RESUMO Objetivou-se com esse estudo automatizar a aquisição da variável tempo bem como o cálculo da condutividade hidráulica do solo saturado pelo método da carga decrescente usando sensores de água e a plataforma Arduino. Para automatizar a medição da variável tempo, foi utilizado a placa Arduino Uno e instalados dois sensores de nível de água analógico nas alturas inicial (h0) e final (h1). Quando a água flui pelo solo e o nível da água passa pela parte inferior do sensor inicial (h0), o registro do tempo começa; termina quando a água está ausente da altura final do segundo sensor (h1). A equação para cálculo da condutividade hidráulica foi inserida no algoritmo para se ter o cálculo automaticamente. Amostras de solo indeformadas foram coletadas em uma área de plantio direto de longo prazo. Os valores médios do tempo e da condutividade hidráulica não apresentaram diferenças significativas entre os permeâmetros. O índice coeficiente de massa residual (CRM) mostrou superestimação da variável tempo, indicando que o permeâmetro automático melhora a precisão da medição do tempo e da condutividade hidráulica do solo saturado estimada pelo método da carga decrescente.

ABSTRACT The objective of this study was to automate the acquisition of water travel time, as well as the computation of hydraulic conductivity of saturated soil by the falling head method, using water sensors and the Arduino platform. To automate the measurement of travel time, the Arduino Uno board was used, and two water sensors were installed at the initial (h0) and final (h1) heights of the water inside the core. When the water flows across the soil and the water level passes the bottom part of the initial sensor (h0), the time recording starts; it ends when the water is absent from the final height of the second sensor (h1). The equation for calculating the hydraulic conductivity was inserted into the algorithm so the calculation was automatic. Undisturbed soil samples were taken in a long-term no-tillage area. There were no significant differences for the time and hydraulic conductivity means between the permeameters. The coefficient of the residual mass index showed an overestimation of the time variable; thus, the automated permeameter improves the precision of time recording and saturated hydraulic conductivity estimated by the falling head method.

ABSTRACT Sandy soils are characterized by low organic matter content and soil water retention and availability. Conventional tillage has been used for the implementation of orange orchards, but it exposes the soil to erosion and promotes accelerated oxidation of organic matter with negative impacts on the soil’s physical quality. The objective of this study was to evaluate the soil physical quality of sandy soils influenced by two soil tillage practices for planting the orange trees in areas after long-time under pastures. Soil sampling was carried out in three experimental areas (one under Lixisol and two under Ferralsol) where the planting of orange trees had been carried out using two tillage practices: (i) conventional tillage in total area; and (ii) localized conventional tillage in a strip corresponding to the orange tree planting lines. A complete randomized design was used with two treatments (total or strip tillage) and four replications. Disturbed and undisturbed soil samples were taken in 2011 (8 to 18 years after the establishment of the treatments) from the 0.00-0.10 and 0.10-0.20 m layers in transects crossing: (i) under canopy projection below orange trees; (ii) under machine wheel tracks in the interrow of the orange trees; and (iii) under grass groundcover between the wheel tracks in the interrow of the orange trees. The following determinations were made for these samples: texture analysis, total organic carbon, soil bulk density, reference bulk density obtained with saturated soil subjected to a 200 kPa, soil resistance to penetration, soil water content, and water retention curves and the least limiting water range. The results suggest that total tillage for the implantation of orange orchards is unnecessary; however, after a long time of establishing orange orchards occurs soil physical quality discontinuity under wheel tracks compared to the other sampling positions. A positive correlation between organic carbon and soil physical quality was identified under the canopy of trees and grass groundcover in the interrow of the orange trees. For similar sand content, the higher soil organic carbon in the Ferralsol provided better physical quality than in Lixisol.

