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Brief review of aspects related to irrigation effectiveness

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Miguel Ángel Monge Redondo
Technical Agricultural Engineer by the UPM. Author of the books: Diseño agronómico e hidráulico de riegos agrícolas a presión.

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  • Brief review of aspects related to irrigation effectiveness

Drip irrigation, whether surface or subsurface, is the one system out of the different ones available that saves more water and consumes less energy. Because it is a more precise system, it is also more sensitive to errors and deviations, both in the design and in the operation phases; this could have a significant influence on the system's ability to deliver water uniformly, more so than in other systems. The design phase should be carefully planned, because once the system has been installed, corrections are difficult and costly to implement. I would also note the sensitivity to blockage and higher requirements in regard to filtration; drip irrigation allows the incorporation and distribution of dissolved nutrients in the irrigation water effectively and quickly, and the possibility of using water with a high content of dissolved salts.

In sprinkler irrigation systems, uniform water application is not so much of a concern as in drip irrigation, because the entire land surface becomes wet. One drawback, however, is the effect of wind, and the distortion it may cause in the distribution of water over the parcel — in pivots, sides, and sprinkler lines — although when irrigation takes place as a block (several groups of sprinklers at the same time), the distortion could even out through time. On the other hand, one limitation of this irrigation system is the use of saline water. Sprinkler systems are suitable to apply phytosanitary and nutritional products because they wet the entire plant.

Gravity or surface irrigation is the type that consumes most water, and handling is not very well controlled; it has greater water losses due to deep percolation. Although this could serve as groundwater recharge, obviously the resource is not efficiently used. In economic terms, it requires the least investment.

The surface area using surface irrigation has dropped considerably, being transformed into pressure irrigation, mostly drip irrigation

Thanks to the modernisation of irrigation in the past decades and the huge efforts of farmers, irrigation associations, and the funding support from national and regional authorities for transformation projects, the surface area using surface irrigation has dropped considerably, being transformed into pressure irrigation, mostly drip irrigation. Currently, out of the almost 3,650,000 hectares of irrigated land in Spain, more than half use drip irrigation.

When it is not possible to secure enough water for irrigation from rivers and reservoirs, we have turned to groundwater sources, using wells. If water withdrawal exceeds recharge, water will be gradually found at greater depths, and this entails, aside from environmental problems, some serious drawbacks for irrigation farmers:

  • You need more energy to extract water, because the pumping height increases. Therefore, the costs per year increase.
  • A lower groundwater level leads to higher salinity, because salts dissolve in a smaller volume of water, therefore their concentration is higher. This can cause lower crop yields in the case of crops that are less tolerant to excess salt, and a higher investment in products to correct that.
  • Moreover, drip irrigation systems will require higher maintenance to prevent the blockage of emitters due to the salts dissolved in the water.
  • The suspended particle content (silt, clay and sand) also increases, so the filtration needs are higher, particularly for drip irrigation. Moreover, these particles cause faster pump wear and tear; therefore, the depreciation costs of equipment are higher and so are maintenance costs.

Finally, the next leap in irrigation technification in Spain is focusing on the monitoring and control of physical and chemical variables in the water, the soil and the plants.

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