Understanding Plant Nutrition: Fertilizers And Macronutrients

Understanding Plant Nutrition: Fertilizers And Macronutrients

When you select a water-soluble fertilizer, the primary goal should be to supply plants with a sufficient amount of essential plant nutrients for good growth and flowering. In this article, we will focus on macronutrients (nitrogen, phosphorus, potassium, calcium, magnesium and sulfur) supplied by water-soluble fertilizers. We will discuss macronutrient sources, fertilizer formulations and the application of fertilizer to the crop. In subsequent articles, we will discuss other aspects of fertilization including micronutrients sources and formulations and controlled-release fertilizer.

Fertilizer Formulations

Water-soluble fertilizers come in two types, either individual fertilizer salts or blended fertilizers. Fertilizer salts are chemicals containing nutrients that can dissolve into a water-soluble form that are needed for plant uptake. For example, potassium nitrate (KNO3) will dissolve into separate potassium ions and nitrate ions. Blended fertilizers are combinations of two or more fertilizer salts that supply several macronutrients. For example, 13-2-13 is a blend of calcium nitrate, magnesium nitrate, monoammonium phosphate and potassium nitrate, and so supplies nitrogen, phosphorus, potassium, calcium and magnesium.

When formulating blended fertilizers, there are eight water-soluble sources of nitrogen commonly used (Table 1), some of which only supply nitrogen, like urea and ammonium nitrate. However, for most other nutrients, the choices are limited. For example, calcium nitrate is the only form of water-soluble calcium. There is also typically only one source of potassium, potassium nitrate. Monoammonium phosphate (MAP) is the usual source of phosphorus. Magnesium is supplied by either magnesium sulfate or magnesium nitrate. Sulfur is supplied by ammonium sulfate or magnesium sulfate.

Because of limitations in the number of salts used to blend fertilizers, the ratio of macronutrients and their compatibility when mixed directly affects the formulation of the fertilizer, for example:

– Fertilizers that are high in phosphorus also tend to be high in ammoniacal nitrogen, because phosphorus is usually supplied as monoammonium phosphate.

– Fertilizers that contain calcium are also high in nitrate, because calcium nitrate is the only water-soluble source of calcium. In fact, all the commercially available fertilizer that contains calcium also has ammoniacal nitrogen levels of 25 percent or less of the total nitrogen.

– Calcium nitrate and monoammonium phosphate or monopotassium phosphate cannot be mixed in the same concentrated stock solution at high concentrations because insoluble calcium phosphate will form. However, the amount of calcium and phosphorus that can be mixed in the same stock tank can be increased by lowering the pH of the stock tank solution. Commercially available fertilizers that contain calcium and phosphorus tend to have low levels of phosphorus (i.e. 13-2-13-6 Ca-3 Mg) and will also contain a weak acid to lower the pH of the concentrated stock solution.

– Since calcium nitrate and magnesium sulfate are incompatible in the same stock tank, a fertilizer that contains calcium will use magnesium nitrate as the magnesium source. A fertilizer that contains magnesium without calcium will use magnesium sulfate as the magnesium source.

Nutrient Concentrations

Most fertilizer recommendations are given based on a concentration of nitrogen applied to a crop. In North America, that concentration is usually given in parts-per-million or ppm. One ppm is equivalent to 1 mg per liter. In other words, one liter (about 33 fluid ounces) of fertilizer solution with a concentration of 100 ppm N will contain 100 mg of nitrogen. Sometimes, concentrations are given in mMol of nitrogen. One mMol of nitrogen is equal to 14 ppm N.

In many cases, the concentration of the other macronutrients are either not known or are ignored. To calculate the concentration of calcium, magnesium or sulfur supplied by a blended fertilizer, you need to know the concentration of nitrogen in the fertilizer solution and the ratio of nitrogen to calcium, magnesium or sulfur that is listed under the “guaranteed analysis” on any fertilizer bag. For example, to calculate the concentration of calcium supplied by 13-2-13 (6 percent Ca) at 200 ppm N, you divide the percent of Ca by the percent of N, then multiply by the nitrogen concentration of the fertilizer solution.

