Effect of compaction on the porosity of a silty soil: influence on unsaturated hydraulic properties

Abstract

Summary Tillage and traffic modify soil porosity and pore size distribution, leading to changes in the unsaturated hydraulic properties of the tilled layer. These changes are still difficult to characterize. We have investigated the effect of compaction on the change in the soil porosity and its consequences for water retention and hydraulic conductivity. A freshly tilled layer and a soil layer compacted by wheel tracks were created in a silty soil to obtain contrasting bulk densities (1.17 and 1.63 g cm−3, respectively). Soil porosity was analysed by mercury porosimetry, and scanning electron microscopy was used to distinguish between the textural pore space and the structural pore space. The laboratory method of Wind (direct evaporation) was used to measure the hydraulic properties in the tensiometric range. For water potentials < −20 kPa, the compacted layer retained more water than did the uncompacted layer, but the relation between the hydraulic conductivity and the water ratio (the volume of water per unit volume of solid phase) was not affected by the change in bulk density. Compaction did not affect the textural porosity (i.e. matrix porosity), but it created relict structural pores accessible only through the micropores of the matrix. These relict structural pores could be the reason for the change in the hydraulic properties due to compaction. They can be used as an indicator of the consequences of compaction on unsaturated hydraulic properties. The modification of the pore geometry during compaction results not only from a decrease in the volume of structural pores but also from a change in the relation between the textural pores and the remaining structural pores.

Soil compaction by machine traffic and least limiting water range related to soybean yield

“…On loose soil (T 0 ), a maximum yield was not obtained, possibly due smaller root/soil contact, which reduces water and nutrient absorptions, as mentioned by Håkansson et al (1998). On loose soils, unsaturated hydraulic conductivity is low (Richard et al, 2001), which reduces water and nutrient movements towards the roots, because of the greater space among soil particles (Lipiec & Hatano, 2003).…”

Consequences on water retention properties of double-porosity features in a compacted silt

“…The water retention curve expressed in terms of water content or degree of saturation and suction is hysteretic, stress path dependent (void ratio) and depends on the pore network [1,10,16,18,19,21,23,25,27,28,31]. To properly describe its evolving water retention character, a multimodal retention model is proposed in the paper by considering a linear superposition of two subcurves of the van Genuchten [33] type.…”

Tráfego de máquinas agrícolas e alterações de bioporos em área sob pomar de laranja

“…Os poros tipo empacotamento e as fissuras são considerados poros estruturais (Ringrose-Voase, 1987), por apresentarem definição da unidade estrutural do solo; já os poros tipo cavidades, canais, câmaras e vesículas não têm relação com as unidades estruturais, podendo ocorrer dentro ou através das mesmas. Os poros estruturais são resultantes do cultivo, tráfego, tempo e da atividade biológica do solo, sendo considerados bons indicadores dos processos de compactação (Richard et al, 2001). Curmi et al (1994), estudando a degradação da estrutura em solos cultivados, mostraram que os poros texturais, provenientes do arranjamento das partículas elementares do solo, não são afetados pelo processo de compactação; os poros estruturais têm seu tamanho e formato reduzido, e os poros provenientes da atividade biológica (bioporos), tipo canais, desaparecem, quando submetidos a processos de compactação.…”