Water and agriculture

Agricultural use of water to irrigate fields represents the main form of consumption of global hydric resources and involves two thirds of global availability of fresh water. Water is not evenly distributed on our planet, hence, very often, human intervention is necessary to modify the natural flows of rivers and build artificial canals to bring water where it’s needed. Hydric requirements in agriculture depend on numerous factors among which are climate, soil characteristics, crop practices, irrigation methods, type of farming and many others.
For example, intensive agriculture practised today in the world, which maximizes productivity of lands, requires much more water in comparison to traditional agriculture as also the amount of water required to irrigate fields in dry and semi-dry areas is substantially higher than the amount used in temperate areas.
Irrigation processes, especially in dry areas, can cause soil salinization, which means that they can elicit progressive increase of salts that over time prevent the use and destroy potential productivity of lands. This occurs when insufficient drainage of soil and strong evaporation of irrigated areas take place: this means that water which the soil isn’t capable of absorbing evaporates immediately and leaves in the soil its mineral content. It’s for this phenomenon that crops in dry or semi-dry areas of the planet have been suffering a productivity decrease in the last decades: it is estimated that 20-30 million hectares of the 270 million hectares of total irrigated areas are suffering salinization.
Crops that grow in salinized soils undergo nutritional imbalances and for this reason require the use of greater energy and substances to grow at the same pace of plants grown in normal conditions.
Only some cultivated species present high tolerance to salinity, among these, beetroot, barley, asparagus, spinach. For the main crops it’s necessary to contain this phenomenon, which means lowering the excess of water that penetrates in the soil and, hence, irrigating according to the actual need of crops, not in excess as, especially in areas where natural drainage is lacking, this could determine an increase in the level of groundwater that makes subterranean water rise to the surface.
Generally, it’s important to use crop and processing systems that don’t deplete organic substance from the soil (as this improves salt catching and increases soil permeability) and it’ s useful favouring crops that use at its best available water in the soil, maybe with roots capable of extracting water in excess in deeper layers. Perennial crops and fodder plants, especially alfalfa, are useful for this, even because they have a long growing season and remove, in comparison to annual crops, more water deeper in the soil.
Fodder plants can also increase the content of organic substance and improve the structure of the soil.
Also subterranean water coming from acquifers can face salinization, for example, due to excessive extractions undertaken by humans to satisfy the growing request of potable water for domestic uses.

Special reports

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