RESUMO A técnica “boundary line” foi proposta para interpretar dados biológicos, onde uma variável é uma resposta biológica e a outra uma variável independente. O objetivo do trabalho foi correlacionar parâmetros de emergência de milho e soja com propriedades físicas da cama de semeadura do solo aplicando o procedimento “boundary line”. O estudo foi conduzido na Fazenda Experimental da Universidade Estadual de Ponta Grossa, em Ponta Grossa, PR. A área é manejada sob sistema plantio direto há 18 anos. Foram determinados o índice de velocidade de emergência e a taxa de emergência para as culturas do milho e da soja. As propriedades físicas avaliadas na cama de semeadura de milho e soja foram: resistência do solo à penetração, conteúdo volumétrico de água, estabilidade dos agregados, resistência tênsil, friabilidade, condutividade hidráulica do solo saturado, densidade do solo e intervalo hídrico ótimo. O procedimento “boundary line” foi aplicado aos pares de valores dos parâmetros de emergência e propriedades físicas do solo, sendo em seguida ajustado um modelo de regressão para os “boundary” pontos. A aplicação do procedimento “boundary line” evidenciou que a emergência das culturas é dependente das propriedades físicas da cama de semeadura do solo. As relações obtidas permitiram conhecer os valores ótimos das propriedades físicas do solo para os parâmetros de emergência das culturas. O procedimento “boundary line” mostrou-se uma ferramenta promissora e complementar para melhor entender a resposta de emergência das culturas em relação às propriedades físicas da cama de semeadura do solo.

ABSTRACT The boundary line technique has been proposed for interpreting biological data where one variable is a biological response and the other is an independent variable. The objective of this study was to correlate maize and soybean emergence parameters with soil seedbed physical properties using a boundary line approach. The study was performed at the experimental farm belonging to the Universidade Estadual de Ponta Grossa, in the municipality of Ponta Grossa, Paraná State, Brazil. The area has been managed under a no-tillage system for 18 years. The emergence percentage (EP) and emergence rate (ER) were determined for maize and soybean crops. Soil seedbed physical properties were evaluated for both crop species and included soil penetration resistance, volumetric water content, aggregate stability, tensile strength, friability, saturated soil hydraulic conductivity, bulk density, and the least limiting water range. The boundary line approach was applied to pairs of values of plant emergence parameters and soil seedbed physical properties, and then the regression model was adjusted to the boundary points. The boundary line approach indicated that crop emergence was dependent on soil seedbed physical properties. It was possible to determine the optimum values of soil seedbed physical variables for crop emergence. The boundary line approach is a promising and complementary tool to better understand crop emergence responses to soil seedbed physical properties.

Resumo: O objetivo deste trabalho foi avaliar as propriedades físicas de um solo com pastagem de capim-tanzânia (Megathyrsus maximus) fertilizado com nitrogênio mineral ou consorciado com a leguminosa estilosantes 'Campo Grande' (Stylosanthes spp.), submetido a pastejo contínuo e à taxa de lotação variável, em uma cronossequência de três anos. Os tratamentos foram: capim-tanzânia e estilosantes; e capim-tanzânia adubado com 75, 150 e 225 kg ha-1 de N por ano. O experimento foi realizado em Latossolo Vermelho distrófico, em blocos ao acaso com três repetições, com parcelas subdivididas no tempo (primeiro, segundo e terceiro anos experimentais). Foram avaliadas, anualmente, as seguintes propriedades do solo: densidade do solo, porosidade no domínio dos macroporos, capacidade de armazenamento de água e ar do solo e resistência do solo à penetração. Após três anos, a maior taxa de lotação animal, em razão do aumento da produção de forragem, não afetou as condições físicas do solo. O consórcio de pastagem de capim-tanzânia com a leguminosa apresenta valores de capacidade de armazenamento de água e ar do solo próximos aos ideais (0,66 e 0,34, respectivamente). Após o segundo ano experimental, ocorre decréscimo dos valores de resistência do solo à penetração, que ficam abaixo do limite crítico de 2.500 kPa. O consórcio de capim-tanzânia com o estilosantes 'Campo Grande' pode ser uma alternativa interessante para a manutenção e o melhoramento das condições físicas do solo.

Abstract: The objective of this work was to evaluate the physical properties of a soil with a 'Tanzânia' grass (Megathyrsus maximus) pasture fertilized with mineral nitrogen or intercropped with the legume 'Campo Grande' (Stylosanthes spp.), and subjected to continuous grazing and variable stocking rate, in a three-year chronosequence. The treatments were: 'Tanzânia' grass and Stylosanthes; and 'Tanzânia' grass fertilized with 75, 150, and 225 kg ha-1 N per year. The experiment was carried out in an Oxisol, in a randomized complete block design with three replicates, in split plots divided according to time (first, second, and third experimental years). The following soil properties were assessed annually: soil bulk density, porosity in the soil macropore domain, soil water and air storage capacity, and soil penetration resistance. After three years, the highest animal stocking rate due to increased forage yield did not affect the soil physical conditions. The intercrop of 'Tanzânia' grass with the legume shows values of soil water and air storage capacity close to the ideal ones (0.66 and 0.34, respectively). After the second experimental year, there is a decrease in the penetration resistance values, which are inferior to the critical limit of 2,500 kPa. The intercropping of 'Tanzânia' grass with stylosanthes 'Campo Grande' can be a remarkable alternative for the maintenance and improvement of soil physical conditions.

