 30 cm), and few studies have been performed on the potential for C accumulation in deeper layers (0–100 cm) of tropical and subtropical soils. In order to determine whether the change from conventional tillage (CT) to ZT has induced a net gain in SOC, three long-term experiments (15–26 years) on free-draining Ferralsols in the subtropical region of South Brazil were sampled and the SOC stocks to 30 and 100 cm calculated on an equivalent soil mass basis. In rotations containing intercropped or cover-crop legumes, there were significant accumulations of SOC in ZT soils varying from 5 to 8 Mg ha−1 in comparison with CT management, equivalent to annual soil C accumulation rates of between 0.04 and 0.88 Mg ha−1. However, the potential for soil C accumulation was considerably increased (varying from 0.48 to 1.53 Mg ha−1 yr−1) when considering the soil profile down to 100 cm depth. On average the estimate of soil C accumulation to 100 cm depth was 59% greater than that for soil C accumulated to 30 cm. These findings suggest that increasing sampling depth from 30 cm (as presently recommended by the IPCC) to 100 cm, may increase substantially the estimates of potential CO2 mitigation induced by the change from CT to ZT on the free-draining Ferralsols of the tropics and subtropics. It was evident that that legumes which contributed a net input of biologically fixed N played an important role in promoting soil C accumulation in these soils under ZT, perhaps due to a slow-release of N from decaying surface residues/roots which favored maize root growth.

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.

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.

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.

A infiltração de água é uma propriedade que reflete as condições físicas do solo, principalmente quanto à sua qualidade estrutural. Foi realizado um estudo na Embrapa Trigo, em Passo Fundo (RS), em um Latossolo Vermelho-Escuro, submetido por longo tempo a diferentes sistemas de manejo, com o objetivo de verificar a influência desses sistemas na taxa de infiltração de água, considerando as diferentes coberturas de solo e condições físicas gerais por eles propiciadas. A área experimental estava cultivada com milho, tendo-se aplicado chuva simulada de 120 mm h-1, durante 90 minutos, em três repetições, em três épocas distintas: (a) 45 dias após a semeadura do milho; (b) logo após a colheita do milho e (c) logo após a semeadura de aveia. As chuvas simuladas foram aplicadas sobre parcelas de 0,81 m2 distribuídas dentro de macroparcelas com os sistemas de manejo em preparo convencional, cultivo mínimo e sistema plantio direto. O cultivo mínimo apresentou, em todas as épocas, as maiores taxas de infiltração de água no solo, e o sistema plantio direto produziu as maiores quantidades de palha na superfície do solo. Soil water infiltration rate may be the soil property which best reflects the general soil physical conditions, especially the structural quality. A field study was conducted at the Embrapa Trigo, Passo Fundo, Brasil in an Oxisol under long-term soil tillage systems, to evaluate the influence of these systems on soil water infiltration rate as a function of the soil cover and soil physical conditions caused by the different tillage systems. During a corn cropping period, a simulated rainfall with intensity of 120 mm h-1 and 90 minutes duration was applied in three replications and three different runs: (1) 45 days after corn sowing; (2) immediately after corn harvest; and (3) immediately after oat sowing. The simulated rainfall was applied on small plots of 0.81 m2 area inside larger plots where conventional tillage, minimum tillage and no-tillage were applied. In all runs, minimum tillage showed the highest soil water infiltration rates, while the no-tillage system yielded the highest amount of crop residues on the soil surface.

