The tiny soil charges that sustain humanity

Everybody knows, or rather should know, that soils sustain vegetation by providing not only physical support, but mainly by providing nutrients to plants. To build organic matter, besides carbon (which is provided by CO2 from the atmosphere), plants need inorganic nutrients, such as nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe) and some other elements taken up in smaller quantities. These elements originate in soil by the same process that forms soils: weathering.
Soils form from the chemical and physical weathering (decomposition) of rocks. When rocks weather physically, they simply break into smaller particles, without any mineralogical changes, but when rocks are chemically weathered, principally by CO2-rich water, newly formed (secondary) minerals appear by the chemical transformation of rock minerals or by the precipitation of dissolved elements. Some of these new minerals, generally belonging to the phyllosilicate mineral family, are very small and present peculiar features, such as exposed electrical charges.
Clays are the main bearers of charges in soil, although soil organic matter also exposes charges. The mineral nutrients in soils also have charges, for example, nitrogen is generally taken up by plants as NO3- (nitrate) or as NH4+ (ammonium). If these compounds are not held (adsorbed) by soil charges, they can be easily taken up by plants or washed away by infiltrating water from rainfall or irrigation. If all minerals could be washed (leached) by water, plants would “starve” and we would have no vegetation. That’s probably the most crucial importance of soil charges: they hold mineral nutrients and when soil solution is depleted of nutrients, they free (exchange) them, so that plants always have “food”. However, the supply of natural mineral nutrients is limited, and when too much is used or lost, man generally has to fertilize soils. Soil charges are also used to hold pollutants, like heavy metals and excess nitrate, and this is an important reason to maintain soils healthy.

Discussão - 1 comentário

  1. manuel disse:

    Dear Ítalo
    Another case to express my admiration to you. You do not forget the soil,when,now,it is the soiless culture your main tool,I suppose.
    Any how,you are right as you said,tiny soil charged particles are the active part,mineral and organic,the colloidal complex,where cations are adsorved,the main source of soluble cations,but in equilibrium,as you know ,with nonexchangeable cations,in clays or other minerals. The Ca,and Mg,as you know,can have other sources. In relation to anions,as nitrate,sulphate,phosphate,are other histories,as you know well.
    To finish,we can not forget the mycorrhizas,the soil microbes in general,because they are very important also to feed the plants,because they can do available elements,cations or anions,as you know well also.
    Again,my admiration,and my praise for presenting so fundamental matter.

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