ABSTRACT Soil and crop management systems change the soil structure, thereby affecting soil quality. The “profil cultural” method (PCM) has been used to identify the effects of management systems on soil structure; however, few studies relate the structures identified by the PCM to quantitative indicators of soil structural quality. This study aimed to quantify soil structures using the PCM and relate these structures to bulk density (Bd), critical bulk density (Bdc), soil aeration capacity (εa), least limiting water range (LLWR), and soil air permeability (Ka) under different soil and crop management systems. The study was developed in a long-term experiment (24 years) involving two systems of soil management (no-tillage and conventional tillage) and two systems of crop management (rotation and succession), resulting in four treatments: no-tillage with crop rotation (NTr), no-tillage with crop succession (NTs), conventional tillage with heavy harrowing and crop rotation (CTr) and conventional tillage with heavy harrowing and crop succession (CTs). The PCM was used to identify the different homogeneous morphological units (HMUs) in the soil profile. Undisturbed soil samples were collected for the HMUs that were most represented in the profiles to determine Ka, LLWR, Bd, and εa. There was agreement between the HMUs and the quantitative indicators. The LLWR showed greater values for Bdc under no-tillage (NTr = 1.36 Mg m-3 and NTs = 1.37 Mg m-3) than under conventional tillage (CTs = 1.31 Mg m-3 and CTr = 1.33 mg m-3). The proportion of samples where Bd > Bdc was 23 % under CTs, 77 % under CTr, 32 % under NTs, and 39 % under NTr. The structures that were most restrictive to root development (CΔ, CΔμ, FmtΔμ, and FmtμΔ) show a lower Ka and greater soil penetration resistance as the soil dries. Pores are more continuous and the structure is less restrictive to plant development in no-tillage than in conventional tillage.

Resumo: O objetivo deste trabalho foi determinar a acurácia em medidas do potencial mátrico da água no solo (ψm) por tensiômetros de punção com cápsulas arredondadas ou pontiagudas, instalados com ou sem “lama de solo”, e comparar o desempenho destes tensiômetros com o de tensiômetros com manômetros de mercúrio. O experimento foi conduzido em Argissolo Vermelho-Amarelo distrófico, em delineamento experimental de blocos ao acaso, em arranjo fatorial, com cinco repetições. Tensiômetros de punção com cápsulas arredondadas, instalados com “lama de solo”, apresentam maior acurácia nas determinações do ψm em uma faixa mais ampla de medidas, assemelhando-se aos tensiômetros com manômetros de mercúrio com o secamento do solo.

Abstract: The objective of this work was to determine the measurement accuracy of the soil water matric potential (ψm) by puncture tensiometers with either rounded or pointed porous cups, installed with or without “soil mud”, and to compare the performance of these tensiometers with that of tensiometers equipped with mercury manometers. The experiment was conducted in a Ultisol, in a randomized complete block design, in a factorial arrangement with five replicates. Puncture tensiometers with rounded porous cups, installed with “soil mud”, present more elevated accuracy for ψm determination in a wider measurement range, resembling tensiometers equipped with mercury manometers in drying soil.

