Abstract
The influence of root growth and water regime on the formation of aggregates was studied in modified minirhizotrons under controlled conditions. Two soils, a black earth (67% clay) and a red-brown earth (19% clay) were ground and forced through a 0.5 mm sieve. Ryegrass, pea and wheat were grown for fifteen wetting and drying (wd) cycles for 5 months. Another set of minirhizotrons was not planted and served as a control. Measurements of aggregate size distribution (ASD), aggregate tensile strength (ATS), aggregate stability (AS), aggregate bulk density (ABD) and organic carbon (OC) were made on single aggregates of the 2–4 mm fraction.
The results showed that aggregates of the black earth which has a high clay content and shrink/swell properties had more smaller aggregates with higher ATS, AS and ABD than those from the red-brown earth. It was also found that for both soils: (1) w/d cycles and higher root length density (RLD) increased the proportions of smaller aggregates and aggregate strength; (2) differences in the ability of the plant species to influence aggregation was evident and seemed to be related to the RLD. The RLD was in the order ryegrass > wheat > pea. Mechanisms likely to be involved in processes of aggregate formation and stabilization are discussed. They include cracking of soil due to tensile stresses generated during drying of a shrinking soil; changes in pore water pressure within the soil mass caused by water uptake by plant roots generating effective stresses; and biological processes associated with plant roots and root exudates.
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References
Aitchison G D 1961 Relationships of moisture stress and effective stress functions in unsaturated soils. In Pore Pressure and Suction in Soils. pp 47–52. Butterworths, London.
Barley K P 1968 Deformation of the soil by the growth of plants. Trans. 9th Int. Congr. Soil Sci. Adelaide 1, 759–768.
Chaney K and Swift R S 1986 Studies on aggregate stability. II. The effect of humic substances on the stability of re-formed soil aggregates. J. Soil Sci. 37, 337–343.
Dexter A R 1987 Compression of soil around roots. Plant and Soil 97, 401–406.
Dexter A R 1988a Advances in characterization of soil structure. Soil Tillage Res. 11, 199–238.
Dexter A R 1988b Strength of soil aggregates and of aggregate beds. Catena Supplement 11, 35–52.
Dexter A R 1991 Amelioration of soil by natural processes. Soil Tillage Res. 20, 87–100.
Dexter A R and Kroesbergen B 1985 Methodology for determination of tensile strength of soil aggregates. J. Agric. Engng. Res. 31, 139–147.
Dexter A R, Horn R and Kemper W D 1988 Two mechanisms for age-hardening of soil. J. Soil Sci. 39, 163–175.
Dexter A R, Kroesbergen B and Kuipers H 1984 Some mechanical properties of aggregates of top soils from the IJsselmeer polders. 2. Remoulded soil aggregates and the effects of wetting and drying cycles. Neth. J. Agric. Sci. 32, 215–227.
Genstat 5 Committee 1987 Genstat 5 Reference Manual. Clarendon Press, Oxford.
Grant C D and Dexter A R 1986 Soil structure generation by wetting and drying cycles. Trans. 13th Int. Congr. Soil Sci. Hamburg 2, 60–62.
Groenevelt P H and Kay B D 1981 On pressure distribution and effective stress in unsaturated soils. Can. J. Soil Sci. 61, 431–443.
Haines W B 1926 Studies in the physical properties of soils. II. A note on the cohesion developed by capillary forces in an ideal soil. J. Agric. Sci. 15, 529–535.
Harris R F, Chesters G and Allen O N 1966 Dynamics of soil aggregation. Adv. Agron. 18, 107–169.
Hettiaratchi D R P and O'Callaghan J R 1980 Mechanical behaviour of agricultural soils. J. Agr. Engng. Res. 25, 239–259.
Hignett C T 1976 A method for sampling and measuring cereal roots. J. Aust. Inst. Agric. Sci. 42, 127–129.
Horn R and Dexter A R 1989 Dynamics of soil aggregation in an irrigated desert loess. Soil Tillage Res. 13, 253–266.
