Know Your Irrigation Water

Irrigation water analysis focuses on the impacts that irrigation water may have on the soil. The repeated application of irrigation water can change the chemical and physical properties of the soil over time. Therefore, the interpretation of data from irrigation water analysis is driven by the prediction of the effects of the irrigation water source on the soil.

The chemical properties of irrigation water drawn from a well is greatly influenced by the bedrock type surrounding the aquifer, as well as the composition of the aquifer itself. For example, an irrigation well drawing water from a limestone bedrock high in calcium will most likely have a high pH, high calcium content, will be high in carbonates, and contain elevated dissolved solids. However, not all limestone is the same. Also, there can be different layers within the bedrock leading to differences in irrigation water quality with the depth of the well.

Good long-term management of irrigated land needs to take irrigation water quality into consideration. The repeated use of irrigation water with a high concentration of a specific element or compound can lead to accumulations and potentially excess levels of that element or compound in the soil. Depending on the specific material, this could lead to reduced plant health and/or yield over time.  For example, the repeated application of irrigation water with high calcium carbonates without acid injection treatment can lead to plugging of irrigation equipment and the continual increase in soil pH over time.  The increasing soil pH, if left unmanaged, could become high enough to limit the availability of plant nutrients, as well as lead to other negative management challenges. This is of greater concern if the same bedrock influenced the formation of the soil. In this example, the soil would also be inherently higher in carbonates and have a higher pH before additional calcium carbonates are added to the soil through the irrigation water.  

For sound management of irrigated land, irrigation water analysis is a crucial tool to identify possible issues associated with the irrigation water source, and to define proper techniques to mitigate those issues. However, proper management also requires routine soil testing to monitor the impact irrigation water has on the soil over time to ensure the overall irrigation water management is working.