Physical properties of a Luvisol for different long‐term fertilization treatments: I. Mesoscale capacity and intensity parameters

Abstract

The physical properties of a Luvisol derived from loess near Bonn, Germany, under different long-term fertilization treatments were examined. For the investigation of the impact of farmyard manure (FYM) on soil strength at the mesoscale (100 to 300 cm 3 soil cores), undisturbed samples were taken from two different depths (10 and 40 cm), either with no fertilization at all, with full mineral fertilization, with FYM only, and with both mineral and organic fertilization. We investigated hydraulic and mechanical parameters, namely precompression stress, pore-size distribution, saturated hydraulic and air conductivity, and calculated pore connectivity. Long-term organic fertilization resulted in significantly more and coarser pores which in addition were more conductant and mechanically stronger by trend. Mineral fertilization also increased pore volume by trend but not pore functionality. Mechanical strength generally increased with fertilization by trend, however, was reduced again when organic and mineral fertilization were combined. Nonetheless, FYM led to relatively higher soil strength as the FYM-treated plots with lower bulk density attained similar soil strength as the unfertilized but denser plots and thus supported the soilimproving impact of organic amendments. The subsoil physical properties were rather unaffected by fertilization, but were dominated by texture.

Comparing the potentials of clay and biochar in improving water retention and mechanical resilience of sandy soil

“…If, however, the kaolinite starts to dominate the mixture, its finer particles and higher water saturation at the given matric potential cause a slightly weakening of the bonds (Fredlund and Rahardjo, 1993;Hartge and Horn, 2016). The values of Integral z have been proven to be directly related to the elastic (resilience) or rigid (stiffness) behaviour of the interparticle particle bonds in several conditions (Holthusen et al, 2012;Markgraf et al, 2012). In the unamended condition, the fine sand particles are largely cohesionless and weakly structured (Abousnina et al, 2015), and can not withstand high shear stress values.…”

“…Integral z provides a semi-quantitative index of the stiffness degradation or mechanical resilience of the substrate, to the shearing force (for more details see Ajayi and Horn, 2016;Markgraf et al, 2012). The shear stress experienced by the sample during the AST indicates the shear resistance of the tested samples and relates well to shear strength parameters obtained from macro scale measurement in shear box and oedometer (Holthusen et al, 2012;Markgraf et al, 2012).…”

“…Rheological measurements and parameters derived thereof, have adequately characterized micro-mechanical behaviour in substrates and elucidate differences in resilience criteria at particle-to-particle scale (Holthusen et al, 2012;Markgraf et al, 2012). The amplitude sweep test (AST) in particular has been used to evaluate the impact of some soil amendment materials, including fertilizers and biochar on the properties of the resulting substrate (Ajayi et al, 2016;Holthusen et al, 2012;Markgraf et al, 2012).…”

“…Rheological measurements and parameters derived thereof, have adequately characterized micro-mechanical behaviour in substrates and elucidate differences in resilience criteria at particle-to-particle scale (Holthusen et al, 2012;Markgraf et al, 2012). The amplitude sweep test (AST) in particular has been used to evaluate the impact of some soil amendment materials, including fertilizers and biochar on the properties of the resulting substrate (Ajayi et al, 2016;Holthusen et al, 2012;Markgraf et al, 2012). Rheological parameters like storage and loss moduli, loss factor tan (∂) and integral z describe the internal strength and maximum interparticle shear stress in substrates (The basic theory as well as a summarizing theory documentation on rheological techniques in soil research could be found in Holthusen et al, 2012;Vyalov, 2013).…”

“…The amplitude sweep test (AST) in particular has been used to evaluate the impact of some soil amendment materials, including fertilizers and biochar on the properties of the resulting substrate (Ajayi et al, 2016;Holthusen et al, 2012;Markgraf et al, 2012). Rheological parameters like storage and loss moduli, loss factor tan (∂) and integral z describe the internal strength and maximum interparticle shear stress in substrates (The basic theory as well as a summarizing theory documentation on rheological techniques in soil research could be found in Holthusen et al, 2012;Vyalov, 2013). Therefore, our objective in this paper was to investigate the changes in mechanical strength and water retention as physical properties that define structure formation and stability in a fine-sand material amended with: -biochar, -kaolinite -a non-swelling clay and -Na-bentonite -a swelling clay, at 3 different rates using rheometry techniques.…”