Are the links between soil aggregate size class, soil organic matter and respiration rate artefacts of the fractionation procedure?

MR Ashman, PD Hallett, PC Brookes*

*Corresponding author for this work

Research output: Contribution to journalArticle

57 Citations (Scopus)

Abstract

Our aim was to see how variations in aggregate fractionation procedures influence the chemical and biological properties of different sized soil aggregates. Soil was fractionated using two different physical procedures: (1) slaking to simulate a major wetting stress in the field or (2) shaking to simulate mechanical disruption by tillage followed by wet sieving. In the slaked treatment, macro-aggregates (<250 mum dia) contained about 17% more soil organic C and had about 30% faster rates of respiration. This was in contrast to the shaken treatment where micro-aggregates (<250 mum dia) contained about 12% more soil organic C and had about 14% faster rates of respiration. The biological and chemical properties of different sized aggregates were used to describe two different models. These were the aggregate heirarchy model and one based on maximum biological activity at soil surfaces. Our results suggest that the chemical and biological properties of aggregates depend on the fractionation procedure. On this basis we suggest that the observed relationships between aggregate size and other properties, for example biological activity, must be interpreted in terms of the disruptive mechanisms used to fractionate aggregated soil. Our results suggest that the aggregate hypothesis has serious weaknesses: the aggregates measured being largely an artefact of the chosen method of separation. We therefore suggest that future work should also consider biological activities at soil pore surfaces. It is at the surface of these channels that parameters such as oxygen supply, plant roots, root exudates and fresh organic matter inputs first interact with the soil. Biological processes in this region are therefore likely to be more important than those occurring in the bulk soil. (C) 2003 Elsevier Science Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)435-444
Number of pages10
JournalSoil Biology and Biochemistry
Volume35
Issue number3
Early online date7 Jan 2003
DOIs
Publication statusPublished - Mar 2003

Keywords

  • soil organic carbon
  • carbon
  • microbial biomass
  • tillage
  • respiration rates
  • nitrogen
  • stability
  • cultivated soils
  • aggregate fractionation procedures
  • dynamics
  • soil aggregates

Cite this

Are the links between soil aggregate size class, soil organic matter and respiration rate artefacts of the fractionation procedure? / Ashman, MR; Hallett, PD; Brookes, PC.

In: Soil Biology and Biochemistry, Vol. 35, No. 3, 03.2003, p. 435-444.

Research output: Contribution to journalArticle

@article{12a1cce9ddd74fe1879d197a39a907d4,
title = "Are the links between soil aggregate size class, soil organic matter and respiration rate artefacts of the fractionation procedure?",
abstract = "Our aim was to see how variations in aggregate fractionation procedures influence the chemical and biological properties of different sized soil aggregates. Soil was fractionated using two different physical procedures: (1) slaking to simulate a major wetting stress in the field or (2) shaking to simulate mechanical disruption by tillage followed by wet sieving. In the slaked treatment, macro-aggregates (<250 mum dia) contained about 17{\%} more soil organic C and had about 30{\%} faster rates of respiration. This was in contrast to the shaken treatment where micro-aggregates (<250 mum dia) contained about 12{\%} more soil organic C and had about 14{\%} faster rates of respiration. The biological and chemical properties of different sized aggregates were used to describe two different models. These were the aggregate heirarchy model and one based on maximum biological activity at soil surfaces. Our results suggest that the chemical and biological properties of aggregates depend on the fractionation procedure. On this basis we suggest that the observed relationships between aggregate size and other properties, for example biological activity, must be interpreted in terms of the disruptive mechanisms used to fractionate aggregated soil. Our results suggest that the aggregate hypothesis has serious weaknesses: the aggregates measured being largely an artefact of the chosen method of separation. We therefore suggest that future work should also consider biological activities at soil pore surfaces. It is at the surface of these channels that parameters such as oxygen supply, plant roots, root exudates and fresh organic matter inputs first interact with the soil. Biological processes in this region are therefore likely to be more important than those occurring in the bulk soil. (C) 2003 Elsevier Science Ltd. All rights reserved.",
keywords = "soil organic carbon, carbon, microbial biomass, tillage, respiration rates, nitrogen, stability, cultivated soils, aggregate fractionation procedures, dynamics, soil aggregates",
author = "MR Ashman and PD Hallett and PC Brookes",
year = "2003",
month = "3",
doi = "10.1016/S0038-0717(02)00295-X",
language = "English",
volume = "35",
pages = "435--444",
journal = "Soil Biology and Biochemistry",
issn = "0038-0717",
publisher = "Elsevier Limited",
number = "3",

}

TY - JOUR

T1 - Are the links between soil aggregate size class, soil organic matter and respiration rate artefacts of the fractionation procedure?

