The effects of long-term fertilizations on soil hydraulic properties vary with scales

A - Papers appearing in refereed journals

Zhang, X., Neal, A. L., Crawford, J. W., Bacq-Labreuil, A., Akkari, E. and Rickard, W. 2021. The effects of long-term fertilizations on soil hydraulic properties vary with scales. Journal of Hydrology. 539, p. 125890.

AuthorsZhang, X., Neal, A. L., Crawford, J. W., Bacq-Labreuil, A., Akkari, E. and Rickard, W.

Soil structural alterations instigated by cropping system conversion and fertilization change have been well documented, but how such alterations vary with scale remains elusive. We investigated this based on the Rothamsted long-term wheat experiment (since 1843) in the UK. Triplicate cores 7cm high and 10cm in diameter were taken from plots that have been under different fertilizations and returned to natural woodland for more than one century for imaging with X-ray computed tomography at resolution of 40µm. We then broke each core and sampled three aggregates from it to scan them at resolution of 1.5µm. For each core or aggregate sample, we calculated its pore size distribution, as well as permeability and tortuosity from pore-scale simulations. The results showed that the fertilization change more than 170 years ago reshaped the soil structure but differently between the core scale and aggregate scale. Macro-porosity of the pores (>40µm) in the cores unfertilized or fertilized with inorganic fertilizers were low and poorly connected in the top 10cm of soil, compared to the cores given farmyard manure or in the woodland. In all treatments, the large macropores in the cores were hydraulically anisotropic with their permeability being higher in the horizontal direction than in the vertical direction, whereas the aggregates were comparatively isotropic. The fertilization affected porosity and permeability of macropores at core scale more significantly than those at aggregate scale, and the aggregates fertilized with farmyard manure and in the woodland were more permeable than aggregates in other treatments. It is also found that, compared to no-fertilization or fertilization with complete fertilizers, fertilizing without phosphorus over the past 20 years increased the porosity and permeability of the aggregates but not of the cores. Fertilization with inorganic fertilizers increased tortuosity of the macropores in the cores but not of the intra-aggregates micropores, compared to no-fertilization. Porosity-permeability relationship for aggregates unfertilized or fertilized with inorganic fertilisers follows a power law with R2 > 0.8. In contrast, the permeability of aggregates in farmyard manure and in the woodland trended differently with the porosity. Aggregates and cores responded differently to carbon in that, with soil carbon increasing, the permeability of the aggregates increased asymptotically while the permeability of the cores increased approximately exponentially. Since soil structure is indicators of soil quality and evolves slowly, our results have important implications for understanding how agronomical practice changes reshape soil structure at different scales as well as the long-term consequence for hydrological and biochemical processes.

KeywordsRothamsted long-term experiment ; Hierarchical soil structural change; Pore-scale simulations; X-ray computed tomography
Year of Publication2021
JournalJournal of Hydrology
Journal citation539, p. 125890
Digital Object Identifier (DOI)
Open accessPublished as ‘gold’ (paid) open access
FunderBiotechnology and Biological Sciences Research Council
Funder project or codeS2N - Soil to Nutrition - Work package 1 (WP1) - Optimising nutrient flows and pools in the soil-plant-biota system
The Rothamsted Long Term Experiments [2017-2022]
Publisher's version
Accepted author manuscript
Supplemental file
Output statusPublished
Publication dates
Online18 Dec 2020
Publication process dates
Accepted10 Dec 2020
PublisherElsevier Science Bv

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