Does organic management lead to enhanced soil physical quality?

- Soils under organic had greater organic matter and stability than conventional.
- Soils under organic were favourable for crops but this is scale and time dependent.
- Meso-porosity was greater in the organic than conventionally managed soils.
- Positive effects of organic farming are not constant over time.
- Organic management showed a negative impact on micro-porosity in long the term.

Conventional management of soils (i.e. intensive cultivations and the use of synthetic agrochemicals) has often been associated with degradation in soil quality whereas organic farming has been suggested as an approach that conserves and protects the soil environment. Several studies have investigated the differences between organically and conventionally managed soils, but few have sought to deal with potential differences of soil physical properties in a quantified manner. This paper describes an attempt to measure soil physical properties, on paired fields of organic and conventionally managed soils taken from various locations in the UK, using soil aggregate stability, bulk density and organic matter as well as soil morphological analysis with the aid of image analysis, focusing on soil structure measured at different scales (meso (mm) and microscale (μm)). The results demonstrated that organic soil management can substantially improve soil structural condition, especially in terms of organic matter level, soil aggregate stability (ability of soil to resist breakdown by forces associated with cultivations) and soil pore characteristics, but that the effects might be both scale and time-dependent. At all sites we found a significant increase in soil pore measurements at the mesoscale associated with organic management. However, at the microscale, only the most recent conversion to organic farming (c. 5 years) had an enhanced pore network compared with conventionally managed soils, with the converse found for soil managed organically for 10 years or more. This suggests that long-term organic management could make soils more vulnerable to a reduction in the quality of the soil physical environment at a highly relevant scale for water and oxygen availability to plants.