Impact of Small-Scaled Differences in Micro-Aggregation on Physico-Chemical Parameters of Macroscopic Biopore Walls

Abstract

Macroscopic biopores, like earthworm burrows or channels which remain after a root decayed, act as preferential flow paths for water, gas, and heat transport processes, and viewing at agricultural production, as preferential elongation paths for plant roots. These processes result in intense alterations of the soil volume and its composition that surrounds the pores. The effects of these processes were analyzed at small-scale and physico-chemical soil parameters, i.e., relative oxygen diffusion coefficient (D s /D O ), oxygen partial pressure pO 2 , Eh and pH of biopore walls, were measured. The analyses were carried out on undisturbed soil samples with different colonization history, excavated from a haplic Luvisol derived from loess. Soil resistance to penetration was determined simultaneously with D s /D O and pO 2 using a coupled, self-developed approach, and four matric potentials (namely, m = −1 kPa; −3 kPa; −6 kPa or −30 kPa) were considered. We hypothesized that physico-chemical soil parameters in biopore walls were altered due to differing influences on the soil aggregation. Aggregation was visualized with scanning electron microscopy, classified and used to explain differences in-soil properties. Plant roots and earthworms altered aggregation next to biopore surfaces in a contrasted way, either by enhancing aggregates diversity or homogenizing it. Roots led to the formation of subpolyeders while earthworms formed subplates. Pore functions of microaggregates were comparable to those of larger scale, and subpolyeders showed much more favorable soil properties in terms of soil aeration (Ds/Do, pO2). Replicates of all parameters scattered intensely and showed deviations up to several orders of magnitude in case of D s /D O underlining the large variability of soil properties in biopore walls.

Permeabilidad y difusión de aire en el subsuelo de un Andisol sujeto a distintas estrategias de mejoramiento de praderas

“…The values of D s /D O are remarkably high, especially under field conditions with values that are comparable to sandy soils with high air-filled porosity (Moldrup et al, 2000); or with a well-structured, more silty soil (Mordhorst et al, 2017). Much lower values were found for European soils rich in clay (Uteau et al, 2013) or for biopore walls of these soils (Haas and Horn, 2018). The ratio D s /D O (Figure 4b) was significantly influenced by drainage to -6 kPa in the upper subsoil (FNP, t = 3.82; dF = 12; p ≤ 0.05) and in the lower part (NFNP and CP with t = 3.22; dF = 12; p ≤ 0.05 and t = 4.565; dF = 12; p ≤0.01; respectively).…”

“…For volcanic ash soil, this can be very relevant due to their shrinkage behavior (Dörner et al, 2010). The penetration of finer root hairs results in the creation of new and highly connected, lateral side pores, increasing the relative diffusion coefficient of the biopore-wall (Haas and Horn, 2018), and consequently, the exchange between biopores and the soil matrix. Furthermore, whenever a new surface is created, swelling pressures occur, leading to the formation of new cracks after the pressure is dissipated (Jayawardane and Greacen, 1987).…”

The interaction between wheat roots and soil pores in structured field soil

“…An exception is the work of Stirzaker et al (1996) , who found that roots were more likely to occupy old root channels compared with artifical pores. In the field, the soil around biopores is likely to have distinct physico-chemical properties relative to the bulk soil ( Kautz et al , 2013 ; Haas and Horn, 2018 ). The biopores in the subsoil are less likely to be disturbed by tillage and, because they tend to have a vertical orientation, they are less sensitive to the effects of compaction and can remain intact for many years.…”

Volume‐related quantification of organic carbon content and cation exchange capacity of macropore surfaces in Bt horizons

“…The density of macropore surfaces can potentially be affected by several factors: 1. Due to the compression of earthworms and roots, the outermost surface layer of biopores can be compacted (i.e., revealing higher bulk density values than the underlying soil matrix; Haas & Horn, 2018; Rogasik, Schrader, Onasch, Kiesel, & Gerke, 2014; Ruiz et al., 2015). 2.…”