Meet the other macronutrients & learn why they matter for potatoes

The “Big Three” get most of the attention when it comes to fertilizer.

October 19, 2023
4 mins
Dr. Jason Haegele
North American Agronomy Lead, ICL Growing Solutions
Christi Falen
Agronomy Technical Services Manager, ICL Growing Solutions
Dr. A.J. Foster
Agronomy Technical Services Manager, ICL

Secondary macronutrients, however, can be just as important as Nitrogen (N), Phosphorus (P) and Potassium (K) in some crops, and especially in potatoes. These nutrients make specific contributions that can maximize crop yield and are especially important to protect potato quality.

What secondary macronutrients are most important for growing potatoes?

The secondary macronutrients that are most significant for potatoes are:

  • Magnesium (Mg). Mg is the central component in the chlorophyll molecule, making it critical for the plant to be able to photosynthesize and grow. It is also involved in the activation of many different enzymes.
  • Sulfur (S). S is vital for the formation of amino acids and proteins. It also plays a role in photosynthesis and improves N-use efficiency. S is critical for carbohydrate production, which is especially important for tuber production.
  • Calcium (Ca): In stressful environments, like those created by excessive heat or rain, Ca moves up through the root system and displaces growth hormones known as auxins. This, in turn, helps the plant regrow roots. Proper Ca levels can also help prevent internal browning and the development of hollow heart, a condition in which a star-shaped cavity forms in the middle of the tuber.

Why is balanced nutrition important for a fertilizer program?

Balanced nutrition doesn’t just promote improved yield, but it ensures the quality of potato crops.  Secondary nutrients, such as calcium and magnesium, are crucial for fertilizing potatoes as they play key roles in enhancing tuber quality. Calcium aids in the formation of strong cell walls, reducing the risk of tuber disorders and improving overall structural integrity. Magnesium is essential for photosynthesis, influencing starch accumulation in potatoes and contributing to desirable texture and culinary qualities. The proper balance of secondary nutrients ensures optimal physiological processes, mitigates nutrient deficiencies, and ultimately promotes the development of high-quality potatoes with improved market appeal and culinary attributes.

Balance is key for any fertilizer program and that holds true for macronutrients, too. It’s also important to keep relationships and antagonism – when two nutrients may have a negative interaction – in mind. Individual nutrient levels should be viewed through the lens of overall crop nutrition.

Secondary macronutrients, like calcium and magnesium, work in tandem with the Big Three and potato growers should give special consideration to K because of its effect on tuber quality and storability. K is essential for sugar and starch formation and increases plant vigor and disease resistance. Proper K levels also help minimize bruising.

Research has shown that increasing the amount of K during the growing season by applying it just after flowering gives an extra boost to tuber production.

Why should growers reconsider their fertilizer source?

Several fertilizer sources can deliver secondary macronutrients, but one of the challenges is that most sources only supply one or two of these nutrients. Finding multi-faceted products that can deliver the right nutrients at the right time, in the right rate is key.

One source that delivers Mg, S and Ca – plus K – is the mineral polyhalite. This naturally occurring mineral is mined exclusively by ICL off the coast of England and distributed worldwide as Polysulphate®. This fertilizer is unusual because it is not a blend of products; instead, it’s a complex mineral structure that contains K, Mg and Ca which are all associated with S in the sulfate form.

The main reason Polysulphate® is a great fertilizer for potatoes, as well as other crops including alfalfa, corn, soybeans, wheat, strawberries, and peppers is its release profile over the course of the season. It provides a season-long, gradual release of S that coincides with the uptake pattern for most annual crops. An advantage for potatoes is that Polysulphate® is a low chloride source of K, containing 2.4% chloride, compared to potash, which typically contains 45% to 47% chloride. It also has a low salt index which is important because, according to the National Institutes of Health, high salinity is a major global threat to agriculture, causing severe damage to crop production and productivity.

How have the ICL field trials for Polysulphate® performed in potatoes?

Potatoes have shown some of the greatest results and have been consistently responsive in ICL conducted field trials for Polysulphate® in the United States and Canada. That’s why we are really excited about the opportunity for this fertilizer for potatoes not only to increase yield, but also to improve quality.

Polysulphate® potato trials were conducted over four growing seasons in Minnesota, Michigan, North Carolina, Manitoba and Prince Edward Island. All trials showed a total yield increase over the control, ranging from 4.3 percent in Manitoba to 77 percent in North Carolina. Other trends observed through the trials included increased N-use efficiency, reduced hollow heart, and better fry quality.

Fertilizer practices vary widely across North America for potato production. Regardless of rainfed or irrigated production systems, and sources of secondary macronutrients such as gypsum and potassium magnesium sulfate, Polysulphate® has resulted in increased marketable yields. The ability to apply more nutrients with a single product has the potential to reduce fertilizer cost per acre or improve grower ROI depending on how Polysulphate is used in a dry fertilizer blend.

The Bottom Line

This is more evidence that nutrient source matters – it’s not just about the rate, it’s also about the availability of the nutrients that are within each fertilizer product. That has a significant impact on yield, and lower fertilizer costs per acre means a better return on investment to the grower.

Secondary macronutrients have an important function in yield and quality and must be taken into account in a crop nutrition plan. Ensuring a balanced supply of nutrients is key to optimizing potato yields and enhancing their market value. When weighing fertilizer options, consider the availability of nutrients and how it will affect the bottom line.