ABSTRACT The Soil Management Assessment Framework (SMAF) was developed in the U.S.A. and has been used as a tool for assessing and quantifying changes in soil quality/health (SQ) induced by land uses and agricultural practices in that region and elsewhere throughout the world. An initial study using SMAF in Brazil was recently published, but additional research for a variety of soils and management systems is still needed. Our objective was to use data from five studies in southern Brazil to evaluate the potential of SMAF for assessing diverse land-use and management practices on SQ. The studies examined were: (i) horizontal and vertical distribution of soil properties in a long-term orange orchard; (ii) impacts of long-term land-use change from native vegetation to agricultural crops on soil properties; (iii) effects of short-term tillage on soil properties in a cassava production area; (iv) changes in soil properties due to mineral fertilizer and pig slurry application coupled with soil tillage practices; and (v) row and inter-row sowing effects on soil properties in a long-term no-tillage area. The soils were classified as Oxisols, with clay content ranging from 180 to 800 g kg-1. Six SQ indicators [pH(H2O), P, K, bulk density, organic C, and microbial biomass] were individually scored using SMAF curves and integrated into an overall Soil Quality Index (SQI) focusing on chemical, physical, and biological sectors. The SMAF was sensitive for detecting SQ changes induced by different land uses and management practices within this wide textural range of Brazilian Oxisols. The SMAF scoring curve algorithms properly transformed the indicator values expressed in different units into unitless scores ranging from 0-1, thus enabling the individual indicators to be combined into an overall index for evaluating land-use and management effects on soil functions. Soil sector scores (i.e., chemical, physical, and biological) identify the principal soil limitations and can therefore be used to establish priorities for specific management actions. The SMAF can be used as a tool for assessing SQ in Brazilian soils, thus helping farmers, land managers, and politicians make better decisions regarding sustainable land-use and management practices.

ABSTRACT Understanding the spatial behavior of soil physical properties under no-tillage system (NT) is required for the adoption and maintenance of a sustainable soil management system. The aims of this study were to quantify soil bulk density (BD), porosity in the soil macropore domain (PORp) and in the soil matrix domain (PORm), air capacity in the soil matrix (ACm), field capacity (FC), and soil water storage capacity (FC/TP) in the row (R), interrow (IR), and intermediate position between R and IR (designated IP) in the 0.0-0.10 and 0.10-0.20 m soil layers under NT; and to verify if these soil properties have systematic variation in sampling positions related to rows and interrows of corn. Soil sampling was carried out in transect perpendicular to the corn rows in which 40 sampling points were selected at each position (R, IR, IP) and in each soil layer, obtaining undisturbed samples to determine the aforementioned soil physical properties. The influence of sampling position on systematic variation of soil physical properties was evaluated by spectral analysis. In the 0.0-0.1 m layer, tilling the crop rows at the time of planting led to differences in BD, PORp, ACm, FC and FC/TP only in the R position. In the R position, the FC/TP ratio was considered close to ideal (0.66), indicating good water and air availability at this sampling position. The R position also showed BD values lower than the critical bulk density that restricts root growth, suggesting good soil physical conditions for seed germination and plant establishment. Spectral analysis indicated that there was systematic variation in soil physical properties evaluated in the 0.0-0.1 m layer, except for PORm. These results indicated that the soil physical properties evaluated in the 0.0-0.1 m layer were associated with soil position in the rows and interrows of corn. Thus, proper assessment of soil physical properties under NT must take into consideration the sampling positions and previous location of crop rows and interrows.

RESUMO A ocorrência de concentração de nutrientes e compactação superficial tem sido relatada após longo tempo de implantação do sistema plantio direto. O objetivo deste estudo foi avaliar os atributos químicos, a densidade do solo e a produtividade das culturas subsequentes a uma única intervenção mecânica complementada com calagem de um Latossolo Vermelho Distroférrico textura muito argilosa conduzido em sistema plantio direto há 17 anos ininterruptos, em Pato Branco, no sudoeste do Paraná. O delineamento experimental utilizado foi de blocos ao acaso no esquema de parcelas subdivididas, com aração e gradagem do solo nas parcelas (sem e com revolvimento do solo com aração a 0,00-0,20 m e gradagem) e calagem nas subparcelas (sem e com calagem para elevar o índice de saturação por bases a 70 %). Foram avaliados a densidade do solo e a produtividade das culturas de milho (6° mês), biomassa de aveia-preta (12° mês) e soja (20º mês) e os atributos químicos do solo (6° mês). O revolvimento ocasional do solo com aração e gradagem em sistema plantio direto consolidado teve duração efêmera de seis meses na redução da densidade do solo. A incorporação do calcário não apresentou vantagens em relação à sua aplicação na superfície do solo. Não houve aumentos de produtividade das culturas subsequentes à calagem e ao revolvimento do solo. As produtividades das culturas de milho, aveia-preta e soja não dependeram do revolvimento e da incorporação de calcário nessa área agrícola.