AU - Ashman, MR

AU - Hallett, PD

AU - Brookes, PC

PY - 2003/3

Y1 - 2003/3

N2 - Our aim was to see how variations in aggregate fractionation procedures influence the chemical and biological properties of different sized soil aggregates. Soil was fractionated using two different physical procedures: (1) slaking to simulate a major wetting stress in the field or (2) shaking to simulate mechanical disruption by tillage followed by wet sieving. In the slaked treatment, macro-aggregates (<250 mum dia) contained about 17% more soil organic C and had about 30% faster rates of respiration. This was in contrast to the shaken treatment where micro-aggregates (<250 mum dia) contained about 12% more soil organic C and had about 14% faster rates of respiration. The biological and chemical properties of different sized aggregates were used to describe two different models. These were the aggregate heirarchy model and one based on maximum biological activity at soil surfaces. Our results suggest that the chemical and biological properties of aggregates depend on the fractionation procedure. On this basis we suggest that the observed relationships between aggregate size and other properties, for example biological activity, must be interpreted in terms of the disruptive mechanisms used to fractionate aggregated soil. Our results suggest that the aggregate hypothesis has serious weaknesses: the aggregates measured being largely an artefact of the chosen method of separation. We therefore suggest that future work should also consider biological activities at soil pore surfaces. It is at the surface of these channels that parameters such as oxygen supply, plant roots, root exudates and fresh organic matter inputs first interact with the soil. Biological processes in this region are therefore likely to be more important than those occurring in the bulk soil. (C) 2003 Elsevier Science Ltd. All rights reserved.

AB - Our aim was to see how variations in aggregate fractionation procedures influence the chemical and biological properties of different sized soil aggregates. Soil was fractionated using two different physical procedures: (1) slaking to simulate a major wetting stress in the field or (2) shaking to simulate mechanical disruption by tillage followed by wet sieving. In the slaked treatment, macro-aggregates (<250 mum dia) contained about 17% more soil organic C and had about 30% faster rates of respiration. This was in contrast to the shaken treatment where micro-aggregates (<250 mum dia) contained about 12% more soil organic C and had about 14% faster rates of respiration. The biological and chemical properties of different sized aggregates were used to describe two different models. These were the aggregate heirarchy model and one based on maximum biological activity at soil surfaces. Our results suggest that the chemical and biological properties of aggregates depend on the fractionation procedure. On this basis we suggest that the observed relationships between aggregate size and other properties, for example biological activity, must be interpreted in terms of the disruptive mechanisms used to fractionate aggregated soil. Our results suggest that the aggregate hypothesis has serious weaknesses: the aggregates measured being largely an artefact of the chosen method of separation. We therefore suggest that future work should also consider biological activities at soil pore surfaces. It is at the surface of these channels that parameters such as oxygen supply, plant roots, root exudates and fresh organic matter inputs first interact with the soil. Biological processes in this region are therefore likely to be more important than those occurring in the bulk soil. (C) 2003 Elsevier Science Ltd. All rights reserved.

KW - soil organic carbon

KW - carbon

KW - microbial biomass

KW - tillage

KW - respiration rates

KW - nitrogen

KW - stability

KW - cultivated soils

KW - aggregate fractionation procedures

KW - dynamics

KW - soil aggregates

U2 - 10.1016/S0038-0717(02)00295-X

DO - 10.1016/S0038-0717(02)00295-X

M3 - Article

VL - 35

SP - 435

EP - 444

JO - Soil Biology and Biochemistry

JF - Soil Biology and Biochemistry

SN - 0038-0717

IS - 3

ER -