About irrigation...

As you well know, the irrigation is the application of controlled amounts of water to plants. Irrigation is useful from many points of view. It helps to maintain landscapes and grow agricultural crops. But in the most recurrent cases, it revegetate disturbed soils in dry areas and during periods of less than average rainfall (humectant irrigation), when natural water supplies and stored reserves are insufficient.

Background
Irrigation is a very ancient practice, just think of the Egyptians and even before of the Indus valley civilization (4500 BC). 
The noria (a water wheel with clay pots around the rim powered by the flow of the stream or by animals where the water source was still), was first brought into use at about this time by Roman settlers in North Africa. 
During the Middle Ages, the Arabs played a fundamental role. Thanks to them, in fact, irrigation took off in the Mediterranean, especially in Andalusia and Sicily.

Today there are several methods of irrigation.

• Surface irrigation
• Micro-irrigation
• Drip irrigation
• Sprinkler irrigation
• Circle irrigation
• Irrigation by lateral move (side roll, wheel line, wheelmove)
• Subirrigation

Regarding the types of irrigation aimed at increasing yield: 
They are the most ancient techniques, based on the contribution of water to reintegrate the plants that not received water by atmospheric phenomena.

1) Normal
Daily and regular irrigation with crop requirements.

2)Emergency
Done to a ground when there are climatic conditions not foreseen such as to jeopardize the yield of the crop in progress

3)Auxiliary
The difference between the auxiliary irrigation and the relief (or emergency) irrigation is that in the emergency irrigation the climatic conditions that affect the yield of the crop are not provided, while in the auxiliary irrigation it is already known when the crop will have difficulties (ex. months of drought), and then water is supplied to the ground to help it.

4)Flushing irrigation aimed at growing non-native crops
Irrigation, evolving over the course of history, has allowed the cultivation of native species of climates different from that of the land considered, which otherwise would not allow their growth.

5)Thermal
The water is able to accumulate large amounts of heat: using this property it is possible to heat the plants, as in the case of a rice field or a rattling lawn.

6)Air conditioning or anti-fog
By exploiting the heat released with the solidification of the water, the vegetative organs (in particular the buds) are kept at a temperature higher than the air, greatly limiting the damage from frost.

7)Subsidiary
In order to integrate and assist the effect of a treatment to the soil, such as spreading a herbicide or to facilitate the execution of a processing.

8)Pigmentation
Irrigation that is practiced, for commercial needs, in order to cause the color change of fruit or vegetables

 

For each of the crops grown on an irrigation scheme the crop water need is determined, usually on a monthly basis; the crop water need is expressed in mm water layer per time unit.

In general, the water consumption of crops depends essentially on three elements:

 

1)the climatic conditions;

2)the degree of development of the crop and of land cover;

3)the dynamic evolution of soil moisture content.

A widespread methodology for assessing the maximum irrigation needs of the crops is based on the calculation of the product between the reference evapotranspiration ET0, which depends on the climatic conditions, and a culture coefficient kc which represents a measure of the vegetative development of a specific crop in different phenological phases.

 

Knowing the rainfall Pn net of the quantity of water intercepted by the foliar system, the maximum irrigation requirement (Irr) is therefore defined as follows: