How often and when should one measure the EC and SAR of irrigation water?
The timing and frequency of measuring the EC and SAR of irrigation water really depend on the flow and cycle of the water source. If the water source is constant (such as a well, lake, pond, or large river), the water should be tested at a minimum during the lowest flow volume when water is to be used for irrigation and at the beginning of the irrigation season. If the source is a cyclic stream or river, the water should be tested any time flow has been low and stable for a long period of time. The best rule of thumb is to measure when flow is representative of irrigation water or when there has been a significant change in flow.
