Factors affecting the selection of an irrigation system

                                                                                      

  

• Effect of land slope, The slope of the target land may determine the type of irrigation to use .If the land is level or can be  made level without  too much expenses any of the four methods can be applied. If sloping land is irrigated, the method applied  is limited to sprinkler or trickle method. Although some types  of surface and below surface irrigation systems can also be used on sloping land, most of these systems require land leveling  or benching.                                          
• Effect of water intake rate, The intake rate of the soil of the target  area must be known to determine the maximum  rate at which irrigation is applied so that puddling and surface runoff will not occur. Several conditions affect the intake rate of the soil. Two of the more important ones are texture and surface sealing due to compaction and salts. The larger the soil particles and the further  apart they are,the faster is the intake rate. For low water intake rate (13 millimeters per hour or less), the sprinkler, surface or trickle method is applied.                                                                                                                                                                                For a high water intake rate (76 millimeters per hour or more) theapplicable irrigation method  is limited to the sprinkler, trickle or subsurface method. With high intake rates it is usually impractical to try using water by surface methods. Too much water is absorbed at  the head of the irrigated area and not  enough water is delivered to the opposite or lower end. Although this condition in surface irrigation methods can be corrected by shortening the length of run, the length of run may be too short to be practical. For a moderate water intake  rate( 13 to 76mm/hr) any of the four methods can be applied.                                                                                                             
•  Effect of water tolerance of crop, Crops that cannot tolerate having their roots stand under water for several hours, the surface method may not be applicable. The reason is that with some types of surface systems and soil conditions, the water  must remain on the field for several hours (2-24 hours) depending on the soil intake rates)before it can  penetrate into the root zone.  At this time, the plants may become damaged. Root diseases are more likely to occur with surface irrigation systems than with sprinkler systems. The surface method is applied for weed control with  flow  water on crops such as rice.                                                                                                                                                                                                  However, the surface methods  may affect  seedlings of some crops. Light seeds may  flock together unless they have established a root system. Crops that are likely to develop fungi or disease under high moisture conditions may have application difficulty with sprinkler method. The presence of water around the leaves due to sprinker irrigation tends to spread some diseases. However this is seldom a serious problem. Since the below surface method of applying water supplies very little moisture to the surface of the ground, this helps reduce weed growth. However it may slow down germination of shallow planted seeds.                                    
• Effect of wind action, Wind action may affect  the water application efficiency of the sprinkler and surface methods. Strong wind action will distort the water distribution pattern of the sprinkler to the extent that very little water on the windward side( direction from which the wind is blowing) and too much water on the other side may be obtained. This affection of the distribution pattern occurs whether the application rate is high or low. High winds will sometimes affect the application efficiency of surface irrigation.                                                   
• Water quality and availability, Water quality and availability affect the selection of irrigation to be used . Where water is in  short supply drip and sprinkler irrigation methods are recommended   as they utilize water efficiently, but they require initial high investigations. Water containing  high sediments is not suitable for drip and sprinkler irrigation methods as may clog their systems. Water containing dissolved salts, it is advisable to use drip method.        
• Other factors, Other factors that affect the choice of irrigation method include  type of crops to be grown, the type of technology, the costs and availability of labour. For example, high valued crops can justify the use of more sophisticated methods like drip and sprinkler methods. Surface methods are more suitable to smallholder farmer  managed schemes as they are less sophisticated and require minimum skills to operate them