Agriculture

Soil structure, between humus and porosity


Theresoil structureis of crucial importance in determining the "goodness of a soil". Most terrestrial plant organisms absorb water and mineral nutrients from theground through a root system.

Thesoilit is a heterogeneous and very complex system; there soil structure it is determined by processes of mechanical, physical and chemical alteration that have affected both the original rocks and the organic material of biological origin that has accumulated there over time. Theresoil structure it is, therefore, the result of the action of numerous biotic and abiotic factors (physical and chemical). Based on these factors, many types of soil originate, all different in physical structure and chemical characteristics.

In the article "How to recognize the types of soil" we talked about soft, medium and heavy soils; similarly, in the article on fertility related to the structure of the soil we described clayey, loamy and sandy soils. In the past we have given you a detailed description of the structure of clay soils. Today we talk about the stages of theground which go to determine itsstructureand porosity, or the percentage of empty spaces (in fact, pores), in a certain volume.

The porosity and the structure affect the ability to retain and release water and also the amount of oxygen circulating in the spaces between the different solid particles that make up aground.

Soil structure
After clarifying what determines thesoil structure, let's move on to the detailed description of different types of soil.

THElandwhich have high percentages of clay, whose particles have a diameter of less than 2 μm, are able to strongly retain water. Clayey soils, in fact, contain little oxygen, have a particular bacterial flora and overall expose the roots of the plant to a high risk of hypoxia.

On the contrary, isandy soilswhere the diameter of the sand grains varies from 50 to 2000 μm, they are generally well-ventilated but very draining soils, so the water easily percolates down where it can no longer be reached by the roots. In clayey soils, since the particles that make up the soil are more compact, the water is retained stably. In clayey soils with capillary-type pores and small spaces between the particles, the cohesion bonds between the water molecules and the adhesion of the water to the strongly extended surface of the soil particles, retain water, reducing the possibility that it flows towards the roots. In this context, the difference is made by clay minerals and the organic component modified in the course of complex transformation phenomena (humus).

Based on what has been said, it is clear that the quantitative relationships between the components of the soil are decisive in the formation of a structure optimal for the growth of plants which, however, have different adaptability to soils of various kinds.

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Video: Soil Structure Lecture (October 2020).