15. Microsprinkler irrigation

Abstract

Micro-sprinkler systems are primarily used to irrigate tree and vine crops. The system designs are similar to other micro-irrigation systems, but micro-sprinkler systems generally tend to require a higher flowrate per unit area. Typically micro-sprinkler installations have one 40 to75 L/h flowrate emitter per tree. The most common (spray) emitters have slotted caps or deflector plates that distribute water in distinct streams. Other designs (spinners) have a moving part that rotates to disperse the water stream more uniformly over the wetted diameter. During the design stage, long-term maintenance costs should be included in the economic analysis. The emitter selection process should consider uniformity as well as other factors, such as cost, wind effects, system constraints, maintenance, and soil type, such that the best emitter for a particular field condition is selected. Micro-sprinkler systems should be capable of applying the maximum crop water need plus any application inefficiency. The emitters should have a coverage area sufficient to allow this volume of water to be stored in the soil without causing unintentional deep percolation. Emitters should also have a sufficient application rate in the wetted area, such that the required run times are compatible with the power unit and labor availability. High application rates can lead to leaching of nutrients and pesticides. By adjusting spray diameter, irrigation duration, and emitter flowrate, systems can be managed to meet tree water needs, while minimizing over-irrigation and chemical leaching.