Understanding Plant Nutrition: Irrigation Water Alkalinity & pH

Understanding Plant Nutrition: Irrigation Water Alkalinity & pH

Water quality is a key factor affecting pH and nutritional management in container-grown crops. Understanding a few technical details about water quality will help you improve nutrient management appropriate for your own greenhouse. In this article, we will discuss the difference between water pH and alkalinity. We will also discuss how to interpret water pH and alkalinity results, and adjust your pH management strategies accordingly. 

pH And Alkalinity Are Two Different Aspects Of Water Quality

The term pH is a direct measurement of the balance between acidic hydrogen ions (H+) and basic hydroxide ions (OH-), and can be measured with a pH meter. The pH of a solution can range between 0 (very acidic) and 14 (very basic). At a pH of 7.0, the concentrations of H+ and OH- are equal, and the solution is said to be neutral. When the pH is above 7.0, the concentration of OH- is higher than H+, and the solution is said to be basic or alkaline (not to be confused with alkalinity). When the solution is below 7.0, the concentration of H+ is higher than OH-, and the solution is said to be acidic.

Alkalinity is a measure of how much acid it takes to lower the pH below a certain level, also called acid-buffering capacity. Alkalinity is not a specific ion, but rather includes the concentration of several ions that affect acid-buffering capacity.

Under most conditions, the ions that have the greatest effect on alkalinity are bicarbonates like calcium, magnesium or sodium bicarbonate and, to a lesser extent, carbonates like calcium or sodium. Several other ions (like hydroxides or sulfides) also can contribute to alkalinity, but their concentration in most irrigation water is usually so low that they can be ignored. 

Units Of Measurement For Total Alkalinity

In a water sample, the concentration of all of the ions that make up the alkalinity term are combined and reported as equivalents of calcium carbonate, CaCO3, which is the main component of lime. Alkalinity can therefore be thought of as the “liming content” of the water.

The concentration of alkalinity (or any other plant nutrient) can be expressed a number of different ways:

1) Parts per million (ppm or mg/liter): A weight per weight ratio. One part per million is equivalent to one unit of something dissolved in a million units of something else. In the case of anything dissolved in water, 1 ppm is equal to 1 mg/liter.

2) Milliequivalent (mEq/liter): A chemistry term that is not only dependent on a materials concentration, but also on its molecular weight and charge. In the case of alkalinity, 50 ppm (or mg/liter) CaCO3 equals 1 mEq/liter CaCO3. Sometimes, the concentration of bicarbonates is also reported on a water test from a commercial laboratory. In most cases, bicarbonate makes up most of the alkalinity. The relationship is 61 ppm bicarbonate equals 1 mEq total alkalinity.

Water Alkalinity Has A Big Effect On Substrate pH

When it comes to managing the pH of a substrate, the alkalinity concentration has a much greater effect than does water pH. Alkalinity (calcium bicarbonate, magnesium bicarbonate and sodium bicarbonate) and limestone (calcium and magnesium carbonate) react similarly to limestone when added to a container media. And just like too much limestone, the use of irrigation water containing high levels of alkalinity can cause the pH of the substrate to increase above acceptable levels for healthy plant growth.

For example, a limestone incorporation rate of 5 pounds per cubic yard will supply approximately 100 mEq of limestone per 6-inch (15-cm) pot. Applying 16 fluid ounces (0.5 liters) of water containing 250 ppm alkalinity to that 6-inch pot will supply about 2.5 mEq of lime. That does not sound like much until you consider that after 10 irrigations, you have effectively increased the limestone incorporation rate by 25 percent.

To compare the effect of water pH or alkalinity on the ability to raise pH (or neutralize acid) in a medium, 50 ppm alkalinity (which is a low alkalinity) would be similar to having a water with pH 11 (i.e. an extremely high pH). A water with a pH of 8.0 would have the same effect on substrate pH as an alkalinity concentration of only 0.05 ppm (i.e., almost nothing).

Don’t ignore water pH, though. Water pH is still important for crop management because it affects the solubility of fertilizers and the efficacy of insecticides and fungicides before you apply it to the crop (Figure 2). Generally, the higher the water pH, the lower the solubility of these materials. 

Minimizing The Effects Of High Alkalinity

The common problems associated with high alkalinity result from its tendency to increase media pH. Since the solubility of micronutrients (particularly iron) decreases as media pH increases, the use of high alkalinity water often results in micronutrient deficiency in the crop (Figure 2).