ABSTRACT Accumulation of nutrients and surface compaction have been reported after a long time under a no-tillage system. The aim of this study was to evaluate soil chemical properties, bulk density, and crop yield following a single mechanical intervention associated with liming in a clayey Oxisol under a NT system for 17 consecutive years in Pato Branco, southwestern Paraná, Brazil. A randomized block experimental design was used in a split-plot arrangement, with plowing and harrowing of the soil in the plots (with and without soil turnover through plowing to 0.00-0.20 m and harrowing), and liming in the subplots (with and without liming to raise the level of base saturation to 70 %). Soil bulk density and yield of maize (6th month), black oat biomass (12thmonth), and soybean (20th month), as well as soil chemical properties (6th month), were evaluated. Occasional soil tillage through plowing and harrowing in a no-tillage system consolidated had a brief effect of reducing soil bulk density for six months. Incorporation of lime showed no advantages over application of lime on the soil surface. There were no yield increases in the crops following liming and soil tillage. The yields of corn, oat, and soybean did not depend on plowing and lime incorporation in this agricultural area.

Machinery traffic in sugarcane (Saccharumsp.) plantations reduces soil physical quality, and hinders both root development and crop yield. We evaluated the physical quality of an Oxisol and the development of sugarcane roots under controlled traffic. The treatments assessed were: without controlled machinery traffic (WCT), controlled traffic by adjusting the tractor and infield wagons to a 3.0 m track width with the operator guiding the machinery (CT1) and the previous treatment using real time kinematic / global positioning system (RTK / GPS) precision auto steer (CT2). Soil samples were collected from the planting rows, seedbed and inter-row center to determine the least limiting water range (LLWR) and soil porosity from scanned 2-D images. The root dry mass was sampled from monoliths, separated from the soil by washing through a 2-mm sieve and dried in an oven. A higher LLWR was observed in the planting row under CT1 and CT2 than under WCT. The planting row had a predominance of complex pores with a diameter > 500 µm in the 0.15-0.27 m depth layer under CT1 and CT2. In the planting rows under WCT, the root dry mass was only 44 % of that measured under CT2. Benefits regarding soil physical quality and growth roots were observed when the tractor-wagon track width was adjusted based on the sugarcane spacing using either precision auto steering or manual operation of the machinery.

A permeabilidade ao ar pode ser utilizada como indicador da qualidade física do solo. O objetivo deste trabalho foi determinar a permeabilidade ao ar e os índices de continuidade de poros para a cama de semeadura em um Latossolo Vermelho distrófico cultivado no sistema semeadura direta e submetido à escarificação mecânica e escarificação biológica, utilizando a cultura do nabo forrageiro. O estudo foi conduzido em área experimental da Universidade Estadual de Ponta Grossa, Estado do Paraná. Os tratamentos implantados foram: sistema semeadura direta por 18 anos consecutivos (SD); semeadura direta submetido à escarificação mecânica (SDE); e semeadura direta submetido à escarificação biológica por meio da cultura do nabo forrageiro (SDNF). O delineamento experimental utilizado foi em blocos casualizados com quatro repetições. As amostragens de solo foram feitas aos seis e 18 meses após a implantação dos tratamentos, correspondentes às semeaduras das culturas do milho (outubro de 2009) e da soja (novembro de 2010), respectivamente, nas camadas de 0,00-0,05 e 0,05-0,10 m de profundidade. A permeabilidade ao ar foi determinada pelo permeâmetro de carga constante nos potenciais mátricos -6, -10, -30 e -100 kPa. Foram definidos os seguintes índices de continuidade de poros: índice N, índice K1 e volume de poros bloqueados; e a porosidade de aeração. Os resultados foram submetidos à análise de variância e, quando significativos, as médias dos tratamentos foram comparadas pelo teste Tukey (p<0,05). Para a camada de 0,00-0,05 m, a permeabilidade ao ar e o índice K1 no SDNF no potencial mátrico de -6 kPa foram significativamente maiores que em SD e SDE. O índice N, o volume de poros bloqueados e a porosidade de aeração não apresentaram diferenças significativas entre os tratamentos em ambas as profundidades. Os efeitos benéficos da escarificação biológica na permeabilidade do solo ao ar e no índice de continuidade de poros K1 persistiram aos 18 meses após sua aplicação. A escarificação mecânica resultou em maior continuidade do sistema poroso do solo, avaliado pelo índice K1, com persistência desse efeito aos 18 meses após sua aplicação.