Changes in residue management resulting from adoption of conservation tillage systems have the potential to alter the concentration and distribution of phosphorus (P) in the soil surface. The objective of this study was to determine the effect of methods of tillage management on the distribution and concentration of organic and inorganic forms of soil P near the soil surface (0–10 cm depth) for an Oxisol in southern Brazil. The tillage systems included zero tillage (ZT) (seeding directly onto the standing stubble of the previous crop), minimum tillage (MT) (seeding the crop after chisel plowing to 15-cm depth and disk harrowing to 7.5 cm), or conventional tillage (CT) (seeding after disk plowing to 20-cm depth with nearly total soil inversion plus two disk harrowings to 10-cm depth). After a period of five years, reducing tillage through adoption of MT or ZT practices increased total P in the surface 10 cm by 15% when compared to CT. Although there were no differences in amounts of total P between MT and ZT systems, under ZT management larger amounts of labile organic and inorganic forms of P accumulated close to the soil surface, followed by a reduction below the 6-cm depth. Under MT, the labile organic and inorganic forms of P were uniformly distributed within the surface 10 cm of soil. The accumulation of high levels of labile P near the soil surface under ZT followed a distribution pattern similar to the accumulation of organic residues in the soil. This would help explain why other workers have found increased P uptake by crops grown under ZT, and why more available P can be extracted by common soil testing methods from the surface 7 to 10 cm of soils under ZT than under CT management.

A compactação altera, negativamente, várias propriedades do solo, como a capacidade de penetração das raízes e a disponibilidade de água e nutrientes às plantas, restringindo a taxa fotossintética, o crescimento da parte aérea e, por conseguinte, o rendimento da cultura. Nesse sentido, quando a compactação do solo torna-se limitante ao desenvolvimento das culturas, faz-se necessária a adoção de medidas mitigatórias. Nesse contexto, este trabalho objetivou avaliar o efeito residual de intervenções mecânicas mediante aração e escarificação do solo, associadas à semeadora com sulcadores tipo discos e discos + haste, como prática mitigadora da compactação de solo manejado sob sistema plantio direto (SPD), sobre os parâmetros de resistência do solo à penetração e o rendimento da cultura da soja. Para isso, foi realizado um estudo no município de Coxilha, na região norte do Rio Grande do Sul, em um Latossolo Vermelho, em experimento instalado no ano de 2001 em área com histórico de manejo sob SPD. Nessa área, a cada ano um tratamento foi submetido à descompactação mecânica do solo sob SPD mediante uma aração e outro mediante uma escarificação do solo, anterior à implantação da cultura de verão, retornando-se o manejo sob SPD após essa intervenção. O delineamento experimental foi de blocos ao acaso com parcelas subdivididas, com três repetições. Os tratamentos foram compostos pela combinação de 13 sistemas de manejo do solo, alocados na parcela principal, e dois dispositivos sulcadores da semeadora, alocados na subparcela. Assim, os sistemas de manejo avaliados foram constituídos pela testemunha, representada pela manutenção ininterrupta do SPD por 16 anos; seis períodos de tempo de manejo sob SPD (7,5; 6,5; 5,5; 4,5; 3,5 e 2,5 anos) após uma intervenção mecânica com arado de discos + grade de discos (A); e os mesmos seis períodos após uma intervenção mecânica com escarificador (E). Os níveis alocados na subparcela foram constituídos pela ação de uma semeadora de plantio direto equipada com discos duplos defasados atuando até 7 cm de profundidade e de uma semeadora equipada com discos duplos + haste atuando até 13 cm de profundidade. Os resultados obtidos indicaram que a intervenção mecânica em solo manejado sob SPD consolidado, mediante a prática de escarificação ou aração do solo, apresenta potencial efêmero para mitigar a compactação e promover a melhoria da estrutura do solo, com efeito residual de até dois anos e meio para a resistência do solo à penetração. A utilização de semeadora de plantio direto equipada com sulcador tipo haste + disco apresentou potencial para mitigação da compactação do solo, promovendo a redução da resistência mecânica do solo à penetração na camada de 7 - 15 cm de profundidade. Contudo, o efeito residual da intervenção mecânica para descompactação do solo e a adoção dos diferentes dispositivos de aplicação do adubo no sulco de semeadura não foram eficientes em alterar o rendimento de grãos da cultura da soja na safra agrícola 2008/2009. Compaction negatively affects a number of soil properties, e.g., resistance to root penetration and water and nutrient availability to plants, restricting the photosynthetic rate, shoot growth and consequently, the yield. When soil compaction becomes limiting to crop development, mitigation measures must be adopted. The purpose of this study was to evaluate the residual effect of mechanical soil plowing and chiseling, by a seeder with soil breakers (disks and disks plus short ripper) as mitigation practice of the soil compaction under no-tillage (NT), on soil penetration resistance and soybean yield. In 2001, a study was conducted in Coxilha, in northern Rio Grande do Sul, on an Oxisol, in an area with a sequence of NT management. In this field, every year a treatment of mechanical soil decompression was applied, consisting of plowing and chiseling the soil under NT, before sowing the summer crop, reassuming the NT management after this intervention. The experimental design consisted of randomized blocks in a split-plot design with three replications. The treatments consisted of a combination of 13 systems of soil management in the main plots and two seed drill devices in the subplots. Thus, the management systems were evaluated by the control, represented by the uninterrupted maintenance of NT for 16 years, six NT management periods (7.5, 6.5, 5.5, 4.5, 3.5, and 2.5 years) after one intervention with mechanical disc plow + disc harrow (A) and the same six NT management periods after one mechanical intervention with chiseling (E). The levels in the subplots consisted of the action of a no-till seeder equipped with double discs reaching a depth of 7 cm and a seeder equipped with double disks + short ripper reaching a depth of 13 cm. Results indicated that the mitigating effect on compaction and on the improvement of soil structure of the mechanical intervention in soil under consolidated NT consisting of soil chiseling or plowing is short-lived, with a residual effect of up to two and a half years for penetration resistance. The use of a no-till seeder drill equipped with short ripper + disc seeder has potential for mitigation of soil compaction, by reducing mechanical penetration resistance in the 7-15 cm layer. Nevertheless, the residual effect of mechanical intervention for soil decompaction and the adoption of different devices for fertilizer application in the plant furrow were not effective in altering the soybean yield in the 2008/2009 growing season.