So at 100 ppm N, you are also supplying about 92 ppm Ca.

An extra step is required to calculate the concentration of phosphorus or potassium. A fertilizer formula reports phosphorus as P2O5, not actual phosphorus (P), and potassium is reported as K2O, not actual potassium (K). To convert P2O5 to P, multiply the P2O5 value by 0.43, and to convert K2O to actual K, multiply the K2O value by 0.83. For example, using the equation above, the P2O5 and K2O values supplied by 13-2-13 at 200 ppm N would be 30 ppm and 200 ppm. This converts to an actual P concentration of 13 ppm P, and an actual K concentration of 166 ppm K.

Applying Fertilizers

Water-soluble fertilizers are typically applied using fertilizer injectors or proportioner. These devices add a concentrated fertilizer solution to the irrigation water at some ratio. For example, a 1:100 injector will add 1 gallon of concentrated fertilizer to 100 gallons of water. If the desired solution concentration coming out of the end of the hose is 100 ppm N, then the concentrated stock solution that the fertilizer injector is adding to the irrigation water has to have a concentration of 10,000 ppm N (or 100 times that of the desired diluted concentration).

The amount of fertilizer needed to make a concentrated stock solution is often listed on the fertilizer bag. If the information is not contained on the fertilizer bag, then calculate it using the formula given in Table 2.

Be careful about adding too much fertilizer to the stock tank or it may not all be soluble. The solubility of potassium nitrate, in particular, is greatly affected by water temperature. The lower the water temperature of the stock tank, the lower the solubility of any fertilizer made with potassium nitrate. If you are using well water (with a temperature of about 55ËšF) to dissolve the fertilizer or the ambient temperature in the greenhouse (and stock tank) is 60ËšF or lower, then it may not be possible to dissolve more than 2 to 3 pounds (48 to 64 ounces) per gallon of stock.

Another way to determine the concentration of fertilizer you are applying is to use the electrical conductivity (EC) of the fertilizer solution. For all fertilizers, there is a relationship between the concentration of nutrients and EC (Table 3). In most cases, the relationship is given between the concentration of nitrogen and the EC.

To determine the nitrogen concentration coming from the hose, two EC measurements must be taken: EC of the fertilizer solution and EC of the irrigation water (with no fertilizer). Because the values given in the EC chart are for the fertilizer mixed in pure water, the irrigation water EC must be subtracted from the fertilizer solution EC, for example, 20-10-20 with a solution EC of 1.2 and an irrigation water EC of 0.5. Subtract the solution EC (1.2) from the irrigation water EC (0.5) to get 0.7, which corresponds to a fertilizer concentration of about 100 ppm N.

Calculate ppm N from a 20-10-20 fertilizer solution with a total EC of 1.8 mS and an using irrigation water with an EC of 0.5 mS.

Using EC values to determine fertilizer concentrations has some limitations. EC values are generic measurements because they measure the conductivity of all the salts in the solution, not just the fertilizer. It is important to remember that the relationship between EC and nitrogen concentration is unique to that specific fertilizer salt or blend of salts in pure water. Never assume that all fertilizers have the same relationship between EC and ppm N.

Understanding how to fertilize your crop requires more than just selecting a fertilizer formulation off the shelf. You need to know what other nutrients are in the fertilizer, the relationship between the concentration of nitrogen and the other macronutrients, and how to supply them to the crop at a desired concentration. In next month’s article, we will discuss micronutrients.

Leave a Reply

6 comments on “Understanding Plant Nutrition: Fertilizers And Macronutrients

  1. 'So at 100 ppm N, you are also supplying about 92 ppm Ca.' I believe it should read '… at 200 ppm N…' 13-2-13 will deliver roughly 46 ppm Ca when mixed @ 100 ppm N. It will deliver 92 ppm @ 200 ppm N.