Air permeability may be used as a soil physical quality indicator. The objective of this study was to determine the air permeability and pore continuity index for the seedbed of an Oxisol cultivated under a no-tillage system that underwent mechanical chiseling and biological promotion of pore formation using the forage radish crop. The study was carried out in an experimental area of the Universidade Estadual de Ponta Grossa (Ponta Grossa State University), Parana, Brazil. The treatments were 18 consecutive years under no tillage (SD); no-tillage under mechanical chiseling (SDE); and no-tillage under biological promotion of pore formation by a forage radish cover crop (SDNF). A randomized complete block experimental design was used with four replications. Soil samples were taken at the 0.00-0.05 and 0.05-0.10 m soil depths at 6 and 18 months after setting up the treatments, corresponding to maize (October 2009) and soybean (November 2010) planting, respectively. Air permeability was determined with a constant head permeameter at four matric potentials: -6, -10, -30, and -100 kPa. The following pore continuity indices were determined: N index, K1 index, and blocked porosity; and air-filled porosity. The results were subjected to analysis of variance and, when significant, the means were compared by the Tukey test (p<0.05). For the 0.00-0.05 m soil depth, the air permeability and K1 index in SDNF at the -6 kPa matric potential were significantly higher than in SD and SDE. The N index, blocked porosity and air-filled porosity did not differ statistically among treatments for either depth. The beneficial effects of biological promotion of pore formation on air permeability and on the soil pore continuity index (K1) continued at 18 months after application. Mechanical chiseling resulted in greater continuity of the soil pore system (K1), and this effect persisted at 18 months after application.

Sistemas conservacionistas em pomares de laranja podem aumentar a capacidade de suporte de carga do solo minimizando os seus riscos de compactação. O objetivo deste trabalho foi avaliar a capacidade de suporte de carga por meio da pressão de preconsolidação e sua dependência a conteúdo de água, densidade e carbono orgânico de um Argissolo Vermelho distrófico latossólico, após 18 anos de implantação de plantas de cobertura permanentes nas entrelinhas de um pomar de laranja. O delineamento experimental foi de blocos ao acaso, com três repetições. Foram estudados três tratamentos de manejo por meio de roçadas nas entrelinhas do pomar, desde o plantio do pomar em 1993: gramínea Paspalum notatum, leguminosa Arachis pintoi e vegetação espontânea. Cento e oito amostras indeformadas de solo foram coletadas em 2011 sob o rodado e entrerrodado das máquinas nas estrelinhas do pomar com textura arenosa nas camadas de 0,00-0,10 m (87 g kg-1 de argila) e 0,10-0,20 m (122 g kg-1 de argila). Determinaram-se as pressões de preconsolidação das curvas de compressão do solo (25, 50, 100, 200, 400, 800 e 1.600 kPa) em conteúdos de água sob três potenciais (-80, -330 e -1.000 hPa), a densidade do solo e o teor de carbono orgânico do solo. A pressão de preconsolidação não foi dependente do conteúdo de água, da densidade do solo e do teor de carbono orgânico do solo. A pressão de preconsolidação sob o rodado na camada de 0,00-0,10 m foi menor nos tratamentos leguminosa e vegetação espontânea. A manutenção permanente da gramínea manejada com roçadas nas entrelinhas do pomar de laranja proporcionou maior capacidade de suporte de carga do solo sob o rodado na camada superficial arenosa.

Conservation tillage systems in orange groves can increase soil load-bearing capacity minimizing their risks of soil compaction. The objective of this study was to evaluate load-bearing capacity through preconsolidation pressure and its dependence on water content, bulk density, and organic carbon of a Typic Paleudult soil 18 years after setting up permanent plant cover between the rows of an orange grove. A randomized block experimental design was used, with three replications. Three groundcover treatments subjected to mowing between the rows of the grove, as of establishment of the orange grove in 1993, were studied: Paspalum notatum grass, the Arachis pintoi legume, and spontaneous vegetation. One hundred and eight undisturbed soil samples were collected in 2011 at the 0.00-0.10 m (87 g kg-1 clay) and 0.10-0.20 m (122 g kg-1 clay) depths under and between the wheel tracks of the machines between the rows of the orange grove consisting of sandy clay texture soil. Preconsolidation pressure was not dependent on soil water content, bulk density, or organic carbon content. Preconsolidation pressure from soil compression curves (25; 50; 100; 200; 400; 800; and 1,600 kPa) at water content under three potentials (-80; -330; and 1,000 hPa), soil bulk density, and soil organic carbon were determined. The preconsolidation pressure under the wheel tracks between the orange rows in the 0.00-0.10 m layer was lower in the legume and spontaneous vegetation treatments. Ongoing maintenance of the grass managed through mowing between the rows of the orange grove led to greater soil load-bearing capacity under the wheel tracks in the sandy surface layer.

