Which of the following is not compatible with drip irrigation?

In the context of drip irrigation, phosphorus is often considered less compatible compared to the other options listed because of its tendency to precipitate and form insoluble compounds, especially in the presence of calcium and iron that are commonly found in irrigation water. When phosphorus is applied through a drip system, it can lead to clogging of emitter outlets due to sedimentation and buildup of precipitates. This can compromise the efficiency of the irrigation system, resulting in uneven water distribution and reduced plant health.

In contrast, nitrogen and chlorine can often be effectively used within drip irrigation systems. Nitrogen, particularly in the form of soluble fertilizers, can dissolve easily in water and promote nutrient uptake without causing significant clogging. Chlorine, used as a disinfectant, helps in controlling pathogens and can be injected without the same risk of precipitating as phosphorus. Fungicides can also be used in drip irrigation, provided they are formulated for solubility and do not form residues that would affect emitter function.

Thus, phosphorus's compatibility issues make it a less favorable choice for use in drip irrigation systems compared to the others listed.