Soil friability: A review of the concept, assessment and effects of soil properties and management

This review gathers and synthesizes literature on soil friability produced during the last three decades. Soil friability is of vital importance for crop production and the impact of crop production on the environment. A friable soil is characterized by an ease of fragmentation of undesirably large aggregates/clods and a difficulty in fragmentation of minor aggregates into undesirable small elements. Soil friability has been assessed using qualitative field methods as well as quantitative field and laboratory methods at different scales of observation. The qualitative field methods are broadly used by scientists, advisors and farmers, whereas the quantitative laboratory methods demand specialized skills and more or less sophisticated equipment. Most methods address only one aspect of soil friability, i.e. either the strength of unconfined soil or the fragment size distribution after applying a stress. All methods have significant advantages and limitations. The use of a mixture of qualitative and quantitative methods to get a comprehensive and adequate assessment of soil friability is recommended. Poor friability can be experienced if soil is either too wet or too dry and there is a range in water contents for optimal friability. There is a strong need to get more detailed knowledge about effects of soil water content on soil friability and especially to be able to quantify the least limiting water range for soil friability and therefore soil tillage. A strong relationship between organic matter and friability has been found but it is not possible to identify a specific lower critical level of organic matter across soil types. Sustainable management of soil requires continuous and adequate inputs of organic matter to sustain or improve soil friability. Intensive tillage and traffic in unfavorable conditions threatens soil friability and may initiate a vicious cycle where increasingly higher intensity of tillage is needed to produce a proper seedbed.