You have to know both the output of your well system, and the demand of your sprinklers. Often, a system demands more than a well can deliver. The pump can supply enough flow, but the water level in the well can drop to the point where the pump is, and that is when the performance drops drastically.
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The above is for a deep well with a submersible pump. If you are operating from a well point, the same general principle applies. Water level too low, and performance is reduced.