  2. What should be the ratio between Nitrogen,Phosperous, Calcium and Magnesium in a fertilizer mix to avoid interactions

More From ...
Syngenta CAST 2015

July 27, 2015

New App Brings Syngenta Flowers’ Portfolio To Growers

Syngenta Flowers' newest app allows growers and brokers to quickly access information, descriptions, photos, culture and more on all of Syngenta's varieties.

Read More
Heating Feature image

July 27, 2015

In Hot Pursuit Of Heating Trends For The Greenhouse

From biomass boilers to hydronic-heating systems, growers have a range of options to fit their operation’s unique needs. Here’s what five manufacturers had to say about the latest trends.

Read More
Suzanne McKee

July 27, 2015

ePlantSource’s Suzanne McKee To Hike Grays Peak To Benefit Charlotte and Gwenyth Gray

Just a few years after welcoming their two daughters into the world, Gordon and Kristen Gray are faced with the agonizing diagnosis that their girls, Charlotte and Gwenyth Gray, both have Batten Disease CLN6, a rare neurodegenerative disorder that currently has no cure and is fatal. Children afflicted with this usually do not survive past the age of 12. Since the diagnosis, the friends and family of the Grays, including Suzanne McKee from ePlantSource, have come together to show an enormous amount of support through viral social media campaigns, silent auctions, lemonade stands and various other events and fundraisers. Celebrity support has also come in droves from celebrities such as Ali Larter, Channing and Jenna Dewan Tatum, Drew Barrymore, Dwayne Johnson, Eva Longoria and countless others. The Colorado friends of the Gray family are hiking Grays Peak on August 29 in support of Charlotte and Gwenyth. McKee and Brooke Michaels […]

Read More
Latest Stories
Syngenta CAST 2015

July 27, 2015

New App Brings Syngenta Flowers’ Portfolio To Gro…

Syngenta Flowers' newest app allows growers and brokers to quickly access information, descriptions, photos, culture and more on all of Syngenta's varieties.

Read More
Heating Feature image

July 27, 2015

In Hot Pursuit Of Heating Trends For The Greenhouse

From biomass boilers to hydronic-heating systems, growers have a range of options to fit their operation’s unique needs. Here’s what five manufacturers had to say about the latest trends.

Read More
Suzanne McKee

July 27, 2015

ePlantSource’s Suzanne McKee To Hike Grays Peak T…

Just a few years after welcoming their two daughters into the world, Gordon and Kristen Gray are faced with the agonizing diagnosis that their girls, Charlotte and Gwenyth Gray, both have Batten Disease CLN6, a rare neurodegenerative disorder that currently has no cure and is fatal. Children afflicted with this usually do not survive past the age of 12. Since the diagnosis, the friends and family of the Grays, including Suzanne McKee from ePlantSource, have come together to show an enormous amount of support through viral social media campaigns, silent auctions, lemonade stands and various other events and fundraisers. Celebrity support has also come in droves from celebrities such as Ali Larter, Channing and Jenna Dewan Tatum, Drew Barrymore, Dwayne Johnson, Eva Longoria and countless others. The Colorado friends of the Gray family are hiking Grays Peak on August 29 in support of Charlotte and Gwenyth. McKee and Brooke Michaels […]

Read More
Bunching onion warrior

July 27, 2015

All-America Selections Introduces First AAS Winners For…

All-America Selections announced another group of edible AAS Winners for home gardeners, gourmet gardeners, farm-to-table growers, market growers and anyone interested in a unique, delicious addition to their vegetable assortment. These three winners are the first for the 2016 Garden Season. Additional winners will be announced this fall and winter as the 2015 trials conclude and the breeders meet specified criteria. The first group of AAS Winners for 2016 includes: Bunching Onion ‘Warrior’ (Regional Winner) Mizuna ‘Red Kingdom’ F1 (National Winner) Radish ‘Sweet Baby’ F1 (Regional Winner) All-America Selections has had bulb onions as award winners in the past, but ‘Warrior’ is the first bunching (or green) onion. Similarly, there have been green mustard AAS Winners, but never a red Mizuna (or Japanese Mustard). ‘Sweet Baby’ radish joins nine other radishes that are previous AAS Winners adding a violet colored beauty to an assortment of radishes that range from white […]