A correlação espacial entre atributos de solo e de plantas espontâneas tem importância agronômica e ambiental. O entendimento dessa correlação é fundamental para a interpretação do seu significado, tendo em conta a influência de fatores como os mecanismos de dispersão, a produção e a sobrevivência das sementes e a extensão da influência das práticas de manejo do solo. O objetivo deste trabalho foi de avaliar a correlação espacial entre atributos físicos de solo e plantas espontâneas em sistema plantio direto (PD) e preparo convencional (PC). Os atributos físicos de solo foram: densidade do solo, macroporosidade, microporosidade, porosidade total, capacidade de aeração da matriz do solo, água retida na capacidade de campo; e os de plantas espontâneas: biomassa da parte aérea das plantas, densidade de plantas, densidade de Commelina benghalensis e densidade de Bidens pilosa. Os alcances das correlações espaciais foram em geral maiores no PD do que no PC. Os variogramas cruzados evidenciaram que muitas variáveis apresentam estrutura de variação conjunta no espaço e, portanto, podem ser mapeadas umas pelas outras pela co-krigagem. A variação conjunta permitiu também fazer inferências sobre os significados físicos e biológicos das variáveis estudadas. Os resultados demonstraram também que os sistemas de manejo do solo exercem influência significativa na estrutura da dependência espacial.

The spatial correlation between soil properties and weeds is relevant in agronomic and environmental terms. The analysis of this correlation is crucial for the interpretation of its meaning, for influencing factors such as dispersal mechanisms, seed production and survival, and the range of influence of soil management techniques. This study aimed to evaluate the spatial correlation between the physical properties of soil and weeds in no-tillage (NT) and conventional tillage (CT) systems. The following physical properties of soil and weeds were analyzed: soil bulk density, macroporosity, microporosity, total porosity, aeration capacity of soil matrix, soil water content at field capacity, weed shoot biomass, weed density, Commelina benghalensis density, and Bidens pilosa density. Generally, the ranges of the spatial correlations were higher in NT than in CT. The cross-variograms showed that many variables have a structure of combined spatial variation and can therefore be mapped from one another by co-kriging. This combined variation also allows inferences about the physical and biological meanings of the study variables. Results also showed that soil management systems influence the spatial dependence structure significantly.

O intervalo hídrico ótimo (IHO) tem sido utilizado como indicador de qualidade física do solo por representar em um único parâmetro as propriedades físicas diretamente ligadas com o crescimento de plantas, exceto a temperatura. O procedimento usual para obter o IHO envolve a determinação, em amostras com estrutura preservada e em laboratório, da curva de retenção de água (CRA) e da curva de resistência do solo à penetração (CRS). A determinação da CRA e CRS utilizando medições realizadas no campo (in situ ) é preferível, mas exige instrumentação apropriada. Os objetivos deste trabalho foram determinar o IHO a partir de dados coletados para obter a CRA e CRS in situ, utilizando instrumentos eletrônicos portáteis, e comparar essas com determinações feitas em laboratório. As amostragens foram realizadas na camada de 0,0-0,1 m de um Latossolo Vermelho distrófico. Foram utilizados dois métodos de quantificação do IHO: o tradicional, com medições realizadas em amostras de solo com estrutura preservada e in situ , com medições do conteúdo de água (θ), do potencial mátrico (Ψ) e da resistência do solo à penetração (RP) por meio de sensores. As medições in situ de θ, Ψ e RP foram realizadas durante um perνodo de quatro dias de secamento do solo. Concomitantemente, foram tomadas amostras com estrutura preservada para a determinação da densidade do solo (Ds). Em razão dos limites de medida do Ψ pelo tensiômetro, foram realizadas determinações adicionais do conteúdo de água no Ψ de -1500 kPa com um psicrômetro (em laboratório). Os resultados evidenciaram que é possível determinar o IHO a partir de medições de θ, Ψ e RP, usando a abordagem e instrumentaηão sugeridas. A qualidade do ajuste da CRS foi semelhante nas duas estratégias. No entanto, as medições de θ e Ψ in situ , associadas àquelas realizadas com psicrômetro, produziram melhor descrição da CRA. As estimativas do IHO foram semelhantes nas duas estratégias metodológicas. A quantificação do IHO in situ pode ser realizada com redução de 90 % do tempo em relação ao método tradicionalmente utilizado.

