Reducing Boron Levels in Crop Irrigation Water

December 3, 2019

Many farmers suffer devastating plant damage due to water and soil with toxic levels of boron, resulting in poor plant quality and decreased crop yields.

(This article was updated on May 19, 2020)
The fascinating thing about the pure element of Boron is that it is actually an essential element to both human and plant health—but only in small micro amounts—and this is where farmers have trouble with it.

Many farms suffer devastating plant damage from toxic levels of boron. Sometimes these excessive levels appear in the specific farm soil, or they are delivered via irrigation water or both, and when they do, farmers are faced with low crop quality and yields.

The mineral boron is a micronutrient commonly found in small amounts in most soils in a variety of compounds—most often sodium borate (borax) and boric acid. Boron is a micronutrient that is critical to proper plant growth because, in addition to calcium, plants require sufficient levels of it to develop cell walls with high structural integrity. Just as people require sufficient calcium to maintain bone density, plants require sufficient levels of calcium and boron.

Boron deficiencies are associated with wilting and rotting of plant leaves and stems, as well as fruits and crops that are stunted or discolored, or which succumb to secondary fungal infections. Growers across the world struggle with natural occurring boron deficiencies in cropped soil, which has led to boron being one of the most commonly used soil supplements in agriculture.

But some growers—such as those in desert regions and the West Coast’s Coastal Range—face the opposite problem: very high levels of boron in their soil and water.

In areas where soils are well irrigated, boron levels are low to normal. This is because as water drains through the soil and runs off, it leaches out and carries away boron and other minerals. The boron levels present in well-drained soils are reflective of the equilibrium which has been reached between the ever-ongoing processes of accumulation from waterflow from areas with high boron levels, and subsequent leaching. It is because this process tends to result in lower than ideal boron levels that many growers supplement their soils with boron-containing fertilizers.

The reverse is also true for some farmers. In general, areas with naturally high boron levels are relatively rare, yet arid and semi-arid regions are particularly noted for having undesirably large amounts of boron in the soil. This is because in dryer regions, there isn’t a consistent flow of water to leach boron out of the soil and prevent excessive accumulation. Instead, water is occasionally deposited—along with dissolved boron and other minerals—which then evaporates directly out of the soil, leaving behind the minerals. Over time, boron levels can become quite high.

Boron accumulation tends to occur alongside salt accumulation, so if you live in a drought-prone area where soils are notably saline, there’s a good likelihood that high levels of boron are also present.

On the wester side of North America, the Coastal Range is also known for having soil with elevated levels of boron. This is because much of the rock comprising the mountains was formed in the ocean, and thus contain large amounts of marine Evaporites, which are mineral accumulations formed through the evaporation of ocean water. (Evaporites also form in arid conditions, which contributes to the previously mentioned high levels of boron found in arid conditions.)

Excessive boron levels are also sometimes found in areas with a history of volcanic activity, as well as in regions where mining has occurred. Areas with soil that has a high clay content are also known to have higher than average boron levels, as clay readily absorbs boron.

Regardless of the cause of boron accumulation, excessive boron in soil—or groundwater—poses a serious challenge for growers.

Excessive boron is toxic, causing a variety of health problems in plants, including damage to roots.

One of the most common symptoms of exposure to excess boron is the yellowing and browning of leaves, sometimes referred to as “leaf burn.” This is particularly evident at the tips and edges of older leaves, which eventually dry out and die. If the issue isn’t remedied, browning and tissue death will spread through affected leaves.

This occurs because boron is carried through plant tissue via a process called “transpiration.” Water is absorbed through the roots, and is then drawn up through the plant due to water evaporating from leaf surfaces—creating a sort of vacuum that pulls water up. Because boron can’t evaporate along with water, it essentially piles up at the end of the line—at leaf edges, where there is nowhere else to go. This means that the pattern of plant tissue death actually tells you where in the plant elevated levels of boron are located. Because transpiration patterns in plants vary from species to species, the pattern of tissue discoloration and death can vary.

As boron levels in plant tissues increase, plants affected by boron toxicity experience a reduction in both total leaf area and overall growth.

But not all plants experience this progression of symptoms. In some plants, such as apples, pears, peaches, cherries, almonds, and so on, boron toxicity can lead to a variety of symptoms, such as the premature stunting and death of fruits, as well as stem dieback and degradation and death of bark tissue.

Reducing soil levels of boron requires access to a clean water source. Unfortunately, growers often rely on groundwater that also contains high or toxic levels of boron.

The single most effective means of reducing boron levels in fields is by leaching the high-boron soil with water that is low in boron. Heavy watering with low-boron water flushes boron from growing soil, forcing it down away from roots or out of the field or orchard altogether.

But the problem is that most growers rely on water that is supplied from local surface waterways or ground water. In both cases, the water source is naturally high in boron, and thus only contributes to the already excessive levels of boron in the soil.

Unsurprisingly, growers have even less recourse when it comes to remedying water sources that are high in boron. We have had many growers in this exact situation contact us, wanting to know what we can do to ‘clean’ water of the toxic levels of boron before using it for irrigation. Traditionally, reverse osmosis has been the go-to remedy for reducing boron levels in water. But reverse osmosis (RO) is a costly treatment solution that doesn’t scale well. Additionally, at best, RO only provides a certain percentage of reduction, rather than complete removal.

Our ozone water treatment system has proven to be effective in removing a variety of biological contaminants and excess mineral content from water. Using that as a baseline, our ozone-treatment system is highly successful in removing boron entirely from water which has previously tested in excess of 25 ppm.

Recently, we were successful in treating a water source with boron levels of 39 ppm pre-treatment. After our ozone treatment, boron levels were reduced to 0.170 ppm, a reduction of 99.6%. From these elevated levels, boron is either reduced to barely detectable levels, or in most instances, to non-detectable levels and is perfectly safe for plants.

Not only does the processed water no longer carry a risk of boron toxicity, but it can also be used to counter high boron levels in soil by leaching and flushing it beyond the bounds of plant root systems, essentially providing a level of soil remediation.

If you have questions as to how our ozone water treatment system can control levels of boron—and address other quality issues—in your irrigation water, contact Watson Well to learn more.

California Groundwater Association
National Groundwater Association