Back to the Basics With a Twist: N, P, K + S

Good soil fertility is foundational to growing productive crops. There are 17 essential nutrients for crop production. While each plays a necessary role in optimal crop health, some are in a class all of their own.

Major Essential Nutrients

Out of the 17 elements that areessential for plant growth, plants get three of them from air and water, and the other 14 are mineral nutrients that plants get from the soil.

Based on their concentration within the plant, mineral nutrients are divided into two groups: macronutrients-required in large amounts, and micronutrients-needed in much lower concentrations.

It is well known that N, P and K are three key macronutrients needed to fulfill specific needs and functions within the plant. Nitrogen (N) supports rapid growth and green crops with more foliage. It is an essential component of amino acids, the building blocks of proteins, as well as chlorophyll and nucleic acids, like DNA. Phosphorous (P) is vital for energy transfer, which is crucial during stress. It also helps with photosynthesis and is essential for general health and vigor of all crops. Finally, potassium (K) contributes to the formation of strong walls, which protect plants from disease. It also helps with the movement of water, nutrients and carbohydrates in the plant tissue and the regulation of the stomate to exchange water vapor, oxygen and carbon dioxide.

In addition to these three well-known nutrients, crops also need sulfur (S) to maximize yields. "Sulfur is the fourth major crop nutrient," said Ron Olson, senior agronomist for The Sulphur Institute. "It is essential for balanced crop nutrition, playing an important role in nutrient uptake and efficiency."

Like nitrogen, sulfur is an essential component of amino acids, the building blocks of proteins. Both nutrients are also critical to photosynthesis since nitrogen is a component of the chlorophyll molecule and sulfur is needed for chlorophyll formation. Due to the close relationship between nitrogen and sulfur in plant structure and physiology, sulfur deficiencies can also hinder nitrogen use efficiency. Given nitrogen's status as the most common yield-limiting nutrient, this further underscores the importance of sulfur as the fourth major nutrient.

In addition, like phosphorus and potassium, sulfur also plays a vital role in plant health. Sulfur is a component of compounds such as phytoalexins and glucosinolates, which are important in helping plants fight biotic and abiotic stress.

Signs of Sulfur Deficiency

Due to a decrease in sulfur depositions from the atmosphere in recent years, the need for supplemental sulfur fertilization is at an all-time high. Without enough sulfur, crops may show physical signs of deficiency during the growing season. According to The Sulphur Institute, signs of sulfur deficiency can resemble those of nitrogen deficiency, with leaves becoming pale yellow or light green. Plants deficient in sulfur also tend to be small and spindly, with short and slender stalks and slower growth. In cereals, maturity can be delayed, while legumes like soybeans often experience poor nodulation and reduced nitrogen fixation due to a lack of sulfur.

The appearance of these symptoms is a serious indicator of the underlying deficiency, as crop yields can decline before these warning signs are visible. But to properly diagnose a sulfur deficiency, Olson recommends conducting both soil and tissue testing.

"We can be surprised about what a sulfur deficiency looks like because there are several other nutrient deficiencies that can cause a crop to turn yellow," said Olson. "Don't try and make a guess. Use both plant tissue analysis and soil test results to make actual diagnostic decisions."

Once a sulfur deficiency is confirmed, a soil application of a fertilizer with readily available sulfur, such as ammonium sulfate (AMS), can help address these symptoms. However, it is often easier to plan ahead to address a crop's nutrient needs rather than trying to cure a symptom of a deficiency during the season.

Nutrient Planning for 2025

As growers are making their fertilizer plans for 2025, it's unlikely they will forget to address their needs for N, P and K. But in order to maximize yield potential, they will need to consider how to address their sulfur needs as well. Sulf-N^®ammonium sulfateis an excellent source of readily available sulfate sulfur and ammonium nitrogen that can be applied to various crops including corn, cotton, soybeans and wheat.

Ultimately, a fertilizer plan that takes into account N, P, K + S is a critical step towards success.

To learn more about how Sulf-Nammonium sulfate helps address sulfur deficiencies in crops, contact your AdvanSix sales rep.

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