Morphological characterisation of soil structure in tilled fields: from a diagnosis method to the modelling of structural changes over time

• Published in: Soil & tillage research Vol. 79; no. 1; pp. 33 - 49
• Main Authors: Roger-Estrade, J., Richard, G., Caneill, J., Boizard, H., Coquet, Y., Defossez, P., Manichon, H.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01-09-2004; Elsevier
• Subjects: Agricultural sciences; agricultural soils; Agronomy. Soil science and plant productions; Biological and medical sciences; Compaction; Cropping system; cropping systems; Cropping systems. Cultivation. Soil tillage; cultivated soils; field diagnosis; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; infiltration (hydrology); Life Sciences; Modelling; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; plowing; soil compaction; soil morphology; soil physical properties; Soil science; Soil structure; Soil study; Soil survey; Soil surveys, classification and mapping; Soil surveys, classification and mapping, soil genesis; Soil tillage; spatial variation; Structure, texture, density, mechanical behavior. Heat and gas exchanges; temporal variation; Tillage; Tillage. Tending. Growth control; Visual examination of soil structure; France; Soil survey; Tillage; Cropping system; Soil structure; Visual examination of soil structure; Modelling; Compaction; Physical properties; Soil tillage; Cultivated soil; Visual observation; Soil investigation; Soil morphological features; Modeling; Structure modification; Soil science; AGRONOMIE
• ISSN: 0167-1987; 1879-3444
• DOI: 10.1016/j.still.2004.03.009

Characterisation of soil structure within the tilled layer of cultivated fields is crucial because the importance of this soil characteristic on the biological, chemical and physical properties of the soil and its repercussions on water cycle, root growth and functioning. We present in this paper a method for field characterisation of soil structure. This method, practised since the 1970s, was designed for field diagnosis of the effects of cropping systems on soil structure. It is based on a stratification of the observation face of a pit dug perpendicular to the direction of tillage and traffic: spatial compartments are distinguished, according to the nature of the mechanical stresses they have been submitted to during tillage and crop management. Characterisation of soil structure is performed on a morphological basis, using two criteria, each of them addressing a specific organisation level of the soil: firstly, clods size distribution, proportion of fine soil and the way the clods are brought together are considered; then, secondly, the clods are classified in three types, on the basis of the importance and the origin of their internal structural porosity. Physical measurements (bulk density, compaction test, and water retention) are presented, which demonstrate that physical behaviour is different between clod types. These results justify the use of the method to model changes with time in soil structure, under the effects of the main factors affecting soil structure dynamics in tilled fields: compaction, fragmentation, climate and biological activity. A model which simulates at the field scale the changes over time of the proportion of compacted clods within the tilled layer is presented. In this model, the tilled layer is represented as a set of 1
cm
2 pixels, regularly located on a square grid. Each pixel is defined by its co-ordinates and a specific structure, compacted or non compacted. The pixel co-ordinates are modified during ploughing, for which the model calculates the lateral and vertical displacement of the soil. The structure of any individual pixel can be changed, depending on the soil condition and the operation type. This model was evaluated by comparing its outcomes to measurements obtained from a long term field experiment designed to study soil structure dynamics.