Structure of a Tilled Soil as Influenced by Tillage, Wheat Cropping, and Rainfall

Abstract

Tillage with a tined cultivator (scarifier) and a rotary cultivator was done on Urrbrae fine sandy loam in South Australia. One‐half of the plots were kept bare, while the other one‐half were cropped with wheat (Triticum aestivum L.). Soil macrostructure (voids and aggregates > 0.5 mm) was observed on sections sawed from blocks of the tilled soil which had been impregnated with epoxy resin. Macrostructure was quantified statistically along linear transects on the sections at 0.25, 0.5, and 0.75 of the depth of tillage at the time of tillage and on three subsequent dates when there had been 10, 135, and 395 mm of natural rainfall, respectively. Soil structures are compared and differences between them are presented. Initial differences in soil structure between the tillage treatments had largely disappeared by the second sampling date. Differences in structure due to the presence of the wheat crop were not significant until the final sampling date when the crop was at 0.66 of its final height. Multiple regression equations are presented for the soil macrostructure parameters as functions of cumulative rainfall after tillage and depth in the tilled soil layer.

The saturated hydraulic conductivity of soils with n-modal pore size distributions

“…Additionally, we re-analyze and discuss briefly some data for the dynamics of the inter-aggregate macro-porosity following tillage for an Australian sandy loam with a clay content of about 17 g/100 g (Dexter, 1976;Dexter et al, 1983). These data relate to experimental plots on which the soil had been tilled to about 0.1 m depth.…”

“…However, with time (and/or rainfall) the soil structure gradually collapses or settles with progressive decrease in macro-porosity. Here, we use data obtained from a re-analysis of those given by Dexter (1976) and Dexter et al (1983). We also note that macro-porosity is defined in these papers as the macro-pore space expressed as a proportion of the total soil volume.…”

“…The theoretical results obtained for regular, "crystalline-type" arrays of equal spheres obtained by Davis et al (1973) showed that this occurs at a porosity of around 0.05 m 3 m − 3 . On the other hand, Dexter et al (1983) noted that it would be impossible to impregnate blocks of tilled soil with resin for values of macro-porosity much smaller than about 0.13 m 3 m − 3 because of lack of macro-pore continuity. Both of these porosities are equivalent to the porosities presented in Eq.…”

“…We can compare these values with the mean results from Dexter (1976) and Dexter et al (1983) who studied an Australian soil. They showed, using measurements on sections such as that shown in Fig.…”

“…Volumetric porosity is obtained from volume and density measurements, areal porosity is measured on soil sections using image analysis, and lineal porosity has been used in studies of the structure of tilled soils (e.g. Dexter, 1976;Dexter and Hewitt, 1978;Dexter et al, 1983).…”