Read More
Home Factory_Dramm2

July 24, 2015

The Dramm Corporation Will Be Featured On “Home Factory…

The Dramm Corporation, a family-owned manufacturer of watering tools, is in the national spotlight for making an eye-catching product. Dramm’s 30-inch ColorMark Rain Wand will be featured in a segment on July 27 on FYI’s “Home Factory.” The Home Factory production crew shot a segment showing the process of making the Rain Wand from start to finish. “Our grandfather, John G. Dramm, a florist by trade, invented the Water Breaker in the early 1940s to provide an efficient and even flow of water for flower growers,” says Hans Dramm, third generation owner of the Dramm Corporation. “This was the beginning of the Dramm Corporation and the foundation of the beautiful Rain Wands you will see highlighted in our Home Factory segment.” Dramm’s Rain Wands allow you to apply large quantities of water quickly to the plant base, where it soaks deep into the soil. The 30-inch ColorMark Rain Wand is equipped with a […]

Read More
Berns_Roberto Lopez_Purdue6

July 22, 2015

Cultivate’15 Greenhouse Learning Tour Showcases G…

Growers took advantage of the Greenhouse Learning tour held Saturday, July 11 at Cultivate'15 to see the strategies and technology two successful growing operations are using to tackle production challenges and come out ahead of the game.

Read More
HGTV HOME CAST 2015

July 22, 2015

Cultivate’15: Keynote Nancy Fire Says Use Passion…

In the second keynote presentation at Cultivate’15, Nancy Fire, founder and creative director of Design Works International, discussed how the horticulture industry can capitalize on the latest design and lifestyle trends. Fire works with companies to help bring their designs to the next level, and she has expertise with textiles and surface design, market analysis and corporate rebranding. She was appointed as design director for HGTV HOME in 2011. Fire says customers today are interested in companies that show passion for what they do. That, combined with following the general direction of trends and maintaining a brand, are what will keep horticulture businesses relevant to their customers. A trend isn’t just a passing fad, Fire says, but rather, it indicates that something is developing or changing in a certain direction. Plants are important to consumers today, and fit into current trends, both inside and outside the home, Fire says. “I don’t […]

Read More
LuxFlora logo feature image

July 21, 2015

Luxflora Launches With Cultivate Speaker Event, New Web…

A new organization for women in horticulture that aims to change the way consumers think about flowers, launched at Cultivate’15 by sponsoring Ketty Maisonrouge, a marketing expert, who presented “How To Create A Luxury Brand.” Luxflora recently launched its website, as well as a page on LinkedIn, to facilitate networking among women in horticulture. The organization is working on next steps, including setting up a board of directors and officers. Updates and information on future events will be available at the Luxflora website as they are scheduled. Read about Luxflora’s mission and what it hopes to accomplish in “Luxflora Wants To Create A Lifestyle Movement.” In the session during Cultivate, Ketty Maisonrouge, owner of KM & Company, adjunct professor of luxury strategy at the Columbia University Business School and the author of “The Luxury Alchemist,” presented her ideas and expertise on luxury strategy marketing, and how it applies to horticulture. […]

Read More
Coleus-Campfire-BallFloraPlant

July 21, 2015

Costa Farms Trial Garden Update: 2015 Late-Season Top-P…

The Costa Farms team announced its late-season top performers in the 2015 Season Premier Trial Garden in Miami, Fla. Its research and development team has been working to grow and evaluate hundreds of varieties and have published their findings here. The plants you’ll find in the link have thrived in Miami’s late-spring conditions. Every spring, the research and development team trials 500 varieties of annuals, perennials and tropical plants from plant breeders around the world. All of the varieties were tested in the 2-acre trial garden. Varieties are assessed for abundance of bloom, crop uniformity and overall performance, which includes factors such as clean foliage, little to no pest damage and the plants’ overall habits and appearances. About 70 varieties scored as top performers during the evaluation period, which lasted from week five to week 19. Transplanting into the trial garden occurred at week 51, and plants were grown in 6-inch pots to finished […]

