Irrigation salts: friend or foe?

Are salts bad or good? The short answer is: YES. 

All essential plant nutrients are present in soil and water as salts. These dissolved ions are fundamental to plant growth, supporting everything from nutrient supply to osmotic regulation and most every physiological function in between. In that sense, salts are not only beneficial, they are indispensable. However, as with most agronomic inputs, the distinction between benefit and harm lies in the rate, timing, and placement.

The amount of nutrient salts that naturally cycle through soil–plant–water systems are rarely sufficient to support the high yields and nutrient demands of agricultural production without supplemental fertilization. At the same time, excessive salt concentrations can damage crops, particularly during sensitive growth stages such as germination and early seedling development. High salt levels near seeds—from concentrated fertilizer bands, for example—can impair water uptake and reduce stand establishment.

Water movement plays a central role in salt dynamics. In humid regions, where precipitation exceeds evapotranspiration (ET), salts leach downward through the soil profile. This ultimately transports salts to ground or surface waters, which is why the oceans are salty. In contrast, soils in arid and semi-arid regions tend to accumulate salts because ET exceeds precipitation, drawing water upward and leaving salts behind in the crop root zone.

Irrigation is essential for most crop production in these drier regions, but these additions introduce an additional layer of complexity. When applied in sufficient amounts, irrigation water—combined with precipitation—can leach salts below the root zone, maintaining a favorable environment for crop growth. However, irrigation water itself often contains dissolved salts, meaning it can serve as both a source of crop nutrients and a contributor to risk for plant growth.

Due to this duality, irrigation water should be viewed as a managed input rather than a neutral resource. Routine testing and interpretation of water quality are essential for understanding irrigation water’s contribution to nutrient supply and its potential to create salinity or soil structure problems. Proper irrigation management allows producers to capture the benefits of dissolved nutrients while minimizing the risks associated with excess salts.

Managing irrigation water quality: A systems approach for CCAs

Irrigation water quality is a foundational—but often underleveraged—component of crop production systems. Certified Crop Advisers (CCAs) routinely evaluate soils, fertility programs, and irrigation scheduling. However, the chemistry of irrigation water itself is often overlooked even though it can quietly shape crop performance, soil function, and long-term sustainability. In many cases, yield limitations, soil structure decline, and/or nutrient imbalances can be traced back, at least in part, to water quality issues.

A comprehensive approach to irrigation management therefore requires integrating water quality into agronomic decision-making. This includes not only testing and interpretation, but also aligning water characteristics with crop sensitivity, soil properties, and irrigation system design.

Start with the data: Water testing and interpretation

Effective management begins with a reliable water analysis. Even when a water source has been used for years, periodic testing is essential, as quality can change due to seasonal variation, aquifer depletion, or upstream influences. Samples should be collected after the irrigation water has run for enough time to get a consistent sample. A clean, non-glass container is used to gather about 1 pint (500 mL). The sample should be submitted to a lab with an excellent quality assurance/quality control (QA/QC) program, which includes proficiency testing (see the North American Proficiency Testing (NAPT) tab at soils.org for a list of laboratories). 

At a minimum, irrigation water analyses should include electrical conductivity (EC) and the ions commonly found in irrigation water (see Figure 1). 

The parameters listed in Figure 1 provide the foundation for diagnosing five major categories of concern: 

• Salinity
• Sodium hazard 
• Specific ion toxicity
• Nutrient contributions
• Lime deposition potential

Additionally, a critical but often overlooked step is validating the analysis itself. Comparing the sum of cations and anions (in meq/L) helps ensure data quality. If the analysis is done correctly, the ratio between the cations and the anions should equal 1.00 + 0.05.

Salinity: more than just ‘too much salt’

Salinity, typically assessed via EC (in dS/m or mmhos/cm), reflects the total concentration of dissolved salts in irrigation water. Elevated salinity reduces plant water uptake through osmotic stress, effectively inducing drought-like conditions even when soil moisture is adequate (see the photos at the top of the article).

Key considerations include:

• Crop sensitivity varies widely (Table 1). Crops such as beans and onions are highly sensitive to salinity, while barley and sugar beet are more tolerant.
• Growth stage matters. Germination and early seedling stages are often the most sensitive to salinity.
• Environmental conditions interact with salinity. High temperatures, low humidity, and/or windy conditions can exacerbate leaf burn when saline water contacts foliage

Salinity management is fundamentally about salt balance: inputs versus removal. Irrigation water, fertilizers, and soil parent material all contribute salts; while leaching and crop removal are the primary pathways for export. When inputs exceed outputs, salts accumulate at the soil surface. In extreme cases, the salts are visible (see Figure 2), but yield damage can occur even without salts being visual at that surface. This is why testing the soil (Zamora et al., 2022) and water (see Table 1) is critical. 