The most common method for minimizing the “liming effect” of high alkalinity is to neutralize it by adding a strong mineral acid (usually sulfuric acid or phosphoric acid) directly to the irrigation water. The acid causes the water pH to decrease, which neutralizes some of the alkalinity. All of the alkalinity has been neutralized when the pH of the water reaches 4.5. For more specific recommendations on how much acid is needed to neutralize a specific amount of alkalinity, you can download the “Acid Addition Calculator” from Purdue University and North Carolina State University at www.ces.ncsu.edu/depts/hort/floriculture/software/alk.html.

Another option for alkalinity control is to use acidic fertilizers. Fertilizers high in ammoniacal nitrogen produce an acidic reaction when added to a container media, which can be used to neutralize the liming effect of water alkalinity. For example, 20-20-20 (69 percent NH4-N) has enough acidity to be used with water containing around 200 ppm alkalinity water without further acidification.

There are several drawbacks to using fertilizer for alkalinity control. Fertilizers high in ammoniacal nitrogen may cause excessive growth and are not effective when the temperature of the substrate is less than 60ËšF. In addition, you lose flexibility because you can only choose commercial fertilizers based on ammonium content. For example, fertilizers that contain more than 40 percent ammoniacal nitrogen do not contain calcium or other key nutrients. 

Low Alkalinity Effects

Not everybody has irrigation water with high alkalinity. In one study from Michigan State University, about 30 percent of the irrigation water tested had alkalinity levels below 40 ppm without any acidification. Even in areas where high alkalinity is considered normal, some growers have switched to low alkalinity sources such as reverse osmosis purified water or rain water.

The primary problem associated with low alkalinity water is a tendency for substrate pH to drop over time, which can cause micronutrient toxicity problems (Figure 3). Low media pH problems are often a result of fertilizer selection. Fertilizers high in ammoniacal nitrogen are acidic, and without any alkalinity in the water to balance the reaction (resist lowering of pH), acidic fertilizers will tend to drive the substrate pH down over time.

Understanding a few technical details about water alkalinity can help you improve pH management. However, irrigation water can affect plant nutrition in more ways than just media pH. In next month’s article, we will discuss irrigation water as a nutrient source.

Leave a Reply

2 comments on “Understanding Plant Nutrition: Irrigation Water Alkalinity & pH

  1. You might have a mistake explaining the term ppm.
    In my opinion 1 ppm is one unit of something disolved in 999,999 units of something else.
    the whole solution (The solvent and the disolved) will contain 1000,000 unites.
    Of course, when you calculate only 100 0r 200 ppm in fertilizers the diference could be ignored, but,,if you calculate other chemicals that could be very significant especially when you use plant regulators of hormones in the water irrigation.

  2. You might have a mistake explaining the term ppm.
    In my opinion 1 ppm is one unit of something disolved in 999,999 units of something else.
    the whole solution (The solvent and the disolved) will contain 1000,000 unites.
    Of course, when you calculate only 100 0r 200 ppm in fertilizers the diference could be ignored, but,,if you calculate other chemicals that could be very significant especially when you use plant regulators of hormones in the water irrigation.

More From Fertilization...
PP&L CAST 2015 intros

April 22, 2015

6 Breeding Companies Serve Up New Varieties At Pacific Plug & Liner

Pacific Plug & Liner’s theme this year, Labyrinth, a conservatory of the world’s most captivating plants, was perfectly topped off (pun intended) with fascinators for the women and newsboy caps for the men. The PP&L team dressed their part to act out the gothic “conservatory of the world’s most captivating plants.” Truly, the displays looked like they practically popped out of a catalog, and the costumes were a nice touch. Retailers take heed, the fully merchandised displays at Pacific Plug & Liner are worthy of emulating. We’ll let the pictures tell the story of all the fabulous variety introductions presented at  Pacific Plug & Liner’s 2015 California Spring Trials, where Cultivaris, Cohen Nurseries, Histil Nurseries, Jaldety Nurseries, Southern Living/Sunset Collection and Pacific Plug & Liner all highlighted their 2016 introductions.  

Read More
Speedling 2015 CAST intros

April 22, 2015

Speedling Inc. Presents New Varieties From ABZ Seeds, Hem Genetics, Thompson & Morgan, Vista Farms & PSI

You name it, we saw it at Speedling's California Spring Trials location in San Juan Bautista, where five companies showed off their new introductions for 2016.

Read More
PittMoss on Shark Tank

April 22, 2015

PittMoss Wins On Shark Tank

Mont Handley, president and CEO of PittMoss, appeared on ABC’s Shark Tank on April 17 to try to get the “sharks” to invest in his peat moss alternative. Three investors from the TV show contributed $600,000 to PittMoss for a 35 percent stake in the company. Check out this clip from ABC’s website in which Mark Cuban, Kevin O’Leary and Robert Herjavec discuss getting on board with the product. PittMoss is an alternative to sphagnum peat moss, made up of a mix of proprietary additives and recycled paper rescued from landfill space. Handley founded the Pittsburgh-based company in 1994. What started as a small experiment grew into a full-fledged business with the help of funding provided by an EPA SBIR grant and Pittsburgh’s Idea Foundry. Today, PittMoss is available to commercial greenhouses and nurseries from Michigan to Maine to North Carolina, with plans to grow. To learn more, visit PittMoss’ website, or check it […]

Read More
Latest Stories

January 9, 2015

6 New Fertilizer Products For Healthy Plants

These five products add even more options for delivering nutrients to the root zone.