A compactação do solo restringe o rendimento de culturas de grãos. Dentre outros fatores, a calagem pode favorecer a dispersão de microagregados e a formação de camadas compactadas. O objetivo deste trabalho foi avaliar os efeitos do calcário e da esterilização em atributos físicos e químicos do solo relacionados com a compactação do solo. O experimento foi efetuado em colunas de PVC, em casa de vegetação, durante 18 meses. Amostras esterilizadas e não esterilizadas de um Latossolo Vermelho distrófico foram incubadas com doses equivalentes a 0, 1,9, 3,8, 5,7, 7,6 e 15,2 Mg ha-1. Após 18 meses, foram avaliados a macro e microporosidade, a densidade do solo, teor de argila dispersa, a condutividade hidráulica saturada, o pH e os teores de Al, Ca e Mg trocáveis e de matéria orgânica do solo. A calagem aumentou a densidade do solo, o teor de argila dispersa em água, o pH e os teores de Ca2+ e Mg2+ trocáveis, e decresceu a micro e macroporosidade, a condutividade hidráulica saturada, os teores de matéria orgânica e de Al trocável. O aumento de pH e a redução da condutividade hidráulica saturada foram maiores no solo esterilizado. Os efeitos da calagem foram mais pronunciados na quantidade correspondente a 3,8 Mg ha-1. A esterilização aumentou o valor do pH em água e reduziu os teores de matéria orgânica e de Ca2+, além da condutividade hidráulica saturada. A dispersão de microagregados pela calagem pode, em parte, contribuir para a compactação do solo.

