Topsoil characteristics from a paired farm survey of organic versus conventional farming in southern England

Results from experimental trials and on-farm surveys have suggested that or ganic farm management is associated with positively enhanced soil physical, chemical and biological characteristics. To test this hypothesis more rigo rously, 30 paired organic and conventional farms were assessed across a ran ge of soil types and management regimes in the south of England. The 60 pai red farms ranged from grassland to horticultural/arable and purely arable. The soils of all chosen farms were measured for a wide range of physical an d chemical characteristics. The data were subjected to a multivariate analy sis and the results interpreted so as to identify the management factors de emed beneficial for topsoil physical and nutritional conditions. The results showed that farm types could be most effectively characterized by organic matter, aggregate stability, humic acid, infra-red absorbance an d pH and that these differentiated organically and conventionally managed a rable and horticultural farms. Pasture farms showed no significant differen ces between organic and conventional management. Conventional horticultural farms showed the lowest values for soil organic matter, aggregate stabilit y, cation exchange capacity and E-4/E-6 ratio. Organic horticultural farms had the highest mean humic acid content, infra-red absorbance, air capacity and available water capacity. Infra-red absorbance values showed a clear a ge trend for humic acid, with older humic acids seen For pasture farms. Man agement factors deemed most important in differentiating between convention al and organic management included frequent farmyard manure applications to horticultural land and the inclusion of grass leys in arable rotations. So me of the soil measurements are suggested as potentially effective indicato rs of sustainability for farm systems.