Read More

January 7, 2015

Fertilizers And The Future

As growers look for new ways to cut costs and conserve resources, fertilizer and equipment companies are offering products that strive to save water, reduce toxic runoff and keep chemicals out of the equation.

Read More

December 31, 2014

Gain Greater Control Of Fertilizer With Automated Ferti…

University researchers look at integrating irrigation and fertilization with the help of water sensors to reduce fertilizer treatments and improve application timing.

Read More

October 30, 2014

Basics & Beyond: Comparing Substrate Fertilizer Ame…

Cornell University researcher determines if substrate-incorporated slow-release fertilizers can be used to replace or reduce the need for liquid fertilizer for four spring crops.

Read More

July 24, 2014

Using Controlled Release Fertilizers To Produce Garden …

Researchers determined whether or not garden mums can be grown with controlled-release fertilizer, and if it reduces fertilizer leaching, as compared with water-soluble fertilizers.

Read More

March 14, 2014

New Foliage Pro Fertilizer Offers Complete Nutrition Pl…

Dyna-Gro Nutrition Solutions has developed a process it says is capable of keeping all 16 essential plant nutrients in solution form.

Read More

January 30, 2014

OASIS Grower Solutions Introduces New One-Bag Hydroponi…

The new 16-4-17 Hydroponic Fertilizer from OASIS Grower Solutions (OGS) is a one-bag solution that replaces two-part systems traditionally used by commercial hydroponic growers. It is specifically formulated for commercial hydroponic production of lettuce, herbs and vegetables.

Read More

December 30, 2013

Fertilizer Changes Growing Mix pH

When considering a fertilizer's influence on media pH, you need to know its acid or basic reaction.

Read More

December 30, 2013

Basics & Beyond: Fundamentals Of Phosphorus Nutriti…

Phosphorus is an essential element, after all.

Read More
Everris Liquid S.T.E.M.

December 30, 2013

New Fertilizers For 2014

New fertilizer products not only deliver optimum nutrition, they also provide for easier application and increased efficiency. Check out these new products to help your operation produce a healthy crop in 2014. Click through on the pages below.

Read More

December 18, 2013

Focus On Fertilizer: Micronutrients And Organics

New fertilizer products are focusing on micronutrients and providing efficient options for organic production.

Read More

August 27, 2013

BioWorks Adds EcoVita To The Verdanta Family Of Biofert…

EcoVita, a homogeneous granular organic fertilizer, has been added to Bioworks Inc.’s Verdanta biofertilizers product family. This fertilizer will be manufactured and supplied to BioWorks by DCM Corporation of Belgium, a producer of natural and organic-based fertilizers in Western Europe. EcoVita is suitable for a wide variety of crops with its gentle release curve including:• Organic fertilization as a base nutrition in potting mixes• Leafy vegetables• Fruiting vegetables (s a top dressing) • Roses and other ornamentals The new fertilizer offers long-lasting and continuous action for 75 to 100 days and contains organic phosphorus (5 percent P2O5) for fast rooting. Nutrients in EcoVita are gradually released by the soil microbes, in addition to producing humus for better rooting and less leaching. EcoVita is OMRI Listed, making it suitable for use in organic production. “We’re pleased to introduce EcoVita 7-5-10 as our organic NPK product to complement our organic products: K-Vita 2-0-20 […]

Read More

April 29, 2013

Rockwell Farms Introduces Ready-To-Pour Container Ferti…

Rockwell Farms has introduced Rockwell Farms Plant Food, a bottled liquid fertilizer that does not need to be diluted before use. Always looking for ways to help the consumer succeeed, Jason Roseman of Rockwell Farms says the operation is also always looking for ways to get consumers to come back and buy more plants and flowers. “We feel like fertilization is one of those things that can be very confusing,” Roseman says. “Not everyone does it, and not everyone knows what they’re supposed to do.” The solution: Rockwell Farms Plant Food. The formulation is 150 ppm of a 20-10-20 fertilizer and is sold in 24-ounce bottles. Rockwell recommends that one bottle be used to fertilize 1.5- to 3-gallon outdoor plant and flower containers every 21 days. The product’s signage shows a young patio gardener pouring the bottled fertilizer on a windowbox with the tagline, “Just pour on your way out […]

