Tóm tắt
The variations in the layer thickness of a Vertisol cropped with sugarcane
were recorded under natural conditions for several months. Drainage pipes were
installed at 1.10 m depth to drain water quickly from macro-cracks. The soil
gravimetric water content was measured from the surface to 1.10 m depth at
weekly intervals. The relation between soil water content and soil bulk
specific volume (shrinkage curve) is not unique. A significant structural
swelling or shrinkage can occur at any water content of the clay matrix while
the macro-cracks remain air-filled. The variations in structural water content
account for >60% and 80% of the total water content
variations, respectively, in topsoil and subsoil. In the latter, the
intra-prism structural porosity is filled and then emptied prior to matric
porosity. This explains the disappearance of the water stress in such dry soil
after any rainfall event. A more detailed description of the intra-prism
structural porosity is required for a better understanding of the processes.
Our work suggests that this porosity is mainly formed by planar
inter-aggregate voids in the tilled layers, whereas its shape is tubular in
the deeper layers. The results already provide guidelines concerning the
modelling of water flow in such Vertisol, i.e. water flow in structural pores
is quite independent of matric and crack flows.
