Chemistry Reference
In-Depth Information
Soils most obviously contribute to food security in their essential role in crop
and fodder production, thereby markedly influencing the availability of food.
The inherent properties of different soils have marked effects on crop
productivity (see, for example, the writings of Cato and Pliny the Elder) and,
while interventions to improve fertility can over-ride these properties, some
soils are inherently more fertile and productive than others.
4,5
However, soils
also have a direct influence on the ability to distribute food, the nutritional
value of some foods and, in some societies, the access to certain foods through
local processes of allocation and preferences. An obvious, if slightly extreme,
example of the influence of soils on the ability to distribute food is seen in the
behaviour of soils containing large amounts of swelling and shrinking clays
(vertisols). These soils are frequently inherently fertile but are often very wet or
waterlogged in one season making it impossible to harvest crops or to move
easily across their surface, while in the dry season the shrinking of the soil
induces large cracks so that engineered structures such as houses and irrigation
ditches fail. The combination of shrinkage in the dry season followed by
considerable swelling in the wet season means that roads are also difficult to
sustain and the distribution of food can be affected.
6,7
The nutritional value of many foods is markedly influenced by the soils on
which they are grown, although processed foods are often supplemented with
essential minerals and vitamins to make good any deficiencies. Crop
production depends on the availability of sufficient quantities of the 14
essential mineral elements required for plant growth and reproduction.
8
These
essential nutrients include the macronutrients required in large amounts by
plants (nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium
(Mg) and sulfur (S)) and the micronutrients (boron (B), chlorine (Cl), copper
(Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc
(Zn)) which are required in smaller amounts.
8,9
Deficiency in any one of these
elements restricts plant growth and reduces crop yields, so that they are often
applied to crops as inorganic or organic fertilisers to increase crop production
9
.
Humans require many more mineral elements for their wellbeing than plants.
10-12
In addition to the 14 elements essential for plants, humans also require significant
amounts of cobalt (Co), iodine (I), selenium (Se) and sodium (Na) in their diet
and, possibly, small amounts of arsenic (As), chromium (Cr), fluorine (F), lead
(Pb), lithium (Li), silicon (Si) and vanadium (V). The majority of these mineral
elements are supplied to humans by plants.
Unfortunately, the diets of over two-thirds of the world's population lack
one or more of these essential mineral elements,
13,14
with over 60% being Fe-
deficient, over 30% Zn-deficient, almost 30% I-deficient, and about 15% Se-
deficient. Dietary deficiencies of Ca, Cu and Mg are also prevalent in many
countries. This mineral malnutrition is attributable to either crop production
on soils with low phytoavailability of the mineral elements essential to human
nutrition, or consumption of staple crops, such as cereals, or phloem-fed
tissues,
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such
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