Cloud seeding is not conducted by passenger jets. Clouds don't need 'seeds' to form.
Cloud  seeding is the introduction of insoluble salts (typically silver iodide) into clouds to prevent the formation of hail, and to cause rain instead.
There is no proof it even works.
Such aircraft are propeller driven, capable of carrying a hopper full of the chemical to be used, and since it is expensive, it is used sparingly and in only localized areas within the cloud itself.
In other words, you will never see a cloud seeding aircraft in the act, since they are in the cloud while dispersing the chemical.
Other aircraft are used to disperse fertilizer or insecticide over fields. These fly at extremely low altitude, and effect only the fields they are hired to treat. Again, they are propeller driven aircraft.