RESUMO

Models that integrate the influence of soil intrinsic attributes on the estimation of soil compaction are scarce for Hapludox. The present study tested the hypothesis that the compressive behavior of Hapludox with wide variations in intrinsic soil attributes can be estimated based on pedotransfer functions (PTFs). The general goal of this research was to determine the effect of intrinsic soil attributes on the susceptibility to compaction, preconsolidation pressure and compression curve of Hapludox, and to develop PTFs that allow the estimation of these parameters based on easily measurable soil attributes. The study was conducted on a soil toposequence that includes a sandy Typic Hapludox, a loamy Typic Hapludox, and a clayey Rhodic Hapludox. The uniaxial compression test was applied to 50 undisturbed soil samples at matric potential values of −10 and −100 kPa. After load withdrawal, soil bulk density, void ratio, gravimetric soil water content, particle‐size distribution, particle density, and organic matter were determined. The compression curves, the compression index, and the preconsolidation pressure were obtained. The relationship between the compression index, soil bulk density, and clay content was statistically significant with R2 = 0.77. Organic matter and soil water content did not affect the compression index. The preconsolidation pressure was significantly related with soil bulk density, soil water content, and clay content (R2 = 0.70), but was unaffected by organic matter. Soil compressibility was dependent on soil bulk density. A nonlinear model fitted the data with R2 = 0.90 allowing to predict the compressibility of soils for a wide range of stresses and inherent soil properties.

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The least limiting water range, LLWR, is the range of soil water content within which plant growth is least limited by water potential, aeration, and mechanical resistance. Little information is available on the influence of soil property or management practice on LLWR. The LLWR calculation is based on the water release curve (WRC) and the soil resistance curve (SRC). This study tested the hypothesis that pedotransfer functions (PTF) that describe the influence of soil properties and tillage on the WRC and the SRC could be used to assess the influence of these factors on the LLWR. Thirty‐two paired sampling sites were located along two parallel transects in a side by side comparison of no‐till and conventional tillage. The transects crossed three soil types: Aquic Hapludalf, Psammentic Hapludalf, and Typic Hapludalf. Clay content (CLAY) varied from 5.8 to 37.4%, organic carbon (OC) varied from 9 to 39 g kg‐1, and the bulk density (Db) varied from 0.96 to 1.71 g cm‐3. Multiple regression analyses showed that WRC was related (R2 = 0.94) with CLAY, OC, and Db whereas the SRc was related with CLAY and OC (R2 = 0.86). Tillage had no independent effect in either of the two functions. Values of LLWR, calculated from the PTF, varied from 0 to 0.3093 cm3 cm‐3. The LLWR was negatively related with CLAY and Db and positively related with OC. The analyses supported the hypothesis illustrating the value of PTF in assessing the sensitivity of LLWR to soil properties.

APPLICATIONS OF THE RESISTANCE CURVE IN THE CONTROL OF THE PHYSICAL QUALITY OF SOILS UNDER GRASSABSTRACT -The degradation of the physical quality of soils has been associated with the soil compaction caused by animal trampling. The soil resistance to penetration (SRP) is a soil physical parameter used to assess the soil compaction degree. However, SRP varies with soil moisture (q) and bulk density (D b ). The objective of this research was to quantify the soil resistance curve and use it to evaluate the physical quality of a soil under short duration grazing system of elephant grass. The soil resistance curve was measured using forty-eight undisturbed cores taken at the 0-10 cm depth of a Kandiudalfic Eutrudox used with elephant grass in intensive system of exploration. The results indicated a negative correlation among SRP and q as well as a positive correlation between SRP and D b . Predictions indicated that at soil matric potential equal to -0.01 MPa the SRP did not reach critical values to root growth. Nevertheless, at the soil matric potential equal to -0.3 MPa, the SRP reached limiting values in the whole area. For the management system and the studied species, the results suggest that soil resistance curve may be used to guide soil management practices for maintaining a good soil physical quality for grass growth.

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T. P. LEÃO (2),

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