Correction of resistance to penetration by pedofunctions and a reference soil water content

Abstract

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.(

Use of penetrometers in agriculture: a review

“…Besides these factors, the determination of SPR values depends on soil bulk density (Db) (OTTO et al, 2011), water content in the soil (ASSIS et al, 2009;FIGUEIREDO et al, 2011;MORAES et al, 2012), soil pore-water pressure (FREUDLUND et al, 1978;KIM et al, 2008), particle size distribution (VAZ et al, 2011), clay content (MOLIN et al, 2006, soil type (SILVA et al, 2004), soil compressibility , and soil-metal friction (DEXTER et al, 2007).…”

“…As an example, there is the penetrometer described by BRADFORD (1986), with 3.74 mm diameter and 60° angle (Figura3c). The determination of SPR values is highly influenced by the soil water content (CONTE et al, 2008;MORAES et al, 2012), when small reductions in the value of this parameter provide a large increase in the readings of SPR values (SECCO et al, 2009). Such increase due to the reduction of soil water content may be explained by theories that relate the pressure of water and air in the soil pores with the soil shear strength (FREUDLUND et al, 1978).…”

“…These authors describe the behavior of the shear strength of saturated and unsaturated soils, and the results show that the decrease in water pressure in the soil pores increases the soil frictional resistance. This exponential increase of the SPR values according to the soil water content restricts comparisons among same soils with different moisture contents; this occurs because a small decrease or increase in this parameter results in a large increase or decrease in SPR values (VAZ et al, 2011), resulting in under or overestimation of the soil compaction state (MORAES et al, 2012). In order to overcome this problem, MORAES et al (2012) suggest the correction of the SPR values according to a water content of the reference soil.…”

“…Dynamic penetrometers are those with the greatest ranges of readings for the evaluation of SPR values in the field, varying from zero to more than 20 MPa (VAZ et al, 2011;MORAES et al, 2012). Static penetrometers and penetrographs of manual insertion provide field measurements of SPR values up to 5 MPa (ASABE, 2006b).…”

“…Determinations of SPR values depend on the soil water content at the evaluation time, as there are exponential increments in SPR values due to the reduction of the soil water content (VAZ et al, 2011;MORAES et al, 2012). Differences in soil compaction may also be masked due to variations of the soil water content (MORAES et al, 2012).…”