Read More
Cornell_annual-bed

July 20, 2015

Cornell Floriculture Field Day To Take Place August 11

Cornell’s Floriculture Field Day will be Tuesday August 11 at the Cornell campus in Ithaca, N.Y. An alumni event will be held the evening prior. More information and online registration for both events is available online. Here is some of what will be happening during Cornell’s Floriculture Field Day: 1. New Cornell Alumni and Friends reception. Come to Ithaca, N.Y an evening early for the 2015 alumni and friends event at the Cornell Plantations visitor center. The event, which will be Aug. 10, 5:30-7 p.m., will feature appetizers, New York wine and jazz. It will take place at the Nevin Welcome Center. 2. Armitage and Konjoian kick off the morning program. During the morning program at the Cornell Veterinary School, Allan Armitage, professor emeritus, University of Georgia, will talk about some of his favorite annuals, perennials and veggies for the landscape. Peter Konjoian, of Konjoian’s Floriculture Education Services, will inspire you to […]

Read More
Aerial_view_of_the_Bayer_cross_high_res

July 18, 2015

Bayer CropScience Welcomes New Head Of Marketing For Tu…

Environmental Science, a division of Bayer CropScience LP, recently announced the appointment of Glenn Rougier as head of marketing for the North American turf and ornamentals (T&O) business. In his new role, Rougier is responsible for driving best-in-class innovation, portfolio development, communications and customer programs through his integrated team. His leadership will help ensure that Bayer continues its journey of marketing excellence through strong customer intimacy and global collaboration. “Glenn brings a wealth of unique insights and experiences,” says Mark Schneid, chief marketing officer of Bayer Environmental Science. “His diverse strategic background and history with Bayer will help us continue our journey to provide best-in-class customer relationship management and insight-driven innovation.” Rougier has worked within the Bayer family of businesses for 12 years, assuming a number of roles in strategy and operations. Most recently, he served as director of strategic marketing for the Bayer Healthcare Radiology business, where he led […]

Read More

July 17, 2015

Young Plant Survey: Do You Grow Plugs And Liners?

If your operation produces plugs or liners for wholesale growers, please take a few minutes to participate in Greenhouse Grower’s 2015 Young Plant Grower Survey. We know you are very busy and we value your time and input. This survey should only take a few minutes. Greenhouse Grower’s Young Plant Grower Survey has played a key role in building our Top 20 Young Plant Growers list over the years. The information helps us zero in on trends taking shape and the challenges you’re facing as young plant growers. If you have any questions about this survey or you are not the right contact for this at your operation, please email me at ldrotleff@meistermedia.com, or please forward the survey link to the appropriate person. We would like to wrap up this survey by July 24, so please take it soon! Thank you in advance for your participation. We value your opinion! » […]

Read More
WaterPulse-retail-mats

July 17, 2015

WaterPulse Irrigation Mats Installed In Wal-Mart Garden…

Just in time for summer, WaterPulse, Inc. recently announced it is working with Wal-Mart to reduce the amount of water used in approximately 3,700 garden centers located inside its stores across the U.S. Through the use of WaterPulse irrigation mats, Wal-Mart will not only increase the health of the plants it sells, but will also significantly reduce water usage in garden centers . Before the implementation of the mats, Wal-Mart associates would manually water the thousands of plants sold in an average garden center. Today, the mats do all the work. Water savings comes from the capillary action of the mats, which enables the soil to take in the water it needs, no more, no less. “Wal-Mart‘s leadership in investing in a technology that dramatically reduces water consumption comes at an auspicious moment,” says Jim Heffernan, WaterPulse CEO and chairman. “Based on WaterPulse tests in other facilities, we estimate that by […]