Read More

April 29, 2013

Plant Products To Be Purchased By MGS Horticultural And…

MGS Horticultural Inc., a full-service supplier of fertilizers, pest control products, seeds and substrates in North America, together with Haifa Chemicals, a global supplier of potassium nitrate for agriculture and industry, specialty plant nutrients and food phosphates, today announced a plan to purchase Canadian fertilizer and pesticides supplier Plant Products Co. Ltd. The deal is anticipated to close by the end of June 2013. MGS will acquire Plant Products’ Canadian distribution business, sales force and name. MGS plans to use both names (MGS Horticultural and Plant Products) in all communications going forward. MGS will maintain locations in Leamington, ON; Brampton, ON; Laval, QC; St. Hyacinthe, QC; and Detroit, Mich. As part of the deal, MGS has signed multi-year agreements with Haifa to maintain exclusive distribution of Plant-Prod Soluble Fertilizers, Acer Controlled Release Fertilizer, Stim-Root and potting soil premix fertilizers for distribution in Saskatchewan, Manitoba and Eastern Canada. “MGS is excited […]

Read More

March 19, 2013

Irrigation And Fertilizer Tips For New Vegetable Grower…

Compared to other variable costs, fertilizers are not the largest part of the budget in conventional greenhouse production. Nevertheless, over the course of the season, mistakes in fertilizer use can lead to significant damages or crop losses. That makes this an important topic for ornamental growers who are experimenting with growing vegetable crops. This article will emphasize major differences between fertilizers used in vegetable production and in ornamentals production. The different nutrition strategies, monitoring and water volume per plant will also be explained. Fertilizer In ornamental production, nutrients are delivered using various water-soluble fertilizers through a fertilizer injector, through the use of controlled-release fertilizers, or a combination of the two. There are numerous fertilizer mixes available with all the needed nutrients already included. The fertilization rate is often given in parts per million (ppm) of nitrogen (N), which is a way of expressing the fertilizer concentration. At younger stages, plants will […]

Read More

March 11, 2013

Daniels Plant Food Rebranded As Nature’s Source

Ball DPF has announced the launch of Nature’s Source, a rebranding in name and packaging for its seed extract-based plant fertilizer product Daniels Plant Food. The new brand will make its industry debut at California Spring Trials. “While we are proud of our heritage, we made this bold decision because we’re expanding sales to our existing market segments and entering new ones. It was a good opportunity to start with a fresh name and a modern look for all our products and packaging,” says Chance Finch, general manager for Ball DPF. “We wanted to make it obvious, beginning with our Nature’s Source brand name, to know our products are sourced from nature. Growers, contractors and gardeners can be confident that our effective and unique formulations remain unchanged. We’re excited about launching updated packaging for all our products, and especially the new ready-to-spray plant food for home gardeners.” The Nature’s Source brand […]

Read More

March 6, 2013

Everris Introduces E-Max Release Technology Coating Che…

Everris has introduced its new E-Max Release Technology, a proprietary coating chemistry for use on a wide variety of nutrient components that are incorporated into controlled-release fertilizer products. According to Chris Buchheit, marketing manager for Everris’ ornamental horticulture products, E-Max will help Osmocote and the company’s other existing brands deliver even better performance and value. “This coating will aid in the development of products that both complement and enhance our Osmocote portfolio and other fertilizer lines. It will increase Everris’ flexibility to create customized nutrition programs designed for horticulture growers,” Buchheit says. E-Max Release Technology is a durable, cutting-edge, reacted polymer coating for use on a variety of essential macro- and micronutrients. Nutrients coated with E-Max Technology are produced to the same performance standards as Osmocote. It will allow for continued expansion of the Everris portfolio, the ability to further enhance nutritional values and an efficient use of a grower’s […]

Read More

February 4, 2013

BioSafe Systems And Daniels Plant Food Company Will Par…

BioSafe Systems has entered into a strategic partnership with Daniels Plant Food Company, a wholly owned subsidiary of Ball Horticulture Inc. BioSafe and Daniels have worked closely together for the past two years and will now look to further develop liquid plant food serving both the conventional and organic markets. In conjunction, BioSafe Systems will be introducing its own branded line of plant food products focusing on turf, landscape and agricultural markets. “Liquid plant food is a natural progression for our company” says Rob Larose, CEO of BioSafe Systems. “It fits perfectly into our current line of green and sustainable products, and we are excited about partnering with Daniels.” Daniels manufactures and markets both conventional and organic liquid fertilizers, using botanical extracts to provide high-value nutrition to plants. BioSafe Systems develops and markets effective and sustainable products to a wide variety of industries, including fruit and vegetable production, turf and […]

Read More