Abstract
AbstractAgricultural 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.
Highlights
Agricultural practices can have beneficial or detrimental effects on soil functions when applied for decades, depending on the nature of such practices (Ashworth et al, 2017; Bronick and Lal, 2005; Denef et al, 2009; Pagliai et al, 2004)
They posited that the greater proportion of organic matter enhanced the elastic recovery of soil structure (Gregory et al, 2009)
Pore size distributions showed a more rapid response to altered management than porosity for the grassland treatment: after only 2-years of conversion, a greater diversity of pore sizes was observed, and this trend was recorded in the data after 7- and 10-years (Fig. 3). The Gini-coefficient indicated that soil converted to grassland established a more even distribution of pore sizes than the other treatments, meaning that grassland treatment had a greater diversity of pores after 2, 7- and 10-years post conversion (Supplementary Fig. 2) leading to enhanced functionality
Summary
Agricultural practices can have beneficial or detrimental effects on soil functions when applied for decades, depending on the nature of such practices (Ashworth et al, 2017; Bronick and Lal, 2005; Denef et al, 2009; Pagliai et al, 2004). Analysis of soil structure indicates that pore size distribution, assessed by X-ray Computed Tomography (CT), plays an important role in aggregate stability (Menon et al 2020). Conversion from bare fallow to arable or grassland increased soil organic carbon, soil nitrogen and the population of meso-fauna and fungi within 3 to 5 years following conversion (Hirsch et al 2017), soil structure modification was not assessed in this experiment. We hypothesised that: (1) plants are an active factor in increasing soil porosity, diversity of pore sizes and pore connectivity, and (2) structural development is more rapid in grassland than arable converted systems due to the greater and more persistent presence of vegetation. G ≈ 1 represents a heterogeneous distribution of pores which means that a majority of pores have the same sizes
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