The least limiting water range (LLWR) has been used as an indicator of soil physical quality as it represents, in a single parameter, the soil physical properties directly linked to plant growth, with the exception of temperature. The usual procedure for obtaining the LLWR involves determination of the water retention curve (WRC) and the soil resistance to penetration curve (SRC) in soil samples with undisturbed structure in the laboratory. Determination of the WRC and SRC using field measurements (in situ ) is preferable, but requires appropriate instrumentation. The objective of this study was to determine the LLWR from the data collected for determination of WRC and SRC in situ using portable electronic instruments, and to compare those determinations with the ones made in the laboratory. Samples were taken from the 0.0-0.1 m layer of a Latossolo Vermelho distrófico (Oxisol). Two methods were used for quantification of the LLWR: the traditional, with measurements made in soil samples with undisturbed structure; and in situ , with measurements of water content (θ), soil water potential (Ψ), and soil resistance to penetration (SR) through the use of sensors. The in situ measurements of θ, Ψ and SR were taken over a period of four days of soil drying. At the same time, samples with undisturbed structure were collected for determination of bulk density (BD). Due to the limitations of measurement of Ψ by tensiometer, additional determinations of θ were made with a psychrometer (in the laboratory) at the Ψ of -1500 kPa. The results show that it is possible to determine the LLWR by the θ, Ψ and SR measurements using the suggested approach and instrumentation. The quality of fit of the SRC was similar in both strategies. In contrast, the θ and Ψ in situ measurements, associated with those measured with a psychrometer, produced a better WRC description. The estimates of the LLWR were similar in both methodological strategies. The quantification of LLWR in situ can be achieved in 10 % of the time required for the traditional method.

Estoques de carbono em macroagregados do solo possuem relação com a taxa de sequestro de C no solo em sistema plantio direto. Objetivou-se avaliar os estoques de carbono em macroagregados (12,5-19,0mm) em função do revolvimento ocasional e/ou da calagem de um Latossolo Vermelho Distroférrico típico textura muito argilosa, sob sistema plantio direto há 17 anos em Pato Branco, sudoeste do Paraná. A partir de outubro de 2009, foi avaliado um experimento em parcelas sub-subdivididas, tendo como parcelas, épocas de amostragens após 6, 12 e 20 meses do revolvimento do solo e/ou calagem; nas subparcelas, manejos de solo, sem e com revolvimento do solo com uma aração e uma gradagem; e, nas sub-subparcelas, níveis de calagem, sem e com calcário para elevar o índice de saturação por bases para 70%. Dos 6 aos 12 meses, a aplicação de calcário em superfície ou incorporado aumentou os estoques de C dos macroagregados na camada de 0,10-0,20m. Após 20 meses, a incorporação de calcário em solo reduziu os estoques de C dos macroagregados somente na camada de 0-0,10m. Assim, a calagem na superfície é fundamental para a manutenção e aumento dos estoques de C em macroagregados de solo sob sistema plantio direto, mantendo-o consolidado

Carbon stocks in soil macroaggregates are related to the rate of soil C sequestration in no-tillage system. This study aimed to evaluate carbon stocks in macroaggregates (12.5 to 19.0mm) as a function of the occasional tillage and/or liming of a Hapludox loamy clayey under no-tillage for 17 years in Pato Branco, Paraná southwest, Brazil. Starting from October 2009, it was evaluated an experiment with split-split plots, with plots as sampling dates after 6, 12 and 20 months of the occasional tillage and/or liming; the subplots as soil management, with and without occasional soil tillage with plowing and disking; and as sub-subplots, liming levels, with and without limestone to raise the base saturation index to 70%. From 6 to 12 months, the limestone application on surface or incorporated increased C stocks of macroaggregates in the 0.10-0.20m layer. After 20 months, the incorporation of limestone in soil reduced C stocks in macroaggregates only in the 0-0.10m layer. Thus, the surface liming is essential for the maintenance and enhancement of C stocks in macroaggregates of no-tillage system, keeping it consolidated