For a soil to provide the most desirable hydraulic and mechanical properties as an ideal medium for crop production, it is necessary that all of the different hierarchical orders of its solid-phase components be well developed and stable against the action of water and external mechanical stresses. According to Dexter , to accommodate almost all of the different soil aspects affecting a soil's capability to provide an ideal medium for crop production, it is convenient to widen the definition of soil structure to the "spatial heterogeneity of the different components or properties of the soil." Such a definition accommodates many aspects of the soil that manifest themselves at different scales and their variable distribution in time and space (soil anisotrophy).
Synthetically, Dexter considers soil structure as the spatial variability of its components and lists a number of soil features with different dimentions (Fig. 4.8). It follows that structure, in the broad sense outlined above, is the most important feature of a soil in relation to plant growth and crop production. Consequently, soil degradation can be envisaged as the consequence of any process or human action negatively influencing soil structure. Conversely, soil regeneration is the result of any natural process and/or human action capable of recovering soil structure from a deteriorated condition and possibly aimed at an improvement of soil structure by ameliorative measures.
The main factors involved in the physical degradation of a soil, in the short and medium term, are
• microstructure degradation, and
Such processes (alone and/or in combination) depend on many factors that are discussed later and are responsible not only for reducing the suitability of a soil for plant growth and
Co mpound particles
Biota clay I silt | sand \ gravel \ rocks domains \clusters\micro \ aggregates| clods aggregates micropores | mesopores \ macropores -
I root i I hairs I
moles, bacterial\ fungal byphae \ r oots\worms\ gophers, etc.
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