Nas regiões brasileiras de clima temperado e subtropical úmido, situadas ao sul do paralelo 24° de latitude sul, as características fundamentais da chuva apresentam potencial para superar a taxa de infiltração de água no solo e gerar enxurrada, em qualquer época do ano, independentemente do uso e do manejo de solo. O sistema plantio direto não tem sido implementado com a plenitude das práticas conservacionistas requeridas pelas condições de solo dessas regiões do País para conter o potencial erosivo de chuvas intensas. A enxurrada resulta na produção de sedimento enriquecido por agroquímicos, que, além de promover prejuízos econômicos ao sistema agrícola produtivo, pode afetar a ambiência. Este trabalho teve por objetivo avaliar a eficiência da prática conservacionista vertical mulching no manejo de enxurrada em lavouras sob sistema plantio direto, por meio da quantificação do índice de enriquecimento do sedimento. O estudo contemplou amostragens pareadas de solo em lavouras sem e com a prática conservacionista vertical mulching. As amostras pareadas foram constituídas por solo representativo de cada lavoura e pelo respectivo sedimento gerado por erosão hídrica. As amostras foram submetidas à determinação de pH em água, índice SMP, P disponível, K, Ca, Mg e Al trocáveis e matéria orgânica, e calculadas a soma de bases, a saturação por bases e a capacidade de troca de cátions efetiva. Os resultados indicam que a prática conservacionista vertical mulching reduz o grau de enriquecimento do sedimento produzido e previne o carreamento deste para fora da lavoura, minimizando perdas econômicas e riscos à ambiência. Em adição, infere-se que o sistema plantio direto, sem práticas complementares para manejo de enxurrada, não representa manejo conservacionista de solo capaz de prevenir degradação ambiental.

There is little information about common bean fertilization in African Savannas. The objectives of this study were as follows: i) to evaluate the common bean yield potential in the environmental conditions of Lichinga, Niassa, Mozambique, and ii) to determine the common bean response to phosphorus and potassium fertilization applied together in order to verify whether the interpretation of soil analysis for the Brazilian Cerrado could be adopted for Savanna soils in Mozambique. The experimental design was a randomized block design in a 5 x 4 x 2 factorial arrangement. Treatments consisted of a combination of phosphorus doses (0, 35, 70, 140 and 280 kg ha-1 of P2O5), potassium doses (0, 50 100 and 200 kg ha-1 of K2O), and different growing seasons (2012/2013 and 2013/2014). The field rainfed experiments were conducted in Lichinga city, province of Niassa. Common bean crops presented high productivity potential in rainfed systems in the environmental conditions of Lichinga, Niassa, Mozambique, reaching grain yields of up to 3,600 kg ha-1 depending on the rates of fertilization with phosphorus and potassium. Common beans responded to phosphorus and potassium fertilization despite high contents of these nutrients in the soil, according to the interpretation of soil analysis for the Brazilian Cerrado. Maximum grain yield in the average of two growing seasons was estimated to occur for 239 kg ha-1 of P2O5 and 141 kg ha-1 of K2O, indicating that further calibration studies for P and K are required for this specific region of Mozambique. Made available in DSpace on 2018-03-29T00:35:16Z (GMT). No. of bitstreams: 1 CNPAF2018agriambi.pdf: 800986 bytes, checksum: 171e8108b32a519ae30ae7469a7240a8 (MD5) Previous issue date: 2018-03-28