Leaching is the ONLY practical method for removing salts from soil. Thus, increased irrigation efficiency—while beneficial for water conservation—can reduce incidental leaching and increase the risk of salt buildup over time. This creates a management paradox with more efficient irrigation systems often requiring more deliberate salinity management.

An important nuance for managers is that very low salinity water can also create problems. Water with extremely low EC can destabilize soil aggregates by leaching calcium, leading to surface sealing and reduced infiltration. In such cases, adding calcium (e.g., via gypsum) or fertigation salts may be necessary to maintain soil structure.

Sodicity hazard: Protecting soil structure

While total salinity affects plant water relations, sodium specifically affects soil physical properties. High sodium relative to calcium and magnesium can disperse soil particles, destroying aggregate stability and reducing water infiltration and permeability (see Figure 3).

The primary diagnostic tool for assessing sodicity is the sodium adsorption ratio (SAR), which expresses the relative proportion of sodium to calcium and magnesium in irrigation water. However, SAR alone is not sufficient; its effect also depends on overall salinity (EC) (see Table 2). 

This interaction of EC and SAR impacts whether or not sodium will result in degradation of soil aggregation. Poor infiltration caused by sodium-affected water can lead to runoff, uneven water distribution, and reduced irrigation efficiency.

The management strategy for sodicity is to increase the soluble calcium in the soil-water system. Common approaches to do this include:

• Applying calcium sulfate (gypsum), calcium chloride, or other soluble calcium sources [note that limestone (calcium carbonate) is not soluble at pH above 7].
• Injecting acid or using an elemental sulfur burner to reduce bicarbonates and improve calcium solubility.

Once the soluble calcium level has been increased relative to sodium, then leaching should be applied to the soil to move the sodium away from the root zone. Preventive management is far more effective than remediation. Once soil structure has degraded, restoring infiltration can be difficult and costly.

Specific ion toxicity: Chloride and boron

Even when overall salinity is moderate, specific ions can cause direct toxicity to crops. The two most common culprits in irrigation water are chloride and boron (as borate).

Chloride injury typically appears as leaf burn, especially when irrigation water contacts foliage. Sensitivity varies widely (see Table 3), with dry beans and blueberries among the most sensitive and barley, sugar beet, cauliflower, and asparagus as some of the most tolerant. Management strategies include switching to less sensitive crops, using irrigation methods that avoid foliar contact (e.g., drip), and/or leaching the excess in the soil. 

Boron presents a narrow margin between deficiency and toxicity. Concentrations as low as 1 ppm can damage sensitive crops, particularly fruit and many bean species. Alfalfa, beets, asparagus, and tomato are among the most tolerant of high boron concentrations. Long-term accumulation in soil can be managed through periodic leaching though removal is slow in many soils.

Nutrient contributions: Irrigation as a fertility input

Irrigation water can supply substantial amounts of plant nutrients, often far more than a crop requires of calcium, magnesium, sulfur, and chloride (See Figure 1). It is often suggested that these nutrients are not plant available. While it is true that some of the ions can precipitate as mineral deposits in the soil, there is a large fraction that remains dissolved for plant uptake. Additionally, foliar deposition can result in direct absorption through leaves. In other instances, irrigation water can have agronomically significant amounts of nitrogen (as nitrate) as well as boron, potassium, manganese, and/or iron that should be accounted for.

The calculation for nutrient inputs from overhead sprinkler irrigation is: 

Nutrient applied (lb/acre) = irrigation applied (inch/acre) × nutrient (ppm) × 0.227

For example, irrigation water containing 10 ppm (or mg/L) nitrate-N applied at 30 inches of irrigation water per acre equals 68 lb N/ac. This “free” input needs to be accounted for, especially given the high costs of fertilizer. Failing to account for it can result in over-fertilization, leading to:

• Excess vegetative growth
• Reduced crop quality and storability
• Increased pest and disease susceptibility
• Greater risk of nitrate leaching

Applying this same calculation to other nutrients commonly reveals more than 50 lb/ac of calcium, magnesium, sulfur, and chloride, which are all far more than is needed by most crops. Incorporating irrigation water nutrients into fertility recommendations represents a key opportunity to improve both economic and environmental outcomes.

Lime deposition potential

Lime deposition potential (LDP) is determined by the balance of carbonates and divalent cations. Water with high LDP forms calcium/magnesium carbonate deposits (“hard water”) and, if found, may require special management (see Table 4). These lime deposits can:

• Leave visible residues on fruits, vegetables, leaves, etc.
• Plug emitters in drip and micro-sprinkler systems
• Reduce system efficiency with precipitation of deposits in piping and nozzles
• Reduce infiltration and percolation in soil due to coating soil pores
• Reduce phosphorus and micronutrient availability in soils

High-risk irrigation water often requires acid injection to reduce pH and convert bicarbonates to carbon dioxide, preventing precipitation. For specialty crop systems, especially those relying on micro-irrigation, managing lime deposition is essential for maintaining system uniformity and crop quality.