Micro-irrigation systems come with many advantages over other types of irrigation. When using such as system, deliver of water and nutrients to the root zone is more uniform and runoff is prevented. In addition, weed population is better controlled and the less humid environment helps better control pests and diseases.





Sub-surface irrigation presents some additional advantages. Drip emitters are protected, and runoff and evaporation are minimized, increasing irrigation efficiency even more. Nevertheless, micro-irrigation systems should be properly planned and managed in order to fully benefit from these advantages.

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One of the main challenges is keeping drip emitters free from clogging, causes of which are categorized into biological, physical and chemical types of debris. It is useful to differentiate between surface water and ground water because different water sources carry different plugging hazards.





Physical Causes of Emitter Clogging in Drip Irrigation





The most common physical causes of clogging of drip emitters are sand particles, which are usually found in surface water. Other suspended solids might be too large to pass through the emitter's opening and might clog it. Under certain conditions, silt-sized particles can form larger aggregates that might cause clogging.

Turbidity is often used as an estimate of the suspended solids, but is not an accurate indicator of the water's clogging potential. An adequate filtration system, designed based on the quality of the water, can prevent physical plugging of drip systems.













Biological Causes of Emitter Clogging in Drip Irrigation





Drip irrigation systems provide a favorable environment for bacteria, fungi and algae that can cause slime accumulation. Bacterial slime can be a direct cause for clogging of drippers, but it can also induce mineral particles to stick together and form aggregates large enough to clog the emitter openings. This phenomenon is specifically significant when manganese, sulfide and iron are present in the water.





Depending on the type of bacteria responsible for the slime, its color might be reddish, yellowish or grayish. Clogging due to micro-organisms is common when using water with high biological activity, relatively high iron or manganese levels and hydrogen sulfide compounds. Proper chlorination and disinfection procedures are the key to controlling biological clogging of drip irrigation systems.





Chemical Causes of Emitter Clogging in Drip Irrigation





The word chemical denotes mineral precipitation, which might form when minerals solubility is low enough. Solubility of a given mineral is dependent on the water temperature, its pH, redox potential and the concentration of the mineral elements present in the water.

The common elements that might clog drip emitters by precipitation and sedimentation are calcium, magnesium, iron and manganese, with calcium carbonate being the most common precipitate. Water that contains high levels of these elements, and has a pH above 7.0, might also potentially cause clogging of drip emitters.





Adding fertilizers to source water (known as fertigation) can potentially cause clogging of drip emitters due to chemical interactions and high mineral concentrations, exceeding their solubility limit. Therefore, it is advised to perform a jar test, or use appropriate computer software, to determine if a specific combination of fertilizers might result in precipitation. Acid injection to reduce irrigation water pH can prevent chemical clogging of drip emitters.





Generally speaking, surface water carries more biological and physical clogging agents, while ground water is usually characterized by higher mineral concentration, posing a chemical clogging hazard. To avoid clogging of drip emitters, it is advised to follow this checklist:





Test source water and irrigation water for the three types of clogging causes

Filter large particles or aggregates, such as sand and clay, before letting the water enter the emitters

Eliminate micro-organisms by proper disinfection and water treatment

Prevent sedimentation of chemicals in the irrigation system by adjusting pH levels, monitoring solubility limits of fertilizers and avoiding chemical interactions between fertilizers

Maintain the irrigation lines and emitters by periodic flushing





Consult the table provided to assess the clogging potential of drip emitters.





Constituent Level of Concern

Low Moderate High pH < 7.0 7.0 to 8.0 > 8.0 Iron (Fe) mg/L < 0.2 0.2 to 1.5 > 1.5 Manganese (Mn) mg/L < 0.1 0.1 to 1.5 > 1.5 Hydrogen Sulfide (H 2 S) mg/L < 0.2 0.2 to 2.0 > 2.0 Total Dissolved Solids (TDS) mg/L < 500 500 to 2000 > 2,000 Total Suspended Solids (TSS) mg/L < 50 50 to 100 > 100 Bacteria Count (#/ml) < 10,000 10,000 to 50,000 > 50,000





In Summary





Clogging of drip emitters is a common problem with significant production and cost consequences. Fortunately, the problem can be easily avoided by testing the raw water as well as the irrigation water (particularly after fertilizers are added). The analysis of the biological, chemical and particles content of the water plays a major role in choosing appropriate prevention measures.