Thursday, 13 July 2006 - 11:45 AM
64-5

Quantifying Physical Aspects of Soil Quality Associated with Organic Agricultural Practices.

Apostolos Papadopoulos1, Nigel R. A. Bird2, Whitmore Andy2, and Sacha J. Mooney1. (1) The Univ of Nottingham, Agricultural & Environmental Sciences, University Park, Nottingham, NG7 2RD, United Kingdom, (2) Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, United Kingdom

Soil structure determines the operating environment for all physical, chemical and biological processes within the soil. In particular, it determines the accessibility of air, water and nutrients for plant roots, as well as seedling emergence and root penetration. The aim of this research was to investigate the effects of organic farming practices on developing and maintaining soil structure and compare them with conventional practices. The study involved implementing quantified image analysis of soil structure at a number of scales of observations (macro to micro) in both two and three dimensions. Soil images were acquired from X-ray Computed Tomography (CT), undisturbed polished soil blocks and soil thin sections (Fig. 1). Key soil physical and chemical properties such as soil organic matter, aggregate stability, hydraulic conductivity, bulk density, soil penetration resistance and water release characteristics were also measured. Soil porosity, pore size distribution and pore perimeter data were collected and fractal geometry was used to characterise pore roughness. Soil samples were obtained from experimental organic sites across the UK, from contrasting soil textures. In conventionally cultivated soils, the pore size distribution was dominated by small number of large pores (>800 µm), while organically cultivated soils exhibited a broader range of pore sizes. Organically managed soils had higher aggregate stability than conventionally managed soils (P<0.05). Where clover (Trifolium pratense) was involved in the organic crop rotation, a significant increase in soil macroporosity occurred consisting of increased roughness of macropores (fractal dimension = 1.45) in the top 5 cm of soil. An understanding of how soil structure is affected by the different farming practices and the impact of structural developments on soil function is vital for sustainable land management.


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