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 notillage 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 (0-7 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. 2015 Elsevier B.V. All rights reserved.

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RESuMOO cultivo de espécies florestais de rápido crescimento tem aumentado no Brasil, devido à diversificação do uso de sua madeira e adaptação edafoclimática. No setor florestal, a técnica do cultivo mínimo tem se destacado como forma de aumentar a produtividade, garantindo a manutenção da biodiversidade e a conservação do solo. O presente estudo foi realizado na área experimental da Fundação Estadual de Pesquisa Agropecuária -Centro de Pesquisa em Florestas em Santa Maria -RS, com o objetivo de avaliar o efeito dos métodos de preparo do solo na densidade, na resistência do solo à penetração e no desenvolvimento inicial das raízes e parte aérea do Eucalyptus grandis, em um Argissolo Vermelho-Amarelo Distrófico arênico com textura franco-arenosa. Foram comparados quatro manejos do solo: plantio direto, escarificado, escarificado mais grade niveladora e enxada rotativa, instalados em blocos ao acaso com três repetições. O solo sob plantio direto condicionou menor crescimento radicular e aéreo do eucalipto devido à maior resistência à penetração e densidade do solo, quando comparado aos preparos com mobilização. A análise da distribuição radicular no perfil, apesar de ser um método qualitativo, foi eficiente em demonstrar o efeito do preparo do solo para a implantação do Eucalyptus grandis. O preparo e a mobilização do solo resultaram em maior crescimento inicial de Eucalyptus grandis. Os efeitos da escarificação sobre as propriedades físicas do solo persistiram após um ano da mobilização do solo. Palavras-chave: florestas plantadas; resistência do solo à penetração; compactação do solo. ABSTRACTThe forest species cultivation with rapid growth in Brazil has increased, mainly due to the diverse use of its wood and climate adaptation. The cultivation with minimum tillage in the forest sector stands out a way to increase productivity, combined with the maintenance of biodiversity and soil conservation. This study was conducted at the experimental area of State Foundation for Agricultural Research -Research Center for Forestry in Santa Maria -RS, with aimed to evaluate the effect of the soil tillage methods on soil physical properties and on initial development of Eucalyptus grandis, in a sandy loam Typic Hapludalf. Four soil management practices were compared: no-tillage; chisel tillage; chisel tillage plus harrowing and; rotary tillage (rotary tiller), installed in a randomized block design with three replications. The soil under no-tillage conditioned lower initial growth of eucalyptus due higher soil penetration resistance and bulk density, when compared with treatments with mobilization. The root distribution analysis in soil, despite being a qualitative method, was effective in demonstrating the effect of soil tillage for the Eucalyptus grandis 1. Parte da dissertação de mestrado do primeiro autor. 2. Engenheira Florestal, Dr a