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 organic farm management is associated with positively enhanced soil physical, chemical and biological characteristics. To test this hypothesis more rigorously, 30 paired organic and conventional farms were assessed across a range of soil types and management regimes in the south of England. The 60 paired farms ranged from grassland to horticultural/arable and purely arable. The soils of all chosen farms were measured for a wide range of physical and chemical characteristics. The data were subjected to a multivariate analysis and the results interpreted so as to identify the management factors deemed 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 and pH and that these differentiated organically and conventionally managed arable and horticultural farms. Pasture farms showed no significant differences between organic and conventional management. Conventional horticultural farms showed the lowest values for soil organic matter, aggregate stability, 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 age trend for humic acid, with older humic acids seen For pasture farms. Management factors deemed most important in differentiating between conventional and organic management included frequent farmyard manure applications to horticultural land and the inclusion of grass leys in arable rotations. Some of the soil measurements are suggested as potentially effective indicators of sustainability for farm systems.