Ability of the “profil cultural” method to assess the soil structure of untilled layers

Abstract

In France, agronomists have studied the effects of cropping systems on soil structure, using a field method based on a morphological description of soil structure. The “profil cultural” method (Manichon and Gautronneau, 1987) has been set up to perform a field diagnostic of the effects of tillage and compaction on soil structure. However, this method was developed and mainly used in conventional tillage systems, with ploughing. As several forms of reduced, minimum and no tillage systems are expanding in many parts of the world, it is necessary to re evaluate the ability of this method to describe an interpret soil macrostructure in unploughed situations.

In unploughed fields, soil structure dynamics of untilled layers is mainly driven by compaction and regeneration by natural agents. Amongst them the role of climate and earthworms is essential and it is of major importance to appreciate the natural processes of soil structure regeneration. The “profil cultural” method is based on a visual observation of the macroscopic structure of different zones in the top part of the soil profile. Therefore, the method must be able to take into account the change in soil properties due to the presence of cracks and macropores. The objective of this presentation is to review the ability of the morphological method to describe the structure of untilled layers. Complementary indicators of biological macropores and cracking are proposed to complete the previous description.