Quantification of the effects of contrasting crops in the development of soil structure: an organic conversion

Soil structure can be greatly affected, and hence manipulated, by agricultural management practices, such as crop rotation. This study aims to illustrate how soil structure under a stockless organic system differed between contrasting crop types using quantified data derived from image analysis. Undisturbed soil samples were collected from five organic conversion strategies in the second year of conversion, during two contrasting seasons in 2001 and following one uniform crop (oats) grown on all the plots in 2004. The samples were impregnated and images of soil structure collected at selected depth intervals. The images were analysed for macroporosity, pore size distribution and pore-perimeter fractal dimension. Significant differences were found between treatments in terms of overall macroporosity (%) and average pore size (mm(2)) in 2001. The red clover (Trifolium pratense) treatments had the highest soil macroporosity in 2001, but showed a dramatic drop in 2004 accompanied by a reduction in average pore size (mm(2)). Pore-perimeter fractal dimensions for four of the five crop treatments in 2001 did not show significant differences. However, there was a significant decrease in the fractal dimensions in 2004, indicating the presence of pores with less rough and irregular pore boundaries following a uniform cereal crop. Benefits to soil structure and porosity from clover were large and significant but were not lasting.