Water is almond orchards’ number one applied input. With irrigation season right around the corner, now is a good time to submit irrigation water for laboratory analysis to see what that water contains. After all, while sampling is easy there are few steps that cannot be overlooked if accurate lab results are to be achieved.
In general, most ag laboratories will provide growers with the appropriate water bottles to use in collecting and submitting water samples. Once you receive the bottles, be sure to fill them to the top. This is important to ensure the water sample is not cross-contaminated with residual liquid from a soda bottle or sports drink bottle, for instance. In addition, many experts recommend pulling enough water for the lab to run the sample twice, just in case one becomes contaminated.
Where to sample
When pulling a water sample, it is best to gather the sample on the downstream side of your filter station after the system has been running for a few hours. This will help prevent filtered particulate from contaminating samples. Then, allow three to five minutes of fresh water to run out of your sample port before collecting the water, as this will ensure that any residual particulate matter that may be in the port is not collected. Also, remember to try and keep the samples out of direct light and heat, as these factors may influence the sample quality.
It is important to get the water sample to the lab within 48 hours of collecting it to ensure accurate lab results. The lab’s analysis should consider the following:
- pH
- nitrogen
- electrical conductivity (EC)
- sodium (Na)
- chloride (Cl) ion
- boron (B)
Growers who notice an emitter plugging from bacterial slime may want to contact a water treatment company that can test and diagnose the cause of the plugging.
Having water sample results on record serves multiple purposes, but first and foremost it allows you to understand your water chemistry, which is the first step in determining what it will take to properly maintain your irrigation system and how your water makeup can affect crop health. A current water sample also is key in developing your yearly Nitrogen Management Plan, as it helps you understand how much applied nitrogen, if any, will be coming from your water source.
The Almond Board’s California Almond Sustainability Program (CASP) includes a Nitrogen Budgeting Calculator that allows growers to input data specific to their orchard and receive a total nitrogen fertilizer recommendation, along with recommended application amounts that are calculated by the stage of crop growth. The calculator, along with ABC’s Nitrogen Budgeting Tool, also provides growers with the proper paperwork they need to submit nitrogen budgets to their local Irrigated Lands Regulatory Program coalition.
Irrigation water and soil salinity
All irrigation water contains dissolved mineral salts, which will be revealed in the lab analysis. Once growers go over their lab results with their PCA or agronomist, they can determine if in-season salinity managment is necessary. This discussion is important because, over time, salts can build up in the root zone and reduce orchard production if they are not managed properly. Salt buildup poses two distinct hazards to almond orchards: the total salt content and the toxic effect of specific salts, such as Na, Cl and B. Visit Almonds.com/Irrigation and check out the “Almond Salinity Hazard and Leaching Requirements” guide for more information about this topic.
Excess total salinity creates an osmotic stress, which reduces crop growth by the concentration of dissolved salts in the crop’s root zone. The more saline the irrigation water, the faster salts build up in the soil, potentially reaching a level which reduces production.
In addition to the effect of salinity at the root level, elements such as Na, Cl and B can be taken up in the tree to a toxic level, burning the leaves and reducing photosynthesis. Because there are differences in tolerance to these elements among rootstocks and varieties, conducing a tissue analysis (assessing leaves for Na and Cl levels and hulls for B levels) will provide the best indicator of the toxic element hazard. B and Na can be leached — just as with total salts — but are more difficult to remove than the other salts.
An accurate analysis of irrigation water will give you the opportunity to understand what kind of affect your water can have on your overall plant health and irrigation system. Accurate analysis depends on accurate data, which begins with consistent collection techniques. A helpful guide to evaluate the suitability of a water supply for irrigating nut crops, which was developed by UC Cooperative Extension farm advisor Allan Fulton, is available here.
Sampling for E. coli
As you are taking water samples, it is a great time to ask your laboratory for E. coli sampling as well.
Monthly testing is highly recommended until sufficient experience with quality, over the course of at least two harvest seasons, is available.
During future seasons, test ANNUALLY at the beginning of each season:
- Closed, underground or capped well systems
Test QUARTERLY throughout the season
- Uncapped wells
- Open canals
- Reservoirs
- Collection ponds/Recycled water
Maintain copies of water quality reports (monthly, quarterly, or annually)
- Municipality or district water systems
Test water for possible microbial contaminants
- Fecal coliform/E. coli. Irrigation water standards have no established maximum contaminant level for microbiological contaminants, but current research suggests that a single-point maximum for E. coli of 126/100 ml is a useful threshold that can be easily met in most irrigation sources in California.
Possible mitigation measures for E. coli detection level of “present” or “positive”
- Re-test using a quantitative or MPN (most probable number) format rather than presence/absence format
- Disinfect water source
- Retest and double frequency of testing
- Add filtration system to water source
- Add chlorination system to water source
- Check condition and protection of capped well
You can find more information on water sampling by checking out ABC’s Almond Irrigation Improvement Continuum, a comprehensive manual of best practices related in irrigation management and scheduling practices. Growers who would like to receive a free orchard evaluation from ABC are encouraged to contact Tom Devol, senior manager of Field Outreach and Education, at tdevol@almondboard.com.
