Development of the “mini 3D soil profile” – A visual method derived from the “profil cultural”

Abstract

Quick and reliable field methods are needed to assess soil structure quality. This is especially true in cropping systems with high proportions of sugar beet, potato and vegetables crops, where the risk of soil and subsoil compaction is high. Visual field methods are a priori well adapted to meeting these needs. These include spade methods and soil profile methods. Spade methods are easy to implement but are mainly used to evaluate topsoil structure quality. The “profil cultural” method allows more detailed structural assessment, particularly in depth, but it requires more training, is time consuming and strongly disturbing for the soil. The proposed method, called "mini3D soil profile", is an intermediate method between spade methods and “profil cultural”: the sampling method is similar to the spade method and the description of morphological units by mapping the structural state on a vertical face is similar to the “profil cultural” method. It consists of taking a soil block with the pallets of a telescopic loader, and assessing soil structure on the vertical face using criteria similar to those of the “profil cultural” method. A study was carried out to test whether (i) extraction and lifting of the soil block did not modify the soil structure and (ii) whether the method produces the same soil structure assessment as that produced by the “profil cultural”. Results show that, despite the extraction and lifting by the loader, the method allows a good characterization of the soil structure by mapping the morphological units on a vertical face. The two methods produced very similar results in the evaluation of soil structure. The correlation between the areas having a massive structure and no visible macropores (percentage of Δ areas) assessed with the “mini3D soil profile” and the areas assessed with the “profil cultural” method was significant (R-squared = 0.79). Similarly, the correlation of the percentage of Φ areas with the presence of cracks was also significant (R-squared = 0.81). Comparing the soil structure assessment in eight fields, the main differences are due to the spatial variability of soil structure within the plot, depending on the location of the soil profiles. In conclusion the method is well adapted to identify the effects of tillage and compaction on soil structure dynamics. Easier to implement than the “profil cultural” method, the "mini3D soil profile" method is an original method to promote the evaluation of soil structure and thus decision-making by advisers and farmers.