Irrigation methods - Scheduling of Irrigation and Fertilizers, Crop Production | Crop Production Notes- Agricultural Engineering PDF Download

Once the quantitative and temporal characteristics of optimal water demand have been determined, a method that can make such water available in the most effective way should be selected. There are three main irrigation methods, namely: 

• Surface (or gravity) irrigation 
• Sprinkler irrigation 
• Drip irrigation.

These methods, and their respective advantages and disadvantages are summarized.

Surface irrigation Surface irrigation involves the application of water by gravity flow to the surface of the field. Surface irrigation can have different forms. In basin irrigation, the whole field is flooded with water. Alternatively, furrow or border irrigation can be used where water can be fed into small channels or strips of land. Surface irrigation is the easiest and least costly method, but is usually highly inefficient – only less than 10% of the water is taken up by the plant. Unfortunately, this is also the widely most used method in the Arab region.

Sprinkler irrigation Sprinkler irrigation systems imitate natural rainfall. Water is pumped through pipes and then sprayed onto the crops through rotating sprinkler heads. These systems are more efficient than surface irrigation, however, they are more costly to install and operate because of the need for pressurized water. Conventional sprinkler systems spray the water into the air, losing considerable amounts to evaporation. Low energy precision application (LEPA) offers a more efficient alternative. In this system the water is delivered to the crops from drop tubes that extend from the sprinkler's arm. When applied together with appropriate water-saving farming techniques, LEPA can achieve efficiencies as high as 95%. Since this method operates at low pressure, it also saves as much as 20 to 50% in energy costs compared with conventional systems. 

Different sprinkler irrigation systems − conventional (left) and low energy precision (right) systems.

Drip irrigation Drip irrigation delivers water through the use of pressurized pipes and drippers that run close to the plants and that can be placed on the soil surface or below ground. This method is highly efficient because only the immediate root zone of each plant is wetted. This system also allows precise application of water-soluble fertilizers and other agricultural chemicals. Drip irrigation is reported to help achieve yield gains of up to 100%, water savings of up to 40-80%, and associated fertilizer, pesticide, and labor savings over conventional irrigation systems.7 Drip irrigation systems can have different levels of sophistication and costs. Drip irrigation systems that are operated by solar-driven pumps are a particularly promising alternative for the MENA region. Figure 5.1 shows a layout of a drip irrigation system. 

Figure 5.1: Drip Irrigation System (Wikimedia – Courtesy of Jain Irrigation)

The variations in soil moisture content usually achieved with different irrigation methods are depicted in Figure 5.2.

Figure 5.2: Comparision of different irrigation systems

With the exception of Saudi Arabia and the United Arab Emirates (UAE), surface irrigation is predominantly used in more than 90% of irrigated agricultural land in the MENA region_.⁹

SOIL ENHANCEMENT MEASURES In addition to the inherent efficiencies of different irrigation methods, a number of additional soil enhancement approaches can be considered to improve the efficiency of irrigation practices.

Proper field leveling, in order to allow the water to travel in an optimum speed, is an approach that assists uniform distribution of water and reduces runoff, particularly in surface and sprinkler irrigation. Furrow diking, which allows the capture of irrigation or precipitation water in small earthen dams within furrows, is another approach that can reduce runoff and increase the effectiveness of irrigation.

Further water savings can be achieved through residue management and conservation tillage, where the amount, orientation, and distribution of crop and plant residue on the soil surface are managed. These practices improve the ability of the soil to hold moisture, reduces water run-off from the field, and reduces surface evaporation. Because conservation tillage can cause disturbances in furrow irrigation systems, they are better suited for fields using sprinkler or drip irrigation.

Further efficiency gains are possible through appropriate measures in water distribution systems. Where water is delivered to fields by canals, for example, lining of the canal surface – by compacted clay or concrete – can drastically reduce water seepage. Covering the canals or putting them underground can further decrease evaporation losses.