Water sampling

Good sampling techniques essential for accurate water analysis

Irrigation decisions when it comes to water quality are only as good as the accuracy of the samples taken

(Exclusive to Western Farm Press))

With the irrigation season in full swing, this is a good time to sample irrigation water for a laboratory analysis to see what it contains. After all, water is our No. 1 applied input. Sampling is easy, but there are a few steps that should not be overlooked to ensure accurate lab results. 

In general, most agricultural laboratories will provide the appropriate water bottles to use in collecting and submitting water samples. This is important to ensure the water sample is not cross-contaminated with residual liquid in, for instance, a soda bottle or sports drink bottle. I always recommend pulling enough water for the lab to run the sample twice, just in case one becomes contaminated.

Where to sample

When pulling the water sample, it is best to take it on the downstream side of the filter station after the system has been running for a few hours; this will help prevent filtered particulate from contaminating the sample. Allow three to five minutes of fresh water to run out of the sample port before collecting the water. This is to be sure you don’t collect any residual particulate matter that may be in the port. Remember to keep the samples out of direct light and heat, as those factors can have an effect on the sample quality.

It is important to get the water sample to the lab within 48 hours of sampling to ensure accurate lab results. I suggest when submitting water samples to ask for a full panel of tests. The analysis should consist of pH, electrical conductivity (EC), sodium adsorption ratio, nitrate nitrogen, calcium, magnesium, potassium, sodium, bicarbonate plus carbonate, chloride ion, boron, dissolved solids and sulfate, at a minimum. If you are noticing emitter plugging from bacterial slime, you may want to contact a water treatment company that can test and diagnose the cause of the emitter plugging.

Having these water sample results on record serves multiple purposes:

  • Understanding your water chemistry is the first step in determining what it will take to properly maintain your irrigation system and how your water makeup can affect your crop health; and,
  • A current water sample is also important in developing your annual Nitrogen Management Plans so that you understand how much applied nitrogen, if any, will be coming from your water source.

Irrigation water and soil salinity

All irrigation water contains dissolved mineral salts, which will be revealed in the lab analysis. Once you go over your lab results with your PCA or agronomist, you can determine if in-season leaching is necessary. To learn how to calculate a leaching fraction, visit Almonds.com/Irrigation and read the detailed article “Almond Salinity Hazard and Leaching Requirements.” It is important to know the salinity hazard of your soil because over time, salts can build up in the root zone and reduce orchard production if not removed by leaching. Salt buildup poses two distinct hazards to almond orchards: the total salt content and the toxic effect of specific salts, such as sodium, chloride and boron.

Excess total salinity creates osmotic stress, which reduces crop growth due to the concentration of dissolved salts in the crop’s root zone. The most common positively charged ions, or cations, are calcium, magnesium and sodium, while the most common negatively charged particles, or anions, are chloride, sulfate and bicarbonate.

Energy drain

To overcome this osmotic stress, plants must expend more energy to absorb water from the saline soil, leaving less energy for plant growth. The more saline the irrigation water, the faster salts build up in the soil, potentially reaching a level that reduces production.

In addition to the effect of salinity on the orchard, elements such as sodium (Na), chloride (Cl) and boron (B) can build up in the root zone and be taken up by the tree to a toxic level, burning the leaves and inhibiting photosynthesis. Because there are differences in tolerance to these elements among rootstocks and varieties, tissue analysis is the best indicator of the toxic-element hazard. Boron and sodium can be leached — just as with total salts — but are more difficult to remove than the other salts.

An accurate analysis of your irrigation water helps you understand how your water can affect overall plant health and your irrigation system. To ensure data is dependable, always practice good collection techniques.

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