Significant structural evolution of a long‐term fallow soil in response to agricultural management practices requires at least 10 years after conversion

Abstract

Agricultural practices can have significant effects on the physical and biological properties of soil. The aim of this study was to understand how the physical structure of a compromised soil, arising from long‐term bare‐fallow management, was modified by adopting different field management practices. We hypothesized that changing agricultural practices from bare‐fallow to arable or grassland would influence the modification of pore structure via an increase in porosity and pore connectivity, and a more homogenous distribution of pore sizes, and that this change exerts a rapid evolution of soil structure following conversion. Soil aggregates (<2 mm) collected in successive years from field plots subjected to three contrasting managements were studied: bare‐fallow, bare‐fallow converted to arable, and bare‐fallow converted to grassland. Soil structure was assessed by X‐ray computed tomography on the aggregates at 1.5 μm resolution, capturing detail relevant to soil biophysical processes. The grassland system increased porosity, diversity of pore sizes, pore connectivity and pore‐surface density significantly over the decade following conversion. However, measured at this resolution, the evolution of most of these metrics of soil structure required approximately 10 years post‐conversion to show a significant effect. The arable system did not influence soil structural evolution significantly. Only pore size distribution was modified in grassland in a shorter time frame (2 years post‐conversion). Hence, evolution of soil structural characteristics appears to require at least a decadal timescale following conversion to grassland. Highlights The physical structure of a compromised soil was modified by adopting plant‐based field management practices. Conversion to grassland increased pore size diversity after 2 years. Porosity, pore connectivity and pore surface density showed a significant modification between 7 and 10 years after conversion.

Impact of bare fallow management on soil carbon storage and aggregates across a rock fragment gradient

“…In comparison with bare fallow studies in the literature (Bacq‐Labreuil et al., 2021; Doran et al., 1998; Paradelo et al., 2016), in our experiment, the direct effect of tillage was excluded since biomass was mainly removed using herbicides. Our soil sampling at 5−25 cm was below the shallow tillage operations limited to the top 5 cm in 2005−2010.…”

“…where the conversion of a Chromic Luvisol under bare fallow with regular tillage into grassland without tillage was shown to affect porosity, pore connectivity, and pore surface density based on X-ray microtomography (μCT) assessment (Bacq-Labreuil et al, 2021;George et al, 2021). In the same experiment, the soil aggregate stability measured as dispersibility of clay-sized particles was shown to recover quickly upon grassland introduction.…”

“…In turn, when the input of OM is inhibited, the OM in stable aggregates may be depleted likely leading to a breakdown of the soil structure. This was tested in the Rothamsted Highfield conversion experiment, where the conversion of a Chromic Luvisol under bare fallow with regular tillage into grassland without tillage was shown to affect porosity, pore connectivity, and pore surface density based on X‐ray microtomography (µCT) assessment (Bacq‐Labreuil et al., 2021; George et al., 2021). In the same experiment, the soil aggregate stability measured as dispersibility of clay‐sized particles was shown to recover quickly upon grassland introduction.…”

An overlooked mechanism underlying the attenuated temperature response of soil heterotrophic respiration

“…The influence of temperature and substrates is described by the parameter k. Apart from k, all other parameters are related to soil architecture. Mathematically, each parameter in equation (2.18) can take an arbitrary value, but in validating the model against experimental data, we take all soil structure parameters as a set, calculating it by mining a soil image dataset consisting of more than 100 X-ray images we have accumulated over the past decade for soils with various textures ranging from clay loam to sandy soils [45][46][47][48][49]. Using a method we developed previously [50], we calculated liquid water distribution within the pore geometry at different water contents, as well as the associated water-air interfaces and wetted pore walls for each soil image.…”

Is ‘soil health’ meaningful as a scientific concept or as terminology?

“…If conversations with decision makers are to be usefully taken further, they will inevitably have to progress into more complex and nuanced considerations. These might include ways of maintaining or increasing soil carbon content (Lal, 2020; Martin et al., 2021; Poulton et al., 2018), addressing trade‐offs between different greenhouse gas emissions resulting from altered management practices (Guenet et al., 2021; Lugato et al., 2018; Pärn et al., 2018), the significance of changes in soil biological populations (Bacq‐Labreuil et al., 2020), or the risk of soil erosion and the sustainability or otherwise of specific practices (Evans et al., 2020). Even if using the term soil health is helpful as a first step in such discussions, there is no escape from delving into greater detail or complexity at the subsequent stage.…”