Intensification of soil compaction process under no-tillage (NT) is motivating the search for alternatives to mitigate soil compaction state. This study evaluated changes in soil physical and hydraulic properties caused by seeder with fertilizer shanks at different depths compared with the double discs lagged seeder, to investigate the possibility of soil decompaction by sowing under NT in southern Brazil. The study was conducted in a clayed Oxisol, for 27 years under NT. Treatments were three planting mechanisms: S0.10m: cutting disc combined with shank acting to 0.10m depth; S0.15m: cutting disc combined with shank acting to 0.15m depth and, D0.07m: double discs lagged acting to 0.07m depth in an experimental randomized block design with four replications. We evaluated the soil mechanical resistance, water infiltration rate, soil bulk density, pore size distribution and unsaturated hydraulic conductivity. Results indicated that the use of seeder with fertilizer shanks acting at 0.15m deep promoted the soil decompaction by the reduction of penetration resistance and increase of porosity and unsaturated hydraulic conductivity. To have significant increase in water infiltration rate the fertilizer shanks of the seeder must be deepened to the lower limit of the compacted surface layer. RESUMO: A intensificação do processo de compactação do solo em sistema plantio direto (SPD) motiva a procura por alternativas para atenuação do estado de compactação do solo. Esse trabalho objetiva avaliar modificações em propriedades físico-hídricas do solo originadas por semeadoras equipadas com hastes sulcadoras que atuam em diferentes profundidades, em comparação à semeadora com discos duplos defasados, para investigar a possibilidade de descompactação do solo na operação de semeadura em áreas sob SPD na região Sul do Brasil. O estudo foi realizado em Latossolo Vermelho Distrófico típico, de textura argilosa, há 27 anos sob SPD. Os tratamentos foram três mecanismos de semeadura: H0,10m: disco de corte combinado com haste sulcadora atuando a 0,10m de profundidade; H0,15m: disco de corte combinado com haste sulcadora atuando a 0,15m de profundidade; e D0,07m: discos duplos defasados atuando a 0,07m de profundidade, em delineamento experimental blocos ao acaso com quatro repetições. Avaliou-se a resistência mecânica à penetração, taxa de infiltração de água no solo, densidade do solo, distribuição do tamanho de poros e condutividade hidráulica do solo não saturado. Os resultados indicaram que a utilização de semeadora com haste sulcadora atuando a 0,15m promove a descompactação do solo através da redução da resistência mecânica do solo à penetração, aumento da porosidade e da condutividade hidráulica. Para que haja aumento significativo da infiltração de água no solo, a haste sulcadora da semeadora deve ser aprofundada até o limite inferior da camada superficial compactada.

