Does the Grass Know the Cost of Fertilizer?

This is an updated version of the original article, which was published in the May-June 2010 issue of the USGA Green Section Record.

Key Takeaways

• Fertilizer prices are on the rise and affect which products superintendents choose.
• Calculating the cost per pound of nitrogen will help you select the product with the best value.
• Urea is often the most cost-effective nitrogen fertilizer and results in the same plant response as more expensive products.
• Applying nutrients over and above plant needs will not improve turf health.
• Reading and understanding the fertilizer label can help you choose the right product.
   

Obviously, every situation is different. As the turf manager who makes decisions on the fertility program for your golf course, these are the choices that only you can make. After all, there are as many different fertilizer programs as there are golf courses. Some are based on science and soil testing, while other fertilizer application decisions incorporate the art of greenkeeping. The thoughtful golf course superintendent combines both the science and the art of turf management to do what is best for the golf course while being mindful of the budget. Saving money doesn’t always mean you have to compromise turf quality. That said, there are some basic factors that should be part of every fertilizer purchase.

Do The Math

To better understand the factors that impact the value of a fertilizer, let’s compare urea to a common and relatively inexpensive fairway-grade, granular fertilizer, 23-0-6. Note that the blended fertilizer also contains potassium. However, if your soil contains sufficient and available potassium, then the potassium in this fertilizer isn't needed. The prudent turf manager should do the math for all fertilizer elements applied to the turf. You may be surprised about what you find. The following are some simple fertilizer comparisons. The examples use prices quoted from 2022 in the Northeast and will vary based on region and customer pricing.

Urea (46-0-0) costs $50 per 50-pound bag

Each bag of urea contains 23 pounds of nitrogen

One pound of nitrogen costs $2.17

To apply 1 pound of nitrogen per 1,000 square feet to 1 acre costs $95

Using the 23-0-6 fairway-grade fertilizer, which costs $39 per 50-pound bag, it costs $148 to apply 1 pound of nitrogen per 1,000 square feet to 1 acre  

When considering an application to 20 or 30 acres of fairways, potentially multiple times per year, the savings in this example can add up quickly.

If we apply this same math to a spoon-feeding program, we find out that using soluble urea to apply 1/8 pound of nitrogen per 1,000 square feet costs $12 per acre. Applying the same rate of nitrogen using jugs of 18-3-6 liquid fertilizer costs $62 per acre. For 3 acres of greens the difference is $150 per application for the same amount of nitrogen.

As mentioned earlier, if the lowest cost per unit of nutrient is desired, fertilizer purchases should be based on the unit cost or cost per acre (or 1,000 square feet) of that specific product as it pertains to nitrogen. Again, nitrogen is most important for turf growth, but this same math can be used to calculate the cost per unit for any of the nutrients in a turfgrass fertilizer. If you’d like to make fertilizer calculations quickly and accurately, visit the Turf Fertilizer Calculator website hosted by Purdue University. It is a simple way to figure out the cost per pound of nutrients and compare products.

What does all this mean? First, nitrogen is the most important element for turf. Although other macro and micronutrients are important, nitrogen is the driving force in plant response – a fact that can be lost as we browse the seemingly endless fertilizer products available. Urea and other basic fertilizers save money simply because they cost less and contain high amounts of the most-needed nutrient.

Macronutrients

In what form are the primary macronutrients available to the grass plant?

Nitrogen mostly enters the plant as inorganic nitrate (NO₃) and ammonium (NH₄) ions which are soluble and move passively into the grass plant via the transpiration stream. Through a series of steps using enzymes and sugars from photosynthesis, the plant converts nitrate and ammonium to basic amino acids, which produce the proteins necessary for growth.

Phosphorus is present in a plant-available form (phosphate) in soil water and taken up by roots to supply the plant’s growth requirements. Phosphorous is fairly immobile in soil so deficiencies are not common, and rarely cause a visual turf response. Visual signs of a deficiency include a characteristic purple coloration and are easy to correct with an application of phosphorus fertilizer.

Potassium is found on cation exchange sites and within soil components and is made plant-available through weathering as minerals are decomposed to potassium cations. In general, more plant-available potassium is present in fine-textured soils than in sandy soils, especially in areas that receive high amounts of irrigation or rain.

Therefore, the primary macronutrients – nitrogen, phosphorous and potassium – are absorbed and enter the plant as inorganic ions. Is there a difference between fertilizers? In the most basic molecular terms – no. The main difference lies in the individual fertilizer product characteristics, including guaranteed analysis, release-rate or burn potential (salt index).

Micronutrients

Many fertilizers contain other ingredients generally referred to as micronutrients or secondary macronutrients. Deficiencies in these nutrients are rare. The most common micronutrient deficiency is iron, one of the most readily available and least expensive micronutrients. Other ingredients in fertilizers, such as humates, wetting agents, seaweed extracts and biostimulants, all have different functions. It is up to the turf manager to determine if these additives are worth the extra cost or if a more basic fertilizer, like urea, is a better choice.

The Value of Using Urea

In cases when they are not needed, extra fertilizer nutrients only increase the cost of your fertilizer program with little benefit to the turf. Urea offers superintendents value by providing an inexpensive, versatile form of the most important nutrient for turf growth, nitrogen. In foliar spray programs, research has shown that only around half of the applied nitrogen is absorbed by the plant and that urea works as well as other foliar-applied products (Henning et al., 2013). Paying a premium for products that advertise increased foliar absorption may not give a worthwhile return on investment.

Urea is completely water soluble and is a good choice for low-rate granular applications of nitrogen. The granular form can also be applied dry and watered-in. Note that there are different-sized urea granules. Turf managers use the smaller, feed-grade urea since it's easier to dissolve and provides better coverage. Urea also is one of the most inexpensive nitrogen sources, has a lower burn potential than the other commonly used soluble fertilizer, ammonium sulfate (21-0-0), and readily dissolves in water, making it ideal for a spoon-feeding program. Urea ammonium nitrate is similarly priced to urea, but because it is a liquid product it is even easier to incorporate into a spoon-feeding program.

Summary

Every golf course superintendent knows their course and its grasses better than anyone else. There is no substitute for experience so don’t change a successful program unless there is good reason. However, current fertilizer prices are an excellent reason to review your fertilizer program.

With today’s tight budgets, it may be time to rethink your fertilizer purchasing practices. The objective is supplying the grass with what it needs as effectively and efficiently as possible, while not overapplying nutrients the grass plant does not need.

Extra nutrients in the soil will not make turf extra healthy. Indeed, too much fertilizer can waste money, increase the risk of runoff and groundwater pollution or injure the grass. More is not always better, and the grass probably doesn’t know the difference in the fertilizer you use.

This is an updated version of the original article, written by Stanley Zontek, which was published in the May-June 2010 issue of the USGA Green Section Record.

Literature Cited

Henning, S.W., R.L. Mulvaney, and B.E. Branham. 2013. Factors affecting foliar nitrogen uptake by creeping bentgrass. Crop Science 53(4): 1778-1783.