Kemper W D and Rosenau R C 1984 Soil cohesion as affected by time and water content. Soil Sci. Soc. Am. J. 48, 1001–1006.
Kemper W D and Rosenau R C 1986 Aggregate stability and size distribution. In Methods of Soil Analysis. Part 1. 2nd edition. Ed. AKlute. pp. 425–442. American Society of Agronomy, Madison, WI.
Martin J P, Martin W P, Page J B, Raney W A and DeMent J D 1955 Soil aggregation. Adv. Agron. 7, 1–37.
McIntyre D S and Stirk G B 1954 A method for determination of apparent density of soil aggregates. Aust. J. Agric. Res. 5, 291–296.
Misra R K, Dexter A R and Alston A M 1986 Penetration of soil aggregates of finite size. II. Plant roots. Plant and Soil 94, 59–85.
Molope M B 1987 Soil aggregate stability: The contribution of biological and physical processes. S. Afr. J. Plant Soil 4, 121–126.
Newman E I 1966 A method for estimating the total root length in a sample. J. Appl. Ecol. 3, 139–145.
Northcote R H 1979 A Factual Key for the Recognition of Australian Soils. CSIRO Division of Soils. Rellim. Adelaide. South Australia.
Oades J M 1984 Soil organic matter and structural stability: mechanisms and implications for management. Plant and Soil 76, 319–337.
Semmel H, Horn R, Hell U, Dexter A R and Schulze E D 1990 The dynamics of soil aggregate formation and the effect on soil physical properties. Soil Technol. 3, 113–129.
Skempton A W 1960 Effective stress in soils, concrete and rocks. In Pore Pressure and Suction in Soils. pp 4–16. Butterworths, London.
Telfair D, Gardner M R and Miars D 1957 The restoration of a structurally degenerated soil. Soil Sci. Soc. Am. Proc. 21, 131–134.
Terpstra R 1989 Formation of new aggregates under laboratory-simulated field conditions. Soil Tillage Res. 13, 13–21.
Terpstra R 1990 Formation of new aggregates and weed seed behaviour in a coarse- and in a fine-textured loam soil: A laboratory experiment. Soil Tillage Res. 15, 285–296.
Tiessen H, Bettany J R and Stewart J W B 1981 An improved method for the determination of carbon in soils and soil extracts by dry combustion. Commun. Soil Sci. Pl. Anal. 12, 211–218.
Tisdall J M and Oades J M 1982 Organic matter and water stable aggregates in soils. J. Soil Sci. 35, 141–163.
Towner G D 1961 Influence of soil-water suction on some mechanical properties of soils. J. Soil Sci. 12, 180–187.
Towner G D 1987a The tensile stress generated in clay through drying. J. Agric. Engng. Res. 37, 279–289.
Towner G D 1987b The mechanics of cracking of drying clay. J. Agric. Engng. Res. 36, 115–124.
Towner G D and Childs E C 1972 The mechanical strength of unsaturated porous granular material. J. Soil Sci. 23, 481–498.
Utomo W H and Dexter A R 1981a Age-hardening of agricultural top soils. J. Soil Sci. 32, 335–350.
Utomo W H and Dexter A R 1981b Tilth mellowing. J. Soil Sci. 32, 187–201.
Williams B G, Greenland D J, Lindstrom G R and Quirk J P 1966 Techniques for the determination of the stability of soil aggregates. Soil Sci. 101, 157–163.
Williams J and Shaykewich C F 1970 The influence of soil water matric potential on the strength properties of unsaturated soil. Soil Sci. Soc. Am. Proc. 34, 835–840.
Yoder R E 1936 A direct method of aggregate analysis of soils and a study of the physical nature of erosion losses. J. Am. Soc. Agron. 28, 337–351.
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Materechera, S.A., Dexter, A.R. & Alston, A.M. Formation of aggregates by plant roots in homogenised soils. Plant Soil 142, 69–79 (1992). https://doi.org/10.1007/BF00010176
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DOI: https://doi.org/10.1007/BF00010176