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SUMMARYSoil penetration resistance is an important indicator of soil physical quality and the critical limit of 2 MPa has been widely used to characterize the soil physical quality, in both no-tillage and conventional systems. The aim of this study was to quantify the influence of different tillage and cropping systems on the soil penetration resistance in a Rhodic Eutrudox. The experiment was carried out in a 5 × 2 factorial, completely randomized block design (tillage systems vs cropping systems), with four replications. The tillage systems consisted of: conventional tillage disk harrow; minimum tillage with annual chiseling; minimum tillage with chiseling every three years; no-tillage for 11 consecutive years; and no-tillage for 24 consecutive years. The factor cropping systems was represented by: crop rotation and crop succession. The soil penetration resistance (SPR) was determined in 20 soil samples per treatment and layer (0.0-0.10; 0.10-0.20 and 0.20-0.30 m) for each soil matric potential: -6, -10, -33, -100, -500 kPa. The SPR was determined at a volumetric soil water content equivalent to the fraction of plant-available water of 0.7. There were no differences of soil penetration resistance between the two cropping systems. Differences in soil penetration resistance among tillage systems were related to the matric potential at which the samples were equilibrated. The critical SPR limit of 2 MPa normally used for conventional tillage should be maintained. However, this value of 2 MPa is inappropriate for the physical quality characterization of Rhodic Eutrudox under no-tillage and/or minimum tillage with chiseling. Regardless of the cropping systems, the critical SPR limit should be raised to 3 MPa for minimum tillage with chiseling and to 3.5 MPa for no-tillage.Index terms: no-tillage, soil chiseling, level compaction.(1) Part of the Master's dissertation of the first author submitted at Federal University of Santa Maria (UFSM) and Embrapa Soja.Received RESUMO: LIMITES CRÍTICOS DE RESISTÊNCIA À PENETRAÇÃO EM UM LATOSSOLO VERMELHO DISTROFÉRRICOA resistência do solo à penetração é um importante indicador da qualidade física do solo, e o limite crítico de 2 MPa vem sendo utilizado para caracterizar a qualidade física do solo, tanto em sistema plantio direto como em cultivos convencionais. Objetivou-se com este trabalho verificar a influência de diferentes sistemas de manejo do solo e modelos de produção sobre a SPR em um Latossolo Vermelho distroférrico. O experimento foi conduzido em um delineamento de blocos ao acaso, em esquema fatorial 5 × 2 (manejos do solo × modelos de produção), com quatro repetições. Os manejos do solo foram: sistema preparo convencional; sistema preparo mínimo escarificado a cada ano; sistema preparo mínimo escarificado a cada três anos; sistema plantio direto contínuo por 11 anos; e sistema plantio direto contínuo por 24 anos. O fator modelo de produção foi composto por: rotação e sucessão de culturas. A resistência do solo à penetração foi determinada em 20 amostras indeformadas...

2018). Mechanistic framework to link root growth models with weather and soil physical properties, including example applications to soybean growth in Brazil. Plant and Soil,, 67-92. https://doi.

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SUMMARYThe soil penetration resistance is an important indicator of soil compaction and is strongly influenced by soil water content. The objective of this study was to develop mathematical models to normalize soil penetration resistance (SPR), using a reference value of gravimetric soil water content (U). For this purpose, SPR was determined with an impact penetrometer, in an experiment on a Dystroferric Red Latossol (Rhodic Eutrudox), at six levels of soil compaction, induced by mechanical chiseling and additional compaction by the traffic of a harvester (four, eight, 10, and 20 passes); in addition to a control treatment under no-tillage, without chiseling or additional compaction. To broaden the range of U values, SPR was evaluated in different periods. Undisturbed soil cores were sampled to quantify the soil bulk density (BD). Pedotransfer functions were generated correlating the values of U and BD to the SPR values. By these functions, the SPR was adequately corrected for all U and BD data ranges. The method requires only SPR and U as input variables in the models. However, different pedofunctions are needed according to the soil layer evaluated. After adjusting the pedotransfer functions, the differences in the soil compaction levels among the treatments, previously masked by variations of U, became detectable.Index terms: pedotransfer functions, Oxisol, impact penetrometer, soil compaction.(