If you have to irrigate it pays to understand what is in your water. Unless you are using rain water or your water source is mainly snowmelt, there is a good chance you have a host of soluble minerals and compounds you are putting in your soil along with the needed irrigation. In some cases these dissolved minerals can cause problems for your soil and plants.
People in arid regions like the American West should be especially concerned about the quality of their irrigation water. Water from big irrigation projects can be high pH and full of dissolved minerals (I’m looking at you, California!) and water from wells can be even worse. In arid regions a lot of water is lost to the atmosphere by evapotranspiration from plants as well as evaporation from the soil surface. This leaves behind whatever was dissolved in the water, causing it to build up in the soil. Rain can wash these minerals down and out of the root zone but that’s only if it rains.
Even if you are using municipal water, but especially if you are on a well, it pays to get a water test. Logan Labs offers a standard water test and an extended test for irrigation water suitability.
As with all tests, the real question is how to interpret them. We have gone through the water test terminology in detail and have written an explanation of how to interpret a water test report.
High amounts of dissolved minerals or “salts” as they are referred to (“salts” are not just sodium and chloride) can limit the growth and germination rate of certain plants. Water can deliver substantial amounts of necessary elements like calcium and magnesium as well.
Of particular interest is the level of bicarbonates in the water. These can interfere with the availability of nutrients to the plant and can even block utilization of iron in the plant. Bicarbonates in conjunction with calcium will create deposits of calcium carbonate, lime, and plug drip emitters. It can leave a white residue on fruits and veggies that consumers may think is pesticide residue. We have a big article about removing bicarbonates from water organically.
We think that it’s a good idea to evaluate your soil with three tests at the same time:
- A standard soil test, either M3 or AA8.2, depending on whether your soil is fizzy or not. This will tell you the soil minerals you have in reserve.
- A saturated paste test, using your irrigation water as the solvent. This will tell you what your plants are drinking.
- An irrigation water test. This will tell you what minerals are being contributed by your irrigation water and whether any of them are a problem.