O desenvolvimento econômico brasileiro depende da crescente produção agropecuária, aliada ao conservacionismo. O sistema de plantio direto é o manejo de solo que reúne o mais amplo conjunto de preceitos da agricultura conservacionista. As áreas agrícolas cultivadas sob plantio direto, entretanto, têm apresentado duas camadas de solo distintas: uma entre, aproximadamente, 0 e 7 cm de profundidade, com condições físicas e químicas favoráveis ao desenvolvimento radicular; e uma entre, aproximadamente, 7 e 20 cm de profundidade, com menor permeabilidade do solo ao ar e a água, elevada resistência à penetração e baixa fertilidade química do solo. Estas condições promovem a concentração do sistema radicular das plantas agrícolas cultivadas na camada mais superficial do solo (0 a 7 cm), motivando perdas de produtividade por estresse hídrico. A magnitude desse problema se estende a mais de 30 milhões de hectares de lavoura cultivada sob plantio direto no Brasil, colocando em risco as projeções de exuberância da agricultura no país. Assim, o desenvolvimento desta tese teve o objetivo de estudar fatores que, além do processo de compactação mecânica do solo, possam estar promovendo a estratificação física e química de solos altamente intemperizados cultivados sob sistema de plantio direto. Dentre os possíveis fatores causadores deste tipo de degradação, foram avaliados: i) a aplicação excessiva de calcário, exclusivamente em superfície, ocasionando, na camada de 0 a 7 cm, a elevação do pH do solo para além do ponto de carga zero do solo, elevando o potencial eletronegativo do solo e por consequência, promovendo a dispersão de argila; ii) a migração da argila dispersa no perfil do solo, pela água de percolação, como um fator promotor de degradação física em subsuperfície; iii) o aporte de fitomassa ao solo em quantidade e qualidade para manter a estabilidade estrutural dos solos cultivados. Os resultados obtidos mostraram que o movimento de calcário no perfil dos solos estudados é muito lento, limitando o efeito deste produto a poucos centímetros abaixo do local onde ele é depositado ou incorporado (2,5 cm em 130 semanas), independentemente da dose aplicada (até 33,2 Mg ha-1). Assim, a calagem superficial promove e intensifica a estratificação dos atributos químicos no perfil do solo, aumentando, demasiadamente, o pH próximo à superfície e sendo ineficiente em mitigar a acidez na subsuperficie destes solos. A concentração de calcário na camada mais superficial dos solos altamente intemperizados aumenta a eletronegatividade do solo, resultando na dispersão de argila. A migração dos argilominerais dispersos no perfil do solo, pela água de percolação, promove uma série de alterações estruturais, incluindo a diminuição da porosidade total e da continuidade dos poros e o aumento da densidade e da resistência do solo à penetração na camada subsuperficial. A diminuição da estabilidade estrutural dos Latossolos sob cultivo também está ligada ao aporte de material orgânico ao solo em quantidade e qualidade inferiores à que ocorre no solo sob sistema nativo. Os Latossolos cauliníticos são mais propensos a diminuição da estabilidade estrutural quando submetidos ao cultivo. Portanto, a recomendação de calagem em solos altamente intemperizados cultivados sob plantio direto, precisa considerar a mineralogia do solo e a possível degradação estrutural promovida pela calagem em excesso. The economic development of Brazil depends upon the increasing agricultural production associated with conservation practices. The no-tillage system is the soil management practice that brings together the broadest set of principles for conservation agriculture. Areas under no-till system, however, generally have two completely different soils layers: a surface layer, around 0 to 7 cm, with physical and chemical conditions favorable for root development; and a sub-surface layer, around 7 to 20 cm, with lower permeability to air and water, high soil penetration resistance, and low soil fertility. The existence of these stratified layers dramatically restricts the development of the root system into the sub-surface soil layer, which may result in reducing plant productivity by water deficit. This problem exists on more than 30 million hectares cultivated under no-tillage system in Brazil, and can compromise the optimistic projections of agricultural growth in the country. Therefore, more research is necessary to explore challenges that come with no-tillage. The aim of this thesis was to study the factors that can promote the physical and chemical stratification of highly weathered soils cultivated under no-till system. Among the factors that could cause this degradation, the following were studied: i) the application of excessive lime only on surface soil, or into the uppermost soil layer, which can increase its pH to levels beyond of the zero point of charge of soil, raising its electronegative potential and promoting, as a consequence, the clay dispersion; ii) the dispersed clay migration thtough the soil profile, by the percolation water, as a factor of physical degradation of sub-surface of soil cultiveted under no-tillage; and iii) the aplication of phytomass to the soil in insufficient amount and quality to maintain the soil structural stability of the soil. The results of this study showed that lime movement into the deeper soil profile, is very slow, as its impacts are limited to just a few centimeters below of where it is applied or incorporated (2.5 cm after 130 weeks), independent of the applied amount of lime. Thus, the surface lime application intensifies the chemical stratification of the clayey soils under no-tillage, increasing to much the soil pH of the uppermost soil layer, and being inefficient to decrease the soil acidity in the subsurface soil layer. The concentration of lime into the uppermost soil layer can significantly increase the electronegativity of the soil system and result in clay dispersion in the topsoil layer (0 to 5 cm). The resulting clay migration into the soil profile led to a series of structural alterations in subsurface layers, including: decrease of both soil porosity and pore continuity; and increase of both soil bulk density and soil penetration resistance in the sub-superficial layer. The structural stability decreasing of Oxisols under no-till system also is linked with the low addition of organic matter to the cultivated soil, in relation to the non-cultivated soils. The kaolinitic Oxisols are more susceptible to degradation than the gibbsitic Oxisols. Thus, it could be conclude that liming practices (rate and application methods of lime), mainly under no-till systems, need to consider both type and mineralogy of soil, as well as considering soil structure degradation promoted by over-liming in the uppermost soil layer.