Read More
P. Allen Smith

July 17, 2015

Sakata Seed Forms New Partnership With Garden Expert P.…

Sakata Seed America has announced a new partnership between the company’s Home Grown Vegetable division and P. Allen Smith Garden Home. Effective immediately, Sakata Home Grown is the official vegetable seed brand of P. Allen Smith. Furthermore, Smith has identified a collection of Sakata varieties and branded it under the P. Allen Smith Home Grown Seed Collection. Smith’s national television and radio shows, digital media, printed publications and social media platforms are followed by a large number of fans. And now, gardeners and cooks alike will be able to tune into Smith’s television shows and subscribe to his YouTube channel, social media platforms and digital communications to learn more about the new collection, how the varieties are performing in the test garden and how to grow and cook with Sakata fruits and vegetables. “A great joy is eating something you have grown in your own garden. I am delighted to share with […]

Read More

July 15, 2015

Cultivate’15 Town Hall Meeting: Not Your Grandma&…

Young and innovative industry minds threw down ideas about future of gardening in the new millennium at the Cultivate’15 Town Hall Meeting. Traditionally one of the most innovative, captivating, controversial, edge-of-your-seat, interesting discussions at the whole show, this year’s Town Hall Meeting was no exception. The set up for this discussion addressed the radical change within the world of horticulture over the past decade, due to economics, demographics, technology, retail competition and the redefinition of gardening. The premise: Change cannot be ignored, and our old strategies won’t win us the game anymore. This session acted as a “callback” to the drawing board to determine what gardening actually means to consumers, how the horticulture industry needs to respond to meet the demands of the new millennium and the consequences that may result if we don’t. The esteemed panel included some of the brightest young and innovative minds in horticulture: Brienne Arthur of […]

Read More
Girl on Smartphone

July 15, 2015

Keynote Curt Steinhorst Says Generational Divide A Prod…

Curt Steinhorst of The Center for Generational Kinetics kicked off Cultivate'15 with a dynamic keynote address filled with humor on how to bridge the generational gaps in the workforce and use it to your competitive advantage.

Read More
Tom Wheeler, Bell Nursery USA

July 15, 2015

Tom Wheeler Of Bell Nursery Named Greenhouse Grower&…

Tom Wheeler of Bell Nursery is Greenhouse Grower's Head Grower of the Year for 2015. His leadership on a company level and throughout the industry and his willingness to share his knowledge to help others makes him a worthy recipient for this reward.

Read More
Dragon’s-Breath-Celosia_featured

July 15, 2015

Greenhouse Grower Honors 2015 Medal Of Excellence Breed…

Greenhouse Grower announced its Medal of Excellence winners at the Evening of Excellence, held Monday, July 13 at Cultivate’15  in Columbus, Ohio. The Readers’ Choice Award was presented to Terra Nova Nurseries for Leucanthemum ‘Luna,’ the Industry’s Choice Award went to Celosia ‘Dragon’s Breath’ from Sakata Seed and the Editor’s Choice Award was given to Basil ‘Balsamic Blooms’ from EuroAmerican Propagators Read on to learn more about the varieties that were finalists for the Medal Of Excellence Editor’s Choice, Industry’s Choice and Readers’ Choice Breeding Awards. Thank you to the 2015 sponsors of Greenhouse Grower‘s Medal Of Excellence Awards, Landmark Plastic, Nufarm and Stockosorb. Editor’s Choice Asclepias ‘Monarch Promise’ (Hort Couture) Basil ‘Balsamic Blooms’ (EuroAmerican Propagators) Celosia ‘Dragon’s Breath’ (Sakata Seed) Dianthus Jolt Series (PanAmerican Seed) Salvia Grandstand Series (Green Fuse Botanicals) Scabiosa ‘Kudos Pink’ (Hishtil Nurseries) Industry’s Choice Basil ‘Balsamic Blooms’ (EuroAmerican Propagators) Bidens BeeDance Series (Suntory Flowers) Celosia ‘Dragon’s Breath’ […]

Read More