Structural differences between bulk and rhizosphere soil

• Published in: European journal of soil science Vol. 56; no. 3; pp. 353 - 360
• Main Authors: Whalley, W.R, Riseley, B, Leeds-Harrison, P.B, Bird, N.R.A, Leech, P.K, Adderley, W.P
• Format: Journal Article
• Language: English
• Published: Oxford, UK; Malden, USA Blackwell Science Ltd 01.06.2005; Blackwell Science
• Subjects: Agronomy. Soil science and plant productions; barley; Biological and medical sciences; bulk density; contact angle; corn; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Hordeum vulgare; image analysis; interface phenomena; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; pore size distribution; rhizosphere; root exudates; roots; soil; soil aggregates; Soil science; soil structure; soil water retention; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Structure, texture, density, mechanical behavior. Heat and gas exchanges; surface tension; Triticum; wheat; Zea mays; Monocotyledones; Cultivated soil; C4-Type; Cereal crop; Matric potential; Gramineae; Angiospermae; Soil science; C3-Type; Hydraulic properties; Bulk density; Zea mays; Hordeum vulgare; Root; Interspecific comparison; Property of soil; Soil structure; Physical properties; Rhizosphere; Image analysis; Soil water properties; Spermatophyta; Porosity; Aggregate; Soil plant relation; Water holding capacity; Triticum aestivum
• ISSN: 1351-0754; 1365-2389
• DOI: 10.1111/j.1365-2389.2004.00670.x

Summary The physical characteristics of the soil at the root–soil interface are crucial because they determine both physical aspects of root function such as water and nutrient uptake and the microbial activity that is most relevant to root growth. Because of this we have studied how root activity modifies the structure and water retention characteristic of soil adjacent to the root for maize, wheat and barley. These plants were grown in pots for a 6‐week growth period, then the soil adjacent to the root (rhizosphere soil) and bulk soil aggregates were harvested. These soil aggregates were then saturated and equilibrated at matric potentials between −600 kPa and saturation, and the water retention characteristics were measured. From subsamples of these aggregates, thin sections were made and the porosity and pore‐size distributions were studied with image analysis. Both image analysis and estimates of aggregated density showed that the rhizosphere soil and bulk soil had similar porosities. Growing different plants had a small but significant effect on the porosity of the soil aggregates. Image analysis showed that for all the plant species the structure of the rhizosphere soil was different to that of the bulk soil. The rhizosphere soil contained more larger pores. For maize and barley, water retention characteristics indicated that the rhizosphere soil tended to be drier at a given matric potential than bulk soil. This effect was particularly marked at greater matric potentials. The difference between the water retention characteristics of the bulk and rhizosphere soil for wheat was small. We compare the water retention characteristics with the data on pore‐size distribution from image analysis. We suggest that differences in wetting angle and pore connectivity might partly explain the differences in water retention characteristic that we observed. The impact of differences between the water retention properties of the rhizosphere and bulk soil is discussed in terms of the likely impact on root growth.